View single post by Jensen Healey
 Posted: 06-04-2013 04:44 am
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Jensen Healey

Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 983
Apparently the o-rings reduce heat transfer from the manifold as well as dampening the vibration from the engine. Obviously they need to be air tight.
This is not a critical tuning parameter, it's adjusting the slop in the system. 
.070 or .040  or anything close will work just fine. If you have older O-rings, make sure they seal and have an even gap.
I doubt the various "anti popping spacers" and o-rings are manufactured to any specific spec. If we knew the thickness and durometer rating of the original o-rings the gap could be set to .070 with confidence.
Use common sense and snug them up 'till they feel right.