Who's heads are on the engine?

Aluminum Chinese imports that have had some port work done. Pro Comp PC3003 (210cc, 64cc)

I had a long conversation with a machine shop (who is old friends with a buddy of mine and they have a great reputation) this afternoon about my engine and having them install an internal balanced rotating assembly. He thought it was interesting that the vibration is hardly noticeable when the engine is revved in neutral, at a standstill. He said anything is possible, but the out of balance engines he's dealt with in the past were noticeable both loaded and unloaded.

He suggested to revisit my driveshaft before pulling the engine. I've had the shaft balanced/checked twice by a reputable local shop and it's "within spec". But, he said has experienced "good" driveshafts on the bench, that present with strange harmonics/vibration on the car.

I'm going to see if I can borrow someone's (known good) Camaro driveshaft to try in my car.

Trying to exhaust all possibilities before pulling the engine...

Daniel

driveshaft does not relate to engine rpm as you have mentioned in the past when the vibration occurs. If it was the driveshaft then it would show up at the same mph every time.

I’ve been fighting this vibration so long, I think it is driving me crazy and my recollection is getting foggy. :confused18:

In my mind, I’ve been recalling that the vibration is much less noticeable at idle. So, I just went outside and warmed up the car and slowly raise the idle up to 2000 and there is definitely a noticeable vibration. Maybe not quite as much as when it’s under load, but it is definitely there.

I’ve been trying to take notes along the way as I’ve been troubleshooting, but this seems like a key piece of the puzzle that I’ve been recalling incorrectly. I’m just getting old I guess. :lostmarbles:

Mike- yes, you’re right, thanks for keeping me on track.

Daniel

I went back and scanned some of the posts. I don't see where you've confirmed 100% your timing.

Do this with a piston stop, or at a minimum, pull your balancer bolt and check the orientation of your keyway with your timing mark. I needed to confirm TDC on my car recently. Here's mine and it was correct:

https://i.hmjimg.com/images/2020/05/...E306E90351.jpg

https://i.hmjimg.com/images/2020/05/...E7722AD703.jpg

A couple of things to consider, if you hadn't yet, add weight to the crank pulley or dampner. Maybe a heavy putty, to look for change. I haven't see a pick of your front runner system, but if you can run it without a belt and try to eliminate accessories.
Best!

I've tried to locate CAT, the crankshaft manufacture that's in your engine and the only thing I could come up with is this company on Ebay. Looks like they work out of Corona, California selling a variety of internal engine parts. Maybe just a depot for distributing stuff from overseas?
https://www.ebay.com/usr/catracingproducts

If you scroll down a bit on the link they are following a company called Perfect Crank.

I know its a long shot but maybe send a message and see if either one of these companies can give any sort of info on your crankshaft. Worth a try?

Thanks for the responses.

I verified TDC with a piston stop a few months back (must have forgotten to mention that in my posts). I check/verified the crank keyway was good when I installed the new balancer over the winter.

I've also run it with the serpentine belt removed with no change in vibration.

I'm leaning towards just sucking it up and having another 383 built by a local shop. That way I'll have known engine specs/parts and local support if needed.

Live and learn...

Daniel

I'd tear into the motor. I bet that crank is jacked up somehow or the timing chain is a tooth off maybe?

I haven't gone all the way back, but have you done a compression test on all cylinders and then a running compression test?

Since you took the belt off that eliminates the of the engine, have you taken the trans and clutch off to see if its still there?