exhaust manifold gasket ???

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jazak5

jazak5

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do I need exhaust gaskets on a 340 when installing the factory hp manifolds???
I see a lot of people not using them
 
thin sheet metal on left w/heat shield, just a thin sheet metal gasket on right
 
I have always used a thin bead of high temp RTV on my stock 340 Manifolds without a gasket and never had a leak. I also check to make sure the flanges/mounting surfaces are flat.
 
Check straightness and factory finish marks. No gaskets should be needed unless there is issue with the machined surfaces. I used a pair many years and miles that way.
 
Since 50 year old manifolds are usually warped, I really doubt if you can get away with no gaskets. Mill them back to real flatness, then they will work.
 
I haven't actually seen that. The 340 castings were incredibly stable, maybe 'cause they were bolted up right. They certainly were not premo examples having been cracked and rewelded by the D/S outlet and the flapper on the p/s removed - holes bolted and later welded. Yes all welding was done with a long sit in an oven but it wasn't bolted to a spare head during those interventions.
 
Because they are cast iron, they are old, and metal can only be heat-cycled so many times. Most of them have been on and off at least once, maybe improperly torqued, and had the wrong gaskets used on them. I have seen quite a few cracked, and not just on the ears. They usually crack when someone bolts a warped one back on not knowing it was warped.
 
I always use a new gasket after removing manifolds, whether the OEM ones, new ones, or aftermarket.
 
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