OHV exhaust nuts

[graeme]

Does anyone have any clues as to how to keep the exhaust nuts as fitted to 20s OHVs from coming loose? I've tightened the ones on the OB as tight as I can and they still persist in undoing.

[Dave]

Have you tried one of the Loctite products Graeme?

Threadlocking
 
 Prevent loosening with anaerobic liquid threadlockers. Invented by Loctite Corporation as a revolutionary method to positively lock and seal threaded fasteners, anaerobic liquid threadlockers cure (harden) in contact with metal if there is an absence of air. That's why threadlockers are perfect for threaded assemblies. The threadlocker adhesive fills the entire air space between the threads, forcing out the air. So the threadlocker can bond to the metal and cure, creating a secure, unitized assembly that will not loosen. Also, the gap between the threads has been completely filled, thus sealing the assembly from moisture, and preventing rust and corrosion. Threadlockers are available in a variety of strengths to fit all of your applications. Most threadlocking assemblies can be easily removed with standard hand tools, or by the application of heat. Cost savings are a major advantage of liquid threadlockers.

More info - http://www.loctite.com.au/int_henkel/loctite_au/index.cfm?layout=4&productline=IND&path=Loctite%20Assembly%20Solutions&pathid=IND

If you go to this page...

http://www.loctite.com.au/int_henkel/loctite_au/index.cfm?&pageid=111&layout=2

... and select Threadlocking in the Application window, a list of data sheets will come up to help find the best one for your application.

Alternatively, you could call and ask their technical dept 03 8710-7600 (Melbourne) for advice.

Repco generally stock Loctite products.

Dave

[Ian]

Graeme, I have used the high temp RTV sealants before with some success on exhausts. Loctite as Dave says is another alternative but you would have to find out which ones can handle the heat - most have quite a low heat tolerance.

[Doug]

Graeme,

You must have some worn threads on your ports/gland nuts for them to keep working loose.  Or perhaps "The vibration-less twin" is not so smooth!  

None of the Loctite thread locking products is going to withstand the kind of heat you are going to see at the exhaust port.  Most break down at 200C and the high temp stuff holds out to 300C.  

I have heard tell of folks using the silicone sealant to seal gaps in sliding joints for tubular exhaust headers and between the silencer and the exhaust pipe joint.  It apparently does not really survive the heat, but is reduced to an 'ash' which still keeps the joint tight and does not weld the two components together (so they say.)  I used it once on a set of silencers and it seemed to work until the oil soot took over and choked up all the cracks!  This ash might provide enough friction to stop the gland nut from working loose.  I would put some on a bolt and nut and apply some heat from a propane torch to see how it 'cooks'.  It will make noxious smoke.  

Also you might try a single turn of narrow asbestos packing string between the flange on the pipe and the gland nut.  The compressibility of this as a washer, and wedging between the gland nut and pipe where it extrudes out, might be enough to stop the gland nut from backing off.  

-Doug

[graeme]

Thanks for the advice fellas. I was pretty sure that Loctite wouldn't work due to the heat.
The threads on both the stubs and nuts are good - in fact they are quite tight to do up. I think the problem is that it is near impossible to get enough leverage on the nuts when doing them up, due to everything getting in the way.
When I worked in a Moto Morini shop in London, to tighten the exhaust nuts on them, rather than bash the spanner with a mallet, we used an old fork stanchion over the c-spanner for added leverage. The exhaust nuts on them were notorious for working loose. Many owners wired the nuts to the head. I also owned a Commando for a while, which also had lousy threaded exhaust nuts! I wired them to the head. I've considered this option for the OB, but am reluctant to take a drill to it.
I'll try the string idea - this looks to have merit. But I still think the secret is in getting more leverage on the spanner.
Cheers, Graeme