Exhaust Manifold Gaskets

Exhaust Manifold Gaskets

Author
Discussion

SLB

258 posts

244 months

Friday 21st June
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I've had similar issues on a 420 SEAC I used to have. I used the same gaskets as you and again a good hand tight not knowing the correct torque. I had one thread fail on me doing this and a helicoil had to be put in when the engine came out partly for other work. I think the thread had been damaged by a previous owner as all the others were completely fine.

What I found was that the bar joining the two halves was springy enough to allow removal of one gasket at a time but the heat generated seemed to affect the gasket and the torque the bolts were tightened to. I recall having to nip them up a couple of times after initial installation but once done had no more issues even after several years. I would suggest you try cleaning the faces with some fine wet and dry before fitting a new gasket and give it another go.

mk1fan

10,591 posts

228 months

Friday 21st June
quotequote all
Tighten the bolts more with a bit of control - ie not like some ape with a four-foot bar. See if that closes it off. 'Hand tight' to me means not tight at all so while the split / spring washers maybe flat (which doesn't take a lot of pressure / force) but that doesn't mean the element is bolted down.

That said, they don't need to be that tight.

You could try a thin bead of high temp, snsor safe, copper RTV like V-Tech - https://www.vitaltechnical.com/product/rtv-gasket-... or Permatex - https://www.permatex.com/products/oreilly/permatex... which is used on the Speed 6 engines to form the manifold gasket.

So like a bead similar to 1mm2 copper wire.

indigochim

1,594 posts

133 months

Friday 21st June
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I had trouble getting some Peninsula manifolds I bought 2nd hand one here to seal. One the 3rd time of having them off I tried them on a straight edge and saw one end was a coupe of mm off the work bench when the other side was flat. I had them linished flat and by by issue. That was on my Chimaera but I guess you may have the same issue.

Avroflyer

Original Poster:

43 posts

154 months

Sunday 23rd June
quotequote all
Thanks for all the tips, PHers.
I've decided to dismantle, clean up the faces as best I can, use two gaskets at each port on the left bank and sandwich a thin bead of Permatek RTV in between each gasket pair. A bit nervous about 16 ft lb as the torque setting - seems a bit high to me, but what do others think?
I'd like to avoid having to take off the manifold if at all possible to not have to split the first joint along the exhaust pipe on that side!
Cheers
John

SLB

258 posts

244 months

Tuesday 25th June
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Best of luck! I've removed the manifolds maybe half a dozen times on a SEAC and a 350i and both were fine on the near side but the starter is an issue on the offside. On the first occasion I removed the starter but after that used a jack to press the manifold between the starter and the chassis - it's so close it just needs a bit of persuasion. I'd prefer not to tamper with the manifold to exhaust seals as the first time they disintegrated and I spent ages trying to find seals which would fit which I think were Jaguar in the end. Don't use exhaust rap as brand new SS manifolds lasted 1k miles on a SEAC - you could see them glowing red hot at idle after a run and they just disintegrated.

I did try double gaskets at one stage but they didn't last. I think if it's right it works. The best thing is to clean them as best you can both sides either on or off the car and use some of the RTV as has been suggested. I think that torque setting is about right.

Avroflyer

Original Poster:

43 posts

154 months

Wednesday 26th June
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Thanks SAB but not sure what you mean by "exhaust rap" and what was it that disintegrated?

Also I'm still concerned about the apparent bowing of the attachment flange on the left hand rear position as in the photo above. Has anyone ever seen this?

Cheers
HERB

Edited by Avroflyer on Wednesday 26th June 08:40

indigochim

1,594 posts

133 months

Wednesday 26th June
quotequote all
Avroflyer said:
Thanks SAB but not sure what you mean by "exhaust rap" and what was it that disintegrated?
They're on about exhaust wrap I presume as you see on many race cars or motorbikes. I believe it can cause the manifold to rust prematurely so presumable they mean the manifolds disintegrated.


Avroflyer said:
Also I'm still concerned about the apparent bowing of the attachment flange on the left hand rear position as in the photo above. Has anyone ever seen this?
As my post above it's entirely possible that the face plate is warped. My TVR guy got a mate to sort it for some beer money.

mk1fan

10,591 posts

228 months

Thursday 27th June
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You could cut the joining peice of metal between the the two ports - like the gasket. Other than for fabrication alignment, I am unaware it serves any function once installed to the engine.

Assuming the faces of the ports are sufficiently true / flat then it would allow you to nip up that port back to the head.

Wedg1e

26,827 posts

268 months

Friday 12th July
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mk1fan said:
You could cut the joining peice of metal between the the two ports - like the gasket. Other than for fabrication alignment, I am unaware it serves any function once installed to the engine.

Assuming the faces of the ports are sufficiently true / flat then it would allow you to nip up that port back to the head.
The risk to cutting the linking bar is that tension in the pipes might then allow the individual port flanges to 'spring' and make matters worse.

Bowing of the mating faces might be due to weld distortion at manufacture and/or persistent blow-by of hot gases eroding the face, but you'd need the manifold off to see it. You could try dressing the face flat but then you've increased the clearance of the whole face to the head...

adam quantrill

11,549 posts

245 months

Friday 12th July
quotequote all
You can do it up tighter but then risk breaking the threads in the head.
I have had two go, because partly I suspect the casting was a bit weak around that area. Front right, and rear left.
Rather than mess with helicoils, I tapped out the hole to M10 and inserted a stud, then an M10 nut bolts it down tight.
To remove, I have to undo the nut, then extract the stud. But it means (much like cylinder head block studs) you have full engagement of the threads into the aly before stressing them and they can take more force.

Also you can slap in more exhaust paste, if you let it go off gently then it's pretty good.

Finally, I gave up on those fiber gaskets and made my own out of copper sheet, which then last forever. It's not difficult to do.

Incidentally the 400SX is also a NEO :-)