383 harmonic balancer; source of vibration? *Picture Update*

[challenger_affair]

1970 383 auto challenger.  I'm noticing a pretty dramatic vibration at certain speeds.  I know the car has had engine, trans, driveline, rearend, tires, at different times over the years (although I only recently re-aquired the care and haven't been around for all the work) and still the vibration persists...  One thing I noticed is the harmonic balancer has the extra weight on it.  I undertstand this is not typical for a 383. 

So the question is, how likely is the vibration related to the balancer?  And I guess somewhat related, if that IS the right balancer what does that tell me about the engine?  Thanks much

[PlumCraZRT]

1970 383 auto challenger.  I'm noticing a pretty dramatic vibration at certain speeds.  I know the car has had engine, trans, driveline, rearend, tires, at different times over the years (although I only recently re-aquired the care and haven't been around for all the work) and still the vibration persists...  One thing I noticed is the harmonic balancer has the extra weight on it.  I undertstand this is not typical for a 383. 

So the question is, how likely is the vibration related to the balancer?  And I guess somewhat related, if that IS the right balancer what does that tell me about the engine?  Thanks much

Has it always  had the vibration?  Is the vibration related to speed or RPM?  If it's related to RPM, it's an engine issue (such as the harmonic balancer).  If it's related to speed, take a look at the driveshaft, wheels, etc.

If it IS the right balancer, it tells you it's a cast, externally-balanced engine.  Is the crank stock with the block?  If so, what year is the block?

[Chryco Psycho]

no 383 with either cast or steel crank had an offset damper , so that should be the problem , you should also check the the converter to see if it has a balance weight on it , it shouldn't .

[PlumCraZRT]

no 383 with either cast or steel crank had an offset damper , so that should be the problem , you should also check the the converter to see if it has a balance weight on it , it shouldn't .

Good call, Chryco.  The cast-crank dampers had a hole drilled in them, correct?

Isn't there a way to tell if it's cast by a feature on the crank?  If memory serves me, there is a feature on the flywheel/flexplate flange (which is probably no help in an already-assembled car).

[Chryco Psycho]

maybe , I cannot remember working on a cast crank 383 .
It is easy to tell a cast crank from a forged one but I need to see the counterweights to tell for sure , you cannot tell from the machined sufaces

[PlumCraZRT]

maybe , I cannot remember working on a cast crank 383 .
It is easy to tell a cast crank from a forged one but I need to see the counterweights to tell for sure , you cannot tell from the machined sufaces

Got it, thanks!

[challenger_affair]

Thanks for the feedback.  Unfortunately I don't know the history of how that balancer wound up on the engine.  The block has a 1970 casting date but the engine has been rebuilt at least once and I don't know what was done in regards to the crankshaft.  It also has a 3 groove crank pulley, although it only needs two.  I've read that some 383's came with cast cranks that were externally balanced  http://www.moparts.org/Tech/Archive/motor/36.html  Is it possible one of these wound up in the block?  I'm having trouble envisioning a scenario where someone would randomly replace the correct balancer/pulley, but perhaps that is the case with this motor...

The vibration is not apparent at all speeds/rpms.  It seems to idle relatively smoothly and there's a rough spot around 2000 rpm i'm guessing, and when i'm driving around 65mph it becomes dramatic (tach is not working so I don't know rpm).  With the wrong balancer, would it necessarily be obvious at any rpm? 

[Chryco Psycho]

no it wouldn't it would shop up a certain rpms
 I would swap the damper just to see what effect it has , you should be able to locate a used one just to swap for a few hours

[challenger_affair]

OK, thanks much for the insight... 

As for the pulley, what is the best way to look for a 2 groove crank pulley that would line up with my existing water pump pulley?  I've seen there are different bolt patterns made, is there a particular part number I should look for or some other way to look for one that will work? 

[Chryco Psycho]

Mancini has pulley sets , all you should need is the crank or crank & water pump

[sprecks]

I wonder if someone used a 400 crank during one of the rebuilds. Most of the 400's had cast cranks.

[Cuda Cody]

You might want to check the torque converter too.  They make both two types for externally balanced and internally balanced motors.  That can give you a vibration too.

[challenger_affair]

Yeah its hard to come up with a good reason why a balancer/crankshaft pair would be broken up...  In any case, can a definitive observation of the torque converter balance weight (present or not) be made from the inspection plate while installed in the car?  what would the weight look like if it exists?  Thanks. 

[Chryco Psycho]

small pair of steel weights welded near the outer edge of the converter .

[challenger_affair]

You might want to check the torque converter too.  They make both two types for externally balanced and internally balanced motors.  That can give you a vibration too.

Well, finally got around to removing the inspection plate to have a look at the torque converter.  I wasn't able to actually see aroud the flex plate to the converter, but cranked it around a few times and in one location I found what looks like a weight on the flex plate itself.  See pic below

Does this help me answer any questions about the vibration or harmonic balancer?  Is that weight on every flex plate regardless of whether the converter has a weight?