Motorcycle Repair: crankshaft, honda s90, ring spacer

Question
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Followup To
Question - i guess you misunderstood the outer race is moving not only side to side with the rest of the crank( not moving on the crank itself) but i can put my hand on it and spin it as it sits  in the case, also if i can find some shims, would i put one on each side of the crank as to make it as centered as possible. john do you think honda would have these shims?

i have a old honda s90 that iam doing an head job and piston replacment. i checked the crank and cant find any play in the bearings but i can slide the whole crank from one side of the case to the other with a good bit of room. .016" and i also noticed that the race for the main bearings also can move against the case . is that way to much room? or does this movment matter? thanks john
Answer -
John, these small motors do have problems in controlling the side play on the crankshaft assembly, especially if they have a lot of miles on them or they have been ridden hard at high rpms.

The races in the case should be permanently in place. The outer crank bearings should fit snugly on the ends of the crankshaft. If the bearings just slide on and off the crankshaft with hand pressure, then something is excessively worn.

You can try to "dimple" the bearing surfaces on the crankshaft and/or use some Locktite (or similar) stud and bearing mount to help secure them in place and give a tighter fit.

.016" is getting out there for sideplay, considering that the rod is trying to go straight up and down and has only a few thousandths side play. There is a little room in the piston on the pin for lateral motion, but you really don't want the crankshaft to be wandering around that much below the piston and rod.

You don't want anything hitting the cases inside, either. Perhaps you can find some kind of thin ring spacer to take up some of the play, if it is just the crankshaft going back and forth in the cases. If the bearings are loose on the end of the crankshaft, then that will need to be addressed as I mentioned above or replaced.

Bill Silver

Answer
John, that clears up the description considerably. The races are cast into the alloy crankcase halves and are not supposed to be loose in any way. The shim idea was if just the bearings were loose in the races, laterally.

Honda makes no repair parts for this problem. Probably cheaper and quicker to find another case half that has good, secure races in it.

Bill Silver