Moparts Tech Archive
Main Cap Q's340 Main Caps
I have a 340 block that I got without main caps. I have been told that small block mopar motors all use the same type caps. Is this true and can I just score a set of 318 pieces and do a line bore?
I think they are the same except for the #3 center cap. That is probably a beefier cap than the 318's is.
the 360 mains are bigger so it would have to be a 318 or 340.
273, 318 or 340 caps will interchange.
buy aftermarket caps for your engine. it will costs you about 200 bucks to have align honed bored. you have to do this whether you use weak factory caps or stronger aftermarket ones.
Caps from a 318 or 273 will work. I've done this operation a few times and it's good to have a variety of caps to pick from to get the best fit. This is especially true for two reasons. One,...ALL the caps must fit at least snug in the block registers, and two,...find a number 3 cap that is as close as possible to the machined surfaces in the block, particularly the thrust surfaces on the sides. The fit here is critical, as bearings only come in one width to maintain crank end-play.
YUP. By the time you get the new 318 mains put on, you will wish you had put on some new Pro-Gram caps. Even MP ductile iron caps are better, by that I mean stiffer and stronger in tension than the stock gray iron stuff.
Just remembered one other little detail....