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Darn Green Elbow Gaskets

wh1278

wh1278

Member
I replaced my risers on my starboard 440...lower elbow, 6 inch extension, upper elbow...and used the OSC121 blocking gasket (FWC). These are the green ones from Thermoseal. I was told by calling Thermoseal that you shouldn't put gasket sealer on them, and sure enough they leaked. Not alot, but every time I take the forward drain plug out of the lower elbow I get water (fresh). I then put a little sealer on the circle between the slots and the exhaust, because the manifolds are old, so they are a little pitted. But still leaking...uuuggghhh. So, question is, do I find use the regular "felt" type? They are what I took off the old risers when I replaced. They worked fine. These new age green composite Thermoseals dont adhere (not hot enough at the elbow), and dont fill the gap. Where do I get the older felt type?
 
wh1278 said:
I replaced my risers on my starboard 440...lower elbow, 6 inch extension, upper elbow...and used the OSC121 blocking gasket (FWC). These are the green ones from Thermoseal. I was told by calling Thermoseal that you shouldn't put gasket sealer on them, and sure enough they leaked. Not alot, but every time I take the forward drain plug out of the lower elbow I get water (fresh). I then put a little sealer on the circle between the slots and the exhaust, because the manifolds are old, so they are a little pitted. But still leaking...uuuggghhh. So, question is, do I find use the regular "felt" type? They are what I took off the old risers when I replaced. They worked fine. These new age green composite Thermoseals dont adhere (not hot enough at the elbow), and dont fill the gap. Where do I get the older felt type?
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I fought this same issue last season in an attempt to seal the new risers, to old manifolds, I lost the battle, and had to replace the manifolds as well. If the mating surfaces aren't perfect, the green gaskets won't seal. I even attempted to use copperlux spray on the green gaskets, and they still leaked. I eventually found an old style black gasket, applied copperlux to that and tried it, still no good. It was recommended to me to pull the manifolds and have the mating surfaces replaned at a machine shop, so I figured, why not just replace them, they're 30 years old anyway, and that was the solution in the end, new manifolds, risers and green thermoseal gaskets. No leaks. Good luck, wish I had a better solution to offer.
 
Make sure you use at least grade 5 bolts or better. Stainless bolts aren't strong enough as I found out. So far no leaks after putting in stronger bolts. Not sure what the torque is supposed to be but tighter is better in this case. Those are some meaty gaskets.

Eero
 
Good points about the old manifolds and the bolts. I know this to be true as I recently replaced one mani on my port...new surface, new bolts, same green gaskets and it works, no leaks. However, before I replace the old mani's on the strbd, I think I want to try the black felt gaskets first. Where do I get those. The riser supply where I bought them (online) only has the green thermoseals.
 
Your wasting your time, if the faces to be joined are rusty & pitted, you'll never get them sealed, bite the bullet & buy new manifods.
 
eero_karppa said:
Make sure you use at least grade 5 bolts or better. Stainless bolts aren't strong enough as I found out. So far no leaks after putting in stronger bolts. Not sure what the torque is supposed to be but tighter is better in this case. Those are some meaty gaskets.
Eero
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I'm not trying to pick a fight, but how can you recommend grade-5 bolts and then say you don't know torque spec but tighter is better?

Ultimate strength of SST versus low carbon steel bolts is about 60%. As for bolt grade (low carbon steel), grade-3 (2 marks on bolt head) 5/16-18 dry torque 17 ft-lb, grade-5 (3 marks on bolt head) 5/16-18 dry torque 19 ft-lb. 3/8-16 grade-3 (2 marks on bolt head) dry torque 30 ft-lb, grade-5 (3 marks on bolt head) dry torque 33 ft-lb. If you introduce a lubricant to the threads you can plan to increase torque by about 35%, this varies with lubricant type.

If you over torque your bolts they will go into torsion and potentially fail, or the female threads can fail. Follow proper torque, not blind advice.

,Noel.
 
This is from page 75 in the Osco catalogue. Thanks for the torque numbers... I'll be going with 19 ft-lbs next time.

Eero

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OLTS: Do not use stainless steel or grade 2 bolts to install the risers or elbows. These bolts are too soft and will not hold a torque
setting, which can cause leaks at the gasket surface. Where bolts are specified, OSCO mounting kits use only grade 5, or better bolts.
Bolt torque should be reset after initial startup, while the engine is still warm. Refer to your original manufacturer's engine service​

manual for specific torque settings. Never use anti-seize type products on bolts or studs. They will allow for loosening of the parts.
 
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