Two Stroke Motocross » Tech

It’s easy to own a 144cc or 300 cc Two-Stroke!

JohnNicholas — Sat, 31 Jul 2010 00:04:49 +0000

One of our passionate readers started circulating a petition to the AMA to allow two-stroke race machines into the Pro ranks. His suggestion was to allow a 144cc two-stroke to compete in the 250F class and a 300cc two-stroke to compete in the 450F class.

While it’s not the ideal many two-stroke fans would choose, it is a step in the right direction.

It’s important to keep one thought in mind, this is a step for the Pro Racing ranks. Many journeyman Pros have to pay for their own race efforts and spend quite a bit of cash in order to make their machines competive with the best in the world.

Of course when 144 and 300cc two-strokes are brought up the first question to come up is who makes machines in those sizes. This is a guide to point you in the right direction. It’s not as difficult as you would imagine.

Let’s start with the simplest, easiest path and move to the more labor and cash intensive.

Which manufacturers provide machines in these sizes?

TM Racing a small manufacturer in Italy builds purpose built machines in both a 144 and 300 size for motocross racing. These machines have been talked about for years, but have had spotty distribution in the USA for many years.

That has now changed since Barker Bros Cycles has taken over distribution rights for the US. In the first year of being US distributor, Dan Barker has placed machines in different parts of the country to allow potential customers to see and test the machines for themselves. In addition he provided Dirt Rider and Dirt Bike with a TM 144 MX for testing. Check out the current issue (August) of Dirt Bike magazine.

For 2011 look for TM Racing and Barker Bros Cycles to make bigger waves in the US market.

For those that don’t know much about these machines, they are hand built, works style machines. The best way to describe them is to say TM Racing is the Ferrari of dirt bikes. Don’t take anyone’s word for it, try one and decide yourself.

Purpose built 144 engine from TM Racing. These machines are super fast!

What other manufacturer build a 300cc two stroke motocross machine? The TM Racing 300 MX

Of course we can not leave the bright Orange machines of KTM out of a discussion of machines with different displacements. KTM builds bikes in many different sizes.

Over the past few years KTM has begun to make inroads into the sales strangle hold that the Japanese had enjoyed for many years. More folks are buying them, liking them and recommending them to others.

The 2011 KTM 150 (actually a 144) has taken accolades from every quarter with this machine.

While KTM does not build a Motocross specific 300cc motocross machine, they offer a 300cc kit for their 250SX. While it is an option it’s more expensive than buying on direct from the manufacturer.

Take the 250 SX and add the $800.00 300cc kit and you have a 300cc MXer.

These are all the parts included with the KTM 300cc kit.

MXA did a test using this kit on a 250SX. MXA KTM 300SX Big Bore

The lone Japanese manufacturer to still build and import two-strokes into the USA is Yamaha, with the YZ125 and YZ250. Unfortunately these machines have seen few updates since 2005.

While they are great machines, they are dated looking and have not had updates applied to them like the four-stroke line-up has.

Still they are good handling machines that can still be bought new from a dealer. That is if you can find a dealer that has any in stock! There seems to be very few of these machines built and made available to the buying public.

Even with these short comings, the Yamaha is a great platform to race in the Pro ranks.

To bring the little YZ125 up to the proposed 144 size there is a few options available. Probably the easiest is the GYTR 144 kit available directly from Yamaha.

The video below is of Pro Racer Max Anstie testing the GYTR kit…

While it’s not an inexpensive option, it certainly is one way of owning a YZ144.

MXA did a test on the GYTR 144 kit. MXA YZ144

With the YZ250 you could also build a 300cc racer using the L.A. Sleeve 270 kit. While this kit is built by using a steel sleeve, it seems to work quite well as the MXA test below shows.
MXA YZ 270 Build

In addition to the solutions listed above there are many companies that perform Big Bore surgery to your 125 and 250 two-stroke machines. Any one of these companies will take your bike and turn it into a 144 or 300.

My suggestion before trying any of these builders, is to ask others that have had work done by them and see what their experience was like. Then if you can talk them into it, try to take a test ride to see what you think.

Athena – Builds big bore cylinders for two-strokes. Available through larger distributors and your local dealer.

Eric Gorr / Forward Motion – Eric has been building 144 kits since 1976! He has tons of experience with big bore two-strokes. There is also some great advice to be found on his site.
http://www.eric-gorr.com/international144kits.html

Eric Gorr big bore kit.

Millennium Technologies – Well-known for there plating services, they also offer big bore services as well.
http://www.mt-llc.com/bigBoreKit.html

Kustom Kraft Performance – Another shop that has been in business for many years.
http://kustom-kraft.com/big-bore-kits.html

MAX Power – Builds big bore kits for all Japanese two-strokes
http://www.maxrpms.net/shop/index.php/motorcycle-kits/mk-yamaha/yz250.html?SID=078130f90c171feaf15eaa36f74c0d72

If you are determined enough to get something done, it can be done. There are machines available or that can be built that will fit into this proposed rule. Next up is to work to get this new rule passed!

