Yet another question on vibration (Not the good kind)

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Pentarockstar

Pentarockstar

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My car is a 69 dart 340 4-speed.

The engine starts to rattle and roll at 3,000 RMP, kinda like a tweaker on a 2 week binge.

An old time Mopar guy told me the flywheel is on wrong.

A bit of background: This is the original engine for the car. At some point a cast crank was put in the place of the steel one. Maybe the steel crank was traded for a bag of the "good stuff" who knows. The thrust on the replacement cast crank went south because of too many clutch drops. So, I had the crank replaced with another cast crank and soon the vibration reared its ugly head.

What I am looking for is a diagram of how to correctly install the flywheel, if this is the issue.

Thanks for your time!!
 
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installation is same, balancing of the flywheel is different. I guess the flywheel is neutral balance for the forged crank? and the rotating assembly was balanced to it? MAYBE a cast crank 340 flywheel would fix it...or make it less obnoxious and destructive.
 
So a cast crank flywheel is different from a steel crank flywheel?
 
Yeah, abdywgn got it- the cast crank uses a differently (external) balanced flywheel than the forged (internal/neutral balance) crank.
It's not a matter of "how" it's mounted- they can only go on one way.
If the crank was simply swapped out, then the rotating assembly is out of balance in addition to the flywheel being incorrect for the crank.
 
I still have the cast crank that was replaced. I looked up the casting number #2653393. That is a 318 crank! No wonder the thrust went out!! What a mess!!
 
maybe pull it apart in put in an aftermarket forged crank? either Scat or Ohio crankshaft has "stock" replacement. IF you wanted a little more torque, I believe one or both companies offer a 3.58 stroke crank with 340 mains...but you need new pistons.
 
Thanks for the advice guys. I needed it. Looks like I will be pulling a motor
 
OK, a 318 is internally balanced, even with a cast crank. A cast crank 340 is externally balanced, and requires a harmonic balancer and flywheel specifically for that motor (or at least a flywheel that is properly drilled for a 340 cast crank).

Although I haven't tried it, I'm pretty sure a 318 cast crank would need rebalancing if used in a 340, with its larger, heavier pistons and (I think) rods. Maybe yours was balanced when the motor was first assembled with that crank. In any event, if your replacement cast crank was a 340 crank, then definitely you'll need the cast 340 damper and flywheel. Or switch to a forged crank. Or mallory metal to internally balance your cast crank. If you want to keep it an externally balanced motor, note that only 73 and some 72 340's used cast cranks, so the cast crank damper is probably hard to find today. The flywheel, well, I think the Mopar Performance Manual tells you where to drill a neutral balance flywheel to bring it to cast crank 340 specs. That's my memory, anyway, and my manual is out in the garage, so I don't have it before me.
 
Ok, I get it. I went out and looked at the harmonic balancer on the car, it is for a forged crank since it has no weights on it. So, when the motor was rebuilt using a 318 crank they balanced the crank to fit the dampener and flywheel. I bought a cast crank for a 340 years ago, did not check casing numbers before installing the crank, so I really don't know what it is. So when i installed this crank, it threw off the balance of the motor.

If we move into a logical pattern....the current crank in the motor must be a cast 340 crank since 318 cast cranks are also internally balanced like forged 340. 340 cast cranks are the same as 318 cranks except for the extra weight of rods and pistons that a forged crank is made to take.
 
They may be internally balanced but dont they both use different balancers?
 
where to drill flywheel (note that the mounting holes are offset so it will mount only one way)
340 flywheel cast crank.jpg

340 cast crank damper (note that is says "use with 340 cast crank only."
340 cast crank damper.JPG
 
67Dart273 said:
They may be internally balanced but dont they both use different balancers?
Click to expand...

273, 318 and forged crank 340 dampers are interchangeable except that the later, long water pump versions would have the timing mark in a different place than the early cast iron short water pump versions.

Oh, and one pulley bolt hole is slightly offset on the later versions. You can still use an early pulley on those dampers simply be enlarging one hole in the pulley.
 
If it were me, I'd pull the engine apart, get a forged crank, and rebalance everything. Otherwise, you're just guessing what to do and what parts to change.
 
vdoalrvto said:
I found this to work as a damper
BluePrint Engines Harmonic Balancers BPP360

Pretty cool unit. Works for pretty much all small blocks
Click to expand...

Yes, cool. Removable weights allow you to set up for neutral balance, 340 cast or 360 cast. I had not seen that before.

If the subject motor was mine, I'd be tempted to get that damper, set it up for a 340 cast crank, drill the flywheel as above, and run it. If it runs smoothly, just leave the motor alone. Would be the cheapest, easiest and quickest way to go.

If you're gonna replace the crank anyway, now would be a good time to step up to a stroker crank. Not the cheapest way to go, certainly not the quickest, but in the long run the best.
 
Yes, I will give this a shot. I do wish to step up to a blue print engine at some point and i can use this damper on that!

Thanks for your help!!
 
Please verify what crank u have in there. A cast 318 heavy duty crank is neutral balanced and used the 340/360 heavy rods. The 318 piston is way lighter than a 340 piston so u need to balance the crank with Mallory metal. Mine needed 2 1/2 sticks. Kim
 
On a side note, u can use a 318 steel crank if u have it balanced. It will need 3 sticks of Mallory. Or u can have the front and rear journals drilled just like the 340 steel cranks. To drill the rear u have to notch the flange to be able to drill the journal. Kim
 
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