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

jeepsr4ever wrote
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.