I own 72 challenger with #'s 340. It started to show a leak from the rear rear main seal and when I dropped the oil pan I found the rear main bearing cap had a crack in it. I have an old 318 block with the caps still on it and was not sure I could use the rear main cap as a replacement. I know it will have to be aligned bored before placing motor back in service. The service manual shows the diameter for both motors the same 2.4995" . Can somebody advise me if this cap is in fact interchangeable. Thanks.
leaky rear main seal
- Thread starter tomstoy
- Start date
it might work but in hate to tell ya this it probably wont the cap is matched to the block it came out of when it was originally line bored also 318 caps are a different material, not as strong. none the less the rest of the caps aren't a s large not sure about the rear main. i think if your main goal is to just get it running and the strength is not an issue you could have your machine shop try it still it will bolt in
Cranky
Well-Known Member
The 340 takes a longer main bolt because the cap has more meat...ie bigger. Bore is the same tho. Kinda doubt the material is different tho. Mom already was using a better grade of cast iron than the other two were. How did the main cap crack?
The myth of high nickel blocks vs low nickel is just that...a myth. They were all high nickel. Machining them tells the story. The Mopar blocks all have pretty much the same sound when machining them. A GM block sounds like you're cutting peanut butter with a spoon....
The myth of high nickel blocks vs low nickel is just that...a myth. They were all high nickel. Machining them tells the story. The Mopar blocks all have pretty much the same sound when machining them. A GM block sounds like you're cutting peanut butter with a spoon....
the caps are not made out of the same grade of material as the block. and maybe material is the wrong thing to type different grade of material is true but this has nothing to do with his problem. cap size maybe true dont know for sure none the less weaker.
Cranky
Well-Known Member
Well if the cap size wasn't different, why would the bolts be longer. I just went through the hassle of finding the right bolts for a 340 because the guy thought they were the same and brought me bolts from a 318. He just brought the whole 318 over to use as a 'parts' engine and the caps are definitely different. About the only things that are the same between the two engines are the bearing sizes, bolt location and stroke. The rods are the same length but the size varies....
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