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MG MGA - exhaust headers

when I checked out the work and cost of obtaining a B manifold and front pipe to fit to my '57 A, I bought a new header [less than aus. $200 ] All is well except that I now had a vibration through the rev range which I cured by retarding the ignition from 16% back to 12%. With the std. manifold 16% and approx 35% max was fine [98 octane ] now 12% and 32% and back to running smothly and cleanly. I can't figure out why this is so ? I run a Moss electronic distributor the [ new ones they sell]
Any comments appreciated thanks Sean
S Sherry

Sean. A vibration should not be caused by the ignition advance (not retard) unless there is audible pinging/pinking going on. Vibration is caused by an out of balance condition in a rotating or reciprocating part, or a loose part on the engine or chassis.

One of the first things I would check is the thickness of the new header flanges as compared to the flanges on the intake manifold. Often, they do not match and the thinner part needs to be spaced out, using shims between the flange and the large steel washer, if the header is to be held firmly against the cylinder head.

Les Bengtson

Thanks Les, I did have to shim the headers. Your comment about the out of balance makes sense, maybe retarding the ignition just dampened it out. Fortunately the engine preforms well at 12% timing
Thanks Sean
S Sherry

This thread was discussed on 17/04/2008

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This thread is from the archive. The Live MG MGA BBS is active now.