How do cylinder studs work?

OK guys. I need some expert advice here. I just put new cylinder studs into the crankcases of a 93 CR125 and am having trouble getting 1 of the nuts to reach the torque spec. When installing the studs I used blue loctite, bottomed them, and snugged up with a wrench (I had heard NOT to overtighten these). Manual calls for 9 lb-ft I think. Now, what allows the cylinder nuts to reach 20 lb-ft?

It just seems to me that since I can only reach about 15 lb-ft on the 1 nut and I'm afraid I'm spinning the stud now. All 3 other nuts torqued nicely to 20. I assume I messed up installing the stud (the 2 ends WERE different!) or I'm just too afraid of stripping it. I'll try removing the nut and retightening all nuts again. When I do that I'll take pics of the stud threads since they were really weird looking.

I'm trying to accomplish 2 things with this post: 1) solve my problem and 2) understand how studs/nuts work as opposed to bolts.

If you apply torque to a bolt, thread friction wears at the threads the bolt screw into. With a stud, the threads in the crankcase don't move while torque is applied, and are only subjected to the pulling load.

But you can't bring the nut up to torque specs, so does the nut reach a certain level and then "rebound", or unwind when you release it, or does it run up to 15 and keep turning without the torque going any higher?

The nut doesn't "rebound" it just seems to continue spinning at 15 lb-ft.

I looked in my manual and it appears they don't spec the torque for installing the cylinder studs, but rather they spec torque for the head studs which have a flange (acts much more like a bolt?). I didn't actually use a torque setting, just snugged it up. Don't think I stripped the stud since I am still getting 15 lb-ft. not zero, but I'm afraid I will strip it if I add more torque.

I figured that if I had left the stud "loose" then when tightening the nut the stud would start turning with it (although I imagine the friction between the flange nut/cylinder interface is more than in the stud/nut threads such that the stud itself would only rotate as much as the nut?).

If the nut turns but the torque value does not rise, the threads are yielding somewhere along the line, and there's already a problem. The most likely spot is the threads in the aluminum. What size are the threads on the cylinder studs?

If the nut bottoms on the upper threads, or otherwise seizes to them to the point where there is less friction at the lower threads, the stud will rotate as it is tightened, but if the threads are healthy, the stud then simply behaves as if it were a bolt, and should feel normal as it tightens up.

Maybe you could mark a line across the top of the stud with a Sharpie or whatever, and see if the stud is turning in the cases.

Ray

If the nut turns but the torque value does not rise, the threads are yielding somewhere along the line, and there's already a problem. The most likely spot is the threads in the aluminum. What size are the threads on the cylinder studs?

If the nut bottoms on the upper threads, or otherwise seizes to them to the point where there is less friction at the lower threads, the stud will rotate as it is tightened, but if the threads are healthy, the stud then simply behaves as if it were a bolt, and should feel normal as it tightens up.

My first suspicion was the yielding of the aluminum in the crankcases. The threads are M8 and I'm using both OEM studs/nuts (brand new too).

Also, I'm now wondering if I shouldn't have used the loctite in on the bottom of the stud when installing. I used the 242 blue version which I heard can't be used with greasy surfaces like the 243 version. So I wonder if there is less friction between the lower stud/case threads than the nut/stud threads...

I'm hoping to just loosen all nuts and torque them in a 20 step sequence (I previously did about 5-10 steps using criss cross pattern). If this doesn't solve it, I'll be pulling the stud and checking the condition of hole/stud. I will for sure take pictures of the threads on the front studs as they are VERY strange looking to me. At first I thought it must've been a manufacturing defect, but both front studs (brand new mind you) were the same which made me think the "defects" actually served a function!

Maybe you could mark a line across the top of the stud with a Sharpie or whatever, and see if the stud is turning in the cases.

Ray

I actually thought of that. I'm pretty sure the stud was turning with the nut by eye. I did not expect to have THIS type of problem at this point in the project! After the 5 minute first start of the bike I can't say I noticed any leaking, although I'm just worried it might be sucking air in...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now