If you have not done it, please sign this petition. http://www.gopetition.com/petition/38076.html

Can a Two Stroke run at 200:1 fuel/oil Mixture?

JohnNicholas — Wed, 30 Jun 2010 18:50:09 +0000

When someone says they can run their two stroke at 200:1 the first thing that happens is that people’s eyes go wide and they say “Huh?” It happens every time the Project Two 50 team mentions they are running a 200:1 mixture. Of course there are many that are skeptical.

How can anyone possibly use such a lean fuel/oil mixture?

The folks over at MicroBlue Racing have the answer. Ten years ago founder Craig LeClaire developed a coating process that virtually eliminates metal to metal friction and wear. When you eliminate friction the need for oil becomes less important.

This process begins with superfinishing all parts before the coating is applied. This removes the peaks created during the manufacturing process, therefore changing the surface profile of the metal. It’s easiest to equate this with a rock versus a skipping stone, a smooth stone skips best.

Once the parts are superfinished, the MicroBlue coating is applied. This process occurs at the molecular level which can be verified by a Stereo Scope.

Because of this interaction, there is now no such thing as a lubricant starved condition. Which is why so little lubricant is required.

Craig say, “MicroBlue actually changes the way lubricants work. You know how slippery you feel in the shower with soft water? Soft water changes the way soap wets your skin, making you feel slippery. When a lubricant comes into contact with any MicroBlue coated surface, it does exactly the same thing-by changing the way a lubricant works on the surface.”

Initial tests of this technology on a two stroke were performed on a Ryobi leaf blower. Once the coating was applied to the cylinder, piston, rings, crank and bearings the engine was assembled, then tested.

The testing consisted of connecting the Ryobi Leaf Blower to a pickle bucket filled with fuel mixed at 200:1 Craig started the leaf blower in the barn, wired the throttle wide open and left the machine to run. This test was an attempt to seize the motor. Craig went back to the barn and amazingly the leaf blower was still running!! Total run time? 60 hours – non-stop!

The leaf blower was sent to a third party for testing. Where an additional benefit of running the lean fuel mixture was discovered, particulate emissions were completely eliminated!!

Of course this piqued the interest of the EPA. Because of the initial tests the EPA has authorized a SBIR Phase 1 Project to study and evaluate particulate reduction in MicroBlue Racing coated two stroke engines.

Next up, a test on a full sized two-stroke motocross machine. When Craig was introduced to Project Two 50, he recognized an opportunity to showcase this process to a wider audience.

After much testing, the Project Two 50 team is now running their machine at 200:1 The bike will make it’s Pro race debut at the Red Bud AMA Pro Motocross race on Saturday July 3rd.

If you’re a fan of two strokes, make sure to tune in to the first moto on Allisport.com and to watch the second moto LIVE on NBC.

http://www.microblueracing.com

http://projecttwo50.com

MICROBLUE Racing sponsors Project Two 50 -Results in Low Emission YZ250 Two-Stroke

JohnNicholas — Thu, 10 Jun 2010 17:19:04 +0000

One the biggest supporters and sponsors of Project Two 50 is our friend Craig LeClaire from Micro Blue Racing located in Rockford IL. His ideas, suggestions and input have taken our simple idea and turned it upside down.

The original idea for Project Two 50 was to compete using a 250 two stroke in the AMA Pro National Motocross class against the 450 four-strokes. In itself an admirable goal.

Once Craig became involved the entire project changed focus. It has grown into a challenge to our entire team, a challenge to build the cleanest two-stroke, emissions wise, in the world.

As you could imagine, this is a very tall order, which involves many ingredients to achieve. The repercussions of achieving this goal are far reaching and in some ways life altering.

The thing is we actually did it!

How can this be possible on a normally aspirated two-stroke engine?

It begins with Craig and his insatiable thirst for improving the Internal Combustion engine. With a background in metallurgy and racing, it was a natural for Craig to begin experimenting.

What other “tuner” uses a high powered microscope to ensure all metal parts are perfect at the molecular level? While I don’t know that answer to that question, I do know that Craig does so with every piece of metal that he comes into contact with.

When you look at the parts from your engine in this light, everything changes. You see that a part that looks smooth to the naked eye actually looks like the dark side of the moon under the microscope.

Craig invented and developed a process that coats metal at the molecular level. This process is called MICROBLUE. Once you see a part that has been treated with MICROBLUE coatings you will never forget it. It’s blue color hue is distinctive.

The main benefit of MICROBLUE coatings are to reduce friction. When you reduce friction you increase power. This can be proved quite easily, by holding a MICROBLUE treated Ceramic bearing in your hand and spinning it. The first time I did this little experiment, my jaw dropped in amazement. It just spins and spins and spins.

Below are a few YouTube videos that show how the MicroBlue Bearings and coatings work on differing applications

Craig also applied the MICROBLUE coating to the moving parts of a two-stroke engine. In his first experiments he treated a Homelight Leaf Blower and performed a test. He connected a large gas tank to the blower, mixed up a few gallons of fuel, wired the throttle wide open and let the blower run for over 20 hours straight.

