All you stroker experts, what's the difference between flywheels for internal and external balanced crankshafts? Can use just use the balance plate or is there more to it? I bought a stroker short block that came with a flexplate (with balance plate) and harmonic balancer. I'm going to be using it with a TKO 5 speed and have a 350 flywheel (internal balance) in great shape. Will it work with the balance plate off the flexwheel?
Thanks for any advice!

Jimbo

 

if i understand correctly, you want to use a 350 flywheel in place of a stroker flexplate? you can only do this if the new crank is INTERNALLY balanced. if its not you WILL need a externally balanced flywheel. youll also NEED an externally balanced harmonic balancer. dont use the one from the 350.

 

agree....you need to find out from the builder if it is internal/external balanced.

 

 

I guess my question comes down to: Is there more to external balancing than the balance plate that bolts on to the flywheel or flexplate? My crankshaft is externally balanced. I do have an external balance harmonic balancer which is definately different than an internal balance HB. However, the external balance flexplate that came with the motor, looks identical to an internal balance flexplate, except for the attached "balance plate". Is the same true for a flywheel?

Jimbo

 

I am not sure if this answers your exact question or if it is what you want to hear anyway. But you need to balance an externally balanced rotating assembly with all the parts that are going in/on the motor, crank, rods, pistons, rings, bearings, balancer and flexplate/flywheel. If any of these parts are changed then "I" would balance the whole assembly again

 

Normal for external balanced engines to require all parts to be balanced together. I would call builder but I suspect he will tell you the same. You can use a 350 flywheel but they will have to add metal and drill to balance to the assembly.

 

Assuming you have an externally balanced small block ... 383 or the like with a 400 or 400-clone crank (3.75" stroke). Also assuming this motor has pre-86 TWO-piece real main seal? Ideally, entire rotating assembly would be re-balanced ... but don't flip out yet ... re-balance probably not necessary ... 30 grams either way ain't gonna mean squat on most street cars. All motors have a specific point where they will vibrate from harmonic imbalance ... no matter how well they are balanced. In fact many race motors are purposely "overbalanced" or "underbalanced"... this moves the point of harmonic imbalance within a range where the race motor spends little time/stress.

Your flexplate balance plate probably has a step in it ... right? If it has a step ... don't use it ... stepped is for flexplate ... flat is for flywheel. Get the correct one for a SMALL block but is FLAT ... use that FLAT balance plate with your 350 flywheel. DO NOT use a balance plate for a 454 ... they have a different weight bias. Also, don't forget you will need a pilot bushing pressed/tapped into rear of crank for manual trans' input shaft ... you can do this, simple. When you bolt the flywheel & balance plate to crank ... make certain you have at least one thread extending beyond the crank's flange ... not too much more or bolts will grab on block's rails. Use loctite on those cleaned threads/bolts & torque to spec.

BTW, '86-up one-piece seal small blocks came with an EXTERNAL balance flexplate/flywheel but an INTERNAL balance front damper.
G'luck.
-edit- for clarity, I am referring to the BOLT-ON balance plates ... bolts to crank flange.

 

When I built my 383 I was troubled by this same dilema. I didn't trust the sheet-metal balance plate and bit the bullet and bought the 400 flywheel. I didn't rebalance the assembly and the engine runs great, strong & smooth.

 

Jackson, Jimmy G.
Thanks for the input. Just what I needed to know. I have the short block disassmebled, I just wanted to be prepared for taking it to the machine shop. It is a 2 piece rear seal motor and the balance plate is stepped. I'll find the right balance plate and take to the machinist with my 350 flywheel. Cost savings of the flywheel should pay for the new balance job.

Jimbo

 

Jimbo:
If you're determined to rebalance you should have the pressure plate, pp bolts & clutch disc with the flywheel.

And since you're going to the trouble to rebalance, I strongly suggest you take a 350 front damper (neutral/internal) to machine shop ... and ... ask the machinist to see if it's practical to INTERNAL balance your assembly with NO rear counterweight and NO counterweighted front damper ... see if he can do it INTERNAL without too much Mallory/heavy/tungsten metal slugs. Crank & bearings will live longer if it's INTERNAL balanced.

 

How can you tell if a flywheel is counterweighted? I just ordered a new GM350/330 and I was hoping to use the same flywheel and clutch from the 350 that I removed.