Removing Crank Bearing Preload?

[SteveSr]

Hello,

How important is it to remove crankshaft bearing preload when reassembling the crankcase of a small two-stroke? Previous experience with a bicycle rear hub reminds me that axial ball bearings don't like thrust loading. How true is this of small two-strokes? Will this preload just work itself out the first time the engine is run?

Here is the situation. Think of this as a very small saw . It is really a 25cc Stihl 4137 engine on an FS85 trimmer. Lacking $400 of special Stihl tools the crankcase was assembled with a small press from the outside. This leaves axial preload on the bearings. The crank turns but it is noticeably tight such that you can feel the bearings roll in their races. I would like to remedy this before going any further with the re-assembly.

I have tried using a suitable size socket, spacer washer, and the clutch/nut to try to pull the crank shaft further into the bearing to release the preload so far without success. I did manage to cup the washer. I am concerned that too much more pressure will hurt the shaft or the clutch.

Anyone have any suggestions short of the special Stihl puller/installer how to accomplish this?

Thanks,

Steve

 

[funky sawman]

I use a block of hardwood to protect the crankshaft then give it a wack on either end till it turns freely. You do not want excessive preload on yer mains.

 

[watsonr]

A BFH! Place the nut on the shaft to prevent thread damage and I use a brass hammer...whack it. Then whack the other side... done.

 

[Aldiehoggydoggy]

Yep I use one of those craptsman rubber/ polymer headed hammers and wack the flywheel and PTO side after install.

 

[chadihman]

yup yup yup a wack on each side

 

[SteveSr]

Hello,

I stopped by the local hardware store on the way home tonight to pick up a couple of metric nuts to protect the threads on the crankshaft.

I used a regular 16 oz. framing hammer and hand held the crankcase. First small taps resulted in no joy. I finally increased the force until the crank started to loosen up. I had to hit it pretty hard, harder than I would have expected. I stopped when the crank started to turn free.

Thanks for everyone's unanimous suggestions and contributions to this board!

Steve