Under these conditions, you would expect that when you returned that the blower would have stopped running. But it was still screaming away when he returned!

Now to the important part, he mixed the fuel using Homelight oil at 200:1 Gas/Oil mix!!

A fabulous by-product of this test was the particulate matter (the part that affects emissions) was virtually eliminated!

When Craig joined us on the Project Two 50 team, one of his goals was to apply this technology to a two-stroke motocross bike. Which is what we’ve been testing over the past few months.

Our race bike uses a 100:1 Fuel/Oil mixture using Amsoil Dominator Synthetic. This fuel mixture accomplishes our goal of lowering the Project Two 50’s emissions to the cleanest seen in a production two-stroke!

There is still more testing to be done. One important step will be for our initial tests to be confirmed by independent testing. Which is on schedule to be done as soon as possible.

For you tuner types reading this, I’d like to point out something for you to think about. Our MICROBLUE coated YZ250 engine requires a 210 main jet to run properly! The standard main jet used in a YZ250 is a 178!

In my mind there can only be one explanation for this change in jet size, this motor is pumping more air than a standard YZ250 two-stroke.

An interesting benefit is the sound coming out of this motor. It just does not sound like a typical YZ250. It has a deeper, more throaty bark. Another important point is the power delivery, which is very usable, with a tremendous mid-range that screams out into an amazing top-end. This is one very powerful machine. To top it all off it’s clean.

So to restate that a powerful, fast, clean and sweet smelling two-stroke!

MICROBLUE Racing has been using the MICROBLUE coating technology since 1999. Racers that understand the idea that friction reduction equals gains in horsepower are drawn to MICROBLUE. Racers involved in forms of racing from soapbox derby racers to Tractor pulling realize that friction reduction equals additional gains.

MICROBLUE Racing first entered Pro Racing in 2004. It is difficult to turn on the television in Motorsports without seeing MICROBLUE technology in action. It has been a race “secret” for many well-known racers and teams for many years.

You could say when it comes to Pro Motosports Racing, that everyone in the know, knows MICROBLUE.

Please take a moment to read the information in the “side bar” below. This is an independent test of the MICROBLUE coating using the standard Falex testing. This will allow you to take a glimpse at the potential of the MICROBLUE coating.

http://www.microblueracing.com/

Falex Testing of MICROBLUE coating

A solid film lubricant coating that has proven to be very effective in preliminary tests is the MicroBlue® tungsten disulfide coating. This coating is patented by Material Technologies, Inc. and is provided by the same company. This coating is applied by a low-cost atmospheric pressure particle impingement process. The coating produces almost no dimensional change (less than 1 micrometer) and is applied at ambient temperature. The MicroBlue® coating provides a low friction surface via two mechanisms. One mechanism is the inherent lubricity of the tungsten disulfide thin film on the surface.4 The other mechanism, which is perhaps more important, is that the tungsten disulfide acts as a wetting agent for hydrocarbon-based lubricants because of their affinity for the coated surface which causes the lubricant to more effectively wet the surface. The high durability of the coating is most likely due to the patented application process in which the tungsten disulfide is mechanically bonded to the surface by filling in micron-scale depressions in the surface.

To evaluate the coating durability, Aerodyne Research, Inc. (ARI) recently had block-onring tribological wear tests performed on standard and MicroBlue®-coated test specimens (Figures 1 and 2).

These tests dramatically illustrated the ability of the coating to provide low wear and friction, and in particular, demonstrate its ability to maintain a lubricant layer between surfaces under very high stress conditions. The tests were performed by Falex Corporation using their Blockon-Ring test apparatus. The test conditions were selected to be somewhat representative of a diesel engine crankshaft bearing under very high load. The test conditions were: 2000 rpm, 100°C, 150 lb force, and 100000 cycles (40 min). The Falex H60 block (SAE 01 Tool Steel, Rc 58-63 Hardness, Ra= 4-8 roughness) and S10 ring (SAE 4620 steel, Rc 58-63 Hardness, Ra= 6-12 roughness) were selected for the test. High quality diesel engine oil, Castrol GTX 20W-50, was used for the test in which the ring was partially submerged in the lubricant. Tests were performed for the standard H60 block and S10 ring as the control test, and for the same block/ring combination after being treated with the MicroBlue® surface treatment. Images of the specimens are presented above in Figures 1 and 2. The data sheets for these tests are presented in Figure 3 for the control test and Figure 4 for the MicroBlue® treated test.

The most impressive aspect of the two tests was that the standard (control) test specimens failed catastrophically in 5 seconds due to galling (see the note at the bottom of the test report in Figure 3) while the MicroBlue® treated specimens ran for the full 100,000 cycle duration of the test and showed minimal wear at the end of the test. The wear volume on the block for the standard specimens was 3.64 mm3 in 5 seconds, while the wear volume on the block for the coated specimens was 0.0354 mm3 in 40 minutes – 1/1000th the wear volume in a 500x longer test. Clearly, the severe conditions prevented a lubricant layer from being present in the interface between the block and ring components for the control test (a boundary lubrication condition), leading to immediate galling. For the coated specimens, on the other hand, the MicroBlue® coating’s interaction with the lubricant evidently maintained a thin lubricant layer between the parts to prevent galling and greatly reduce wear (mixed or mixed+elastohydrodynamic lubrication regimes).

