za50 crank shim advice/help in mass

I have been building a za50 and found that my stock crank was bent, so i purchased new bearings, seals and a race crank off of 1977. I measured my stock crank with races from end of race to race and got a measurement of 58.32mm. I then pulled my old races off the crank and took out a .2mm shim from the clutch side on the stock crank and it looked like there was a .005mm shim that had adhered to the crank on the flywheel side.

I then ordered a .2mm, .005mm x2 shims from treats for the flywheel side.

I have pressed the races into the case along with the .2mm and .005 shim onto my race crank with a 40 ton shop press to make sure they are straight on.

I have since tried every combination of the shims i have to get the crank to stop binding but have not succeeded.

When i close the case with the gasket in and the bolts tightened in a star pattern I am still getting bind (when I assemble my transmission the sprocket spins the piston in both ways)

I assume this means my crank is still binding and has not been shimmed correctly.

Any advice would be appreciated as I am stumped and would love any and all input.

Also if anyone in new england could help i would make the trip/ pay you for the help.

Also i have been checked the bind by not putting the transmission cover on as to make sure it is not the tranny side endfloat that is causeing it. im not sure if that is helping or hurting.



Re: za50 crank shim advice/help in mass

Oh, I wish I had it in front of me. Let me type a response... give me a couple minutes.

Re: za50 crank shim advice/help in mass

I'm still a little bit confused as to weather it's binding when you put the two case halves together or only after you put the transmission cover on.

IF it only binds when you put the trans cover on, it's either #3 or #7.

IF it binds when you assemble the case halves and nothing else, it's #1, 2, 4, 5, or 6.

Either way, here are the possibilities:

1. You shimmed your races incorrectly, causing your crankshaft bearings to bind.

2. You didn't press the outer races the correct depth into the case halves.

3. Your over-enthusiasm with the FORTY TON press bent your new crank, putting a bind on it.

4. You're assembling the case halves in a vertical orientation like this = instead of vertical (as if they were on the bike). Sometimes if you assemble the case halves the wrong way the bearings won't be centered on the races and will bind.

5. Your starter clutch is out of adjustment with the new crank.

6. Your 2nd gear clutch is binding on the crankshaft after tightening the clutch retaining nut. This can be checked if you tighten the nut and then check to see if the 2nd gear clutch spins freely. If this is the problem, let me know and I'll expand on it.

7. Your trans cover shims are incorrect.

Re: za50 crank shim advice/help in mass

wow! thanks for the response.

I think I can rule some stuff out, It is binding before I put the transmission cover on. I can rule out the press because i barely used its capabilities, it was unfortunately the only one i could get my hands on but I made sure to barely put pressure on the crank with it. I am however unable to spin my second gear clutch when I tighten the clutch nut, I noticed this before and assumed it was bind. It spins in unison with the first gear. It is a possibility that i did not put the races in the correct depth in the case, they feel as though they are flush. When I have the starter clutch on with the spring and c clip on it does not appear to grab at all.

Again Thank you so much for the detailed help!


Re: za50 crank shim advice/help in mass

Ok, I know exactly what your issues are. First, after your starter clutch you have the spring, c-clip, a shim, and then the metal starter plate, correct? Now, do the splines of the metal starter plate extend above the shoulder on the crank?

My guess is yes, and if so you have to either have the splined part of the starter plate lathed down below the shoulder on the crank or do it carefully with a belt sander, etc.

After you have that done, put the 2nd gear clutch on the crank along with the starter plate and the spacer between 1st and 2nd gear clutches. The spacer should sit down on the crankshaft shoulder that is now above the splines. If there is a gap between the spacer and the shoulder (which there probably is), the 2nd gear clutch must be modified by turning down the 3 cheeks.

If you want pictures, let me know. I can pull apart a motor or just highlight the stuff on factory drawings.

Re: za50 crank shim advice/help in mass

I think I get what you are saying and that is definitely my issue. My only question is couldn't I just turn down the second gear spacer or will my second gear still be to high? Also if i measured the gap between the second gear and spacer would that give me the distance that I need to turn down the splined part of the starter plate?

Again thank you so much for the help, I would have never guessed that the part I bought was the issue. It is kinda depressing that I paid so much for something that is wrong, but there are no other options i guess,

Thanks ben

Re: za50 crank shim advice/help in mass

Nope. The spacer shouldn't need to be modified. In fact, I wouldn't modify it or it might break.

I've had to do stuff like this with all 5 aftermarket ZA crankshafts I have installed so far. It makes me think that having a needle bearing connecting rod pressed into a stock crank would be a easier solution...

Re: za50 crank shim advice/help in mass

well luckily i have a harbor freight near by so im gonna pick up a belt sander and see what i can do. I'm just glad I wasn't going crazy.

Thanks for all the help.

Re: za50 crank shim advice/help in mass

Ok, I want to repost some pictures so you are 100% confident before you start removing material... check back in a jiffy.

Re: za50 crank shim advice/help in mass

Re: za50 crank shim advice/help in mass

Matt Mahloch -- MBM Customs /

Just to make sure. When you have the crank in the case and the two halves bolted together your end play is in spec correct? and the crank spins by hand?

Re: za50 crank shim advice/help in mass

Give up and send it out to Chris Paz. He's the god of these things and will build it right for way less than the cost of a new crank. Cram the block into a flat-rate box and send it to Cali for $15. Get that shit done right and call it a day.

Re: za50 crank shim advice/help in mass

awesome, that is what I was thinking, thanks for the pics they help show it better.

Re: za50 crank shim advice/help in mass

yes the crank spins by hand. If you saw how much the crank is off by you could tell that it is not a shimming issue.

