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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 26057
Experience:  Service manager and technician for all brands of engines with 40 + years of experience.
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D902 crank has been reground and spins freely no.1 and 2

Customer Question

d902 crank has been reground and spins freely no.1 and 2 main bearings bolted in to block.
when fitting rear mains cover with its seal and gaskets the crank will lock as the cover is tightened, thrust washers are new and standard, main shells are new and standard, rods and pistons not fitted yet, crank is free until the cover is gradually tightened diagonally and using correct torque settings.
Submitted: 5 months ago.
Category: Small Engine
Customer: replied 5 months ago.
I think that the rear main bearing housing which has the bolt holes to accept the inner ring of bolts on the rear mains cover is being pulled up against the block, would it help to fit the rods and pistons? would that limit lateral movement of the crank?
the crank spins nice and freely until the rear mains cover is tightened. I have tried fitting the bolts innermost first/outermost first and have not exceded the torque figure. the cover has a new inner gasket round with 8 holes and a new outer gasket and will only fit one way the is an up arrow cast into the cover. I cannot work out what is going on. the crank was reground on the big ends by a motorcycle engineer on account of the narrow journal (19mm) but as stated is perfectly free until the rear mains cover is fitted.
Expert:  Curtis B. replied 5 months ago.

Did you try it without the seals and gaskets? did you try it without the thrust bearings? And does it lock solid? The bearings are all for the undersize crankshaft? Do you see any bright spots on the bearing, that indicates a high spot? Putting the pistons in will not help, just have to remove them again! If it still locks up, with seal and gasket off, and correct bearings, the block my need to be line bored to true it up!

Customer: replied 5 months ago.
cured , on these engines the main bearings one and two are free to rotate until the securing bolt in the block is fitted. the number two bearing will fit either way round but does in fact have a very slight offset so that if incorrectly fitted pushes the whole crank assembly rearward causing it to lock when the rear main bearing cover is fitted.
Expert:  Curtis B. replied 5 months ago.

Yes, bearing cap location has to be exact! Thanks.

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