While the conditions for these tests were very severe, they demonstrate the important aspects of the coating – its interaction with the lubricant to maintain a lubricant layer between parts and nearly eliminate wear, and its very high durability as demonstrated by its survival under these severe conditions for 100,000 cycles and showing minimal wear at the end of the test.

Reader Rebuild – 2005 KTM 200 EXC

JohnNicholas — Mon, 31 May 2010 15:29:46 +0000

Here is the story of my rebuild of my 2005 KTM 200 EXC, twostrokemotocross.com inspired me to have a go and do it myself.

Since starting racing as a 10 year old in 1984, I have had two dirt bike ambitions I really wanted to fulfil, first to ride a 500, second to rebuild my own motor. Well the first was ticked off last year in the dunes at Lancelin, north of Perth, Australia, thanks to the kind Kiwi who said in response to my request for a photo of his gleaming 2001 model CR500, “Take it for a spin if you like.” Needless to say I took the offer up, let me tell you holding that baby wide open in 5^th in a pair of shorts and sandals was quite a thrill. I have a neat little scar on my left calf to remind me of when the curve in the pipe branded me on that great day! Anyway, after 5 heavenly minutes I figured I would be wise to hand it back while I was still in 1 piece.

On my return to England I was reunited with my 200, which has since seen another year’s hard use. The routine I’ve been following is do the top end myself every 100 hours, get someone else to do the mains every 200hrs. Almost immediately after the 200hr full rebuild I drowned it good and proper, it seemed like I pumped a whole gallon of brown water out of the old girl, which was pretty depressing, but she seemed to shrug it off, but when I recently drowned it again in a huge mud hole at the 380 hr mark, I figured it was time for a strip down. When the next day I landed off a log and there was a horrible squealing noise that lasted about 30 seconds my mind was made up. Later in the day it boiled over when I had to scream it to get up a sandy climb in a wood, so I knew I had to get to work. I had followed the CR 250 rebuild on the site with interest, and done lots of google searches about splitting crank cases, so armed with my workshop manual I set to work.

I bought a KTM clutch holder and primary gear holder as well as the inner ring tool, for removing and fitting the bush that slips on the crank and sits in the roller bearing. As their rotor holder is $160-00 here, no joke, and the shift roller holding key was out of stock, I asked my friendly neighbour Phil the farmer and his cousin Steve if they could help me out and 1 hr later I had a DIY rotor holder and key blank. The blank took about 20 minutes of filing to get a good fit and I was good to go.

I opted to take the motor out before removing the primary gear nut and clutch hub nut, they both came off with the motor sat on the bench, with me holding the motor in 1 hand and a breaker bar in the other with no problems. I did remember the primary gear nut is left hand thread! At this point I discovered the source of the horrible noise, the intermediate starter gear had spat a tooth off, which had done some pin ball action before shredding the water pump drive. New parts were duly ordered.

This motor doesn’t require a crank case splitter , the cases eased apart with no problems, I tapped away gently with a plastic mallet and used the tabs on the cases to prise them apart by hand. I was a bit concerned about putting the tranny back together so I took lots of pictures and made running notes as I disassembled it. Actually there was nothing to worry about, the important thing is to make sure the stop discs on the end of the shafts don’t get forgotten, and keep a grip on the lower end of the whole assembly when removing it so gears don’t come flying off.

I had decided because of all the water that’s been in the mill I would replace all the high speed bearings while I had it in bits, I opted to leave the gear shift and kick start roller bearings and the shift drum bearing in, as they showed no signs of corrosion and don’t lead too hard a life. I was pleased to see that the cylinder looked just as it did 100 hrs before, you can still see all the original hatching marks, and there isn’t any sign of wear. The piston with over 100 hrs on it had just a few signs of blow by.

I took the crank and rod assembly to my KTM dealer for assessment, using the time honoured technique of grabbing hold of the rod and giving it a damn good yank in two directions, mechanic Nick determined that the big end was at the end of its life so fitted a ProX kit, considerably cheaper than the factory parts and just as good so they say.

With that sorted and a bag of new bearings in my possession it was time to get the old bearings out and stick the new ones in. At last I would have a 2 stroke engine in pieces on my kitchen table! I started out by applying localised heat with a hot air gun, this worked fine for the main shaft and countershaft bearings, but the crank bearings were much tighter and I didn’t want to start whacking them too hard.

Next I put the cases in the oven for about 5 minutes then tried again. It is possible to get a socket on the inner race of the ball bearing and drift it out from the outside in, this worked fine without the need for too much force. I had the case sat flat on a large wooden chopping block. Next up was the roller bearing side, there is no clearance to get a socket on to the bearing on this side, so I used a drift and worked my way around the bearing, hitting the ends of the rollers. Several rollers quickly fell out, so I was then able to hit the bottom of the race. Not pretty but it worked fine. I think for next time I will make a draw bolt and sit a big piece of plate across the case and pull the bearing out from the inside to avoid having to hit anything.

