Exhaust Manifold Gaskets

[Avroflyer]

Hi all - can anyone help, concur or console?

NEO (400SE) developed a ticking sound on the way back from Brooklands in May which I thought was a noisy tappet but hoped it was the exhaust. Have probably done about 5 - 600 miles since (incl WedgeFest) and it has slowly got louder. Took her out today and parked in a lay-by, bonnet up and had a real good listen. Definitely seemed to be loudest around no 7 exhaust manifold. Back to the garage with torch and mirror (and a decent pair of specs!) and the tell-tale signs are there. Blowing gasket.
So a few queries if you will.

1. The gaskets seem to be joined in pairs, unlike any pictures in Steve Heath's Wedge Bible. I guess that means you replace two together?
2. All four exhaust manifold flanges are joined so that they would want to move as one. Does that mean you're obliged to loosen the whole bank of four and replace all four gasket "positions" (ie two gaskets if one serves two)?
3. Most opinion says don't leave it and keep on using the car as the mating faces will pit, especially the alloy cylinder head side. I had booked to go to Silverstone Classic Show on Sat 27th July but that's a 450 mile round trip which I'm loathed to do if I run the risk of having to reface the head. Grrr. I am resigned to not going. Am I being too cautious?
4. Is it possible to change the gasket(s) without removing the manifold? I'd have thought that if you undo all four, there should be enough spring to open up enough gap to slip one out and one in. However, do they stick and have to be scraped off?
5. Some exhaust manifold gaskets are designed to be used dry with no jointing agent. Should you use jointing compound for these gaskets or not? I guess if you do, it makes getting them off a pain!

Well, can't think of any more questions but any advice anyone can give will be most appreciated!

Cheers

[Avroflyer]

Thanks for all the tips. I bottled out and skipped Silverstone, despite he advice to the contrary. Anyway, PDW - will I really need to replace the spring washers? And also, Adam, where do you get your gaskets at a tenner a set? Sounds like a bargain to me considering what I paid for a pair (one side)!

Cheers

John (Avroflyer)

[Avroflyer]

Thanks for the tips all. I bought two gaskets from David Gerald and undid all four ports on the offending (nearside) side. The old gaskets fell out easily and intact with the rear (no 8) port showing definite signs of leakage. Had enough clearance to wipe the soot off the mating faces at the leak, slip the new gaskets in, hold them in place with a couple of bolts each and put the rest of the bolts in. There's a definite order in which to put the bolts back and tighten up as the curvature of the pipes restricts the amount of bolt you can have showing without fouling on the manifold pipe!

Question is, what is the correct torque for the bolts? Haven't managed to find it written down anywhere yet.

Also, the gaskets that came out have metal faces with the heatproof compound sandwiched inside. The new ones are the reverse - metal inside with a grey compound faces. Which is better?

I've hand tightened with a spanner and will run the engine for a few minutes but then am stuck for the retorque value. Can anyone help?

Cheers

John

[Avroflyer]

Thanks Danny
Hmmm. The ones I took off are like yours ie metal on the outside and the leaking one doesn't appear to be damaged but the bolts weren't very tight, certainly nowhere near 16 ft lbs. That was the backpair. On the front pair, which wasn't leaking, the bolts were much tighter. That may well have been the root of the problem, the back pair being too loose...

Cheers

John

[Avroflyer]

Hi all

Oh dear, it’s happened again but it’s so long since the last time, I’d forgotten all the advice and help that flowed back from PistonHeadders back then. Until I found my old post on the Forum.

The manifold gasket on NEO, a 400SE, started blowing recently on the rear cylinder, left hand side. Managed to undo all the bolts, slip out both gaskets (they are paired - one joined gasket covering two adjacent cylinders) slip in two new ones and fit the bolts.
The first question was does anyone know the correct torque values for the 8-off exhaust manifold attachment bolts? Reading back through this post of old, 16 ft lb seems to be the favourite so unless there are any other thoughts, I’ll go with that.
Second question is more of a problem. On re-assembling as above, I spanner-tightened the bolts to a firm hand-tight, enough to flatten the spring washers and didn't want to go any further until I could find out the correct torque setting. But in looking closely at the joint at the blowing cylinder, I noticed it looked as though the manifold branch end attachment flange that bolts to the cylinder head exhaust port appears to be bowed. I could slip a 20 thou feeler gauge in between the gasket and the flange.
Has anyone seen this before and can recommend a remedy?

Here are the removed gaskets, manifold side up. The bottom one is the blown one. It looks as if both cylinders have been blowing in fact, although I only noticed the back one.




Here's the feeler gauge going in:



All help gratefully received!
Cheers
HERB

[Avroflyer]

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

[Avroflyer]

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