Exhaust port threads

[trident sam]

What type and size is the exhaust port threads on a Commando.
I intend to have some flanged, screw in exhaust ports made with protruding stubs a la Triumph . Then get some st/st downpipes made to fit. Anyone done this before, or know a reason not to (not bothered about originality) ?
sam

 

[Al-otment]

From my Mk3 manual it says 1.997 in. x 14T.P.I. If you are trying to stop the exhaust lock rings from loosening get some made in dural. This will expand with the head as it gets hot and wont come loose, or is less likely to.

 

[bwolfie]

Here is the port thread tap I have. 1 15/16 - 14

 

[Al-otment]

1" and 15/16ths sounds more like it. Double checked figure in manual and states 1.997". Should read 1.937" which is 1" and 15/16ths. Somebody mis-typed by 0.060".

 

[trident sam]

Thanks for the replies guys.

Reason for doing it is I've never liked the stock arrangement, (though I've lived with it for 30 years) it's always seemed a slip away from a crossed thread.
sam

 

[Jeandr]

There are some threads (haha) on this very subject if you don't mind modifying your head a bit.

exhaust-port-repairs-t3373.html

Jean

 

[trident sam]

Thanks Jean,
Lots of food for thought there.
Also like where Ludwig has mounted an oil cooler,
sam

 

[Jeandr]

Ludwig is a fanatic on saving weight, if he placed it there, it is because the oil lines are shorter I would guess. His Commando weighs 300 pounds which is quite an acheivement for a street bike complete with lights...

Jean

 

[Chris]

Hi Sam

I had these on my Featherbed Dommi. I don't know who made them but I thought it was a good idea. One piece item, threaded part into the head & long enough stub to fit push over pipes on.
Ended up without the clamps & springs fitted to hold them to the head.
Don't know who has them now?

Chris

 

[trident sam]

Hi Chris,

Yes, something like that was what I was thinking but with a flange part screwed into the head, a bit like pushover conversions to T140s.
cheers
sam

 

[swooshdave]

What is the advantage of the pushovers? So they can leak more?

 

[grandpaul]

There are plenty of wheel-reinventors here.

 

[trident sam]

What is the advantage of the pushovers? So they can leak more?

None of my bikes with stubs and pushover pipes leak.

 

[Chris]

Hi

My bike was a racer not road & it meant I could remove the engine as & when without worrying about undoing the exhaust from the head.
I had the threads on my current race engine repaired by Steve Maney. Nice job, but I think the previous owner saved himself a bit of worry with his design.

Chris