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post #1 of 3 (permalink) Old 08-02-2018, 05:40 PM Thread Starter
 
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fresh 428

having a 1969 4 bolt main 428 built for my 1965 GTO. motor was stroked. Been at engine shop 1 year. went with all forged internals, new crank, rods, pistons, KRE heads, roller rockers, RPM manifold. all done to the tune of 9K. engine just went on dyno and was informed the rear main was leaking bad. he said he used the new neoprene seal. Engine has to come down now to replace seal. He does a lot more chevy motors than Pontiacs so not sure what his next move is. any suggestions?
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post #2 of 3 (permalink) Old 08-03-2018, 05:22 PM
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The big journal 421-428-455 engines are somewhat known for rear main sealing problems with the Viton type of seals. A lot of guys go to the square-cross-sectioned BestGasket rope type seal on these engines, which will conform to any slight machining discrepancies, and seal well. I've used the Viton neoprene seals on several small journal Pontiacs with a 100% success rate. They seem to have a spotty record on the big journal engines, though.
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post #3 of 3 (permalink) Old 08-05-2018, 07:24 PM Thread Starter
 
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Originally Posted by geeteeohguy View Post
The big journal 421-428-455 engines are somewhat known for rear main sealing problems with the Viton type of seals. A lot of guys go to the square-cross-sectioned BestGasket rope type seal on these engines, which will conform to any slight machining discrepancies, and seal well. I've used the Viton neoprene seals on several small journal Pontiacs with a 100% success rate. They seem to have a spotty record on the big journal engines, though.
Thanks Geeteeohguy for the excellent information. I am always lurking on this forum trying to learn from you GTO experts
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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