ok a newbie here...i have a rebuilt 350 with number 3970010 (which is from 69-79 right???) that I want to put in my 85 iroc with a th700r4 tranny... my question is, is this a internally balanced engine.. I was asked this when oderering a flexplate...something about getting one with a wieght on it or not.. idk so i need help

 

or maybe a bigger question is if a gen 1 will even fit to a 700r4??? help please

 

Yes it's an internally balanced engine.

The bellhousing will be the same and the 700R4 will bolt up.

 

ok so if its an internally balanced motor than i need a internal balanced flexplate???? so every two piece main seal 350s are internally balanced which is any 350 before 86?? That is what i guess i have (2 piece rear main seal) sorry for the noobness...

 

i believe most all 350 are internal balance....(although you still might have a weight on the flexplate)....but all 400's are external balance...

 

so i should just order a flexplate from summit or where ever for a gen 1 sbc 350?? the only reason i ask is some guy at advance said that if i order the wrong flexplate then my engine will vibrate badly and ruin it and since the only reason im fixing up my iroc is cause my daily driver now has a craked block i need to make sure i get all the right parts

 

yes....order the flexplate for your motor.....the trans. should bolt up to it anyway....but get the one made for you block..gen 1.....

 

Ok thanks you guys!!!

 

I can't offer suggestions on the newer engines, but all the old SBC engines are internally balanced except the 400. There wasn't enough room inside the engine for the extra crank weight so they moved it outside the engine with an offset balanced harmonic dampener and flexplate/flywheel.

When building a 383 using factory 400 parts, it also becomes an externally balanced engine.

With the availability of better aftermarket parts, it's now possible to build just about any engine size as internally balanced and use simple neutrally balanced dampeners and flexplate/flywheels.

The factory BBC engines were all internally balanced except for the 454 which was externally balanced for the same reasons as the 400 SBC. My 540 uses an internally balanced crankshaft so I use a dampener designed for a 396/427 and my flexplate is for a 350 SBC.

Internal/externally balanced engines just deal with where the counterweights are positioned. It has nothing to do with reciprocating weight balance when you get an engine balanced.

 

Uh, actually, a 350 is SLIGHTLY externally balanced. But it is not considered to be an externally balanced crank. 400's and 454's are considered to be externally balanced and require the flywheel/flexplate and harmonic balancer from a 400 or a 454 for each application. These pieces have some pretty substantial balance weight areas on them.

What do I mean when I say a 350 has some external balance? The flywheel flange has the offset "rectangular" section that serves as a slight balance weight.

Newer one- piece rear main seal 350's have a perfectly round flywheel flange, but still have a need for this small balance weight. So a flywheel/flexplate for the newer one- piece rear main seal 350 crank has a small piece spot welded to it (flexplate). This piece is not as big as the one found on a 400 flexplate.

 

why not just use the flexplate off your 305?

 

Since your 305 is a 1985 model and 2-piece rear main seal, it will be exactly the same thing as needed for the 010 block.

Just reuse your 305 flexplate unless it is in need of replacement, anyway.

 

well actually i got the car without the 305 in it so i cant go that route... I found a guy that will sell me one for cheap but it doesnt come with bolts so i wa wondering if anyone knew the bolt sizes for the flexplate... and maybe for the transer case too... i dont know if 3/8x 1 1/2 is right for the transfer case i have heard 3/8 x 1 1/4 too

 

Transfer case? You have a 4x4?

 

hahahahaha no... typo... i meant the bolts from tranny to block