cylinder head nut tightening

M

macavity99

Full member
Location
Bedfordshire, UK
Got a problem torqueing down the cylinder head nuts on my SF3.
Nut No 2 gets to 30 ftlb and then spins. Removed nut to examine nut/stud threads which look ok. Get the same thing with a different nut. Examining head directly below the copper washer I can see what appears to be shiny curly bits. Looks like ali swarf to me.

Is there any history of soft crumbling ali on these cylinder heads?

Anyone have a method of getting a spanner on these awkward nuts with engine bolted in the frame?

I want a "nice" answer please, nothing scary.

Cheers, Steve in UK
 
Hello, Steve.
I once came across the same phenomenon. It turned out to be a worn thread in the
upper case.
Concerning tightening the inner nuts there have been various solutions e.g. self-built
adapters proposed here.
I personally don't favour them, because the most limit free movement. The torque
wrench must be operated in one go, stopping in between makes it useless.
Lowering the engine with the lower 2 bolts still in place might help you.

hth, Ernesto
 
Hi Steve, is the swarf in the cylinder head or in the cylinder? If you are tightening down the cylinder head onto the cylinder the studs will just pass through the cylinder head itself. Given you mention crumbling on cylinder heads I assume that you're talking about tightening the cylinder head cover onto the cylinder head (if not ignore the rest of this!).

If the nut is attached to the stud when you tighten it in (ie acting as a bolt), depending on how far down the nut is, there may not be enough thread available at the other end when the nut comes to a stop on the cover. Can you lock 2 nuts together as close to the top of the stud as possible and try screwing this in as it may screw down further (into better threads). Then unlock the top nut and tighten the nut left down.

30 lb/ft sounds more than enough for such an interface - if this is the recommended torque setting you could try 25 lb/ft (the main thing is to set them all the same evenly). The worst thing that can happen is there may be an oil seep but then you can always adjust the torque at that time.

 
This occured during final assembly (I hope).That is, final torque tighten onto cam cover. When I had the barrel off, all the cylinder studs were screwed completely into crankcase to full thread depth, so far as I can remember. Therefore I don't think Brian's idea with the two nuts at top of stud will be successful. The "swarf" was on cam cover where the nut/washer touches the boss. The recommended torque is 36 ft/lb.

Ernesto appears to be suggesting that the stud is pulling out of the crankcase (eek! not the "nice" answer I was hoping for).

Anyway, all nuts are at 36 ft/lb except no 2 which is as tight as it will go at 30 ft/lb.

The engine is now bolted into frame, rear chain is on, and I don't want to disassemble. Will have to see what happens. Where's that silicone sealant......

Cheers, Steve in UK
 
Steve, It's a while since I worked on a 750 so I can't remember whether its possible to remove the stud in situ. If it is possible you might want to consider removing the stud and then fixing it back in with some Loctite 638. If you give the Loctite a few hours to cure, the stud should be fixed firmly enough to safely apply some torque to the nut. If you ever want to remove the stud some local heat from a blow torch will de-bond it.

I've bonded a lot of aluminium dome nuts to steel king pins using Loctite 638 and I'm fairly confident this will do the trick for you...assuming you can remove the offending stud. Cleanliness is the key to a decent bond strength.
 
Steve - There should only be copper washers under the domed head nuts - can't see how they would pull swarf from anywhere? - I'm presuming that there's no chance of stud thread being too long to suit the domed nut - Regards - Phil
 
macavity99 said:
The engine is now bolted into frame, rear chain is on, and I don't want to disassemble. Will have to see what happens.
Click to expand...

Fair point - if they are 30lb/ft+, swarf cleaned up and no leaks, don't lose sleep. You're bound to be working in this area some point in the future anyway so why stress now. If there is a problem you will see oil drips on the floor. Many bolts/nuts/studs take major stress, these don't..
 
Brian, I like your thinking.

Just following-up Bob's idea:

This "feels" like the stud is pulling out of the casing -- you know that awful feeling when the nut tightens and then rotates with a constant torque as the stud slides under friction. Not like a thread strip where the nut tightens and then suddenly becomes loose.

I've got some Loctite 603. Similar to 638 but for cylindrical gaps to 0.1mm and where you cannot get the parts absolutely clean. Could be ideal for this application. I could tilt engine forward and remove stud through barrel and head in situ.....

..... or just leave it and see what happens, as Brian suggests.

Cheers, Steve in UK
 
Lowering the engine with the lower 2 bolts still in place might help you.
Click to expand...
Like this ;o)
4657582372_05cb722f17.jpg

You gotta break the chain to do it but at this point it's no big problem to pull the jugs or just remove the engine.

 
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