Re: za50 crank shim advice/help in mass

why would I give up, when It is the right way to fix this the crank was machined wrong to begin with so the transmission parts need to be corrected to compensate for it, fifteen is cheap but with the price of shipping a whole engine out not worth it/ my stock crank was bent on the flywheel nut threads.....

Re: za50 crank shim advice/help in mass

Jake, do you absolutely need to have a shim present on the crank under each of the bearings or can you just space it with a feeler gauge?

i am replacing my bearings and i have shims for the transmission, but none have a large enough ID to fit over the crank shaft.

treats has shims with an ID of 18 mm but that doesnt seem like it would be wide enough, tho they label it as a crank shim.

I was planning on doing the cold crank/ hot bearing method for bearing install and carefully tapping on the inner race to seat the bearing, but i will need to find a pipe or seat post or something of the appropriate diameter and length first. i don't have access to a press down here. any suggestions?

also, one of the bearing cups is still in the case (from the stock bearing) my new bearing seems to fit in it fine with no extra play. can i just re-use that cup or should i use the one that came with the new bearing? just trying to avoid unnecessary work of taking out the old cup and putting the new one in if i don't have to.

Re: za50 crank shim advice/help in mass


The thin shims that go between the inner races and crankshaft cheeks may or may not be necessary. You can measure the dimension and compare it to the shop manual spec to see if you need shims, but the races should always be pressed on until they stop; shims or not. If you're feeling lucky I guess you can just skip the shims on that part, but it's better to do it right.

I've found that you don't really need to heat or cool either part down, just use a tube with the right ID and a hammer or press.

If you're doing new bearings, replace the races that are pressed into the crank too. The new races that came with the bearings are matched to the shiny new bearings. The races can be a real pain to get out though. Some of them can just be punched out with a slender punch, others have to be cut to release pressure first. It may also help if you put the case in the oven for a while and then punch the race out. The aluminum expands faster/more than the steel race.

Re: za50 crank shim advice/help in mass

thanks Jake, was thinking i would try to bake that case half first and then get something in there to pry that cup loose.

i'll have to find some bigger ID shims for the crank bearings/ races. seems like if they are all the way flush to the cheeks that they would bind when the crank heats up and expands.

Re: za50 crank shim advice/help in mass

I just did a ZA50 stuffed crank in a rebuild and no shims were needed.

Re: za50 crank shim advice/help in mass

Robert, where did you get the crank from? Have you started/ran it yet? Did you check the tolerances/float according to the shop manual?

Re: za50 crank shim advice/help in mass

It was a stuffed crank from Treats. I pressed the bearings on and everything is in spec. No shims were needed. I did it about a month ago.

Re: za50 crank shim advice/help in mass

yes well mine is stock with new rod pressed in so i expect some shimming. i ordered some more large ID shims from mcmastercarr for the crank bearings along with some other stuff i needed for my other bike.

new pucks are in and got the old races out of the case last night.

hoping to get this done by the end of august, but only money and resources will allow that.

Re: za50 crank shim advice/help in mass

I went to napa and got some plasti gauge, made checking endfloat approximately 1 bagillion times easier..........

Oh and tammiecat, I would not worry about your shimming the crank yet it should stay almost the same. I replaced the bearings and did not run into shimming issues with that, just the crank being off in milling because I bought the race one from 1977.

Re: za50 crank shim advice/help in mass

Ben, What did you find wrong with the milling? What did you modify/shim on the transmission side? Starter clutch? 1st/2nd clutches? shims?

Re: za50 crank shim advice/help in mass

I ended up doing what you said. It was very hard to measure but it appeared that the spot on the crank that the spacer between the clutches sits on was roughly 1mm off from where it should have been. I had my crank shimmed so that my endfloat was correct but I was still sitting above that lip or whatever it is called do I then shimmed my flywheel side to try and compensate and there was no way of getting it to sit level with the splined piece so I just ended up grinding it down. When I measured it against my stock crank it was somewhat smaller but it was a big enough gap that it was not able to be compensated by shimming.

Re: za50 crank shim advice/help in mass

Yep yep. Don't understand how Robert didn't run into this problem...

Re: za50 crank shim advice/help in mass

yeah same

Re: za50 crank shim advice/help in mass

No, I ran into the same problems as everyone else. All I was saying was that I did a stuffed crank in a ZA50 and no shims were used and the crank is in spec.

Re: za50 crank shim advice/help in mass

It might of been the bearing brand you used.

I wouldn't run that needle bearing in that wrist pin unless you like siezing the little end of the rod. Very poor qc. buy ina bearing for it..

Re: za50 crank shim advice/help in mass

Its all luck really the shims are there to take up manufacturing tolerances.

If the crank webs on one crank are .002" narrower on one crank vs another then that crank will probably need an shim. Due to the fact that the crank bearings would sit .002" closer together.

A number of times I have pulled old bearings off an stock crank and put new ones on and not needed to change the shimming at all. Then again you never know until you know.

Also when you get an con-rod pressed into the stock crank the withe of the crank webs will have most defiantly changed = re-shim. This is due to the gap between the webs and the big end of the con-rod the machinist left. If it is any more than .008" of a gap you will probably have binding issues. I ran into that the first time I had a crank pressed together, without shims on either bearing the crank binded up when the bolts were torqued down. Reason being my machinist was use to pressing 250 and 500 cc dirt bike cranks and the con-rod gap ended up being around .012".

Not sure what you are referring to Ben, any chance you could post a photo of what you had to grind? I have assembled around 20 motors with the 77 crank and had no real issues.

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