Triumphrat

Steve McMahon

I can't figure out how to tighten the stub pipes that come out of the cylinder heads, the ones that the exhaust headers clamp on to.

One is tight, the other loosens up and comes out of the head about 1/8". I can tap it back in, but it loosens up again as soon as I run the bike. They don't seem to be threaded, How are they held in, and how do I tighten them up?

Thanks
Steve

OzBloke

Steve,
The 76/77 model came standard with exhaust port holes, and push-in pipes. A Previous Owner (a.k.a. "PO") has had the stubs fitted, probably from an earlier or later model. As far as I know, the normal way these were fitted was the exhaust ports were bored out, threaded, and the stubs screwed in. There is supposed to be a hole drilled through both sides of the outer portion of the stub (where the push-over pipe fits on), so a piece of bar or philips screwdriver could be used to tighten the stub.

If one of yours is coming out 1/8", I'd suggest they are either not threaded (just an interference fit - jammed in there), or your threads have worn down with vibration.

How do you fix it? Couple of suggestions, based on your wallet size.

1. Take the head off, take it to a machine shop, get them to check the clearance around the hole, bore it out slightly (to clean it up), and make a slightly larger stub for you - on the end that fits into the head, not the end that the pipes goes over.

2. Work the existing (loose) one out, give it a layer of high-temperature silicon, and fit it back in. While it's out, drill a small hole from below through the head alloy into the exhaust port, tap it (cut a thread in it) and insert a grub screw. When you put the stub back in with the silicon, tighten the grub screw to keep the stub in tight. Make sure the right-angle brackets holding the exhaust to the front of the engine are secure.

__________________
Per Ardua Ad Astra
(Through difficulties to the stars)

Emanthehorse

There was an aftermarket stub that was pretty popular for a while. They had a knurled section you could tap into the head and there was a 1 3/4" stub facing out.
Vibration indeed loosened them up over time, you will see a lot of T140 heads with little holes drilled in the fins around the exhaust where people hooked springs to the exhaust clamps to hold them in place.
Popular cures include welding up of the ports, then boring and rethreading to T120 specs so you can use the old screw-in stubs, or machining an aluminum adapter with a 1 3/4" stub and welding it into the head.

None of this would have been necessary had the aftermarket produced decent alternatives for the push-in style pipes.