I`ve got to replace some crank bearings on a gy6 in the next few days, but I`ve noticed on the crank there is a sprocket on each side which have to come off first. Do these simply pull off with a puller ? Also the left one runs the cam chain so it has to be in a specific spot for timing, is there a keyway which holds it in place or is it simply a case of marking both it and the crank, and then re installing in the same spot ? Cheers Rob
The sproket on the right side is for the oil pump. Just press it off and put it back on. no alignment needed. The left side is for timing chain and needs to be put back in the same place as removed. I mark the top tooth clooses to the crank pin. Now mark the crank pin with a mark that lines up with the said tooth. I use a engraver pencil. When you reinstall just line up your marks. You will be good to go.
When you do remove the right side bearing sometimes there is a shim that must be put back on before the bearing is installed. Some cranks have a shim some do not. It is used to set crankshaft to case end play.
Cheers lads, very helpful. The engine has been a bucket of bits for a couple of months now as we`ve been waiting on a warranty claim. Today we had a parts delivery so looks like I`ll be popping it back together tomorrow. There wasn`t a crank shim when I took it apart so all should be ok, I`ll take extra care when setting the valve timing.
Put the new bearings on the crank today, all went well, just waiting for a new left crankcase to turn up as the old one was chewed up by the bearing failure. We`re moving to a new workshop so I was putting all the bits into a box, and did come across a large shim, it must`ve been stuck in one of the crankcases and fell out when I moved the bits. The question is does it go in the left or right crankcase ?