Advice on 'Commando' exhaust crack

Nielsen · Oct 22, 2014

Hi All: Once again the neophyte asking for help and advice. You've never steered me wrong.....

So the exhaust pipe on my '74 Commando has a crack in it along the weld of the balance pipe and across the pipe itself. I'm told this is common. Here's what I think my options are, but there may be others. What should I do?

1) get it welded. The downside is that will presumably look pretty awful.
2) get a new set of exhaust pipes. If that's the case, do I go with a set with a balance pipe or without? What's the difference (and I should say the bike is entirely original so going without the balance pipe would mean becoming non-original, but maybe its the best idea anyway).
3) Just leave it alone and run it as is until the crack presumably goes all the way around and the exhaust disconnects.
4) 'treat' it with something--but if there is anything, what is it?

Rohan · Oct 22, 2014

Doing nothing is not an option.
Running lean could burn a piston, or wreck your engine.
And if the pipe disconnects and folds under the bike, could be quite painful.

Getting it welded with something like stainless might be a shade ugly,
but it will be sound, not damage your engine and not rust later on.

Lotsa folks here go for unbalanced pipes, and report no loss of anything.
And needs less looking after, and no repeat problems...

P.S. Do you have that Thor in your avatar ??!

midnightlamp · Oct 22, 2014

Put the pipe on a shelf, replace with a set of non-balanced pipes, put them back on if you ever want to sell the bike would by my options. If you don't mind unbalanced, you can get pipe sets down to $150 shipped for a pair nowadays that won't crack and fit nicely. You can do mufflers from the same source (so fitment is nearly perfect) for around $300 shipped for the whole setup (pipes + peashooters).

It'll take to welding badly, brazing will look awful in my opinion, and you're probably looking at ~$100 to strip the pipes, cost to repair, and maybe $100 at a minimum to rechrome. Worth it down the road if selling.

Rohan · Oct 22, 2014

midnightlamp said:
It'll take to welding badly, brazing will look awful in my opinion,.

Brazing is not an option.
That close to exhaust port, braze loses its strength when it gets hot,
and will separate again.
And is then unweldable by any other method.

Needs to be migged or tigged, with a little of the chrome ground off for the weld to get a good grip.
Probably going to cost almost as much as a new pipe would, if done professionally...

concours · Oct 22, 2014

They all do that. Replace, take this opportunity to convert to UNbalanced pipes. engineering-compromises-leading-exhaust-threads-stripped-t14363.html

Emergency field repair to finish the day

Nielsen · Oct 22, 2014

thanks for the advice. Sounds like a new exhaust is the way to go. I had a Morgan +8 years ago with a balance pipe on the exhaust. I removed that pipe and the result sounded 'orrible, to the point where I put it back in. That experience makes me wary of not having the balance pipe on the Norton, but it seems pretty common to go that route with the Commando. What difference can expect to hear/feel if I go with two straight pipes rather than the balanced system?

concours · Oct 22, 2014

Nielsen said:
thanks for the advice. Sounds like a new exhaust is the way to go. I had a Morgan +8 years ago with a balance pipe on the exhaust. I removed that pipe and the result sounded 'orrible, to the point where I put it back in. That experience makes me wary of not having the balance pipe on the Norton, but it seems pretty common to go that route with the Commando. What difference can expect to hear/feel if I go with two straight pipes rather than the balanced system?

wee bit louder, sharper pops

Nielsen · Oct 22, 2014

wee bit louder, sharper pops[/quote]

louder is OK! 8)

midnightlamp · Oct 22, 2014

I just got the commando specialists system, which works wonderfully and is cheap!

Nielsen · Oct 22, 2014

midnightlamp said:
I just got the commando specialists system, which works wonderfully and is cheap!

I'm not familiar with the 'Commando Specialists'. Can you provide a link?

Deets55 · Oct 22, 2014

might be referring to :
http://www.commandospecialties.com/

drones76 · Oct 22, 2014

Deets55 said:
might be referring to :
http://www.commandospecialties.com/

+1

Had the same crack. Commando Specialties is where I got mine along with new peashooters. Nice fit and they look and sound great.

midnightlamp · Oct 22, 2014

that'll be the one, not the first time I accidentally mixed up that name

Bernhard · Oct 23, 2014

Nielsen said:
thanks for the advice. Sounds like a new exhaust is the way to go. I had a Morgan +8 years ago with a balance pipe on the exhaust. I removed that pipe and the result sounded 'orrible, to the point where I put it back in. That experience makes me wary of not having the balance pipe on the Norton, but it seems pretty common to go that route with the Commando. What difference can expect to hear/feel if I go with two straight pipes rather than the balanced system?

