Resonating vibration

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oldirish

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I have a 72 Duster 360 magnum with a 518a transmission. It's just been put together and there is a vibration when parked and I accelerate and when driving around 2000 to rpm. I've read about the crank vibration damper and the magnum flex plate.

I'm attaching pictures of what's on the car.

There is no scallop or drilled holes on the flex plate that I can see.

Any help is appreciated.

IMG_20241005_111615476_HDR.jpg


IMG_20241005_104639268_HDR.jpg


IMG_20241005_111853432_HDR.jpg


IMG_20241005_112056140.jpg
 
No weights on the converter? Hard to tell about the balancer since it's installed and aftermarket. Unless it has a weight bolted to the back of it, it's the wrong balancer. Unless there's a weight on the converter, it may be wrong, too. Probably put together by someone who doesn't know Mopars.
 
That's an LA flexplate- very wrong for a 5.9 Magnum, and who knows what kind of aftermarket balancer.
Is this a stock 5.9 shortblock, a stroker, or what? Was it rebalanced during a rebuild? Unless it was, you got the wrong mishmash of parts for a Magnum.
Time to figure out what you've got before the motor eats itself.
 
Great info and exactly what I was looking for. Any recommendations on a flex plate and balancer, this isn't a race or show car, I plan on driving it.
 
oldirish said:
Great info and exactly what I was looking for. Any recommendations on a flex plate and balancer, this isn't a race or show car, I plan on driving it.
Click to expand...
Can't make any recommendations until you answer the previous questions-
Is this a stock 5.9 bottom end, or a stroker, and was it rebalanced during a previous rebuild?
And, if it was rebalanced, to what specs? Neutral balance or external balance?
 
Damper looks like the Summit SFI unit, they come with weights for 360 LA and 5.9 Magnum and there should be one bolted on the back side.

Factory 5.9 Magnum flex plate will work.

All that said, those parts will only work if it has stock rotating assembly, or was balanced to factory 5.9 Magnum external balance specs.
 
This is what I know, I bought the Duster with the engine/ transmission out of the car.

The heads on the engine were built at a machine shop in Albany Ga where I bought the car.

I don't have any specs on the engine. I was told that it had a mild Comp cam in it.

Once the car was assembled it cranked right up, had a little valve clatter but that is mostly gone.

It has the Sniper2 EFI and Hyperspark ignition.

I believe all 360 magnums are externally balanced from the factory so I'm going to be checking the damper and flex plates to start.

I'm also going to have the sniper checked out because I've read some comments about it causing vibration.

I'm fairly certain it's engine related since it vibrates in neutral at idle and higher rpm's
 
MopaR&D said:
Damper looks like the Summit SFI unit, they come with weights for 360 LA and 5.9 Magnum and there should be one bolted on the back side.

Factory 5.9 Magnum flex plate will work.

All that said, those parts will only work if it has stock rotating assembly, or was balanced to factory 5.9 Magnum external balance specs.
Click to expand...
Are the 360LA and Magnum dampers the same? I thought some 360LA's were internally balanced?
 
Just a note, I've tried to get more info from the seller of the car with no luck.
 
oldirish said:
Are the 360LA and Magnum dampers the same? I thought some 360LA's were internally balanced?
Click to expand...

No, the 360 LA uses more offset weight as the stock LA pistons are heavier than the Magnum pistons. All 360 Mopar engines whether LA or Magnum were externally balanced from the factory.

All other SBM engines (273, 318, 340) were internally balanced except for the 1973 340 engines that had cast crankshafts.
 
oldirish said:
This is what I know, I bought the Duster with the engine/ transmission out of the car.

The heads on the engine were built at a machine shop in Albany Ga where I bought the car.

I don't have any specs on the engine. I was told that it had a mild Comp cam in it.

Once the car was assembled it cranked right up, had a little valve clatter but that is mostly gone.

It has the Sniper2 EFI and Hyperspark ignition.

I believe all 360 magnums are externally balanced from the factory so I'm going to be checking the damper and flex plates to start.

I'm also going to have the sniper checked out because I've read some comments about it causing vibration.

I'm fairly certain it's engine related since it vibrates in neutral at idle and higher rpm's
Click to expand...
So, are you saying it's 5.9 with a stock bottom end, no mods?
If so, put a stock 5.9 Magnum flex plate in it, make sure the aftermarket balancer has the 5.9 weight on it, and you should be good to go.
And no, Magnum and LA 360s are completely different, although both are externally balanced it is still a different balance. The dampers do NOT interchange.
 
