360 vibration ....help

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sirmopar

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so , car has vibration between 2,400 rpm and 3,000 rpm in park, neutral and driving. It seems to rattle the steering wheel and dash the worst. its a 1977 360 bored 40 over with Kb107 pistons and scat I beam rods. cranks has been turned 10 under on mains and 20 under on rods. edelbrock rpm heads, cam and air gap intake, also edelbrock 800 carb. running B&M flex plate for external balance 360 part#10236 and summit harmonic balancer for 360 part#163318. it seems to run good, just has a bad vibration. vibration starts small about 2400rpm gets worse as rpm increase and above 3000 rpm it seems to go away.

The car is a 69 valiant that had a 1973 cast crank engine, after I removed the engine I removed a weight from the flex plate side of the torque convertor. transmission is a 727.

Let me know if you guys see something that jumps out that could be causing the vibration. Im thinking of trying a new torque converter, but that is an expensive gamble. Thanks in advance.
 
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Summit brand dampers are JUNK and known to spin. Both my sons and mine did so it’s ATI or we tried a Powerbond damper on one budget build. So far so good.
 
You changed piston and rod weight, did you have the assembly balanced? There is your problem
 
Third agree- vibration is either internal and she needs balancing And Or you removed the weight off converter.

Also now that you need to remove all to get engine balanced... send converter and flex plate AND a better harmonic balancer. Let machine shop balance all before you cause serious damage. IMHO.
Joe
 
sirmopar said:
so , car has vibration between 2,400 rpm and 3,000 rpm in park, neutral and driving. It seems to rattle the steering wheel and dash the worst. its a 1977 360 bored 40 over with Kb107 pistons and scat I beam rods. cranks has been turned 10 under on mains and 20 under on rods. edelbrock rpm heads, cam and air gap intake, also edelbrock 800 carb. running B&M flex plate for external balance 360 part#10236 and summit harmonic balancer for 360 part#163318. it seems to run good, just has a bad vibration. vibration starts small about 2400rpm gets worse as rpm increase and above 3000 rpm it seems to go away.

The car is a 69 valiant that had a 1973 cast crank engine, after I removed the engine I removed a weight from the flex plate side of the torque convertor. transmission is a 727.

Let me know if you guys see something that jumps out that could be causing the vibration. Im thinking of trying a new torque converter, but that is an expensive gamble. Thanks in advance.
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I have to ask what inquiring minds are waiting to know......what made you remove the weight from the converter???
 
Red63440 said:
I have to ask what inquiring minds are waiting to know......what made you remove the weight from the converter???
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It would appear he removed the weight from a external balanced converter because he is using the b&m flexplate instead. jmho
 
Are you SURE the counter weight is attached to the balancer? It is a removable weight so that it can be used with both internal and external balanced engines. Run your hand around the back and make sure the weight is THERE. If not, there's the issue.
 
Jadaharabi said:
It would appear he removed the weight from a external balanced converter because he is using the b&m flexplate instead. jmho
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I’m going to go out on a limb here and say that the removal of that weight for whatever reason is why he has the vibration. The flex plate is neutral balanced but it isn’t made to balance the torque converter which is now out of balance because it’s missing the weight which gave it neutral balance. If he replaces the converter I feel his vibration will cease.
This is like taking all the wheel weights off just because the engine is externally balanced and yes it makes no sense what so ever to assume that would be the case because the weight that balanced the torque converter was removed because he installed a neutral balance flex plate.
 
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Thanks for the input. Yes the weight is on balancer.

When I took the cast crank to a local machine shop the guy told me I was crazy for wanting to balance that crank and it wasn't worth it.

I assumed (I shouldn't have) the pistons and Rods would be closer than than stock and wouldn't have to be balanced. Maybe I'll try a converter, if that doesn't work should I tear down the engine , maybe look for steel crank ?
 
sirmopar said:
Thanks for the input. Yes the weight is on balancer.

When I took the cast crank to a local machine shop the guy told me I was crazy for wanting to balance that crank and it wasn't worth it.