According to Dunstall many moons ago, without the balance pipe you will lose 3-4bhp in the midrange.

acotrel · Oct 23, 2014

Bernhard said:
Nielsen said:

thanks for the advice. Sounds like a new exhaust is the way to go. I had a Morgan +8 years ago with a balance pipe on the exhaust. I removed that pipe and the result sounded 'orrible, to the point where I put it back in. That experience makes me wary of not having the balance pipe on the Norton, but it seems pretty common to go that route with the Commando. What difference can expect to hear/feel if I go with two straight pipes rather than the balanced system?

Click to expand...

According to Dunstall many moons ago, without the balance pipe you will lose 3-4bhp in the midrange.

Probably depends on how restrictive the mufflers are. I would have thought that with a balance pipe, a more restrictive pair of mufflers would be the norm to make the bike quieter. (With the balance pipe the system is always exhausting through the two mufflers. ) If you are replacing the headers, I'd replace the mufflers at the same time, as previously suggested by others. Personally I don't like exhaust systems with a balance pipe, I don't believe the standing wave is ever quite right with that set-up. It is the sort of thing you would fit to the family motor car. The Laverda SFC750 system with the cross under the motor seemed to work well.
I think with Paul Dunstall there are two things - what he used himself, and what he sold to other people.

Bernhard · Oct 23, 2014

According to Dunstall many moons ago, without the balance pipe you will lose 3-4bhp in the midrange.[/quote]

Probably depends on how restrictive the mufflers are. I would have thought that with a balance pipe, a more restrictive pair of mufflers would be the norm to make the bike quieter. (With the balance pipe the system is always exhausting through the two mufflers. ) If you are replacing the headers, I'd replace the mufflers at the same time, as previously suggested by others. Personally I don't like exhaust systems with a balance pipe, I don't believe the standing wave is ever quite right with that set-up. It is the sort of thing you would fit to the family motor car.[/quote]

I respect your opinion Acotrel, but how come there are an awful lot of Jap bikes that are twin cylinder four stroke fitted with balance pipes , usually on the bottom under the sump, and this dates back to before the noise restrictions came in force.

midnightlamp · Oct 23, 2014

The OEM balance pipe is in the wrong place to really capitalize on the benefits of it. I'd have to pull out the books, but from the last time I did it and scaling up for the norton port velocity I'd guesstimate around 20-24" down from the exhaust valve is where that pipe should be to make a big difference. Balance pipes are one way to do that, an X pipe would be better but require different placement.

The main problem though is that the placement is based on letting the pipes move and flex and bit when the engine moves, and even that wasn't really done well enough considering how regularly they break :roll:

Also if you get new headers/mufflers, if you want the best response stick to the stock bore system. The big bore one is too big, but it sure does look nice.

acotrel · Oct 23, 2014

With my two into one pipe, the headers are exactly the same ID as the exhaust stub - so there is no internal step, and the tail pipe is the ID which provides the same crossectional area as the sum of the header pipes. The header pipes look skinny, however it is not about looks. I know of guys who believe the fat exhaust is better on a 500cc manx. My friend was the top Victorian A grader on manxes in the early 60s. I was in his business one day, and the pipe off the manx was hanging off one of the rafters. I mentioned to him how skinny it was, and he said 'you notice too much'. You will note that the pipe which was part of the race kit for the Tiger 100 and GP Triumphs was not the fat type which was used on the road bikes, and the later 650s all had skinny pipes. I suggest that in the end the exhaust system has to act in the same way as an organ pipe when the motor is revving, establishing the standing wave is important. I think it is easier with a skinny pipe with no internal interruptions. My own system is made up of welded sections, a consideration is the weld flash on the inside of the joins. It works well however 'ass beats class'.

ILLF8ED · Oct 23, 2014

But then no guarantee the unbalanced pipes won't crack right at the exhaust port flang....have seen this before. Careful set up when tightnening up the system is needed to prevent any binding that the engine shake will turn into a stress area. I fit up everything loose tighten the exhaust rings first, muffler hangers then muffler clamps last.

Rohan · Oct 23, 2014

We still haven't seen any back-to-back dyno chart comparisons of balanced and unbalanced exhausts. ?
To see if there really is a difference....

Advice on 'Commando' exhaust crack

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