5.9 Magnums are externally balanced. 5.2 Magnums are neutrally balanced. I use the latter when I run a neutrally balanced Magnum bottom end. As mentioned, it requires one mounting hole to be oblonged.

200R4 3 (Large).jpg
 
MopaR&D said:
Damper looks like the Summit SFI unit, they come with weights for 360 LA and 5.9 Magnum and there should be one bolted on the back side.

Factory 5.9 Magnum flex plate will work.

All that said, those parts will only work if it has stock rotating assembly, or was balanced to factory 5.9 Magnum external balance specs.
Click to expand...
So, if the torque converter is weighted than I don't need a weighted flex plate? Will the LA flex plate already installed work with a weighted converter?
 
Post # 15, "NO". Use the correct 5.9 balancer with the weight and the 5.9 OEM flex plate. If not corrected, it will soon destroy itself due to the harmonics being totally out of whack.
 
Demonracer said:
Post # 15, "NO". Use the correct 5.9 balancer with the weight and the 5.9 OEM flex plate. If not corrected, it will soon destroy itself due to the harmonics being totally out of whack.
Click to expand...
So if the torque converter is weighted what should I do?
 
oldirish said:
So if the torque converter is weighted what should I do?
Click to expand...
You need to determine what you have.
Where on the convertor is this "weight"?
If it is on the outer shell it is just a weight to balance the convertor to neutral specs.
A weight for balancing to LA 360 spec is located on the forward face of the torque convertor.
Early 5.9 Magnums ('93-'94?) had a neutral flexplate and a completely different weight on the convertor.
All later Magnum 5.9s do not use any external balancing weight. The weight is on the flexplate.
Weighted LA360 convertor:
1728443961895.png
or
1728444176326.png
depending on year. The balance remains the same, they just split the weight into 2 so they could add a drain plug.
Weighted 5.9 Magnum convertor:
1728444263301.png

Weighted 5.9 flexplate:
1728444435691.png

LA flexpate (all varieties):
1728444694770.png
 
Maybe this will help.
All 5.9 and 360 need the external weight.

A 360 calculates out to 5.9L but in Mopar world, they are DIFFERENT engines and need DIFFERENT weight. The holes drilled for balance in Magnum 5.9 flywheels are much smaller than the holes in a 360 flywheel.

Make sure you get the balance system for a 5.9 if you're running the Magnum 5.9, not the weight for a 360/5.9, because some sites will list it that way.

Mopar sure created a cluster **** with this deal.
 
It sounds like the OP has a cobbled together combination after reading back through the post. Back in my earlier days, these were referred to as "grenade" engines. They weren't built for longevity, they were built to only make one or two all out passes. My suggestion would be to make sure that the builder didn't have the reciprocating parts balanced, first. From there, if it isn't balanced get the casting date of the block and then get the correct balancer, flex plate and converter. As I stated earlier, continuing to drive it is going to get in your pocket big time when the engine eats itself from improper parts and pieces.
 
Demonracer said:
It sounds like the OP has a cobbled together combination after reading back through the post. Back in my earlier days, these were referred to as "grenade" engines. They weren't built for longevity, they were built to only make one or two all out passes. My suggestion would be to make sure that the builder didn't have the reciprocating parts balanced, first. From there, if it isn't balanced get the casting date of the block and then get the correct balancer, flex plate and converter. As I stated earlier, continuing to drive it is going to get in your pocket big time when the engine eats itself from improper parts and pieces.
Click to expand...
I'm not driving it until I get the vibration fixed. Unfortunately I can get any info on the engine build so I'll need to do it the hard way by putting on the parts I think it needs any test it for vibration.

I will get the date code off the front of the engine to make sure I'm getting the correct parts.

Thanks for everyone input, I've learned a lot.
 
The casting date will be on the side of the block, post the date and the block casting number. Both of them will be a great help to identify exactly what you have.
 
Professor Fate said:
You need to determine what you have.
Where on the convertor is this "weight"?
If it is on the outer shell it is just a weight to balance the convertor to neutral specs.
A weight for balancing to LA 360 spec is located on the forward face of the torque convertor.
Early 5.9 Magnums ('93-'94?) had a neutral flexplate and a completely different weight on the convertor.
All later Magnum 5.9s do not use any external balancing weight. The weight is on the flexplate.
Weighted LA360 convertor:
View attachment 1716313401orView attachment 1716313403depending on year. The balance remains the same, they just split the weight into 2 so they could add a drain plug.
Weighted 5.9 Magnum convertor:
View attachment 1716313404
Weighted 5.9 flexplate:
View attachment 1716313405
LA flexpate (all varieties):
View attachment 1716313406
Click to expand...
Thanks professor.
 
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