I assumed (I shouldn't have) the pistons and Rods would be closer than than stock and wouldn't have to be balanced. Maybe I'll try a converter, if that doesn't work should I tear down the engine , maybe look for steel crank ?
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When parts are made for an engine they have to meet weight specs so they all work together without destroying the rotating assembly, not everyone who builds an engine has it balanced. The factory doesn't balance each engine by weighing each part and this shows if you weigh each rod or piston when you disassemble an engine, they will be within so many grams of each other. Is a perfectly balanced engine better, you betcha!
As far as the guy in the machine shop, he has a job because of people like you so he should have said, "yes sir, anything else I can do for you?". With that being said I truly believe the problem is due to the removed weight that was on the converter.
 
sirmopar said:
Thanks for the input. Yes the weight is on balancer.

When I took the cast crank to a local machine shop the guy told me I was crazy for wanting to balance that crank and it wasn't worth it.

I assumed (I shouldn't have) the pistons and Rods would be closer than than stock and wouldn't have to be balanced. Maybe I'll try a converter, if that doesn't work should I tear down the engine , maybe look for steel crank ?
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Somebody should slap that guy. Go back and tell that dumbass every single factory Ford 351 Cleveland crank was cast nodular iron. Ask him what the hell does he think they ran in those NASCAR Cleveland engines that spun past 9K RPM and if he thinks they weren't balanced. Find a new machine shop, man.
 
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Your machine shop guy is a idiot. Dont waste time on the converter, that's not the issue. Tear the engine down and have it ballanced.
 
replicaracer43 said:
Your machine shop guy is a idiot. Dont waste time on the converter, that's not the issue. Tear the engine down and have it ballanced.
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Unless he finds an issue with the balancer itself, I tend to agree with you.
 
When the shop balanced the crankshaft, did they have the balancer and flex plate you are currently running? If not, were you charged for heavy metal or mallory metal as part of the balance job?
I am actually wondering if they internally balanced your rotating assembly to neutral balance? This would make the flex plate and balancer wrong for this application.
Ask the shop that balanced it specifically how they set it up, internally or externally, before you go changing up your combo.
 
Bobzilla said:
When the shop balanced the crankshaft, did they have the balancer and flex plate you are currently running? If not, were you charged for heavy metal or mallory metal as part of the balance job?
I am actually wondering if they internally balanced your rotating assembly to neutral balance? This would make the flex plate and balancer wrong for this application.
Ask the shop that balanced it specifically how they set it up, internally or externally, before you go changing up your combo.
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Did you even READ what he posted?? The machinist told him it was a waste of time to balance it. It WAS NOT BALLANCED, just thrown together with aftermarket parts.
 
Replicaracer43 is correct , it was just thrown together with the parts I listed.

I obviously don't have much experience building engines like this. I was hoping to hear from somebody who has built something similar and hear about the results they have.

Thanks guys ! This forum is a bunch of help !
 
sirmopar said:
Replicaracer43 is correct , it was just thrown together with the parts I listed.

I obviously don't have much experience building engines like this. I was hoping to hear from somebody who has built something similar and hear about the results they have.

Thanks guys ! This forum is a bunch of help !
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Just as a example, I had a customer with a steel crank 340, rebuilt back to stock specs, with the exception of a set of Keith black pistons, it had a vibration, and it had to have the assembly balanced to fix it.
 
The fundamental imbalance of the rods and pistons is 100% the issue. I just ran the numbers: By going from stock 360 LA rods and pistons to KB107's and SCAT rod, the bobweight has dropped by approximately 300 grams versus stock. That is massively off. So unfortunately, this is going to have to come out.

You will indeed have to take the crank, rods, locks, bearings, rings and pistons to a shop to have the assembly balanced, along with the flextplate and present damper as a check. I think this can be balanced as an internal balance system; if so, you can remove the external weights (remove the weight on the damper and change to a balanced flexplate and TC).
  • I would personally prefer to do this as an internal balance system; the extra external weights just add some extra stresses on the crank that can be eliminated. If this is a cruiser car, then that is not so important.
  • If the external weights are maintained, then it will require extra metal to be removed from the counterweights on the crank. This might become a practical problem, by making the end coounterweights into swiss cheese!.
  • FYI, the bite out of your 360 flexplate is equivalent to a weight on the other side of the flexplate.

