Gator77
Well-Known Member
What are my options? I was thinking about picking up a 340 that's for sale with out caps is it even worth it thanks for info
340 main caps
- Thread starter Gator77
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I still don't know why anybody would separate main caps from the block. That's just stupid. Somebody sells caps. Try Summit. You have to get the line bore re-machined though.
Gator77
Well-Known Member
I know such a easy task to put them rite back on when disassembling
No doubt. Even used caps on that used block should be sent to the machine shop for machining.
grimreaper
Cross Member
You wil have to find a good rear main cap from somewhere. (these can come from a 318 as they are the same but 318 forward caps are shorter.) The others can be bought aftermarket from places, like ProGram, and fitted. If you get used factory replacements or aftermarket they will need to be fitted and line bored which can be pretty expensive. If the block is still standard bore or has numbers you need it might possibly be worth it but you need to figure in additional costs for getting it in condition to use.
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MOPAROFFICIAL
Oogliboogli
How the registers are cut in relation to the cap is the problem there little different in each block, you end up with the cap sitting off set to the main bore. So Machining the register one way or the other to scoot the cap over and then if possible Re swedging/staking them to snap in...then a line hone hopefully is enough...
Anytime though you have to 'line bore' you're definitely going to end up with a chain that's jus a little loose..sometimes even a .010 under chain is loose.
Anytime though you have to 'line bore' you're definitely going to end up with a chain that's jus a little loose..sometimes even a .010 under chain is loose.
I would imagine they fit the caps to the block and then machine the bores. We should ask @krazykuda. He worked at a Mopar engine plant.
CMcAllister
Well-Known Member
Worth it? Depends on the price, condition, etc. If this was going to be a basic engine or was it going to be a race deal that could benefit from aftermarket caps and/or a line bore anyway. Plenty of worn out, broken blocks out there that could donate caps. Missing caps wouldn't be a deal breaker for me, but it would have to be a deal to begin with.
Anytime I build an engine, I always have the crank checked for straightness, & the block align bored this eliminates any possible problems later on in the build.
gzig5
Well-Known Member
I picked up a '73 340 block for a good price ($100). Realized when I got it home that the caps likely are not original to the motor, mainly based on surface condition. Motor is standard bore and if/when I build it will get a 3.79 or 4" crank but won't be a max effort build. Strong street and road course motor. I realize that I'm going to have to have it line bored now, but is there anything else that I need to look at on them? It there any benefit to a set made from alloy steel in this type of application? I can machine and grind a set pretty easily and they'd get honed anyway.
yellow rose
Overnight Sensation
If you don't have any caps, FABO member Rocket is selling the best caps out there (IMO) and you get all 5 caps if you buy from him.
The three center caps are 4 bolt caps, but you can cut the out bolt bosses off of them a go.
If I needed all 5 caps that's what I do. They are the caps that came on the R blocks.
gzig5
Well-Known Member
I've seen the ones he has, but I have caps. Just don't think they are from that block so they are going to have to be line bored/honed no matter what. I didn't think that a 550hp-ish build would require something like that. Does the extra meat do anything in a two-bolt main stock block without any other reinforcement?
CMcAllister
Well-Known Member
Some people say they are better support, some say the blocks are so thin, they don't really help. I have no experience with 4 bolt caps on a stock block to have an opinion. "550ish HP" on an OE block is getting up there to where you need to pay attention to the details. Especially with some stroke in it.
Wyrmrider
Well-Known Member
I don't think 4 bolt caps make any sense on a stock block
also I do not think stroke if lower rpm than short stroke (the old school way with limited heads)
back in the day we were head limited
now you can get heads to make power with a stroker at high rpm
light weight pistons which means the longest rod that makes sense with your stroke
also I do not think stroke if lower rpm than short stroke (the old school way with limited heads)
back in the day we were head limited
now you can get heads to make power with a stroker at high rpm
light weight pistons which means the longest rod that makes sense with your stroke
Like MO said used caps won't necessarily line up sideways.
After they line bore it then they line hone it. Cost me $500 plus the cost of the caps. I got my last set from Rocket.
[FOR SALE] - 4 Bolt Main Caps - 340 and 360 Ductile Iron - New
MOPAROFFICIAL
Oogliboogli
And if you read my post again and use a little bit of imagination ...picture snapping in the wrong main cap in a block and there's about a .020 lip of the cap main bore over hanging on one side and under hanging on the other...
