When I installed my exhaust on my new engine I used new Rapco 77611 gaskets on each flange. After an hour of operation I noted some white blow by on the bottom of three cylinders directed towards the spark plug. Is this just a torque issue or can I reinstall these gaskets wet with some high temp RTV? I torqued the exhaust nuts I could get the wrench on to 180 in-lbs, for reference.
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Sealing no-blow exhaust gaskets
- Thread starter 00Dan
- Start date
All nuts need to be torqued with pipes in a neutral position. With a three out of four failure rate, I would say they were installed improperly.
This is how it´s done. See attachment.
https://s28490.pcdn.co/wp-content/uploads/2020/05/DSC_0024-2.jpg
Good luck
https://s28490.pcdn.co/wp-content/uploads/2020/05/DSC_0024-2.jpg
Good luck
And High-Temp RTV just isn’t “THAT” high-Temp - you’ll just make a mess, and not seal anything…..
As Ironflight says - RTV is not a good choice in this location.
You shouldn't really need any additional products in that area with new cyclnders and a new exhaust because the mating faces should be nicely machined and square. Ensure that the installation of the exhaust has been done correctly - that's to say that the entire assembly has been fitted up and loosely bolted on before tightening any of the nuts. Always tighten the inner nuts first and do the outter nuts last. The reason for this is the flange can float a little and if your socket is a little heavy in the wall thickness then at least you can get the back nut tight and use a spanner on the front nut. If you tighten the front nut first you might find you can't get your socket onto the back nut.
If you have to use anything, a light smear of Maniseal is the best product to use here and I would only use it on the face between the cyclinder and the exhaust flange. The No-Blo Gaskets are supposed to crush up a small amount as you tighten the nuts so if eveything is in good order you shouldn't need much, if any Maniseal in there.
You shouldn't really need any additional products in that area with new cyclnders and a new exhaust because the mating faces should be nicely machined and square. Ensure that the installation of the exhaust has been done correctly - that's to say that the entire assembly has been fitted up and loosely bolted on before tightening any of the nuts. Always tighten the inner nuts first and do the outter nuts last. The reason for this is the flange can float a little and if your socket is a little heavy in the wall thickness then at least you can get the back nut tight and use a spanner on the front nut. If you tighten the front nut first you might find you can't get your socket onto the back nut.
If you have to use anything, a light smear of Maniseal is the best product to use here and I would only use it on the face between the cyclinder and the exhaust flange. The No-Blo Gaskets are supposed to crush up a small amount as you tighten the nuts so if eveything is in good order you shouldn't need much, if any Maniseal in there.
rocketbob
Well Known Member
Disagree.
Blo-proof gaskets are not "blo-proof". I will not put an exhaust gasket on without ultra copper RTV smeared on both sides. Holds up fine, seals as intended. The machined surface at the exhaust port is typically coarse. The RTV takes up the gaps and prevents erosion from starting. On exhaust ports with existing erosion, which is very common, it becomes even more important to do this.
rmarshall234
Well Known Member
I'm with rocketbob
There is a guy over on the Beechcraft forum named Lew Gage and he is a proven and recognized expert with 50 years of experience and all the right credentials. He recommends the Ultra Copper RTV so that's what I use too.
I would also agree with jrs14855 in that stepping the torque up until you get to the final torque is critical as well.
There is a guy over on the Beechcraft forum named Lew Gage and he is a proven and recognized expert with 50 years of experience and all the right credentials. He recommends the Ultra Copper RTV so that's what I use too.
I would also agree with jrs14855 in that stepping the torque up until you get to the final torque is critical as well.
That’s fine if you disagree. I’ll only point out two things:
1) Permatex Ultra-Copper RTV is only good to 700 degrees F (most EGT’s measured 2” away from the exhaust flange run about 1400 degrees).
2) Exhaust manufacturers like Vetterman make no mention of sealant with the Blow-Proof gaskets.
Got a reference other than “that’s what I do”? I am honestly happy to learn more if there is an authoritative reference source.
I’ve never had an issue with the no blows. They are extremely soft and thick as we all know. I have also never heard of using any kind of sealant nor have I ever needed to.
I suspect the exhaust nuts were not torqued properly. As was mentioned earlier. Start at a lower torque and alternate from one side to the other to insure the flange stays square. If that doesn’t do it, check the exhaust flange for square and against the cylinder with no gaskets and make sure they fit against each other with no or minimal gap.
I’m sure there’s a spec somewhere for how much gap is acceptable.
L
I suspect the exhaust nuts were not torqued properly. As was mentioned earlier. Start at a lower torque and alternate from one side to the other to insure the flange stays square. If that doesn’t do it, check the exhaust flange for square and against the cylinder with no gaskets and make sure they fit against each other with no or minimal gap.
I’m sure there’s a spec somewhere for how much gap is acceptable.
L
rocketbob
Well Known Member
Why doesn't the inside of the exhaust port melt since 1400 degrees is well above the melting point of aluminum?
Ultra copper works, because it does. The manufacturer tells you to use silk thread and run rich of peak.
rmarshall234
Well Known Member
Paul, with all due respect and this is a serious question...wouldn't the temperature that the RTV is exposed to be closer to cylinder head temperature than the temperature of the exhaust gases going past that sealed and clamped joint?
Just an example.
One might be surprised at the durability of RTV near combustion temps. My employer had 110 diesel engine test cells. One was mine. Cylinder pressure transducers were located in the head (4 valve) directly exposed in the combustion chamber. The transducer life was extended by several hundred hours by a small recess and application of RTV up to the head plane. I was quite surprised to learn this little fact. This would indicate the surface temperatures are quite a bit lower than combustion or exhaust temperatures.