Installing the bearings was straightforward, I heated the cases up and dropped them in, the crank shaft ball bearing started to go I out of square but the lightest of taps got it out again and I got it right the second time. I made sure they were all the way home by tapping in with a socket on the outer race and went back up to the workshop for reassembly.

The workshop manual instructions were very clear, and I got the gear assembly in to the right hand case at the second attempt, it was a little bit fiddly. Putting the shift forks and drum back in was straightforward. Then it was time to stick the left hand case on. I sat the right hand case on a big pile of rags to allow for the shaft end sticking out and popped the left side on. I tapped away gingerly with the mallet again and got it seated without difficulty.

Then I put the bottom end back in the frame before replacing the primary gear and clutch hub. At this point I have a confession to make. Following the details in the manual, I torqued the primary gear nut to 180NM using a pretty gnarled old wrench I’d borrowed from Phil, it was only later, looking up the engine mounting bolt setting in the owner’s manual that I noticed the figure for the 05 model is 130 NM. The workshop manual was written in 02 and I didn’t check for revisions. Lesson learned.

I figured too tight could not be a good thing so whipped the clutch cover off and slackened it off then went to torque it to 130NM. I got to the point where I was thinking the wrench should have clicked but it hadn’t, so I slackened it off and inspected the thread on the crank and the nut, to my horror there was damage to the thread and not the nut, but it was fairly slight, and with a 4 day riding trip to France 2 days away I had no choice but to stick it back on. From the amount of force I was applying I was pretty sure there was over 100 NM of torque so just had to cross my fingers. Maybe the wrench was under reading and that initial go at 180 started the damage, the nut certainly went on square, I put it on with my fingers to start with so it wasn’t cross threaded. I hope that next time I pull it apart it can be fixed on a lathe, going a size down on the nut.

The rest of the rebuild was a routine affair, so with the whole bike back together I prepared to fire her up. I had, of course, turned it over by hand at every stage of the build to check nothing was amiss. Well it’s fair to say I have never heard so many strange noises from the motor, I was a bag of nerves as I warmed it up. A friend pointed out that it’s only because I was listening so hard! It turned out the noise that really freaked me out was the very bashed about pipe touching the bash plate and creating a harmonic at mid rpm. I’ve put about 40 hrs on it since and it’s running perfectly, so I think I’ve got away with it.

At the same time I set about a much needed fork service, and took the shock to the shop for a rebuild, the seals were completely shot and the whole bike felt like an old sofa. I purchased a motopower fork service dvd which was brilliant, I made notes as I watched it in the house then went up to the workshop and set to work. The process was easy and straightforward, instead of a seal driver I used a piece of 6inch roofing lead rolled around the slider with a nice smooth edge filed on to it instead and it worked fine.

At this point I have to make confession number 2, my note taking failed me and I put the seals in the wrong way round. D’oh! What I know as a result is that over 4 days riding each fork leg lost 250ml of oil, and I got a good insight in to the effect of an increasing air gap on the feel of the whole bike. As a result I’m running and 10mm larger air gap (120mm instead of 110mm) and for the trail it’s perfect. I can also vouch for the fact that the seals work a whole lot better installed the right way roun! They were undamaged as a result of being in the wrong way round.

I really enjoyed the whole process, I got a huge sense of satisfaction and achievement from doing it, and it confirmed to me that it is indeed true that you can service your 2 stroke at home with some basic skills and a decent tool kit. Sure the bottom end needs doing by the shop because the crank has to be balanced after driving the pin out, but this is not an expensive job. I saw on Thumpertalk a guy talking about his son’s KX80 with 1800 hrs on it, so hope I can maintain my bike in good condition for many a year to come. I only have to look up clips of the World Enduro Championship from 2005 on utube to remind myself that it’s me that holds the bike back, not the other way round, if I ever get a bit of new bike envy. The motor is bog stock, the suspension has been revalved and sprung for my weight and I have a Scotts damper fitted which has really calmed the whole thing down. I ride some rocky terrain up here in northern England and never ever felt comfortable at speed on rocks until I fitted it. It is a great piece of kit. An Enduro Engineering seat recently replaced the original which was getting seriously uncomfortable over the course of a day and is a big improvement.

It sits me slightly higher than the original which I prefer too. I also have a 12.5 litre tank. Overall I love the package, it’s super light, plenty fast enough, and always fun. One of our mags over here always complains about the fierce power delivery of the 200, saying you never know if it will wheelie, spin or drive. Well excuse me, get used to it! That’s my idea of fun, why would I want to ride something with a dull, linear power delivery. My bike is more challenging, sure, but more rewarding. I had a go on a friend’s 04 WR250 and never want to repeat the experience. I think I’d have had more fun pedalling. Maybe the tester doesn’t know what the clutch is for!

Engine Build HPP Valve Honda CR250 – Part 9

dogger315 — Mon, 29 Mar 2010 14:34:05 +0000

This is part nine and the final part of the CR250 engine build and will cover head, reed valve and carburetor installation. I will also perform the initial leak down test.

