Centering The Crank In The Cases

[gasgas]

Hi guys,

it was maintenance time, so replaced a few bearings inside the cases.

Did everything as per instructions. Shrink the crank in the freezer, heating the rightside bearing to get it wider, dropping in the crank untill she bottomed. Putting the leftside case on, has a slip-on fit on all bearings, so no sweat there. Closing her up, with the bolts, nice and tidie. Everything turns and goes, great.

Only thing is, the crank is not evenly centered between the cases. The rightside, where the primarygear sits, has more clearence between the cranksheek and case as the other side. Can not center is by hiting the left, so it is as it is. I can live with it, as the piston and big-end has enough side clearence anyway, but have others noticed this too?

Stupid thing is, i have done this job one other time before, but did not noticed it then. So any one who is experienced with the job, pls reply.

Thanks in advance.

[baldilocks]

is the crank supposed to be symmetrical or are you saying its not central in the crankcase mouth where the barrel fits ?

[gasgas]

central in the crankcase mouth where the barrel fits, you are right. Normally you try to achieve a crank that has the same play between the cases both left and right. That wld be the perfect fit. But now my crank is a little bit to one side. More play at the primarygear side , so to say, but still crank won't touch the case, lucky enough. Anyway, seemed that it was like that before splitting the cases so i let it be. Time will tell if it causes a pinch crank/case situation.

[peterb]

Hi gasgas,

When I fit up the crankshaft in the cases, I always install the main bearings first as they are an interference fit into the cases and the LHS bearing has an oil drain hole that must line up with the crankcase bearing housing drain hole. I prefer to put the bearings into the freezer for an hour and use a heat gun on the housing to fit up the bearings. The crankshaft fit into the bearing ID is not as tight as the bearing OD into the housing, the crank can then be gently tapped with a nylon hammer to centralise in the crankcase by eyesight. I haven't noticed any centralisation problem with this method. There should be no play (endfloat) in the crankshaft and it is normal for the crank to line up centrally.

Are you sure the LHS bearing drain hole is aligned?

Bye, PeterB.

[jmck]

Hi gasgas,

When I fit up the crankshaft in the cases, I always install the main bearings first as they are an interference fit into the cases and the LHS bearing has an oil drain hole that must line up with the crankcase bearing housing drain hole. I prefer to put the bearings into the freezer for an hour and use a heat gun on the housing to fit up the bearings. The crankshaft fit into the bearing ID is not as tight as the bearing OD into the housing, the crank can then be gently tapped with a nylon hammer to centralise in the crankcase by eyesight. I haven't noticed any centralisation problem with this method. There should be no play (endfloat) in the crankshaft and it is normal for the crank to line up centrally.

Are you sure the LHS bearing drain hole is aligned?

Bye, PeterB.

I have found over the years that even "lightly tapping" a crankshaft in place can knock it out of "true", if even only slightly. If you don't believe it, put the crank in a truing jig, record the measurements, tap into the bearings, then remove it and check the measurements again on the truing jig. They will be different.

[gasgas]

Yes, you can hit a crank out of true. I have done that before

I also install the bearings first, and they have a tight fit in the house.

Thanks for yr replies.