Edit: Paul has a good point below - why is it leaking in the first place? The exhaust flanges and head flange should be checked for flatness. If there is no metal/metal contact, then the pipe flange will quickly heat and attempt to approach exhaust temps. The aluminum head will always be a lot cooler -and it has the fins. If the non-contact areas are small, then the RTV could remain within its operating temperature.
One might be surprised at the durability of RTV near combustion temps. My employer had 110 diesel engine test cells. One was mine. Cylinder pressure transducers were located in the head (4 valve) directly exposed in the combustion chamber. The transducer life was extended by several hundred hours by a small recess and application of RTV up to the head plane. I was quite surprised to learn this little fact. This would indicate the surface temperatures are quite a bit lower than combustion or exhaust temperatures.
Edit: Paul has a good point below - why is it leaking in the first place? The exhaust flanges and head flange should be checked for flatness. If there is no metal/metal contact, then the pipe flange will quickly heat and attempt to approach exhaust temps. The aluminum head will always be a lot cooler -and it has the fins. If the non-contact areas are small, then the RTV could remain within its operating temperature.
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That’s a good point - anything squeezed off inside would burn away pretty fast. And if it isn’t exposed to the hot exhaust gas directly, then….there isn’t a leak in the first place?
And I’d still like to see some documentation from the folks who build the engine, exhaust, or gaskets that recommend a sealant.
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rocketbob
Well Known Member
Its accepted practice to use a sealant on NPT plugs such a oil drain plug.
Nowhere does any Lycoming document specify what sealant is appropriate for a drain plug. What does one use then? Or not?
Try Fiberfrax
I used the 1/8 in Fiberfrax on top of the no-blow to fix an unstoppable leak on a O320 cylinder. The material is good for about 1500F and compresses and seals well.
Available on Amazon - used by the ceramic pottery folks in their kilns. I used it a lot at the steel company I used to work at (a lifetime ago). About 20 bucks for 18in x 12in piece.
Ron
I used the 1/8 in Fiberfrax on top of the no-blow to fix an unstoppable leak on a O320 cylinder. The material is good for about 1500F and compresses and seals well.
Available on Amazon - used by the ceramic pottery folks in their kilns. I used it a lot at the steel company I used to work at (a lifetime ago). About 20 bucks for 18in x 12in piece.
Ron
I know this is old, but had a question on orientation. The 77611 has a lip on one side. Does that lip go on the pipe or Cylinder?
Datapoint of 1. We installed the no-blow gaskets without any goop and torqued to spec. No leaks after 150h.
Our standard practice is to place the flatter surface towards the cylinder and the more rounded surface towards the exhaust pipe.
Given the opinions expressed here you'll no doubt find another 30 posts on what others do, however this has always worked well for us. The reason we do it that way is so that if anything moves, it hopefully means the softer aluminium face of the cylinder is less likely to get damaged as it might if the gasket was placed with the rounded face towards the cylinder.
11 RV's and use of Ultra Copper (very minimal use) and no blow outs or messes. I know what the temp rating is but if you don't have any blow outs and you also don't have mess, then it's hard to argue with the results. I've used them without any sealant and did the torque up in steps and had issues with sealing. So I would agree that too much is not going to work but they do work better with a little bit.
Regardless of what the temp. rating is, I have seen indications that a thin coating of Ultra Copper or High Temp Red RTV on both sides of the gasket does seem to help blow proof gaskets actually be blow proof.
Been doing it that way for 25+ years and I don't remember ever having a leak.
Been doing it that way for 25+ years and I don't remember ever having a leak.
These are static seals. If they don't leak right off the bat, they're good for the entire engine life/maintenance cycle.
No RTV or Ultra copper is going to provide any sealing function. That said, it's easy to conceive that it helps the metallic surfaces find their seats; not too different from lubing static O-rings prior to installation. Paraphrased below
and BTW unless things have changed. "High temp" RTV is regular RTV with iron (oxide) mixed in to help distribute/dissipate heat. It works better for transient conditions than steady state.
There's some useless knowledge for a Friday.
No RTV or Ultra copper is going to provide any sealing function. That said, it's easy to conceive that it helps the metallic surfaces find their seats; not too different from lubing static O-rings prior to installation. Paraphrased below
and BTW unless things have changed. "High temp" RTV is regular RTV with iron (oxide) mixed in to help distribute/dissipate heat. It works better for transient conditions than steady state.
There's some useless knowledge for a Friday.
I have used ultra copper on auto exhaust systems to help gaskets seal when parts are misaligned slightly. Have also used it on Exh manifold to head applications where there was pitting and the gasket alone wouldn't seal it well enough (symptoms are popping). Always sealed for me.
If it works for you, great. I had to look it up. It's still RTV with a temperature range is "up to 700F intermittent", slightly less than Red RTV. I'd still surmise it is helping the gasket proper find its seat. I'd also keep a close eye on it. Eroded exhaust port faces can get expensive. please don't ask me how I know.
Ultra Copper link
My tacoma had a bunch of erosion on the exh manifold. I put a bunch of silicon bronze (basically brazing) on it with TIG, then ground it flat. Crazy what they wanted for a manifold.
There's a product called Taber's Flo-Ex that works great for sealing up exhaust flanges. A lot of hot rodders swear by it. We used it at my old job on Enstrom helicopters, and some of the old Bonanza guys use it as well. I've used it from time to time on leaky flange/gasket combos.