Tools needed: Torque wrench, leak down tester, metric tool assortment

Apply oil to the six cylinder head studs and install them into the cylinder. Torque the studs in three steps and in a criss cross pattern to 9 lb.ft.
Again use a stud tightener or two opposing flange bolts to properly torque the studs.

Place a new head gasket with the “up” mark facing up and aft

Install the cylinder head and apply oil to the cylinder head studs and landings.

Install the six cylinder head nuts and hand tighten. Torque the nuts in three steps and a criss cross pattern to 20 lb.ft.

Install the reed valve with a new gasket into the cylinder

Install the intake manifold with the intake oriented to the left. Apply oil to the six intake bolts and install the bolts along with the throttle cable
retainer. Torque the bolts in three steps and in a criss cross pattern to 7 lb.ft.

Now is a good time to perform the initial leak down test. Cycle the piston to bottom dead center (BDC). Install the spark plug and torque to
13 lb.ft. Install a exhaust plug to seal the exhaust outlet. Attach the tester to the inlet and seal with a hose clamp.

Pump the tester to 6 psi and start timing. An acceptable loss rate is 1 psi/min. Less is better.

Remove the test equipment and the exhaust plug. Install the carburetor aligning the tab on the carb intake bell with the notch in the rubber intake boot. Tighten the intake clamp snugly and give yourself a big thumbs up for completing a total engine build.

Engine Build HPP Valve Honda CR250 – Part 8

dogger315 — Sat, 20 Mar 2010 15:37:41 +0000

This segment will cover piston, rings and cylinder installation and power valve adjustment.

Tools required: Torque adapter, torque wrench, standard assortment of metric tools.

Most people have rebuilt the top end of their ride so a lot of this information is old news. I am presenting the techniques that have worked best for me over the years. Hopefully you will see something that might be helpful the next time you tackle this job.

First order of business is protecting the crankwell from debris. Stuff a shop cloth in and around the connecting rod.

Apply oil to the cylinder studs and install with the rounded portion of the stud facing down. Use either a stud installer or a couple of nuts tightened together and torque to 9 lb.ft.

Coat the small end bearing with two stroke oil and install it into the rod.

Install a circlip into position on the piston. Coat the wristpin with two stroke oil. Place the piston over the connecting rod orienting it with the skirt cutout facing aft (If you are using an OE piston, orient the piston with “IN” facing aft.

Install the other circlip insuring both are correctly seated in their grooves. Also, never re-use circlips, you’re just asking for trouble for a dollar’s worth of parts.

Apply two stroke oil to the piston rings and ring landings. Orient the rings with the mark (next to the gap) facing up and install with the ring gap straddling the pin in the ring groove.

Apply oil to the two dowel pins and install.

Install a new base gasket.

Apply grease to the pinion shaft and make sure it is oriented correctly.

Liberally apply two stroke oil to the cylinder wall. Place the cylinder over the studs with one hand while compressing the top ring with the other. Carefully lower the cylinder over the top ring then compress the second ring and repeat. Once the cylinder is past the rings, be careful not to turn the cylinder anymore than absolutely needed to orient the cylinder over the studs – It is very easy to snag a ring on one of the ports and break it.

As you carefully lower the cylinder, take a look under the right front corner and “eyeball” the line up between the upper and lower power valve pinions, you may have to rotate the power valve clockwise slightly to get a good join up. The pin on the lower pinion goes in the gap in the upper pinion. The cylinder should seat without any gaps. If you have a gap, chances are the power valve pinions aren’t joined correctly. Simply lift the cylinder an inch or so and manipulate the power valve linkage as you lower the cylinder again.

Once the cylinder is firmly seated with no gaps, give the power valve linkage a tug to make sure it doesn’t move. Apply oil to the cylinder studs, install the four flange bolts and finger tighten. You will need the torque wrench adaptor to tighten the front two nuts. Please do not use an open end or even a box wrench and guestimate the torque. Unless you have been doing this a long time and have a calibrated hand, you are setting yourself up for a blown base gasket or possibly a warped cylinder base. Buy the adapter and do the job right.

Tighten the flange bolts in a crisscross pattern in three steps.

Using the kickstarter, cycle the piston a few times. It should move freely and quietly.

Next up is the power valve adjustment. Now that the power valve is connected to the governor, the slack in the linkage can be adjusted out.
Using a 4mm hex bit on a socket wrench or a T-handle (something you can generate some torque with), loosen the socket bolt on the pinion shaft slightly. Turn the power valve fully counterclockwise and insure the flap valve is fully closed (check the reference mark on the left side inspection port points to “L”). With everything fully closed, rotate the pinion shaft slightly more to the left with the 4mm hex bit and tighten and torque to 4 lb. ft. The power valve linkage is now slightly preloaded and their should be no slack in the linkage. Honda recommends 0-0.5mm gap between the pinion spring and pinion lever for this setting. I like to set mine right at 0.5mm.

