Does anyone know if this balancer with the number A 128668 is for a 340 internally balanced or externally balanced ? I have a 73 with a cast crank but I been told this is the wrong balancer.

What brand name is it

Mr p body it is a factory original one

Does it have the elliptical weight? If yes, cast crank external balanced.

no weights just round on both sides, but looking at pics of aftermarket factory replacement it looks the same. I even looked up one for a 74 318 and it is the same part number. They are not showing the weight on them,unless it is like a stock photo just to give the idea.

The number you're looking at isn't a part number.

An OEM 340 cast crank balancer/damper will actually say "For 340 Cast Crank Only" on the counterweight on the front. (The one on the right.)



Aftermarket balancers/dampers can have the counterweight "hidden" on the back side.

What happens when you use the wrong balancer? My 340 have a forged crank, and I have been running it with the cast crank balancer for 2 years, (bought the car that way) and I have not noticed anything. Engine has been running fine. Just saw it now when I took the engine apart. I thought that would be very noticable, but nope...

Sometimes it will shake at an idle if out of balance. I had a cast crank 340 that didn't run, it came in a 78 aspen I bought. I got it running and it shook at idle very noticeably. It was hooked to the lockup 904 that came in the car originally with no weights on the converter or flex plate that would balance the externally balanced crank.

Are there different balancers for 318, 340, 360, other than for cast and forged cranks?

Yes, early, 318/340, pre 1970(1969 and earlier) had the timing marks on the balancer on the passenger side. Mopar decided to move the timing tab from the passenger side to the drivers along with switching the lower radaitor hose from the drivers side to the passenger side, why who knows All the 1971 360 came that way also and they where the first V8 motor Ma Mopar made externally balanced with a cast iron crankshaft 340 came externaly balanced with a cast crank also in 1972

When I look at balancers on Summits website, seems like its the same for all small block, except for internal or external balance. Will any small block balancer for internal, fit my 340 w. forged crank?

Physically yes all small block balancers will fit...

but as noted above...some are for externally balanced engines...and the pre 1970 cars will have problems with the timing marks on the driver side were the bottom radiator hose will block the timing marks.