The Dodge Challenger Message Board

Hi,

are the cast crankshaft and the forged crankshaft in a 340 block, both external balanced ?

I think the forged is internally balenced from memory, the 340 cast crank has a unique damper

The cast cranks are external balanced and need the special damper as well as the weight on the torque convertor or flex plate. However it is possible to have them internally balanced.

Don't forget that all 273, 318, 340 cranks are interchangable as they are the same stroke. the 360 cranks as well as having a longer stroke also have larger main bearing journals.

Dave, OK the cast crankshaft is externally balanced.

Is the forged crank internally balanced ?

Is it possible to change from an original 340 cast crankshaft to a 340 forged crankshaft ? What parts have to be changed (damper ?). Can I simply remove the weights at the torque converter ?

Regards, Jens

A forged crank 340 is internally balanced. You can change to forged by replacing the cast crank for a forged one with the matching damper. Also remove the weights from the converter. But it could be that you have a little bit of unbalance, but I guess it's not that bad when you use the forged crank with the matching damper. Say if I'm wrong please...

Yes forged is normally internal balanced but it pays to have the whole thing (damper/crank/rods/pistons/flexplate) balanced as a unit anyway if the individual parts have not been balanced together before. Plus it is just possible that some did come external balanced and it it does not have the original damper and convertor with it you will not be able to tell.

You can tell a external balance damper because it has an offset shape to it. I am sure I posted a scan of a drawing of one on here somewhere.

To balance external you need the weight on the convertor or flex plate and the offset cast damper. To use an internal balanced crank you need the right damper and no weight on the flex plate or convertor. From the factory the weight is on the convertor but as most aftermarket convertors are made without this you can buy a flex plate with it on.

The bottom line of all this is get it balanced anyway. I doubt the factory did a good job of it it they did it at all.

Chrysler had the absolute worst production balancing of any manufacturer back then, I have heard storys of pistond being a ridiculous amount out of spec, get the whole set up done properly.

Thanks, all your answers helped me. I will tell you more, may be we can find out together, what´s the problem.

It is a 340 engine from 1971 (cast no.), it is rebuild by a professional machine shop.

The engine has vibrations at idle speed and they get more at higher rpm. The vibrations are from the engine, not from the drivetrain.

The machine shop changed the crankshaft, it could be, that they changed from a cast to a forged one OR from a forged to a cast one. I do not have the old crank anymore.

How can I tell, what kind of crank was in there original in 1971 and what kind of crank is in there now, without stripping to engine ?

Jens, check if there are any weights on the converter. Take off the dust shield and let somebody else turn around the engine at the crank (don't start it) when you lay under it. If there are weights on it these will be attached to the convertor in the bolt circle between two flexplate-to-converter bolts.

Also try to take a picture of the damper and post it here. Then maybe we can see what damper you have. If we have this info I guess we can tell you what crank SHOULD be in it.

Form your post I understand that the engine didn't vibrate before the rebuild? If so, did they change the convertor also or not? And remember to always check what you had before a stranger works on it and after it. A lot of people will try to make an extra profit out of your car...

The only way to tell whats in there is to drop the sump and have a look, you should be able to get it donw low enough to get a light in there and have a peek

A cast crank has a casting line through the middle of it. A forged crank has a wide parting line.

Look.
If you use the SEARCH facillity at the left you can find other threads with the information in.

I just did a search for you and found this.

Thanks again. The picture is great.

I will check the damper first and take a picture of it next days. I´ll post it here and let you know.

Regards, Jens

Hi

I have news. The 340 engine in my challenger had a forged crank (internally balanced) from factory.
The machine shop replaced the crank with a forged crank (100% sure), so everything should be OK. The damper is the original factory unit, for an internally balanced crank. The flexplate is also factory stock, there are NO weights on it.

Has someone an idea ? Is it maybe the ignition, making this vibrations ?

Jens

This may seem overly obvious, but I'm sure it has happened to all of us at one time or another.
Make sure all eight plug wires are fimly snapped into place and you've got them wired correctly.
My son recently gave his car a quick tuneup and afterwards it ran awful. Problem, two plug wires installed wrong.
Also as someone mentioned before check you converter for weights. You said the machine shop replaced the crank ( your old cast iron crank )with steel crank. If you've got a steel crank, your converter shouldn't have any weights on it. If your using your old converter from the cast iron crank on the steel crank, it will vibrate for sure.

Hi Graham,

it was original a forged crank engine and the new crank is forged, too. There are no weights at the converter. So this should be all ok.

I replaced the plugs and the wires (solid core), but the vibrations are still there - no difference.

The original ingnition box (black) is now over 30 years old. Could this be the problem ?

Hi Jens.
Is there anyway you can put some kind of scanner or scope on the engine so you can look at the electrical output. I'm not a trained mechanic by any stretch of the imagination, but a lot of years in the auto business has taught me to investigate before replacing parts that need not to be replaced.

I am waiting for a distributor cap and rotor, I have ordered, it should arrive next days. This has to be changed anyway, because both parts in the car are around 10 years old. I check the ignition system and the box, too.

Jens

I had the same problem once with engine vibrastion
I changed the cap,rotor,wires,coil and it still
would vibrate.Two months later changing oil and
looking at the fan blade I noticed it was missing
one of the blades.I replaced the fan and the
vibration was gone.You might want to check it out

Anything like a bent pulley will do it too.

auto or standard trans?????