Exhaust Manifold

[GaryF]

Hi All, Merry Christmas & all that,

Just looking for a bit of advice, my manifold on the RHS of a '73 450SLC was blowing and a local reputable indi replaced the gaskets but told me that the manifold was warped and still blew a little.
Well after a few weeks it now sounds as bad as it did before the work, is it possible to skim the manifold or replacement the only option. Is there anything else (cheap & easy) that I can do? I was thinking of doubling up the gaskets to allow a bit more tolerance?
A friend suggested that silicon sealer can be used either side of the gasket and after it has burnt off what's left leaves a seal although sounds a little too easy to me.

Any suggestions welcome,
Thanks,
Gary

[alabbasi]

If it got worse over the last couple of weeks, try tightening the bolts first before removing the manifold. I have a 77 SLC engine with manifolds on it. But I don't know if they are the same.

Do not over tighten the bolts as they make snap which is a giant pain in the butt.

[Todd Miller]

Hard to beleive that a shop would install a warped manifold, and not have it "skimmed" (called "surfaced" here in the US).

There is no way around this. The manifold needs to be removed and surfaced to make it flat. A machine shop with a belt sander style surfacer would be ideal, and be the cheapest and easiest method.

Do not retighten the manifold nuts. The V-8 engines are notorious for broken studs in the heads, and if you break them off, you will be very unhappy!

Do not use silicone "high temp" sealants. They don't work, especially when you have a warped manifold.

The exhaust sealant of choice (and again, it won't help because your manifolds are warped) is the black asphalt based "Muffler Paste" sold by Walker. It's similar to the brush on roof tar that you can buy in a bucket. I use it on all exhaust gaskets.

My suggestion would be to call around and find a machinist who can surface your manifolds, and then work out a deal with the repair shop, where they take the manifolds off and either take them over to the machinist, or you take them over. Then reinstall using muffler paste and new gaskets. I'd also recommend replacing all of the exhaust studs because they get brittle from having exhaust gasses blowing over them.....and then they break during installation. Use only hardened automotive grade studs!!

[JimFreeh]

Another risk in tightening the manifold fasteners, is a cracked cast iron manifold.

Get a skim cut.

Jim

[GaryF]

Thanks for the fast responses guys,

The shop had 3 studs snap on them when they replaced the gaskets as the manifold probably hadnt been touched in 35 years so should come off easily this time. I'll do as you suggest and find someone here to machine it.

Regards,
Gary

[Todd Miller]

Originally Posted by GaryF

The shop had 3 studs snap on them when they replaced the gaskets

Whenever I'm working on something that's been run with leaking exhaust manifolds I always replace the studs for this reason. They just become crystalized by the blow torch effect of the leaking exhaust gasses.