doug russell wrote:
>Long time since I've posted but I need some help diagnosing a problem I am
>having with a new Dual HS4 SU conversion I made on my 77B.
[snip]
>
>2. I have an exhaust leak at the head-exhaust manifold connection for #2 /
>#3.
[snip]
>Are there torque specs?
I can help you with that, at least, since I just did this on Sunday. The
manifold studs are spec'd at 15 ft/lbs. This sounds awfully feeble, I
know, but when I got them all snugged up it seemed nice & tight. I kind
of snuck up on 'em a little at a time, alternately. Anyway, I've only
been on one short trip but it was definitely not leaking.
In my case the gasket replacement was prompted by one of the nuts having
worked itself loose (and falling off!) until I had an intake leak. It's
been almost ten years since I had the manifold off so I can't blame it
too much.
Did you use the original style nuts? Since your car didn't originally
have dual SU's you may not know what they look like. They're about twice
as "thick" as you'd expect a nut of that thread size to be. Since they
are fine thread (of course) I assume it's to give them extra gripping
power. You don't use lock washers with them, either (or at least mine
never had them).
Also, I wouldn't think using two gaskets would actually help. They
wouldn't crush properly unless you overtorqued, and it's very easy to
strip those fine thread studs.
One thought--have you compared the shoulder depth of the the intake and
the exhaust manifolds (the flanges where the big hold-down washer sits)?
I suppose you may have wound up with parts from the opposite ends of the
range of production tolerances, or someone had previously machined down
the exhaust manifold flange. Thus preventing it from properly crushing
the gasket, since you'd be torquing down against the intake manifold
flange, only. Just a guess...
My experience is with a stock '66 set-up, so YMMV...
My 2 cents, FWIW. Good luck!
--
Max Heim
'66 MGB
runs great, looks scabrous
mountain View CA
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