do you know what year the motor is? do you know if its susposed to be a 50 or 28 oz imbalance? you need to make sure the flex plate/flywheel is the correct balance for the crank that is in that motor. you may get lucky by changing just the balancer and that is the easyest thing to try but figure out if what imbalance pices your replaceing.
I just had this problem with a brand new engine as well , turned out I had a 79 302 that needed the 28oz flywheel and balancer, and I had a 50 on both ends it was like holding on to a jack hammer , changed them out and now she is smooth as can be.
I would bet that the wrong balancer (28 vs. 50) would feel more like a jack hammer, as described above, not a weedeater. A spun balancer would be more weedeater-ish. I also think the motor would tear itself apart if you ran the wrong balancer even for a short period of time at 5000 rpms. I know we have stout little motors in these cars, but I wonder how long you could run it with the wrong balancer before things started to break?
A little more info... I bought the rotating assy (347 ci) from a company on ebay, they sent me the balancer and flexplate as well. Neither of them have a brand name nor a part number on them but they both say that they are SFI approved. On the flexplate the weight looks like it had a portion removed, I always assumed that was done to make it from a 50 oz to a 28 oz. The rotating assy was also supposed to be balanced but there was not a balance sheet included with the parts so who really knows if it was done or not. I put this motor in the car in mid 2006. Since I install the motor I have found that both my front wheels were bent, the drive shaft was bent and the trans tailshaft bushing was bad. So the car had many vibrations!! When I replaced the C4 with the toploader I installed centerforce 28 oz flywheel and the vibrations seemed to get better, now it is more of an annoyance than the car about to shake apart like before. The main question is: is it worth swapping balancers to see if that is the vibration or would the wrong balancer be a lot worse of a vibration and I should look somewhere else to find the problem. Side Note: This morning I was looking under the car and noticed one to the bolts holding the shifter to the trans is touching the trans tunnel. I know that I need to fix it but could that cause the vibration I am having. Sorry for the long post and thanks for all the help thus far.
The bolt touching the floor pan/tunnel would give you a metallic buzz along with the vibration.As for the balancing...Sounds like the rotating assembly may not be or was poorly balanced.Allmost every aftermarket rotating assembly I have dealt with needed to be balanced before installation.(hope its just a balancer/flywheel issue for you man) Good luck.
I'm confused... Did you put a 50oz flywheel on in place of a 28oz, therefore you swapped to a 50oz balancer to match the flywheel? Or did you swap to a 50oz crankshaft and therefore changed to 50oz flywheel/balancer combo? The way you word it, it sounded like you put 50oz balancer/flywheel on a 28oz crankshaft.... As for the weedeater vs jackhammer arguement: When my balancer spun, it would spin time to time, so occaisionally it was spun near stock position and would have light vibration. Then there were times I could hit a dip in the road or bump, and it would slip 180* out of place, and the steering wheel felt like holding a jackhammer at that point. From that experience, I'd imagine that an extra 22oz of having the wrong balancer would be somewhere in between weedeater and jackhammer. If you think about it, the 50oz slipped 180* would actually be 100oz out of balance. (the balancer I had slip was 50oz) I don't know about 22oz, but I have seen pictures of a spun balancer that broke the crankshaft from vibration.
I think I would work under the assumption that the engine builder put 50oz parts on a 28oz engine. Just from your statement that things improved with a new 28oz flywheel. All of this would shake my confidence in the engine builder quite a bit. Unfortunately... Hope it all works out for you. Sounds like a nice combo.
Alright i just swapped balancers with a friend of mine and got the same vibration. He has a replacement engine from autozone for his 69 mustang and he is pretty sure the paperwork said it was 28 oz balance, it is a 3 bolt balancer so it should be. I went ahead and clearanced the tunnel around the shifter bolt, that didn't help either. So I guess it is something that I either live or pull the motor for. It runs really well, last time I had at the drag strip it went 7.76 @ 92 MPH 1/8 mile on street tires. That was with the C4 as well, I haven't been made it back up there with the 4 speed yet.
It is not the engine builder that is the problem, the company I bought the stroker kit from was suppose to balance it. The crank has holes drilled in it but none of the rods looked like they had any metal ground off and nothing was marked so..... I should have had the machine shop that put the short block balance it just to be sure but money was tight and I am impatient, live and learn I guess. I will never buy from that company again.
Well, maybe it's something harmless... like a warped pulley or something silly that won't damage anything. Good luck! I hope you exceed expectations next trip to the track! Those are great numbers with the C4...
