350 Chevy flywheel sizes?

Hello,I have a few questions about flyweel sizes or I guess I should say Flexplates (Auto Trans.) I need to replace the flexplate on a street rod of mine. I can not seem to find a flex plate with the center hole big enough to fit on/over the crankshaft. Also the the bolt holes will not line up.
Question number #1. Is there a difference between a truck and a car when it comes to fleplates? How about if it is a 4 bolt main? I do not kow the year of the engine. The orginial owner had it built and knows nothing about the specs.. It was a short block engine and the car was built in 1992 so I would assume it is around that year engine. Is the flexplate something that GM would of changed much threw the years or was it pretty much a standard size? Any help would be great! thank you very much for your time.

I look forward to learning the answer to this as I have a '72 Chevy 350 four bolt main that I plan to put into a '46 Ford pickup. Well if I don't keep putting it off. I purchased a good but older turbo 350 transmission to use which was out of a car.

Haven't tinkered with cars for a long time so there might be better transmissions to use by this time.

Anyway, good post.

from what i remember,there are two sizes or types.one fits engines that use a two piece rear main seal.the other firs engines that have the one piece seal.the holes are ofset so the plate has to be rotated until the holes line up.

don't know about the newer ones' but they made about 4 maybe 5 driffent ones in late 70 early 80' mostly when by what tranny you had, some were so close to each other you had to sit one on top of the other one and put 3 long bolts in them to see the driffents. might be a part # on the old one. just replaced one in my 75 3/4 ton 4x4 power by 4 cly. isuz torbo diesel, tore out the center of it.

another think to watch for, dont use one off a small block 400 motor. it and the 454 were externally balanced, all the others were internal.

im wondering if the block was built as a stroker motor, good chance if its in a rod, that will have a crank from a 400 in it, try one for a 400 and see if it will fit, otherwise all the older chevys small block center hole should be the same as mentioned the tourque converter holes will varry with the trans used

I think you're onto it, twopop. As I recall the flex plates were different between the one piece and two piece rear seals. The one piece rear main seals emerged with fuel injection in the mid '80's.

And as someone else said, do NOT use a flex plate off of a small block 400, unless you can verify for dang sure that's what the crank is.

You need to know for sure what you have. I'm building a 383 with a custom crank to fit in a late model 1 piece rear main seal block. It was a lot cheaper to custom balance and use a 400 harmonic damper, than add a bunch of weight to the crank. This engine is going to be trailer towing in a pickup and not high RPM, so it made sense to do it this way.
It would take a very sharp eye to catch the 400 balancer.

as the one person said, the difference is between the one and two peice rear main seals, you should need the one from the 1986 up engine if it is the original 92 engine, which side is the dipstick on??? if it is on the left or drivers side then it will use the older one, but the passenger side dipstick does not mean that it is a one peice because i think they started that in 81 or 82. Then you go to like another person said, if it is a stroker engine, if they used a crank built for the 383 or if they used a modified 400 crank. I am going to say that since you are having trouble getting one with a hole big enough that you have the later engine, so any flexplate from 1986 up should work.

Now for the other question from greenbeanman, i think most of the aftermarket flexplates are of the dual bolt pattern design, saying that they will bolt up to the torque converter of a 350, 400, 700r4, ect transmissions, not to confuse the first two with engines, any of those transmissions will work fine for your 46, just if you use the 700r4 get it built first if you plan on rodding it out any as the early overdrive trannys were kinda known for bein a little weak

On the older SB Chevy flex plate, there's a 153 tooth gear and a 168 tooth gear. The starters are also different. The 153 tooth starter mounting holes are inline with the flexplate. The 168 tooth starter is diagonal to the flexplate.

The 86 and newer motors used one piece rear main seal.

I don't think there are different flexplates for the transmission to used. You should be able to bolt a 700R4 torque converter to a Turbo 350 flexplate.

Remember this...flexplates are ALWAYS matched to engines and not transmissions. The difference you are speaking of is between the early engines and the later ones with 1 piece rear main seal. Most flexplates have a dual converter bolt pattern for 3 bolts. The smaller pattern bolts to TH350 and 700R4 converters, the larger one is used for TH400. Some flexplates, and especially those used on the diesels were drilled with a single pattern 6 bolt setup, because the diesel converters had six mounting lugs on them. As long as your converter fits 3 holes, you can use either style flexplate. Be sure the plate you use is the right one for the ENGINE.

Thanks for the enlightening information!

Thank you Glennster for your reply. I have noticed while looking threw parts catologs they do mention "internal" and "Externatal" balance. I'm going to be dumb and ask what are they talking about? I've never seen a flywheel or anything that rotates fast not have weights on it for balance. I'm not normally one to be working on cars (always tractors) so I'm a little confused here. LOL. the biggest problem is I do not know exactly what motor I have (or what was done to it) Only thing the old owner knows is its a 350. It does have some changes made to it such as roller rockers and a mild cam. So I am told. Thank you again!

Thank you Ericlb. That is a possability. Like i said this is so hard to look for a part when you don't even know what you got. The old owner just wrote checks while somone else built it. I did find one that seems to be a perfect match at a local transmission shop. I measured and matched it up and it seems to be correct. However they don't even know what it is off of. Its been hanging on the wall for who knows how long. Looks like it has never been used either. Do you think it would be woth a shot to try it out?

Thanks Random-FarmHick. The dip stick is on the passanger side. I was told by someone yesterday that all Chevy engines have a serial # stamped in the block at the front on the passanger side. I have not seen anything. I believe this short block was ordered from Summit Racing. I'm not sure if them engines show anything like that or not. I can not find anything with GM casted in it at all.. I did find a part number or something on the flex plate. On monday I'll call a chevy garage to see if they can find that number. That would be great if they can... Thanks again for all who is trying to help!! I posted a pic (hope it works) of the car.