A roadmap for mounting CB / C mufflers

[jensen]

I come across a lot of fractured or cracked mufflers and I thinks this is partly due to the material and thickness of it, engineering issue's, but also due to the order of assembling.

A two piece muffles is less fragile and prone to cracks then a one piece system, and I tried to find a way to do this the best way for both systems.

It's not described in Bill Silvers manual, nor in the Honda manuals, so I figured out a way how I should do it. This information is mainly based on my experiences, so it is discussable.


Step I :

Put the bike on the main stand, preferably on a piece of wood, so that the rear wheel is of the ground.. If you have a jack, use this jack (with a piece of wood) to put underneath the engine, otherwise put a few pieces of wood under the engine, so that the engine rests on the wood.

Step 2 :

Start with losing all the engine bolts (mounts) before putting the mufflers on, it sounds weird, but the engine can move around a little when the bolts are loose, because of the tolerances on the mounting holes / diameter of the bolts. Just make sure that the engine is loose, and try to move it around a little by pushing.

Step 3 :

Put the copper gasket in place with a little (copper)grease, so that they stick to the cylinder head and not fall out.

Step 4 :

Place the headers onto the head and make sure the copper gasket is in it’s place. If having the two piece system, assemble the collars, heat sinks, washers and nuts, but do not tight them jet.
Put the mufflers on the header pipes and place the muffler on there mounts, make sure it won’t fall of, but do not tighten them yet.

With the one piece mufflers you have to put it first to the bike, and then put the collars, heat sink, washers and nuts on it.

Step 5 :

Make sure that the mufflers are loose, they should move around a little, if this is not the case jack up the engine a bit, move it around a little until BOTH mufflers can move a bit (without stress).

Step 6 :

Tighten the engine mount bolts / nuts of the engine a little, but make sure that both mufflers can move around a bit. Also start to tighten the nuts around the header on the head.

Step 7 :

Tighten the muffler mounting bolts / nuts a bit, but make sure that you don’t stress the mufflers, check while tighten the bolts.

Repeat steps 6 and 7 as long as it takes, where you tighten the bolts / nuts a little further every time.

Especially when you have a one piece system, it is very important to make sure that there is no stress involved while doing this.


Step 8 :

If everything is tightened, take the jack away. Pull the bike from it’s main stand and ride it.
When starting the engine there will be a little smoke because of the grease, but that will disappear after a while.


Note :

If you see or feel that there’s no way of doing this without force or pushing hard, you have to check if everything is aligned. These machines are old, and there history probably unknown, you don’t know if the frame is perfectly straight, or in the case of a CB72 / 77, the mufflers mounts are on it’s place. If there’s a problem, try to figure out why, instead of using force to get that mufflers in place.

If the muffler is mounted under stress, and / or when it takes a lot of force to put it in place, the mufflers will crack, it’s just a matter of time.

Jensen

[toastyhamster]

Good tips, unfortunately I had to use a bit of force to get mine on, I've got David Silver exhaust headers and they're not quite the same profile as the originals and hang slightly lower, not much I can do about that - take the choice and use some force or only use the rear mounting point.

[jensen]

Hi,

I encountered this problem too, even the original exhausts are not easy to fit without a little stress.
The CB72 / 77 mufflers (one piece version) is the worst. Unlike other exhaust system on different motors, a hanger bolt goes through a pipe, welded in the exhaust. Normally you can make a hole a little bigger, or make a slot hole out of it., but with the CB mufflers this is impossible. Next to that, the production tolerances are not what they are today, and when comparing different mufflers, you see differences of mm.

But the main reason is the position of the engine and how it's bolted to the frame. Most people hang in the engine with a jack, push the bolts threu the holes, get ride of the jack , and start tightening the bolts. Due to gravity and the weight of the engine, the engine is always fixed in the lowest position, and that's not always a good thing.

In the method I described, you can place the engine in a way that the mufflers are mounted with minimum stress. Like described, this stress eventually destroys your muffler, cracks start to appear, especially in the neighborhood of the hangers.

This stress starts to make the metal brittle, and after that it cracks, or simply falls off.

The stainless mufflers (luckily always a two piece system) are very prone to this process.

The process of getting brittle, is not always due to stress by static stress, but more due to dynamic stress. Another particular part on the CB's that encounter this process is the chain guard, and unfortunately, Vince Loupo knows everything about it. The material is too thin and the dynamic stress too high (due to vibration), and the results are unobtainable chain guards.

Mr. Robert Pirsig also encountered this phenomenon, but in that time there where very good welders, as he describes in his book "Zen and the Art of Motorcycle Maintenance".

Jensen

[bech]

Installing new mufflers on the CB250 I faced this problem on just one side.
While the right side muffler fitted fine, the left side one was about 5cm off position.
Losing the 2 nuts at the head of the pipes was enough to fit it - and tight the nuts - without stress.

Since the pipes are tight fixed on the cylinders as the mufflers are on the frame, isn’t the junction between the pipes and the mufflers - and how we attach it - a decisive factor on that stress?

[jensen]

Hi,

A CB72 / 77 two piece mufflers is connected via a packing only. The tube (header pipe) can move freely into the mufflers and back, it's a loose fit. With your CB250 the construction is maybe different.

Jensen

[sarals]

This one needs a bump! Excellent stuff, Jensey!