Engineering compromises leading to exhaust threads stripped (2012)

concours

VIP MEMBER
Joined
Dec 29, 2011
Messages
4,652
Country flag
Best I can see is, the exhaust threads being a problem area, is the result of multiple engineering EVOLUTION compromises. In the beginning, the head was cast iron and the threaded attachments probably worked just fine. Then the thread (head) material changed to softer aluminum... and they probably still worked OK. Then the Commando with Isolastic engine mounting system introduced lots of motion. And the four foot long pipe with a muffler hung on the end was hard to move from one end, overstressing the threaded joint. Then, in '74, the crossover pipe was added, requiring a shorter nut to make room for the split keepers now mandated by the crossover. 25% less threads engaged, failing even faster than ever. Item 17 here: http://www.oldbritts.com/1973_g23.html
exh_nut_sets.jpg

As much as I want to keep my bike original, the crossover pipes are being binned. The longer nuts to engage all the threads will be added, along with a better engineered mounting system, to be detailed later.
 
Joined
Oct 31, 2009
Messages
5,193
Country flag
Re: Engineering compromises leading to exhaust threads strip

Good part are key.
Many things can lead to this thread failure, but none so much as running these nuts up dry. Steel to alloy is inherently bad. It is not so much running them up as much as snugging and tighten that will produce galling. Once damaged a little, the harder it is to tighten, damaging the thread even further until full failure occurs.

A dab of anti seize will protect the threads and assure a snug nut after a few re torques.
 

batrider

VIP MEMBER
Joined
Aug 9, 2008
Messages
2,186
Country flag
Re: Engineering compromises leading to exhaust threads strip

I don't think it is a design problem - more of an owner problem.
 

concours

VIP MEMBER
Joined
Dec 29, 2011
Messages
4,652
Country flag
Re: Engineering compromises leading to exhaust threads strip

batrider said:
I don't think it is a design problem - more of an owner problem.


I couldn't agree more.
 

concours

VIP MEMBER
Joined
Dec 29, 2011
Messages
4,652
Country flag
Re: Engineering compromises leading to exhaust threads strip

pvisseriii said:
Good part are key.
Many things can lead to this thread failure, but none so much as running these nuts up dry. Steel to alloy is inherently bad. It is not so much running them up as much as snugging and tighten that will produce galling. Once damaged a little, the harder it is to tighten, damaging the thread even further until full failure occurs.

A dab of anti seize will protect the threads and assure a snug nut after a few re torques.


Never-Seez has been a staple in my garage for the past 35 years.
P4281061.jpg
 
Joined
Dec 5, 2009
Messages
303
Country flag
Re: Engineering compromises leading to exhaust threads strip

1975 style exhaust nuts and header pipes. Anti size and take off exhaust as a complete unit. Exhaust nuts never come loose and threads don't get messed up!
 
Joined
Sep 26, 2009
Messages
2,210
Re: Engineering compromises leading to exhaust threads strip

Good picture, anti-seize next to a repaired head, and no locking tab used.
I agree with the original post ,regarding the statement suggesting all that four foot of pipe hanging from the head,with just a bit of rubber supporting the end, poor idea.
Jims posting saying he as replaced loads confirms this :!:
When Iso's wear the leverage increase's as the engine "shakes " and the rear wheel pulls more,
It's a case of keeping the nuts tight, or should i say firm? as over tight strains the thread,
 
Joined
Jan 21, 2011
Messages
639
Re: Engineering compromises leading to exhaust threads strip

concours said:
Best I can see is, the exhaust threads being a problem area, is the result of multiple engineering EVOLUTION compromises.

Actually that is the definition of the entire Commando motorcycle. But those with a bit of intelligence can keep it on the road.....
 
Joined
Sep 21, 2009
Messages
1,609
Re: Engineering compromises leading to exhaust threads strip

The last time I installed my header pipes I used some High Temp goop from Permatex. It lubed them going on and has kept them from vibrating loose for thousands of hard fast miles & it seems to me if they are kept from shaking loose they won't get damaged. My only concern now is how they will come off so I can put the stainless pipes on I bought two years ago. I'm glad I own British bikes, I might not allways like it but they do keep me busy!!
 

speirmoor

VIP MEMBER
Joined
Apr 11, 2010
Messages
1,474
Country flag
Re: Engineering compromises leading to exhaust threads strip

Exhaust mount to cradle you did on the white bike Jean also a great idea.
 