The crank balance to your measured piston/rod assembly bobweight can be achievable by taking off weight from the present crank, regardless of whether you end up internal or external balanced. So that is good.

I cannot comment much on the shop situation. I am actually quite amazed at the reaction, but do not know the whole situation.
 
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nm9stheham said:
The fundamental imbalance of the rods and pistons is 100% the issue. I just ran the numbers: By going from stock 360 LA rods and pistons to KB107's and SCAT rod, the bobweight has dropped by approximately 300 grams versus stock. That is massively off. So unfortunately, this is going to have to come out.

You will indeed have to take the crank, rods, locks, bearings, rings and pistons to a shop to have the assembly balanced, along with the flextplate and present damper as a check. I think this can be balanced as an internal balance system; if so, you can remove the external weights (remove the weight on the damper and change to a balanced flexplate and TC).
  • I would personally prefer to do this as an internal balance system; the extra external weights just add some extra stresses on the crank that can be eliminated. If this is a cruiser car, then that is not so important.
  • If the external weights are maintained, then it will require extra metal to be removed from the counterweights on the crank. This might become a practical problem, by making the end coounterweights into swiss cheese!.
  • FYI, the bite out of your 360 flexplate is equivalent to a weight on the other side of the flexplate.

The crank balance to your measured piston/rod assembly bobweight can be achievable by taking off weight from the present crank, regardless of whether you end up internal or external balanced. So that is good.

I cannot comment much on the shop situation. I am actually quite amazed at the reaction, but do not know the whole situation.
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wow thanks for the info, 300 grams is quite a bit ? I bet a lot of people end up in my same situation ? or maybe most people keep stock rods and only change pistons, in that case maybe they don't get the vibration. Thanks again for the info.
 
Stock rods are 745 grams....Scat I beams 590 plus or minus on both
stock pistons 584 grams plus pin....KB 107 piston 507 grams plus lighter pins...

should have been balanced....internally it would still take a slug of mallory....externally they would have removed alot of weight from the crank....
 
sirmopar said:
wow thanks for the info, 300 grams is quite a bit ? I bet a lot of people end up in my same situation ? or maybe most people keep stock rods and only change pistons, in that case maybe they don't get the vibration. Thanks again for the info.
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300 grams off is more that quite a bit; it is a ton. And no, changing just the pistons will result in a vibration too, just not as bad as what you have; a 340 case showed up here within the last year where the pistons alone were changed to KB's and the bobweight was something like 170 grams off; IIRC a 'friend' said it would be OK LOL. So, yes these things happen.
 
replicaracer43 said:
Did you even READ what he posted?? The machinist told him it was a waste of time to balance it. It WAS NOT BALLANCED, just thrown together with aftermarket parts.
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Yes, I read it. No, he never specified it was not done, he only stated he was told it was a waste. So I asked a specific question so I knew, instead of assuming.
 
Well I'll get slammed but the problem is in the damper or flywheel.

Before we got so smart tens of thousands of engines were built without any balancing going on...none.

I drag raced Chevy's and Pontiacs....none were balanced.

My first dozen or so Ford stock car engines weren't balanced. Never an issue.

Balancing was for Indy cars or USAC stockers running mile tracks.

I knew of one shop in my hometown of 800,000 folks that had an engine balancer.

Those new rods are very close on weight to each other...within a few grams. Same with the pistons.

I have sets of stock SBC and NASCAR rods in my shop that were never touched by a grinder to balance them and they are within a few grams of each other.

Pro shops will admit most of these full balance jobs are a great profit center but do little good in the average build.

Here come the slings and arrows....

Just one post about balancing tolerances...

balancing question - Page 2 - Don Terrill’s Speed-Talk
 
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we got 150 grams difference in each rod...plus another 80 grams or more in each piston...230 grams per hole....which is a half a pound...times 8....

i believe a stock pin is about 150 grams...KB are 125....so add another 25 grams to the pistons ...probably closer to 110 grams on the pistons...

and as the rpms go up the out balance get worst.....

save money on not balancing....lol
 
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