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(want to BUY)1972 340 main cap set (all 5 main caps)

gzig5

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It is my understanding that the 340 caps are thicker or taller at the top. Not the same as a 318. I have both on hand but I haven't had time to measure the differences. It isn't supposed to be much, but a little different. For anything but a max(500-600hp) effort build, I would think the 318 caps will work just fine if you can get them to fit properly and have them line bored and honed. The trick is finding a set that will fit your block well enough, there isn't a lot of room in the bolt holes and the width of the boss can vary enough to be problematic.
 

Ele115

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318 caps will work, in theory but the caps were machined to the engine and putting in caps from another engine may or may not cause you problems. I have seen them where they are out of alignment a bit and by then you need machining work which may take a lot off the caps to get them to line up right. Undersize caps can be found, then machined to fit as if they were original to that block. Swapping main caps can be a headache, but I realize you have no choice here and I would never discard a 340 unless it was really out to lunch. Best of luck.
 

heminut

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When changing maincaps they ALWAYS have to be machined! The caps are cut down where they mate with the block, and then the block is align honed. There have been stories where another cap has been swapped without any machine work and it worked okay, but I wouldn't spend the money on a build and take that kind of chance.
 

Steve340

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You could swap on another set of caps - theoretically - but the work could only be done by a competent machine shop.
As earlier posters have mentioned they are almost certainly not a set and forget deal.
It is probably cheaper to get another block unless it happens to be the correct block for the car. That would justify the extra cost of doing the work.
 

heminut

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You could swap on another set of caps - theoretically - but the work could only be done by a competent machine shop.
As earlier posters have mentioned they are almost certainly not a set and forget deal.
It is probably cheaper to get another block unless it happens to be the correct block for the car. That would justify the extra cost of doing the work.
As another poster pointed out, 340 blocks are not easy to come by, and putting a set of 318 maincaps on and having the machine work done would definitely be cheaper than buying another complete block! The machine work for something like that is not that expensive!
 

gzig5

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hey chryco the only option i saw from Mancini was the 3 center main caps 4 bolt only
The three in the middle are apparently the ones most stressed. Apparently (so I was told) it was common to use the stock 318/340 #1 and #5 caps but upgrade the middle three. On a standard 340 block the extra bolts can be cut off the caps because you actually weaken the block if you add four bolt mains to a stock block.
 

BSG

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I have an entire 340 thats at the machine shop I dont need I bought as a donor for the 340 that is in my car now as it was overheating and I couldn't find the issue. Turned out my block was good and I didn't need it. It took 4 or 5 months to get it back and its in and runs great I was gonna just have them go through it and then sell it. I dont think they have started working on it as they are slammed. I'm in Los Angeles.....
 

BSG

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Anyone know what a 340 is worth either stock or 30 over in rebuildable cond ?
 

CUDAOwner

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I have an entire 340 thats at the machine shop I dont need I bought as a donor for the 340 that is in my car now as it was overheating and I couldn't find the issue. Turned out my block was good and I didn't need it. It took 4 or 5 months to get it back and its in and runs great I was gonna just have them go through it and then sell it. I dont think they have started working on it as they are slammed. I'm in Los Angeles.....
my offer to you is 600.00 an ill come out to pick it up ....
 

BSG

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Its a short block and I paid $1200.00 for it. But I have a set of x heads straight out of machine shop I didn't use. I don't think I can take a $600 loss on it. My plan was to freshin it up and sell it as a complete longblock. I'll mull it over. I hit the machine shop guy up as to what cond its in right now and to let me know what I owe him and he hasn't responded to my email yet.
 

CUDAOwner

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Its a short block and I paid $1200.00 for it. But I have a set of x heads straight out of machine shop I didn't use. I don't think I can take a $600 loss on it. My plan was to freshin it up and sell it as a complete longblock. I'll mull it over. I hit the machine shop guy up as to what cond its in right now and to let me know what I owe him and he hasn't responded to my email yet.
sorry 1200 is to much i already have a motor just need the maincaps to get my motor complete good luck to you an thanks
 

BSG

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sorry 1200 is to much i already have a motor just need the maincaps to get my motor complete good luck to you an thanks
I hear you I'll hit up the machine shop when he gets back at me.. its a pretty big place you never know what they have laying around....
 
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