The registers hold them that way...so you have to scoot them over, file, swedge... however you have to... just remember the bore and bolt holes will pretty much be spot...but not if the register were cut diff..and they are by a hair 90% of the time... then its off to one side and nothing lines up. I worked in a machine shop and line honed blocks, resized rods, straighten rods, cut and installed seats, ran the mill, sunnen ck 10 honed a number of blocks.
Btw ask karl all you want, wont change ****.
MOPAROFFICIAL
Oogliboogli
Op might have to find a couple sets of caps set them on and see which ones lineup the best, see which ones are even close to snapping in and lining up to the bolts.
Go with the ones that line up the best and massage ,file, swedge, the registers to accept them...you will need a dial bore gauge to this properly....you will only get them close, not perfect, until its honed.... you will focus on getting an even amount of lip if lip is what you have or recess if recess is what you have once you get those dialed evenly side to side... then you can take it to the Machine shop for a line hone IF you did it right.
You can use 318 caps...but as already said, they are shorter by 3/8 or 5/16..but will still work...stud them if you want. The main problem was the no.1 main 318 cap likes to crack under big power/rpm.
Go with the ones that line up the best and massage ,file, swedge, the registers to accept them...you will need a dial bore gauge to this properly....you will only get them close, not perfect, until its honed.... you will focus on getting an even amount of lip if lip is what you have or recess if recess is what you have once you get those dialed evenly side to side... then you can take it to the Machine shop for a line hone IF you did it right.
You can use 318 caps...but as already said, they are shorter by 3/8 or 5/16..but will still work...stud them if you want. The main problem was the no.1 main 318 cap likes to crack under big power/rpm.
yellow rose
Overnight Sensation
And then, you end up cutting the crap out of the cap if you can't move the cap far enough to get some materiel so you can get the mainline back in.
That's why if you need to replace the caps for whatever reason, you'd better have a bunch to screw with to make sure you have some options.
Or just buy new caps that are far enough undersize so you have something to work with.
I used to save every cap off every block that was broken just so when the need arose, I had something to work with.
MOPAROFFICIAL
Oogliboogli
Brutha I hear you, exactly...and that's why I told him get a few sets of caps and find the ones that fit 'the closest', that only require filing/cutting the register and staking/sledging the iron over 'to the cap'...milling the caps sides would be last on the list after all else is exhausted. I had a 360 get line honed and studded one time ..and when I got it back the Caps didn't snap in...they just fell in then I checked'em with a bore gauge n was not happy ...some twisted .0003-.0005 I fiddle fkd that cap set for about 2 hours, torque n check torque n check
...and finally got it to where I'd call it perfect.
Something the op will need to do once he gets the caps to sit down in there..
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Well you guys are the experts. It sounds like you have saved quite a few by matching caps from other engines. I was curious as to how the factory did it. Maybe someone stood around and trial fitted caps and then sent the block to be line bored. May be they just snapped the caps on and then line bored to correct the dimensions. I mentioned Karl because I know he worked in engine assembly. I was just curious as to how they did it at the plant.
MOPAROFFICIAL
Oogliboogli
I get it.
Blocks are rough machined 1st, registers are cut....caps then fitted , drilled/tapped...line bored/honed to spec. Caps are steel. block is iron. Caps are manufactured separately to a spec.
CMcAllister
Well-Known Member
I understand, it may be a process to find usable caps for a block they've been lost from. But I wouldn't trash a good block just because the caps were missing or pass one up that was a deal.
True that but where did the caps go and why. After reading through this thread I don't know if I could trust that the block is any good. Seems like the caps get robbed before the block gets scrapped.
True that but where did the caps go and why. After reading through this thread I don't know if I could trust that the block is any good. Seems like the caps get robbed before the block gets scrapped.
CMcAllister
Well-Known Member
People are sloppy. I've gotten good blocks without caps, caps thrown in a bucket, caps from a couple of blocks thrown in a box together. I don't know why it was so hard to put the caps back on the block.
On our engine the main bearing caps came in a bundle all in one casting... We had a machine line separate from the block line near the block line that machined the caps and the channel for the register, rough bored the caps, then sawed them apart...
Then the caps were installed in the block before the main bearing bores were align bored with the caps on the block so the bores were all in proper alignment with each other...
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