Montesa barrel thread repair?

[crash n bern]

I've got a 74 Montesa 250 cappra and the thread where the exhaust flange screws in is stripped out. Is there a fix for this or am I up for a new barrel?

[Hoony]

have you heard of "helicoils", "Recoils" etc. any good tool supplier will be able to supply them.

are they standard M6 or that crazy M7 thread?

[All Things 414]

Nah. That's a big thread! A good engineering shop may get you out of trouble. I guess it depends on what size the cylinder is at bore wise. If it's on it's last size it may be easier to get another barrel. Someone must have really been leaning on that collar to strip it....... Jared may have some ideas.
That's the big collar we're talkin' about Hoonster.

[090]

Had the same trouble with my '69 Monty. Easy fix though.... i sold it! Maybe you should set it up like the majority of exhausts and rig a spring from the collar to the head.

[Lozza]

You can make an insert with say 10x1.5mm thread on the outside and 6x1mm or 8x1,25mm on the inside.Here's the trick is to NOT use Loctite or such but 'Stag' jointing paste the only thing that handles the heat.Pretty simple really.
Ooops sorry IIRC the Monty has a big screw in flange, if it has I would just by a thread file and repair the thread,

[David Lahey]

I'm familiar with the thread you are talking about as I have the same arrangement on an OSSA and a round barrel Bultaco.

The cylinder thread usually fails because the bike has been ridden with the nut loose.

Options are:
- Make a tap for a bigger thread, bore the hole bigger, tap the hole and make a bigger nut.
- Build up the hole with weld, bore it back to standard size and make a tap then tap the hole standard.
- Buy a ready-made aluminium insert from a specialist Spanish bike parts supplier, bore the thread out and weld in the insert.

If you want I can send a photo of what the aluminium insert repair looks like as I have just had it done.

David

[BultacoMacca]

What is the collar O.D. and what pitch thread?
I've got some threaded steel rings made up for Bultaco barrels, they bolt to the outside of the exhaust port on Bully. Can also be recessed. They're 10mm deep.

[Hoony]

Nah. That's a big thread! A good engineering shop may get you out of trouble. I guess it depends on what size the cylinder is at bore wise. If it's on it's last size it may be easier to get another barrel. Someone must have really been leaning on that collar to strip it....... Jared may have some ideas.
That's the big collar we're talkin' about Hoonster.

I'm with you now Rossco

[crash n bern]

Thanks for the feedback guys. I probably should of worded it a bit better. I know with a bit of brain work anything can be fixed. I was just wondering that if it was a common problem there may of been an over the counter fix from a Montesa supplier.