Joined
Jan 26, 2012
Messages
178
Country flag
Re: Engineering compromises leading to exhaust threads strip

So I should put some anti-seize on the threads when I take the pipes out to replace the leaky gasket...

Those alternate clamping methods look pretty good. I've always wondered why bolted-in spigots as illustrated weren't mated to slip-fit joints with spring retainers as is common on modern sporting exhaust systems. My RD350 also has stubby little spigots bolted to the head, with the header pipe slipped over. Obviously if you are machining the head and fitting black pipes, etc., originality isn't an issue. Would allow minor movement and reduce the fretting stress on the collars, head and exhaust flange.

Anybody done it?
 
Joined
Jun 30, 2012
Messages
10,741
Country flag
Re: Engineering compromises leading to exhaust threads strip

I don't use those finned nuts to hold my exhaust pipes on. I've made threaded inserts to fit into the head and protrude a stub which a sleeve on the pipe fits onto. I use tags on two rocker box screws to stretch a spring onto the pipe at each side of the motor. The result is that the threaded inserts tend to tighten, and vibration of the pipes moves them on the sleeves rather than banging the threads in the head.
 
Joined
Feb 5, 2011
Messages
2,131
Country flag
Re: Engineering compromises leading to exhaust threads strip

+1 jrb that is exactly what i was thinking too.
john robert bould said:
Is this the Russian way? :lol: But thanks for the tip Steve, I remember you shared it with us before and I've made a mental note of it and will try it in the future. I have a set of Interstate pipes and silencers that I'm chomping at the bit to try out. Cj
 
Joined
Aug 18, 2008
Messages
198
Country flag
Re: Engineering compromises leading to exhaust threads strip

I used locktite - probably the opposite of the the anti sizes compounds recommended here - have I stuffed up?
 
Joined
Jun 30, 2012
Messages
10,741
Country flag
Re: Engineering compromises leading to exhaust threads strip

To release loctite, you usually use mild heat.
 

concours

VIP MEMBER
Joined
Dec 29, 2011
Messages
4,652
Country flag
Re: Engineering compromises leading to exhaust threads strip

beng said:
concours said:
Best I can see is, the exhaust threads being a problem area, is the result of multiple engineering EVOLUTION compromises.

Actually that is the definition of the entire Commando motorcycle. But those with a bit of intelligence can keep it on the road.....


That leaves me out :lol:
 

concours

VIP MEMBER
Joined
Dec 29, 2011
Messages
4,652
Country flag
Re: Engineering compromises leading to exhaust threads strip

As much as I wanted to stay original, the design was going to keep spoiling the fun, so a bit of help. The head had been sleeve repaired before I got the bike.

draped for surgery
P9021215.jpg


weapons of mass destruction
P9021219.jpg


internal pipe wrench to grab the old sleeve
P9021220.jpg


out with the old
P9021222.jpg


thanks to Don Hutchinson for supplying the sleeve
P9071218.jpg


a stitch in time... sleeve TIG welded in
P9101260.jpg


some new old style rose nuts from Fred and Ella
P9161259_zps75a83086.jpg


see how much MORE threaded goodness on the older style? YUM!
exh_nut_sets.jpg


threads tidied up
P9211266_zps88cb3f08.jpg


test fit feels good.. SWAG says 60-70% thread engagement
P9211268_zps361d9e1f.jpg


P9211269_zpsbacb7bf2.jpg


and some bracket fab, CNC plasma cut from 3/16" CRS
P9211271_zps0a679749.jpg

P9211270_zps4729a060.jpg


test fit, drilled, painted, dried on the furnace while I slept quick
P9221277_zpsfc2e8bb4.jpg


R.H. side fitted with grade 8 bolts, 1-3/8" clamp
P9221278_zps970e1c7e.jpg

P9221280_zpsff2da3aa.jpg

P9221279_zps865eb93d.jpg

L.H. side harder to see, but sticks neatly out between frame and primary case
P9221274_zps668865fa.jpg

P9221275_zps322df1f2.jpg

P9221276_zpsf242cba8.jpg

80 mile test ride today, no loosening anywhere... gaurded optimism. Long term testing will be ongoing :lol:
 
Top