crank shims

[coater87]

 Hello,

 I am in the process of turning the timing bush, and am starting to think ahead a little.

 I have read a few comments here and there about the thin shims disintegrating. I am thinking I am best off to figure out the total amount of end float, divide by 2 and make two thick shims. What I am wondering is if anyone has an opinion on what the best material would be for this?

 I have thought about Stainless simply because it will work harden, but then my sump magnet would not catch any bits that went south.

 Tool steel shims I can make- but are they the best choice?

 Before I broke the cases, I measured what I had at .015. It was not until I got a good look did I notice there were NO shims on the crank at all. Now whether this was over-site by the past owner, or they tore off- I dont know. But I think I am best off making two shims at .0075 then trying to sandwich some together?

 Lee

[muskrat]

G'day Lee, the shims go behind the roller bearing not the bush and if the roller is on the crank tight the shims will not wear. Most of the old bike shops have the proper shims, I would try to use 1 instead of 2. If you wish to shim both sides the timing side shim should go behind the bush spigot.
Cheers

[RichardL]

Muskrat,

Even I got my shimming, I believe, right on, but it took multiple shims behind the bearing. I think it is probably common to do as I did and sandwich thinner shims between thicker. Also, if we believe SRM, and obvioulsy I do, a cush nut come loose will cause enough lateral crank pounding to destroy shims behind the bearing.

Lee,

Shim kits are readily available at reasonable cost.

Richard L.

[coater87]

 Hi guys,

Maybe I got this all wrong, I thought the idea was to get the crank centered between the cases which should make the rods center to the bore? I know we are only talking talking a few thousandths here,but that was my understanding of this.

 I thought I would shim behind the lip of the bush, and maybe behind the bearing, inside of the case itself?

 Now I am confused here, exactly where do the shims go? Should I only use one, or many thin ones?

 The only company I have found that has an NOS shim kit is Rabers, and they want $25.00 for 4 shims. I kind of use them as a benchmark for parts as far as price, if others have a shim kit for $3.00 I automatically think "junK". I am probably wrong there also?

 Making the shims would be quite easy for me, and if I can make them myself, know WHAT they are made of, and save a few dollars not having to compromise with "close enough" I would be all the happier. But now I am completely confused...

 Lee

[RichardL]

Lee,

The centering tolerance is at the little end of the connecting rods where they can move laterally on the gudgeon pin.

Shims from, dare I say, SRM are 6.17 GBP (around $10) for a set of 5. I don't know if it is a standard mixed set or if you can request exact thicknesses.
 

[Josh Cox]

G'day Coater,

Most bearing places sell shim material, usually in largish rolls, being the lazy bastard I am, I'd buy them from SRM.

One thing that keeps being mentioned by all I have spoken to is try to make them distance with as few a number of shims as possible.

I concour with the statement about shimming at both ends, the Bacon book also mentions this, Haymes on the other hand recommend chucking the old ones back in.

Edit to Add:

Was just down the local hobby shop buying bits to fix my oil breather, they sell shim material in smaller peices, good luck.

[muskrat]

G'day Blokes, Lee shim between roller & crank, use as few as possible. make sure cush nut stays put. I have made my own out of brass or steel. BUT if you make your own peen the cut edges, as cutting with snips tends to make them thicker on the edge. I have raced with the cush as std and also with the cush all locked up (no spring at all) with no probs. Make sure the shims are sandwiched firmly. I made a sleeve to go over the shaft, and heat the bearing in boiling water, drop it on the shaft, put sleeve on and use the cush nut to apply light pressure on the bearing till it cools. Use WD spray to disperse water. Under anything less than DRAG RACING conditions the shims will stay put. The shims that do take a beating are the ones that space the engine sprocket to line up primary, but thats another can of worm's.
Cheers

[Josh Cox]

Sleeve with cush nut, now that's a great idea.

[beezalex]

Coater, I use Arbor shims made of spring steel from McMaster-carr.  I can usually find a combination to limit it to 2 or 3 shims.

[A10Boy]

Shims are designed to pack out a gap not to act as a thrust washer.

In the pre units, the crank runs against the timing side bush which acts as a thrust on its flange. The shims always go on the roller end between the bearing and crank web and are clamped tight when the cush nut is tightened. As has been said, if this comes loose the bearing can turn against the shims and burn them.

[RichardL]

Andy,

Thank you for saying this clearly. Though I knew it would be, I didn't have the guts or, maybe, experience to say directly that it would be a waste of time and incorrect procedure to shim on both sides.

Richard

[Josh Cox]

I'd like to retract my previous statement about shimming both ends, whilst it is mentioned in the Bacon book and the engine I've just pulled down had shims at both end, was talking with a very experienced engine guy, quite frankly he thought I must have been smoking crack when I suggested it to him.

Live and learn.