I have a '84 vette with the original crossfire 350 and the 4+3 tranny. Is the motor internal or external balanced? I want to buy a new 383 shortblock and need to know which type to buy, while hopefully retaining my original flywheel.

Thanks in advance.

 

Your 350 is internally balanced.
I believe the 383 uses a 400 crank, therefore it requires an externally-balanced damper and flywheel/flexplate.
But, hey, I have been wrong before...

Larry
code5coupe

 

Any idea where I could buy a flywheel that is externally balanced?

 

I know Summit has them, GM Performance Parts more than likely does, too.

Larry
code5coupe

 

Thanks.

 

Just make sure you get a 153 tooth flywheel for the 400 (and 383) external balance. Chevy never used a 153 tooth 'wheel on a 400, so it's a non-production item. Two alternatives would be, one, to use a production 168 tooth 400 flywheel and a starter for 168 teeth, or two, buy an internally balanced 383 rotating (or short block) assembly.

RACE ON!!!

 

We need to clarify balancing here...

GM internally balances the motor at the front, externally at the rear. This is why the flywheel and flexplate are so important.

It is best to have the entire mass internally balanced, then get the flywheel zero balanced.

 

I have about the same question. I have a 383 with the 400 crank. I purchased a replacement 8" 400 damper and a SFI external flex plate. Is there any specific's top mounting them? Dosent seem it? I assume the flexplate and balancer don't need to be checked?

 

Also, this thing was eating up starters and flexplate teeth. How many theet are on a 168 or 153 starter?

 

Sorry, but that is not correct for two piece seal crank shafts. A two piece seal crank for a 350 or smaller is 100% internally balanced. When GM went to the one piece rear main seal they had to change the flywheel flange to accommodate the new seal. 1986 and up 350's have a small imbalance in the rear, only because of the seal type. This applies to the thread originators 1984 car.Sorry, I don't
understand the question.


The starters use the same drives. As a matter of fact, you can simply change the nose piece on one starter for it to work for the other. The difference is in the mounting holes, and where they place the starter in relation to the centerline of the crank. Check your starter to flywheel tooth clearance. I'll bet you need to shim your starter.

RACE ON!!!

 

Is the whole engine put on a machine, to be balanced,
or, is the, crank, bobweights, HB{if not neutral},
flywheel/flex{if not neutral}, put on a machine?

 

Ah, thanks for the clarification.

 

Usually 383 recip kits have the crank, FW or flexplate and a new harmonic balancer. I would think the seller maintains the correct balance relationships. I can see you wanting to re-use the FW but not a harmonic balancer. Why not just spring for the three items all new?
You have a chance at this juncture to also get a mini-starter. It's like night and day difference(as far as weight is concerned).

Pistons and wrist pins are weighed on an electronic scale. Then they do any machining necessary to get all the pistons to match weight. They do the same for the rods(both ends). I am not sure if they include the rod bearings in the measurement. They do weigh the rings.
Then they replicate the piston/pin/rod/ring weight with a bob and put it on the crank(times 8). It spins and the computer detects where the differences are. A drill press is usually located right next to where the crank spins. They slide it over if they need to drill into one of the counter-weights to remove material.
If you want full internal neutral balance, they figure out where to put the slugs of mallory metal and install them with a press-fit(actually just pound them in with a BFH).
Otherwise, they bolt on the harmonic balancer and FW/FP.
Either way, if you have the recip assembly out, it wouldn't hurt to take it over to a capable, competent machine shop and have them check it for you. Maybe an hour of shop labor. $60.00?

Congrats on the 383. Sounds fun!

 

Only $60 !!! I asked around here while I had mine out and it was way more than that! I can't remember exactly how much but if it was any where close to that I would have jumped on it. I was already 650 into the machining so even if it were arother $100 I would have done it. Anyone in Atlanat GA know of a shop that can and will do it
?

 

Don't use a standard 400 sbc crank you can buy an internally balanced 3.75 in stroke crank just for the 383. It has the right size journals and allows you to use a standard balancer.

 

To late for that. Motor is already built. If I do a rebuild of the 383 I would seriously consider something like the Eagle pre-balanced crank, rod, pistons, ballancer and flexplate assembly.

 

Question, when you see engine builders describe the short block assembly as 'internally balanced' does that mean the whole motor is internally balanced or does 'internally balanced' mean that the front is internally balanced?

This custom short block engine assembly from SDPC features a race prepped LT1 block with Milodon steel splayed center main caps. It also comes with a Lunati 4340 forged crankshaft, Lunati Pro Mod 5.850 rods, SRP forged dished pistons, JE file-fit rings, Federal mogul race bearings, and is internally balanced.

 

If *I* made that statement, I would be representing it as 100% internally balanced. But why take a chance on a possible failure in communications? As you read in bogus's post above, the stock 1 piece seal crank, engines have a slight amount if imbalance in the rear. You want to find out if it is factory balance where you can use a stock flywheel/flexplate or if you need to specially, neutral balance one.

RACE ON!!!

 

I bought that block from SDPC and I did ask. They said their engines are 100% balanced and to use a neutraly balanced flywheel and balancer. I was just wondering when people say internally balanced they mean "GM" balanced or 100% balanced.... coined phrase

 

It may be semantics and it may be that the one answering the question doesn't understand it. As I said in my response to bogus, 2 piece seal crank 350s are 100% internally balanced. I don't mean just 100% balanced. I mean 100% INTERNALLY balanced. 1986 and up engines have a slight imbalance (different than the 400 imbalance) in the rear due to the revised, 1 piece rear seal flywheel flange on the crank. You CANNOT use a pure, 100% neutral balanced wheel for a 2 piece seal on the back of the 1 piece crank. The bolt pattern is different. A true neutral balanced flywheel/flexplate for a 1 piece seal shaft would be a specialty item, because Chevy never made them that way. ASK!!!

RACE ON!!!