Check that the power valve position indicator is still pointing to “L”. Apply two stroke oil to a new O-ring and install the left side cover and torque to 9 lb.ft.

I like to spray some Permatex gasket adhesive on gaskets that don’t have alignment dowels. Just a few quick sprays of Copper spray in this case.

Let it tack up a couple of minutes and position the gasket right where you want it. This spray is available in Copper (hot areas) and silicone and is also good insurance for areas like center case gaskets.

Install the right side power valve cover and torque the bolts to 9 lb.ft.

Starting to look like a motor now.

Engine Build HPP Valve Honda CR250 – Part 7

dogger315 — Tue, 16 Mar 2010 21:24:26 +0000

Part seven of the CR250 engine build. Now that the bottom end is done, we can turn our attention to the top end. Top end segments include, cylinder and cylinder head prep, power valve installation and set-up, piston and rings, reed valve and carburetor.

This segment will cover power (or exhaust) valve installation.

The exhaust valve or HPP (Honda Power Port) on these engines was very effective and comparatively low maintenance.

Tools needed: circlip pliers, torque wrench that will measure down to 4 lb.ft. and standard metric tool assortment.

Thoroughly decarbon and clean the power valve components. I have found that a common oven cleaner aerosol does a good job of removing the carbon buildup on these components. Once you remove the carbon, clean all the parts in a solvent based cleaner and dry with compressed air

Power valve components. The two shafts are identical. Most of these parts came out of a high time CR. They were cleaned, NDIed, decarboned and checked to be in spec. Items out of spec were replaced, the rest will function as good as new.

Apply moly 60 grease to the flap valve shaft and install the flap valve through the exhaust outlet with the ridge facing up. Line up the round hole in the flap valve and insert the flap valve shaft. Check that the flap valve moves up and down freely. Coat the left sub exhaust valve with your favorite two stroke oil and set it aside. Apply moly 60 grease to the sub exhaust valve shaft and insert it into the left sub exhaust valve you just oiled. Insert the sub exhaust valve assembly into the cylinder passing the shaft through the elongated cutout on the flap valve. Apply an anti seize compound to the threads of the stopper bolt and install it along with the flat washer into the top of the cylinder and torque to 4 lb.ft.

Coat the bearing with two stroke oil and install.

Apply two stroke oil to the right sub exhaust valve and install it into the right sub exhaust valve port lining it up with the sub exhaust valve shaft previously installed.

Coat the bushing with two stroke oil and install it.

Now install the washer.

Finally, install the circlip making sure it is seated.

Mix up another batch of molybdenum disulfide grease and transmission oil at 50/50. Aplly the mixture to the joint areas of the valve link. Assemble the valve link components.

Apply grease to areas indicated.

closeup showing spring orientation.

Install the valve link assembly into the cylinder, attach the valve lever to the right sub exhaust valve with the socket bolt and torque to 4 lb.ft.

Coat the drive shaft and bushing with multi- purpose grease and install through the bottom of the cylinder and seat the end of the drive shaft in the drive pinion. Snug the socket bolt on the drive pinion but do not tighten yet. Install the spring clip.

Socket bolt on drive pinion.

Operate the exhaust valve lever by hand and check that the flap valve opens and closes. Now check that the mark on the left sub exhaust valve points to “L” when the valve lever is fully counterclockwise and the flap valve is closed.

Left sub exhaust valve pointing to “L”.

valve lever shown fully counterclockwise.

Flap valve shown in closed position

Turn the valve lever fully clockwise and check that the left sub exhaust valve point to “H” and the flap valve is open.

Image of valve lever fully clockwise

Image of the flap valve open.

Once you have completed the functional check, tighten the socket bolt on the drive pinion to 4 lb.ft.

Engine Build HPP Valve Honda CR250 – Part 6

dogger315 — Fri, 12 Mar 2010 20:03:55 +0000

Part six of CR250 engine build. This is a short segment on the installation of the ignition components, countershaft sprocket, kickstart lever and ignition cover.

To install the stator plate, match the mark at the bottom of the plate to the casting mark on the case

Apply a thread-locking agent to the two mounting bolts and tighten securely.

Install the woodruff key into the slot on the crankshaft spindle

Install the rotor, washer and flanged hex nut and torque to 40 lb. ft.

Place a new gasket in the grooves of the ignition cover and install the ignition cover with the four pan head screws and washers

Install the kickstart lever onto it’s splined shaft and tighten the bolt to 20 lb.ft.

Install the countershaft sprocket with the recessed side facing toward the engine

Place the cone washer over the countershaft sprocket with the “out side” mark facing out and tighten the bolt to 33 lb.ft.

Congratulations, you have just completed the bottom end of your engine build

Engine Build HPP Valve Honda CR250 – Part 5

dogger315 — Mon, 08 Mar 2010 18:56:27 +0000

Part five of the CR250 engine build. This segment will cover the installation of the clutch pack, right side cover, power valve governor and water pump cover.

Before installing the power valve governor, coat the throwout balls and the rack with a 50/50 mixture of moly 60 grease and transmission oil. Place the 12mm plain washers on each end of the governor. Align the rack yoke with the bearing race on the governor and install as a unit in the right side center case.

