Exhaust Crush Washers

StandardGuy · Oct 7, 2012

Have owned my 74 850 for about 6 mo. In that time, my left exhaust pipe start nut has always loosened no matter how much I tightened and yes, I used a lock ring. On a ride today, my exhaust came out of the head, completely. I pulled over, got out some wire and sealed the header for the trip home. Now that the exhaust is cooled, I see that the threading is battered for the first few threads making threading the start nut back impossible if the crush washer is in place. So, if I remove the .10in crush washer (which seems totally solid to me, no crush to it) I can thread the star nut. I did put anti-seize on the threads, and did reinstall the lock ring. Question 1) can I run this way, and 2) are their thinner crush washers out there?

Thanks
Guy

drones76 · Oct 7, 2012

StandardGuy said:
Have owned my 74 850 for about 6 mo. In that time, my left exhaust pipe start nut has always loosened no matter how much I tightened and yes, I used a lock ring. On a ride today, my exhaust came out of the head, completely. I pulled over, got out some wire and sealed the header for the trip home. Now that the exhaust is cooled, I see that the threading is battered for the first few threads making threading the start nut back impossible if the crush washer is in place. So, if I remove the .10in crush washer (which seems totally solid to me, no crush to it) I can thread the star nut. I did put anti-seize on the threads, and did reinstall the lock ring. Question 1) can I run this way, and 2) are their thinner crush washers out there?

Thanks
Guy

Are you saying that the threads on the rose nut are bad or the threads in the head? If the threads in the head are stripped, it will need some surgery. I just had mine done.

And you may be better off without the lock rings. It seems they cause more rattle and hum instead of locking anything.

concours · Oct 7, 2012

Welcome. Have a read here: engineering-compromises-leading-exhaust-threads-stripped-t14363.html but bear in mind, the problem doesn't really exist :mrgreen:

concours · Oct 7, 2012

StandardGuy said:
Have owned my 74 850 for about 6 mo. In that time, my left exhaust pipe start nut has always loosened no matter how much I tightened and yes, I used a lock ring. On a ride today, my exhaust came out of the head, completely. I pulled over, got out some wire and sealed the header for the trip home. Now that the exhaust is cooled, I see that the threading is battered for the first few threads making threading the start nut back impossible if the crush washer is in place. So, if I remove the .10in crush washer (which seems totally solid to me, no crush to it) I can thread the star nut. I did put anti-seize on the threads, and did reinstall the lock ring. Question 1) can I run this way, and 2) are their thinner crush washers out there?

Thanks
Guy

The gasket (crush washers) I've been getting are steel wrapped ceramic fiber, only about .060" thick. But, that small amount won't buy you much thread. Sorry. You'd be doing well to NOT run without the crush washer, that would simply wallow out the sealing face in the head.

StandardGuy · Oct 7, 2012

The thread damage is in the head. I am going to go ahead and run without. I mean, what have I got to loose, the damage is done and I do seem to get a pretty good fit, very minimal blow by.

concours · Oct 8, 2012

StandardGuy said:
The thread damage is in the head. I am going to go ahead and run without. I mean, what have I got to loose, the damage is done and I do seem to get a pretty good fit, very minimal blow by.

Any pics?

fredful · Oct 8, 2012

Those crush washers are just another cause of the header pipes coming loose, as they compress the nuts get rattly and wear the threads in the head. My Commando has been running minus sealing washers for years and they have never come loose. trouble you may have is the thread is already worn to the extent that further tightening will strip the thread completely. Good luck Fred.

johnm · Oct 8, 2012

If the threads in the head are gone then you can perhaps gain a bit of time by

1 not using the crush washers
2 checking to see if you can find screw in "rose" pieces with better threads. I have been through boxes of these and some are a much tighter fit than others.
3 using high temp rtv on the threads. I have used this for years on my race bike and no issues.
4 Nip up the rose pieces when the bike is fully warmed up.
5 lock wire the rose pieces.

In the end you will have to fix the head but this may buy you a year or two.

Mark · Oct 8, 2012

^^^ That's pretty much what I was gonna post.

StandardGuy · Oct 8, 2012

Yep. I agree 100% with the last points made.

At this point, I have the nut in place without the washer, plenty of thread and I did put some high temp anti-seize on the remaining threads. I also put the lock ring into place and wired the nut.

I did order some copper crush washers and will give them a last shot. If they don't allow me to grab some thread, then I will run without through to next winter then pull the head and get to a real fix. Assuming of course that this situation does not go south beforehand :!:

Thanks for all the comments guys, much appreciated.

Guy

bmwbob · Oct 8, 2012

1975 style exhaust nuts, header pipes and no keeper. Anti seize and take off exhaust as a complete unit. My exhaust nuts never come loose and threads don't get messed up!

concours · Oct 9, 2012

bmwbob said:
1975 style exhaust nuts, header pipes and no keeper. Anti seize and take off exhaust as a complete unit. My exhaust nuts never come loose and threads don't get messed up!

I haven't laid eyes on '75 pipes, the parts illustration looks like an attempt at a spherical shape? Any good clear images? Was the head port machining any different?

Torontonian · Oct 10, 2012

Honda CB 350 copper crush washers. If the preciou$ port threads are mangling then try using Lots of RTV high- temp copper silicone. No retaining rings. Also not all exhaust nuts were threaded the same lengths. 75 type go in deeper and press the crush rings in tighter to seat home.

rvich · Oct 10, 2012

Are you running the balanced pipes, collets and all? Seems like another reason to go to the unbalanced pipes and 750 nuts.

Russ

Whitworth Ranch · Oct 10, 2012

I've been running the factory crossover on mine but just bought new 750-style non-crossover and the longer-threaded nuts. Seems like a better idea than all that split-collet stuff. Then again, the threads in the head are fine and the exhaust on my bike isn't cracked... I actually wish I'd bought Interstate type so I could go full-touring conversion. Maybe in a few months. Would be cool to have a set of touring bodywork in a different color than roadster and just swap as the mood/usage dictates.

bmwbob · Oct 10, 2012

concours said:
bmwbob said:

1975 style exhaust nuts, header pipes and no keeper. Anti seize and take off exhaust as a complete unit. My exhaust nuts never come loose and threads don't get messed up!

Click to expand...

I haven't laid eyes on '75 pipes, the parts illustration looks like an attempt at a spherical shape? Any good clear images? Was the head port machining any different?

I use the 1975 head pipe with a conical insert and a collar with the longer 1975 exhaust nut and stock pea shooters. System allows the pipes to fit slightly off center if needed with proper seal and I don't use locking ring. Exhaust nuts haven't come loose in 20 years! But use ant size and remove exhaust as a complete unit or threads get chewed up!

http://www.ebay.com/itm/Norton-Comm...Parts_Accessories&vxp=mtr&hash=item35bf9c3073

Exhaust Crush Washers

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