Stainless exhaust collars

[Oli Hulme]

I bought one of these to replace a chromed/bronze one that had to be destroyed to remove it. It only screws in about halfway, and then sticks. I've tried on three different heads, and it's the same on each. My remaining Bronze collar screws in just fine. Do the bronze collars wear, making them easier to put in? Or are the thread sizes variable on stainless ones? ~Or are they simply tight because they are new?
All advice gratefully received

[George 350]

Hi Oli.
It suggests that the thread is not parallel on the stainless nuts. Can you measure the thread diameter at the beginning of the thread and closer to the plain section? This would give you a clue as to why it is jamming.
The other scenario is whether the thread pitch is correct or not. Laying your 2 nuts together and holding up to the light should show if the pitch is correct or not.
Hope this helps,
George

[Oli Hulme]

well, that nuisance. it appears the stainless one is about half a mil wider than the original. I have a bloody expensive paperweight, then

[3potjohn]

Could it be for a 500?

[Oli Hulme]

are they bigger by that much? It was sold as for a 350

[Stempy]

From memory 350 are 42mm and 500 are 45mm the castellated head sizes are also different

[Stempy]

IMG_1666.jpeg (149.15 KiB) Viewed 132 times

[Oli Hulme]

the old one is 42mm. the new one is 43mm...

[George 350]

Hi Oli,

Where did you get the stainless ones from?
The supplier needs to know that they aren't fit for purpose. Can you not return them?
They shouldn't become expensive paperweights for you.

Glad you resolved it without wrecking the head(s).

Good luck and hope you don't have any more surprises on the rebuild and thanks for the publicity you are giving the club.

Regards,
George.

[George 350]

Another thing Oli,

As an addition to your rebuild, you mentioned in CBG about M7 nuts and bolts.
DW Middleton stainless sell them, in nyloc too.
Perfectly ok for rocker trunnions and brake torque arms on Sports/Stradas. (Bolt only there to hold torque arm in place on welded on collar).
It's only the M7 kickstart bolt that I worry of stainless being strong enough to cope , but they have worked ok for the last 30+years on the Sport so probably are ok!

Regards,
George