Topic: Exhaust leaks at top

[1978CB750SS]

What am I missing?   I changed my oil which made me pull my 4 into 1 pipes off.These pipes always had a nice seal. I put them back on.Started up, exhaust leaks at head. I tried pulling them off, re setting them, checking for a good line up, nothing. I can feel the air escaping the pipes and it's loud as heck.I spent all afternoon, back is toast.I had to give up as I play in a band tonight.  The lip on metal 2 piece gaskets I have facing the head. I believe they can only go in one way.I centered the pipe over the holes best I could.Everything fought me the whole way.

[madmtnmotors]

There is no "two piece gasket". The later model CB750's (77/78 K/F) use a two piece collar inside the solid clamping collar. The two piece collar is oriented so that the straight edge faces the head and bears down on the flange at the end of the pipe, while the flared lip fits against the solid outer collar. The gasket is smashed into the head by the flange on the end of the pipe and usually require some pursuasion to remove. They are often made of copper. While they can be reused, if you develop a leak upon reassembly you might consider replacing these gaskets, especially since they can be found very cheap.

[Handlebar]

Yes. Make sure the collars are positioned right. They will install both ways but only seal one way. I did this last year on a 76F ,I had the collars backwards and it will not seal,big air!!!

[1978CB750SS]

Thank you, that must be the case then with mine.

[Phinn]

I just did the same thing last weekend. I spilled oil all over the header/muffler connection, so I figured I should pull the whole thing off and get it clean, lest it burn.

The collars that go around the ends of the header pipes (and under the flanges that bolt onto the head) have flared ends that point away from the head. The flared end of the collar needs to seat firmly in the recessed space that’s on the inner surface of its flange. The straight side of a well-seated collar is what pushes on the flared end of the header pipe, firmly onto the crush washer.

The seal comes from the crush washers. The collar just pushes on the header pipe. Those collars are pretty flimsy, though. They get bent out of round. You have to be sure they sit in the notches inside the flanges.

I found that it helps to bolt up the headers loosely, then rest the muffler end on a stack of wood or something, so that it doesn’t keep sagging and pulling the headers away from the head. The headers don’t line up perfectly square to all four holes. They need to be coaxed and pushed and pulled into place. So you have to bolt it all up loosely, then tighten here and there, then wiggle the header pipe, then tighten some more, then wiggle some more, etc.

If you tighten one flange fully in one go, you end up with another one that doesn’t seat properly.

[1978CB750SS]

Thank you all for the tips.I got it together!I t sounds great, plus I got my new speedo cable on, got all four pipes getting hot,airbox in place with new filter, and new oil and filter. I just went for a spin and this baby will get up and go!