401 balancing issue?

[RossCJ]

I bought a 401 long block that was a fresh rebuild. Not knowing that 401's had different balancing, I bought an aftermarket harmonic balancer and flywheel. Assuming they were all the same (401s) I never looked into the possibility of it being an unmatched setup. After getting the motor installed and broke in I realized that it is vibrating and is most noticable at around 1200 to 1500 rpm's when held at that level. Initially I thought it was just needing to be tuned. It's now tuned and running great except for that vibration. What I need help with is finding out exactly what the different balances are. I bought an Omix-Ada flywheel #16912.09 and a Professional Products harmonic damper with the interchangable weights. The interchangable weight are so that this same damper can be used with the 304 through the 401. I have the 180 deg. weight installed as per the directions. Do I need to remove the oil pan to get a # off the crank to find out exactly what crank I have or can I just use the 120 deg. weight? Any help would be appreciated. I'm not running this thing another second without getting it figured out.

Thanks, Gordon

[jeepsr4ever]

Its your flywheel that stinks. Those cheap import flywheels are way off on weight.

[RossCJ]

Its your flywheel that stinks. Those cheap import flywheels are way off on weight.

Can you recommend a good one? I've pretty much had to start from scratch with AMC V-8's I've always ran a 258 in my Jeep. I dont have the knowledge yet to know what's junk and what's not. I'm starting to learn pretty quickly though. I know I dont like the non adjustable rockers. I think some Harland Sharp rockers will be on order today.

[jeepsr4ever]

You will need guideplates and larger tapped holes with the hardland sharps unless you order the expensive ones for the 5/16 studs. Their is no good stock replacement for a 401. You may have to get that one balanced or source a 401 flywheel. Some on here have them laying around I am sure.

[tufcj]

Any chance you have the original flexplate from the 401? You could remove the flywheel and have it "match balanced" to the original flexplate.

Bob
tufcj

[RossCJ]

Unfortunately I dont. I bought a longblock and had to start from there. I did'nt have a core. I used brackets off a 360 and bought everything else aftermarket.

[JohnA]

I had to re-balance my 360 flywheel which has a 75 gram imbalance weight cast in it so that I could bolt it to my rebuilt 401 which has a 110 gram imbalance. I added a 35 gram weight to the existing weight on the 360. Both have the same phase angle.