Hey guys, I had my 71 340 overhauled at a reputable shop and when I got it in and running it vibrates. Not real bad but enough to know something isn't right, he said he balanced it, to back up a bit , when I put the distributor in the timing mark was way over on the passenger side with the # 1 piston on TDC, So I called him and he told me that he put on a used balancer he had off another engine because mine was grooved to much and that the one he put on was probably off an earlier year. My question is could that be the problem or are all small block forged crank balancers the same?
340 engine vibration
- Thread starter fitterod
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Locomotion
Well-Known Member
All forged 340 balancers are the same, flat face, like a 318 also. cast crank 340's had a ring & counterweight cast into the front which said "For cast crank 340 Only", or something like that. Cast crank 340 came out later, '72-'73.
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rklein383
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Yes, wrong balancer can do it.
MoparLeo
NRA BENEFACTOR LEVEL LIFE MEMBER
If he put the wrong one on and says it was ok I would worry about the rest of te work. Did He balance the engine personally ? or have it done for you.? Who ever balanced it should have documented the varios component weights so you can change a part in the future based on those weights.
He had it done by another shop, he use them for all his balancing jobs
512Stroker
We are all here because we are not all there.
If the timing mark shows up on the passenger side that is a balancer for a pre 1970 engine most likely a forged crank internally balanced.
Your 1971 engine is a cast crank and most likely external balanced?
This being the case you have the wrong balancer?
Time to do a bunch of homework.
2 major configuration of the SBM 340
Someone will chime in to give you better guidance
Locomotion
Well-Known Member
Good point about the TDC mark on earlier balancers. However OEM cranks were forged in 1971 and I believe started to go cast late in '72. Cast will have a thin parting line on the casting and sharp corners on the counterweights. Forged has about a 5/16"+ wide machined parting line with rounded counterweights.
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I took it apart and researched it then and your right about the years and the identifying marks, I'm just wondering if the earlier forged crank balancer can be used on the later forged cranks ?
512Stroker
We are all here because we are not all there.
I knew there was some difference's, I'm not up on the fine points
Glad you chimed in.
What are you using for a transmission/ convertor ? Was the car 360 powered in a past life? OOPS you posted while I typed! Flywheel, was it attached to a 360?
A-833 came with the car behind a/6, I bought the 340 without a trany ,flywheel or ring gear. It did have a pilot bushing in it
nm9stheham
Well-Known Member
Yes. The forged crank dampers were all neutral balanced the same. Only the mark on the damper ring was in a different position.
So is the engine running evenly? I'd run a compresison check, look at all the plugs, and listen to the exhaust pipes when idling. To detect any un-eveness.
Under what circumstances does this vibrate? Idling and all RPM's? Mid to higher RPM's only?
Wyrmrider
Well-Known Member
so find out where ballance weights would be on a cast 340 or 360 flywheel and make sure your flywheel does not have them
good points NM
good points NM
I checked the damper after the info I got yesterday and it has no weights on it. Smooth front, I can't feel vibration at idle but about 1500 i can start feelingbit and it continues as far as I want to rev it, I will say that it's a rithmic vibration
yellow rose
Overnight Sensation
Didn’t some of the later 318 dampers come with a recess in the outer ring on the backside of the damper? I’ll look and see if I can find a picture, but I’m pretty sure I’ve seen that.
If there is no Mallory in that crank it ain’t balanced correctly. Not even close. And that makes the whole thing suspect.
If there is no Mallory in that crank it ain’t balanced correctly. Not even close. And that makes the whole thing suspect.
nm9stheham
Well-Known Member
OIK, well, that is a possible sign that is due to imbalance.
On the flywheel for the 340 is has a small hole further out. See the diagram here:
A question of balance..............(Mopar related)
Here is for the 360 FWIW:
Mopar Performance Flywheels P4529110
And here is weight kit for the Mcleod flywheels for external balance use.... I cannot say if this particular weight pictured is for the 340 or the 360. COUNTER WEIGHT KIT PNS
nm9stheham
Well-Known Member
IIRC, my 273 damper has a recess like that but it is all 360* around the back edge.
Locomotion
Well-Known Member
Later year 360's are the only LA small blocks that had a partial recess in the OEM balancer/damper for balancing purposes. It was directly opposite of the earlier 360 counterweight rings. I guess using less cast iron on the opposite side was a way to save a few cents per balancer!
Note the keyway position.
Note the keyway position.
yellow rose
Overnight Sensation
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