I just installed my 383 this week but have a problem with the flexplate-it does not seem to be perfectly round and when I installed it rubs very slightly against the transmission bellhousing on one side-on the other side it's fine-I was thinking that I would just get another flexplate and see if that cures the problem but the engine builder said that it was balanced with that particular flexplate and a stock one would throw off the balance for the whole engine- he said to grind a bit of the bellhousing where it rubs and that should cure the problem-I have not started it yet as I do not know what to do about this.I can't believe that a flexplate for this engine can't be replaced. this one came off my old 350 and he welded a weight of some sort on it when he balanced the whole assembly. what do I do?? any help is greatly appreciated.

There are two different 383 rotating assemblies made. One is an internally balanced assembly, the other is an externally balanced assembly. The externally balanced assembly uses the Chevy 400ci vibration dampner (weighted and or drilled) and flexplate (weighted). Your engine builder should have used a new externally balanced flexplate instead of welding a weight to the old 350 flexplate (it's possible that the heat may have warped it). There is no reason why it should be out of round and rubbing the bellhousing, and grinding the bellhousing is not the correct solution, although I have heard of this being done before. I myself would be concerned with weakening the bellhousing depending on how much grinding needs to be done. I suspect that he's not good at engine balancing. I have seen plates available that bolt to the crankshaft between the flexplate and crankshaft. These allow you to install an internally balanced (non-weighted) flexplate on an externally balanced rotating assembly. I do not know what is involved with installing one of these plates or how well they work. I myself would not choose to use one. If any others are considering building a 383, I suggest using an internally balanced assembly, they can be bought from suppliers already balanced for an extra fee. If you have a particular machine shop you use, ask questions as to their ability to balance engines before you turn your engine over to them for work, not all machine shops (small) can balance internally balanced rotating assemblys, the machine that does this is too costly for them. When it comes to machine shop work, you get what you pay for...a cheap job is exactly that...cheap! Any shop can claim they know how to build you a 383...doing it correctly is something else. And for info...all BBC 454's and SBC 400's are externally balanced, all other Chevy V8's are internally balanced. If you have the money, Chevy sells a bareblock 383 #88962516...this with a (pre balanced) internally balanced rotating assembly of your choice is the way to go. Jeff, the best thing I can tell you is, if you only need to remove a small amount from the bellhousing, go ahead and do it, anything else is going to be more money. And find a better engine builder next time.

Thank you for your input Mike.-It seems like it was possibly warped by the welding of the weight- It just seems like he should have used a new flexplate at least-but would the process warp a new one as well?I have taken a small amount of material off the area where it rubbed with a small file and it no longer rubs- this area is near a fairly thick part of my TH 400 (where the bolt goes through the housing)and the starter gear looks like it will still engage ok-I have about 1/8" clearance on driver side and 1/16" on the starter side-It bothers the heck out of me that I have this problem but I won't be going back to that machinist- he claims he builds about 3 or 4 383's a month.

Jeff, he should have used a flexplate from a 400ci, he used the 350 flexplate to cut the cost. Had he used a 400, the weight comes already welded to it. Did you buy a 383 rotating assembly or did the builder piece one together? Anyway, I'm glad to hear that things seem to be working out for you. The little amount that you ground down should be ok. Now fire that bad boy up! 8)

Mike brought up some great points. What effect will a warped flexplate have while the motor is running???? Even though its balanced at speed, won't it be unbalanced at other speeds? Should Jeff remove the flexplate to see how bad it might be? I don't have an expertise, call me Just Curious.