850 Exhaust nuts

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madass140

madass140

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850 Exhaust nuts


Some time ago I did a batch of these ( stainless) (with spanner) for 750's, If I get around to doing some more, I'll do some for 850's as well.
Info needed for the 850 : Length of thread
: Inside diameter
If anyone has an 850 Ex nut to measure.
It may never happen but I'll give it some thought
Don
 
For a stock crossover exhaust with collet keepers, the thread depth is .6" or 15.2mm. The inside diameter has to be 1.67" or 42.4 mm to clear the pipe flange.
 
No probs. Just ripped the pipes off the flood victim, so I had nuts laying around.
 
They look nice .I have found the stainless to loosen off quicker than others in my experience .I am not sure about the different expansion rates .But the bronze ones look great and hold better??
 
When my 750 head returned from Jim Comstock with his exhaust insert repair, I tried my Stainless EX nuts and they were a perfect fit.
I did find they would come loose so I drilled thru one of the nut tightening holes and tapped a thread and now lock the Ex Nut after tightening
with a grub screw which tightens against the head.
My biggest concern is ensuring the thread on the Ex nuts fit all heads, no doubt there are a lot of worn head threads out there and having comebacks
because my exhaust nuts were not a good fit in someones worn head is a concern.
I may have to rethink producing these.
Don
 
I had a set of inserts made by a machinist friend when I first bought the bike, because the PO had stripped the threads in the head. He made them to fit the old style rose nuts on the bike (he must have thought he would try them instead of the 850 nuts in the spares bucket). When he made them he said that the threads were somewhat different on each nut, and we discussed him making a R/L insert based on the slight differences.

I cant remember what he did, but as it turns out the 850 nuts also fit fine. The threads may be coarse enough to accommodate any small differences.

I would be more than willing to test a new 850 set for you on my old head, and on my new FA head!
 
Bronze does have a closer coefficient xpansion rate to aluminium than stainless steel does and together with an external thread taper of 1.8deg which is the NPT standard for example you should have no problems. It's out of your control if people are fitting male threaded components to female threads whree the female thread may not be fit for purpose but the taper thread may overcome some of thses problems and also provide an interference fit. Bodging usually results in failure!
 
gortnipper said:
I think if you match a new AN 850 rose nut thread pattern you probably can't go wrong.
Click to expand...

From some of the information I have learned from this forum so far the exhaust nuts come lose dont they or they require lock tabs or lockwire. S o standard thhread pattern and material is not a goo ddesign in this instance IMO.
 
The trick with the Commando exhaust nuts is to get the engine good and hot then tighten the nuts very tight.
After that, no lock wire or locking tabs etc are needed.
If the nuts are not tightened this way and are allowed to come loose a few times, thread damage happens pretty quickly.

Glen
 
Fixodent. said:
Bronze does have a closer coefficient xpansion rate to aluminium than stainless steel does and together with an external thread taper of 1.8deg which is the NPT standard for example you should have no problems. It's out of your control if people are fitting male threaded components to female threads whree the female thread may not be fit for purpose but the taper thread may overcome some of thses problems and also provide an interference fit. Bodging usually results in failure!
Click to expand...

Actually austenitic stainless steel [303/304] and bronze have nearly the same rate of expansion.

All are much higher than steel. Bronze nuts are just much weaker and wear faster.

303 SS 9.9 x 10-6

304 SS 9.7 x 10-6

bronze 10 x 10-6

Rates are from 68 to 392 degrees F.
1020 CRS 7.0 x 10-6

In comparison to the aluminum cylinder head

356 Al 12.5 x 10-6
 
comnoz said:
Fixodent. said:
Bronze does have a closer coefficient xpansion rate to aluminium than stainless steel does and together with an external thread taper of 1.8deg which is the NPT standard for example you should have no problems. It's out of your control if people are fitting male threaded components to female threads whree the female thread may not be fit for purpose but the taper thread may overcome some of thses problems and also provide an interference fit. Bodging usually results in failure!
Click to expand...

Actually austenitic stainless steel [303/304] and bronze have nearly the same rate of expansion.

All are much higher than steel. Bronze nuts are just much weaker and wear faster.

303 SS 9.9 x 10-6

304 SS 9.7 x 10-6

bronze 10 x 10-6

Rates are from 68 to 392 degrees F.
1020 CRS 7.0 x 10-6

In comparison to the aluminum cylinder head

356 Al 12.5 x 10-6
Click to expand...

Not sure I understand your wear faster comment. With the exhaust nut tight in the cylinder head I can not see there being any wear as there are no moving parts? Bronze also is a more suitable material as that it has a much higher rate of heat transfer than stainless steel.
 
Fixodent. said:
comnoz said:
Fixodent. said:
Bronze does have a closer coefficient xpansion rate to aluminium than stainless steel does and together with an external thread taper of 1.8deg which is the NPT standard for example you should have no problems. It's out of your control if people are fitting male threaded components to female threads whree the female thread may not be fit for purpose but the taper thread may overcome some of thses problems and also provide an interference fit. Bodging usually results in failure!
Click to expand...

Actually austenitic stainless steel [303/304] and bronze have nearly the same rate of expansion.

All are much higher than steel. Bronze nuts are just much weaker and wear faster.

303 SS 9.9 x 10-6

304 SS 9.7 x 10-6

bronze 10 x 10-6

Rates are from 68 to 392 degrees F.
1020 CRS 7.0 x 10-6

In comparison to the aluminum cylinder head

356 Al 12.5 x 10-6
Click to expand...

Not sure I understand your wear faster comment. With the exhaust nut tight in the cylinder head I can not see there being any wear as there are no moving parts? Bronze also is a more suitable material as that it has a much higher rate of heat transfer than stainless steel.
Click to expand...

There is wear, every time it expands and contracts. That is why the original threads in the head fail eventually -even when the nut has never been run loose.

The biggest problem I had with the bronze nuts when I tried them was I ended up breaking the fins off when tightening them.

If the threads on the nut are a close fit to the threads in the head then the nut will stay tight no matter what it's made of.

There is a large variance in the thread size of the available nuts. That's the biggest problem. Jim
 
comnoz said:
There is wear, every time it expands and contracts. That is why the original threads in the head fail eventually -even when the nut has never been run loose.

If the threads on the nut are a close fit to the threads in the head then the nut will stay tight no matter what it's made of.

Jim
Click to expand...

That would take an awful lot of expanding an contracting to wear away thread material to the point that the threads fail! Mating threads have to have clearance anyway otherwise you would not be able to screw them together without expanding the female thread with heat.

Mating parts which have an interference fit use heat to fit them together and also separate them due to different expansionrates so it's no different with a steel male thread going into a aluminium threaded hole. When heated the aluminium hole gets bigger than the steel male thread and the nut comes loose as there is no interference between the two diameters.
 
nortonspeed said:
comnoz said:
The biggest problem I had with the bronze nuts when I tried them was I ended up breaking the fins off when tightening them.
Click to expand...

True, however Andover Norton took care of this problem years ago :wink:
https://andover-norton.co.uk/en/shop-details/15848
Click to expand...

Obviously Andover has improved on the design.
The last pair of bronze nuts I purchased from a popular US distributor were so loose in the threads that they would not stay tight in my yellow roadster. When I tried to get them tight enough to stay put they simply broke the fins.

I went back to the prior nuts which were old beat up Schultz tooling nuts which are still on the bike today and stay put with no problem.

Of course I don't use bronze nuts with the aluminum bronze thread inserts I install in most heads. I would be afraid of fretting problems due to similar metals. Jim
 
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