Hi everyone. Earlier today idecided to investigate a metalic noise coming from the engine of my WM20.On removing the gudgeon pin all was revealed.The small end bush has been revolving in the conrod causing wear.Luckily most of the wear appears to have been confined to the bush.The conrod i.d is.940. The small end bush on a part with no wear is.942 the worn part is.935. So if i buy a new small end bush hopefully it will still be a snug fit.Can anyone suggest a type of locking compound for the bush to prevent this happening again.? Thanks.
Hi Mike ...This doesn't happen very often. If your new bush is a good fit in the rod and requires some effort to pull it in should be alright. A little retaining fit Loctite may help but will only be a temporary fix if you have lost the interference fit between the rod and bush.
I usually drill additional oil holes through the bush after it is fitted (in the slot in the top of the rod) but before reaming to finished size.
The problem can be caused by the bush to pin clearance being too small after fitting..the pin then overheats and goes tight in the bush. Ensure that after reaming the pin is an easy sliding fit in the bush, but with minimal play. When the piston is fitted with an oiled pin it should fall easily to each side under its own weight.
If the new bush slides easily into the rod you will need to get an oversize bush made to cure the problem...a .002" interference will make it nice and tight. Remember to cover the crankcase opening when fitting to prevent bronze particles falling into the cases and avoid applying any side load to the rod...use the correct tool for pulling in the new bush...You will also need an adjustable hand reamer to ream it to finished size. Take very small incremental cuts to bring it up to size, checking the pin for fit after every pass of the reamer....Ian
Hi Ian. I'll pop up to Russells and get a bush and see how it fits ,I'll also get some Loctite just in case.I've got an ancient adjustable reamer that should do the job. So fingers crossed. Thanks. Mike.
