I’m alittle disappointed to say the least. I got this from a well know shop 20 years ago so no going back. First thing I find out is the crank is a 318 forged crank. No holes drilled in the front and rear rod journals. Got a useable 340 crank now. Pistons are new and pretty close in grams so not much work there. Rods are another story. Beans are ground down, nice job. Shot peened and resized with HD bolts. But the weight mismatch really bothers me. 732.0/734.9/736.8/737.8/741.9/748.7/762.7. I know I can probably make the 748.7 rod work, but this 762.7 is over an ounce heavier. So another rod is in order I’m thinking. What does the FABO crowd think of this. Thanks in advance Kim.
Balancing my 340
- Thread starter oldkimmer
- Start date
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Marcohotrod
Well-Known Member
I bought a 340 over the counter crank at the dealer in 1971 . It is a 318 truck crank, rod throws not drilled = stronger , running to 7000 today , balanced no problem with 340 rods and 610 gram pistons. I have seen small chevy and ford cranks break at the drilled hole between the 1 main and 1 rod. I would talk to the balance guy, pair a light rod with a heavy rod? no problem if kept in order and the complete assembly is balanced. the beans are ground down, can we grind down the balance pads on the heavier rods more?
PRH
Well-Known Member
That’s a pretty big weight mismatch on the rods imo.
If there are pretty substantial balance pads on both ends of those heavy rods, you could try and see if you could get them down to a usable range.
If they can’t be brought into range....... I’d step up to something new.
Total weight is only part of the equation...... the two ends also have to be close to one another(small ends all equal, big ends all equal).
If there are pretty substantial balance pads on both ends of those heavy rods, you could try and see if you could get them down to a usable range.
If they can’t be brought into range....... I’d step up to something new.
Total weight is only part of the equation...... the two ends also have to be close to one another(small ends all equal, big ends all equal).
I asked Graham to post pics when he gets a chance. On the crank issue the pistons are old forged 2332P. There like 888 grams. That coupled with the heavier journals of the 318 crank it would of needed 2 sticks of Mallory metal to balance it. I can use it with really light pistons and it will balance out great then. I’m thinking now I should of just bought pistons and rods and used the 318 crank, but these pistons are already sized to the bores on the 340. Years ago I had a buddy that just threw in a 318 crank into a 340, never had anything check and it seemed to run fine. I don’t remember any kind of a vibration. Kim
dano
Evil Handy Man
How good are the rod lengths? I had that issue with my 340's "balance job". Some were just junk, ended up going with Scat I beams.
daddio4048
Daddios72
You said ounce; thought they balanced engine parts in Grams?
MOPAROFFICIAL
Oogliboogli
Send it back...to another shop.
Speak with them on their method.
Speak with them on their method.
They were supposed to be a matched set. Haven’t checked the length yet. Yes grams, but the difference is an ounce, no that can’t be right. It’s 32.7 grams from lightest to heaviest. That is 1.153 ounces difference. Kim
nm9stheham
Well-Known Member
Those rod weight mismatches are waaaay off from what I have measured in stock sets. I have found less than +/- 10 grams from nominal in a few stock sets. Sounds like someone threw in that 762 rod as a replacement and did not do anything to weight match it to the others.I don't think these were weight matched at all.
Those rods need to be gone through 100% and weighed for small and big end weights, and all those numbers matched up closely for the level of quality that it seems you want to achieve. (As well as the heavy pistons...) Those weights being matched effects one vibration in the overall balance, and are used to set the other balance factor that we deal with 'in the field'. And yes, you could conceivably mix and match the light and heavy rod end weights and get things closer but that takes more trickery that most are capable of.
'it seemed to run fine' is always a questionable assessment of balance LOL
Those rods need to be gone through 100% and weighed for small and big end weights, and all those numbers matched up closely for the level of quality that it seems you want to achieve. (As well as the heavy pistons...) Those weights being matched effects one vibration in the overall balance, and are used to set the other balance factor that we deal with 'in the field'. And yes, you could conceivably mix and match the light and heavy rod end weights and get things closer but that takes more trickery that most are capable of.
'it seemed to run fine' is always a questionable assessment of balance LOL
Let me clarify. I got this motor unassambled from the machine shop when I bought a 74 duster 360 4gear car. The car owner had the motor there for machining. All it needed was to be assembled. It was a buy all or nothing deal. Too good to pass up. Kim
I’m probably being on the overly cautious side but it may be helpful to post pics of the rods side by side so we can see how much material is left on the balancing pads. More than likely there is enough to get them balanced equally end to end, but if anyone notices something obvious that would merit a new set of rods then you wouldn’t be out the cost of having them checked.
Please elaborate! Start with the confirmation that the rod set is in the ball park to each other before checking the end weights! Step two, inform Kim there appears to be a mismatch of stuff. I can easily weigh ends but a 30+gram discrepancy is an issue!
I finally caught the detail where you said you where getting Graham to post pics. I’m curious as to how close they are to one another without the caps installed and how much variance there is with the pin end weight. If most of the variance is in the mostly the caps and and less in pin ends it would be correctable, but Im afraid the stock removal of the beam polish may be the greater issue at hand here.
So would it be a sin to pick the lightest rod and make the rest match?
yellow rose
Overnight Sensation
If there is enough material to remove. It sounds to me like a set of mismatched rods. Chrysler used something called mass balance and most OE Chrysler balance jobs were way off. I’ve had to use rods from several sets to get 8 that were close enough to balance.
That’s usually how it goes. That 1 will be replaced if the others check out ok. They are all resized with good bolts, I hate not to use them. Or I may have to do get another set of some kind. Kim
I have heard that YR. I have another rod that is in the middle as far as weight goes. May just go with it. I can have another set of factory rods checked. Depends on what Graham says. Kim
Wyrmrider
Well-Known Member
looks like you have plenty of meat on either end
were the rods magged after side grinding?
so check the lengths and if all ok
weigh the big ends by hanging the small ends on a small rod or a j hook, whatever
then weigh the small ends hanging the big ends
then use a belt sander and remove enough weight to balance both ends wear eye protection and gloves
go easy toward the end as taking weight of the far end of the big end makes the small end weigh heavier and vice versa
this can be DIY Kim
were the rods magged after side grinding?
so check the lengths and if all ok
weigh the big ends by hanging the small ends on a small rod or a j hook, whatever
then weigh the small ends hanging the big ends
then use a belt sander and remove enough weight to balance both ends wear eye protection and gloves
go easy toward the end as taking weight of the far end of the big end makes the small end weigh heavier and vice versa
this can be DIY Kim
Thanks. Not sure anymore as I got them I’m 1998. The rods are at the machine shop that is about 3 hours from me. He is doing the balancing. Kim
And, with stock rods, sometimes you still have to start at the band saw. Like you said you are better off with a bunch of rods to choose from. It is funny how sometimes the real heavy big end won't have much balance pad to work with.
Marcohotrod
Well-Known Member
my 340 with 318 forged truck crank and stock 340 rods and 620 gram pistons and stock pins balanced with no added heavy metal
Just wondering how much it will cost to match up a complete set of rods as opposed to a set of these, mostly positive comments here from members who have used them.
Eagle SIR I-Beam Connecting Rods SIR6123CB
Eagle SIR I-Beam Connecting Rods SIR6123CB
yellow rose
Overnight Sensation
Years ago, Hot Rod magazine built up a 340 using a 318 forged truck crank. It was a balanced assembly, with no weight added, all of the weight was taken away to balance.
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