787 Exhaust Leak At Clamp. At my wits end...

[Krispy]

Ok, So I have dropped my engine back in my hull on my 96XP.

I finally have everything connected and I do a test fire.

I find an exhaust leak from the juncture of the head pipe and the cone pipe.

This area is held together with a stainless v band clamp and gasketed with a copper ring gasket.

I have tried now on 3 seperate occasions to stop this exhaust leak (smoke) from showing up in this area.

1st assembly I used the old copper gasket with some high temp RTV (ultra copper) on the gaskets No luck,

2nd attempt I pulled out the head pipe, cleaned the RTV off both the head and cone pipe, and sanded the copper gasket lightly to bring back the shine, reinstalled with more ultra copper. No luck

3rd attempt I removed everything again, pulled the copper ring from the cone pipe and annealed it with my torch, reinstalled with no ultra copper (left the existing ultra copper on the pipes, didn't add any more)

Still have a leak.

Is there something that I am missing?

Any tips to where the nut should be positioned on the band clam in reference to the rotation of the clamp?

Any alignment tricks between the two pipes? Torque order of exhaust fasteners that help aid alignment?

Please give me a hand in solving this issue.

Thanks,

Chris

 

[Minnetonka4me]

787s dont usually fight, 951s are a total PITA. Gotta do one today.

Look for any place the edge on the pipe may have been damaged, not allowing it to come together perfectly. Loosen up the bolts on the lower pipe too so it can move around.

I would dry fit it without the SS clamp and make sure it comes together perfectly. Then RTV it up, put it in place with loose upper bolts. Then tighten the clamp and get it all the way tight. I would then back it off just a little so it can twist, and bolt up everything else....then retighten the clamp.

 

[Krispy]

It appears the leak is occurring where the 3 semi circles join together.

This joint was at the bottom of the clamp (black exhaust oil goo)

Is the clamp supposed to have that shape when loose?


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[Krispy]

Pic when tight

Notice the uneven gaps between the semicircles?


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[Krispy]

Head pipe sealing surface cleaned up .


Only spot of concern is the little area at 3:00 , on the lower flange.


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[Krispy]

Well, I got it sealed back up no leaks. Had to bend the clamp back into round a bit.

More importantly I think I paid extreme attention to the assembly and alignment, I thought that the band clamp would push things where they need to be but I guess not.

At any rate exhaust is fixed, thanks Nick for your help!


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[Strizzo]

glad you got it back together, the band clamp doesn't pull the two pipes together like you'd think, you kinda have to get the surfaces mated up as you twist the upper flange onto the stud. if you can get them lined up flush you can hold the tension on the clamp and spin the nut down. the gaps in the flange allow it to wrap around the junction, that being the source of your leak i think is a red herring because thats where whatever leaks inside will come out, at the gaps in the flange.

 

[Minnetonka4me]

One other trick I use is that clear tube that they stick over the threaded part. Usually you can see where the thread was before, if its not lined up it wont reach the thread marks inside the tube.

 

[TheMachin0]

ok I just had the same prob when putting mine together third time was the charm. what I did was clamp the u canal in the vice a couple inches at a time till the clamp was tighter all the way around "it has been clamped sprung open for 20 years" clean her up and do it dry I put some wd on the clamp when I it helped the clamp seat to the pipe nice for me it will be a bit harder to start the nut but she will be golden when done