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View Full Version : It's a Triumph again!



EVguru
12-27-2012, 04:38 PM
Triumph twins have a problem with their screw in exhaust stubs coming loose. There are various solutions, but for my friend Phil's race bike we've agreed on the simple solution of welding in a plain Aluminium stub.

The first job is boring out the ports;
http://www.compton.vispa.com/Pictures/trihead1.jpg

oldtiffie
12-27-2012, 06:47 PM
Paul.

The link to your pic is not working and neither is the link to your site.

rohart
12-27-2012, 07:11 PM
To be more specific, the link to your site fails as if your site is not on line, but if you have a link to anything following the reference to ports, the link is not visible.

On topic though, I have been lucky. I have managed to get by with new steel stubs. I have never had pipes that fit my existing brackets. I have always had to make up new brackets. As life has gone on, the fit of the brackets I have made has got better. I suspect that good brackets that really hold the pipe nicely and in the right place are crucial. By that I mean when the pipe is fitted to the stub, and hung from the silencer bracket, the downpipe bracket should be a perfect fit with the bolts sliding in with no clearance.

Having said that, I think that there is meant to be a bracket across the frame just below the swinging arm that I've never used. I have that on my project list.

If you do weld in aluminium stubs, I would recommend threading them as standard, or slightly OS, and screwing them up tightly, before welding them lightly both around the outside and inside where they abut the port. The alternative is boring out the port and press fitting. The danger in heavy fillet welding is softening the insert so that only the weld is holding it against the vibration. The more the vibration forces are taken up by the fit, the better in my view.

flylo
12-27-2012, 09:03 PM
Early Lycoming 50,55 & 65 HP aircraft engines have the same problem. The early ones had a roll on the stub & later were threaded which didn't help. The culprit was owners didn't support the exhaust properly which may be a factor here, My '69 Bonny's were cut off under the pegs.

topct
12-27-2012, 11:25 PM
I seem to remember seeing some heads that were just bored out at the ports. Weren't 750's just bored out? The exhaust header just went into it, no spigot. There was a brace on each pipe going to the front motor mount to keep it in place. There was another bracket towards the rear of each pipe under the engine going to the frame. The mufflers had brackets that went to the passenger peg mounts. I'm not sure of the years that had those heads and or if it was an export only?

When I was working on these I would run into a lot of bikes that for some reason they had removed or left off the head to frame brackets (head stays). This would let the frame twist, sometimes to the point of breaking the down tube in back of the engine. It would also cause the the exhaust system to move around and then the exhaust pipe tightened on the spigot would cause it to be twisted loose in the head.

thaiguzzi
12-28-2012, 04:26 AM
Back in the days when i ran PSP Engineering, my Triumph shop in the UK, we converted literally hundreds of "push-in" heads (very late OIF 650s and most T140 750s) to "push-over", using a std Triumph 1.625" x 16tpi tap, a jig mounted on the top slide of a Colchester Student lathe holding the head, and drilling from the headstock end using a special drill ground up. Could do a pair in less than 30 minutes inc set up time. For knackered "push-over" heads where the original threads were gone, we simply had them nicely tig welded up, down the road at our favourite welders, and re-threaded them with the same procedure as above. Would not recommend alloy stubs for ex port conversions. Also not recommend the common easily available 1.250" BSP thread conversion, as the threads are too coarse, and the stubs WILL eventually unscrew and make a mess of things. Christ i've seen some ex port bodges in my time, inc. self tappers etc etc. Still, not as bad as the screw in ex port Norton Commando heads. Simplest and best exhaust fixing, is what the Japanese have been doing for decades and most manufactures do nowadays - two bolt flange. But the British never thought of that one. Took HD till '84 to do it with the EVO, anyone seen how Shovelheads hold the pipes to a head - ya gotta laugh.
Regards,
Mike.

John Stevenson
12-28-2012, 05:25 AM
BMW's are the worst, Mein Gott.

Course alloy thread with course alloy nut, alloy on alloy ????????????

http://www.stevenson-engineers.co.uk/files/bmw1.jpg

New nut and stripped head.

http://www.stevenson-engineers.co.uk/files/bmw3.jpg

Head mounted on angle plate on POS Bridgy to locate centre, fortunately these have the stub square to the head face.

http://www.stevenson-engineers.co.uk/files/bmw5.jpg

Setup for removing the thread with a LH boring tool, you can use a RH and reverse the head but stand the chance of the head unscrewing from the shank if you have that type of head. Witness mark visible inside from finding centre.

http://www.stevenson-engineers.co.uk/files/bmw6.jpg

All cleaned up and for some reason lost the last picture which shows a bronze ring pressed on and secured by 3 M4 screws screwed in and the heads cut off flush.

Started doing these for a private guy who specialises in working on BMW's. Went to see the main BMW agent who's very local and I used to work with some years ago before he set the agency up but they said they were not interested in any repairs, they just fitted a new head everytime.

EVguru
12-28-2012, 05:34 AM
To be more specific, the link to your site fails as if your site is not on line,

Yes, it looks like the web server is down although I can ftp in fine (using windows explorer). Support may be a problem since this is my old ISP and the webspace still being in existence is a side effect of paying them a small annual fee to keep my old email address running.


If you do weld in aluminium stubs, I would recommend threading them as standard, or slightly OS, and screwing them up tightly, before welding them lightly both around the outside and inside where they abut the port. The alternative is boring out the port and press fitting. The danger in heavy fillet welding is softening the insert so that only the weld is holding it against the vibration. The more the vibration forces are taken up by the fit, the better in my view.

Since my CNC mill is still a pile of bits, I can't mill a thread into the ports and there isn't the budget for a tap of sufficient size, so the stubs will be a light press fit before welding.

I'm going to be making the exhaust too, so I can ensure it puts the minimum strain on the stubs.

This is the first major overhaul the bike has had in about 20 years, when it's not on track it's daily transport (along with a couple of other bikes).

thaiguzzi
12-28-2012, 08:43 AM
Nice work John. Bronze is a good material for any ex port repair. Remember the old p/unit 500 ALL BRONZE head, heavy, georgeous and nowadays worth a mint.
I believe the Commando specialists even helicoil their ex port thread repairs. Now that is a BIG helicoil. None of this was a problem in the olde cast iron head days. Advent of alloy heads and a lot of manufacturers had this problem, inc as John says BMW. In the BMW and Norton case, the thread is fastened and un-tightened every time pipes are removed or the head has to come off. At least with the Triumph design, once the screw in stubs are in, they are meant to stay in.
Mike.

EVguru
12-30-2012, 01:40 PM
I believe the Commando specialists even helicoil their ex port thread repairs. Now that is a BIG helicoil.

The ones I've seen have bored and tapped the head oversize and screwed in a Bronze insert.


None of this was a problem in the olde cast iron head days. Advent of alloy heads and a lot of manufacturers had this problem, inc as John says BMW. In the BMW and Norton case, the thread is fastened and un-tightened every time pipes are removed or the head has to come off. At least with the Triumph design, once the screw in stubs are in, they are meant to stay in.

Trouble is, the Triumph stubs often don't. That's why you can buy stubs with +10 and +20 thou threads to try and avoid having to repair the ports.

I've done a few Morini V-twin heads, they either have problems because they've been together for so long, or because people try and pull poorly fitting aftermarket exhausts in with the nuts. I'm not sure the exhaust on my 1977 3 1/2 Sport has ever been off!

I made split nuts for a friend's Beemer. The exhaust had been on for around 150,000 miles before rusting through, so we just cut the original nuts leaving the threads on the heads intact.