Apply the same lubricant mixture from the previous step to the pinion shaft and bushing and insert into the right center case from the top until it meshes with the rack.

This picture shows the correct orientation of the pinion shaft before cylinder installation with down being the front of the case. Pack the area around the pinion shaft with grease to prevent air leaks.

To install the clutch outer (clutch basket), soak the bushing and double row needle bearing in transmission oil and install on the mainshaft end that protrudes from the right side center case.

Place the clutch outer on the mainshaft and turn it until it meshes with the idle wheel gear and the primary gear.

Coat the two dowel pins in transmission oil and install in the respective holes in the right center case. Hang a new gasket onto the dowels and install the right side cover onto the right center case.

I like to pre-soak the fiber clutch disc in transmission oil before installation. Find a suitable container that can be sealed against airborne contaminants, fill with transmission oil, place the fiber disc in the container and close the lid. Pre-soaking assures the disc are thoroughly saturated with oil and aids in clutch life and consistent clutch action.

This is an old salad container I swiped from the kitchen.

Next up is the clutch center. Install the large thrust washer then the clutch center followed by the small thrust washer, locking washer and nut. Clamp a clutch holder tool onto the clutch center and torque the nut to 60 lb.ft.
DO NOT TRY TO WEDGE A SCREWDRIVER OR SIMILAR DEVICE BETWEEN THE INNER AND OUTER FOR THIS.

You have a better than even chance of ruining one or both of the components if you do. Once the nut is torqued, use a pair of adjustable pliers to bend two of the locking tabs against the nut.

Load the clutch pack by alternating fiber and metal (or aluminum) disc, starting and ending with fiber. Here is an oportunity to “tune” your power delivery. If you ride on hard pack or otherwise have trouble getting the power to the ground without excessive wheelspin, install metal clutch plates instead of aluminum. The metal plates add rotational mass and will tame the “hit” a little. Also, bare aluminum plates shill and foul the transmission oil with aluminum particles in short order necessitating frequent oil changes. Some may have already noticed the brown metal plates in the previous picture. These are akadised aluminum which is a hard coating designed to give you the benefit of aluminum plates without the shilling.

Apply Moly 60 grease to both ends of the clutch actuating rod and insert it into the hole (line) in the mainshaft.

Install the clutch “hat”

Install the pressure plate and six clutch springs

Install the six bolt/washers and tighten in three steps in a crisscrosspattern to 7 lb.ft.

Next up is the water pump. Coat the two dowel pins with oil and install. Place a new gasket on the dowel pins.

Place the separator plate over the first gasket.

Place a second gasket over the separator plate.

Now install the water pump cover and insert and tighten the bolts to 9 lb.ft. Install a new copper washer and the check bolt (black) and torque to 7 lb.ft.

Install and tighten the remaining right side cover bolts to 7 lb.ft. By the way, if you are using titanium bolts (like I am here), coat the bolts with a ti-prep grease to prevent dissimilar metal galling.

Engine Build HPP Valve Honda CR250 – Part 4

dogger315 — Sat, 27 Feb 2010 19:40:00 +0000

This is part four of the CR250 engine build and will cover the assembly and installation of the kickstarter, idle wheel and gear change mechanism.

To assemble the shift pawls and springs, coat the springs, plungers and pawls with transmission oil. Insert the pieces into the shifter and place the completed assembly into the plate guide. Place the assembly aside.

Mount the drum stopper and drum stopper spring onto the right case with the pivot bolt and torque to 9 lb.ft. Don’t forget the thrust washer between the drum stopper and mounting boss in the case.

Use a screwdriver to move the drum stopper and install the shift drum center onto the shift drum making sure it is seated. Install and tighten the shifter pin (bolt in drum center) to 16 lb.ft.

Mount the previously completed plate guide into the end of the shift drum center (use a small screwdriver to depress the shift pawls until they seat into the shift drum center). Apply a locking agent and torque the three bolts to 9 lb.ft.

Install the return spring, circlip and thrust washer on the gearshift spindle (first picture) and install the collar on the shifter (line in second picture). Apply grease to the gearshift spindle and install it into the case. Use a soft mallet to coax the spindle until seated.

To assemble the kickstarter, install the thrust washer and circlip on the kickstart spindle

Next, allign the punch marks on the small ratchet gear with the punch mark on the spindle and install the ratchet gear

Next, install the large ratchet gear and thrust washer. Install the return spring in the hole in the spindle and insert the sleeved spacer.

Finally, install the thrust washer and small spring at the opposite end of the assembly and insert the whole assembly into position in the right center case and wind the return spring clockwise until you can insert the spring end in the hole in the case.

Next up is the idle wheel. Coat the idle wheel bushing with transmission oil and Install the idle wheel bushing and idle wheel on the countershaft. Spin the wheel, it should spin freely and quietly along with the kickstart large ratchet wheel. If the idle wheel does not spin freely and quietly, remove it, turn it over and check it again. This is the functional check for the idle wheel and kickstart disengagement.