Engine Build HPP Valve Honda CR250 – Part 1

This is part one of a nine part series documenting the assembly of a Honda CR250 engine.

Round one includes the center cases and right side case cover.

There are many ways to install bearings. These bearings were installed by heating the cases to 225 degrees in an oven (do not use a torch) and placing the bearings in a freezer and cooling them to 0 degrees. The heat expands the case and the cold contracts the bearings. The cold bearings drop right in the hot cases then develop an interference fit when both reach room temperature. I recommend this procedure because it has the least potential for damage.

All retainer bolts should be coated with a locking agent (imagine the carnage a loose 6mm bolt could do inside your transmission).
And finally, clean is the word. Do not do engine work on a dirty engine and do not do engine work on a dirty work bench. Don’t sabatoge all your effort by introducing contaminents into your engine internals.

Engine work is straight forward and relatively simple. Jump in and save yourself some money.


Clutch side of the right side center case with bearings and shift lever return pin (line) installed


Crankshaft side of the right side center case. Note rubber vent baffle (line). A potential air leak if not installed.


Crankshaft side of left side center case with bearings and retainer installed


Right side case cover at water pump housing (crankshaft side) showing water pump impeller oil seal installed


Same section with water pump impeller shaft bearing installed. It is safe to heat this casting to 225 degrees even with the seal installed to facilitate bearing installation.


Same section again with water pump impeller drive gear installed


Clutch side of right side case cover with water pump water seal installed. This seal is prone to damage when installing. Use of a specialized seal driver or silicon lube and extra care is recommended


Water pump impeller installed and torqued to 9 lb.ft. Use extra care when tightening the impeller nut. You will need to hold the plastic drive gear. I recommend a gear jamming device available from Motion Pro and others. Use of pliers or screwdrivers may damage the plastic gear.

Stay tuned for part 2……

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