Wishmaster's87IROC

iTrader: (4)

when I got my 383 it was already together..I have since taken it apart down to the short block and sold most of it.....when I got it ..it had a stock new 6.75" balancer on it.....I want to buy an aftermarket balancer...do I have to use a 6.75" balancer or can I use an 8"...and can I use an aftermarket...or do I have to stay with what came on the motor?

thanks!

AlkyIROC

Unless you're using an internally balanced crankshaft, you need an externally balanced dampener and flexplate/flywheel for a 400.

I wouldn't recommend using an old factory 400 dampener since the newest one is about 30 years old. An aftermarket replacement or a performance dampener for a 400 will do fine. To my knowledge, all the SBC 400 dampeners are 8".

If your engine has in internally balanced crankshaft you can use whatever size dampener you want since they will all be neutrally balanced. You timing marks may not be accurate unless you use an adjustable timing light and only use the TDC mark.

Wishmaster's87IROC

iTrader: (4)

im pretty sure the engine was internally balanced....cause there was no flywheel attached to the back side of the crank...alls it had was the dampener on it.....so should I get an aftermarket 6.75" like was on there or should I gt an 8" dampener?

thanks!

AlkyIROC

Without knowing if the crank is internally or externally balanced, guessing at what dampener to use is going to be just a guess. Does the crankshaft have a dowl pin on the back? A dowl pin normally indicates it's externally balanced so that the flexplate/flywheel can only go on one way.

Pull the oil pan and check the crankshaft. There are ways to see if it's internally balanced or not from the position and size of the counterweights.

If you buy a neutrally balanced dampener and the engine is externally balanced, you'll have a terrible vibration. Same thing the other way around.

Yes there are internally balanced 383 stoker cranks available but the most common is the externally balanced 400 crank which need a special dampener and flexplate/flywheel. If you don't know what's in the engine, don't guess at what it needs. Are you even sure it's a 383? If the heads are off, measure the stroke. So far from the sounds of it, you only have a 350 (maybe even a 305). Casting number on the block will tell if it's a 4" bore block or not if the heads are still on.

Wishmaster's87IROC

iTrader: (4)

the heads are off....I will take some pictures later on tonight and post them here so maybe you can help me figure this out!......thanks for all the help!

Wishmaster's87IROC

iTrader: (4)

heres some pictures..its a 1970010 block...if that means anything...I dont know what casting numbers your wanting..and I dont know how to measure the stroke...I measured the rods and from hole center to center they are 6"

I know I know..I dont really know alot about engines but Im trying!

AlkyIROC

That looks like a 400 crank but doesn't have the dowl pin. See if you can get a casting number off the crank. The 010 casting on the block is a 4" bore block is it's definitly not a 305.

A 400 crank is casting 3951529. It will be at the front of the #3 main.

Measure the stroke. The piston at TDC should be at the top of the cylinder or very close to it. Measure the distance from the top of the piston at TDC then at BDC. If it's about 3.5", it's a 350 crank. If it's 3.75", it's a 400 crank.

If you do have a 400 crank, it's possible but very unlikely that it's been changed to be internally balanced. If it's a 400 crank, you should be buying a dampener and flexplate for a 400.

If it's an aftermarket stroker crank then it could be internally balanced and can use any neutrally balanced dampener and flexplate.

Wishmaster's87IROC

iTrader: (4)

I couldnt find a casting number on the crank...I turned the motor over and looked at all visible parts of the cranks but couldnt locate a number...I also measured the stroke and it came out to 3.75 from TDC to BDC.

stand still?

AlkyIROC

Sounds like an aftermarket stroker crank then, making it a 383 in the 4" bore block (+.030"). Take a chance and buy whatever size neutrally balanced dampener and flexplate on the gamble that it's an internally balanced crank. After all these checks, it doesn't look like you have a factory 400 crank and there are a lot of internally balanced stroker cranks available now.

Wishmaster's87IROC

iTrader: (4)

would the numbers on the crank be very visible or hard to find? I just want to make sure and not be missing where the numbers should be...

what dampener would you recommend? a 6.75 or 8? whats the difference?
I have seen a few on ebay in the $100...

Damon

I'd always do an 8" balancer, espacially on a big curbe motor. All stock/externally balanced 400/383 balancers are 8" diameter, but there are also 8" balancers that are NOT designed for a 400/383. The flexplate/flywheel on an externally balanced 400/383 is likewise the same diameter as other motors but also has special balancing weights.

I agree that you really need to find out if that motor is internally or externally balanced. If it's externally balanced and you install "neutral blanced" dampener and flexplate you'll tear it to pieces in no time. However, if it's internally balanced and you buy externally balanced dampener and flexplate you'll also tear it to pieces in no time.

You NEED to know how it was built. THEN you can easily determine what dampener/flexplate you need.

84 Z-28 350

U can get a balencer W/ bolt on weights

Wishmaster's87IROC

iTrader: (4)

where would I take it to find out if its internally or externally balanced?..how much would that cost me?

Apeiron

Assuming whoever you bought it from can't tell you, you'd have to take it apart and take the rotating assembly to a machinist to have it spun up on the balancer.

Quicc Silver Z

I also have a 383sbc wit about 50miles on it. Its vibes or knocks from the bottom. We change the piston bearing around the crankshaft(which I dont think was the problem) and its still doing the same. It is a new rebuild engine..We took off the harmonic balancer, started it and the noise stop. Im guesting that since the balancer is off my old (305sbc) I need an 8" balancer anyone can help?

Apeiron

It sounds more like you need an externally balanced dampener from a 400.

Quicc Silver Z

What is the difference between 8"ext. balanced dampener and a 8"dampener


Thank u answer in the "bobweight" post

Apeiron

A dampener for an internally balanced engine is neutrally balanced, like on a 305 or 350. The outer ring on the balancer is a smooth uniform ring all around.

A 400 doesn't have room inside the block to fit all the weight needed to balance it, so some of the weight goes outside on the flywheel in the rear and the dampener on the front. The outer ring of a dampener for an externally balanced engine isn't a smooth uniform ring, it has a section missing from the back side.

Quicc Silver Z

Going to buy a ext. balancer this weekend and give it a try....prolly an 8"...If it still vibe, knockin then it could be a wist pin, which I really dont want to deal with. Pretty sure we torque the piston rods and mains down the right way for the second time..

AlkyIROC

Don't forget, an externally balanced crankshaft needs the special dampener and flexplate. The flexplate has a weight welded onto it and the flexplate is installed on a dowl pin so that it's in the proper position.

Wishmaster's87IROC

iTrader: (4)

Im pretty sure I was able to figure out that the engine has been internally balanced...after taking the oil pan off and looking around in there each piston has been wrote on with a sharpie pen and each connecting rod has been worte on with a sharpie also...both having the same corresponding number on them...so each piston and rod are placed in the same cylinder. thats what Im thinking..plus I remember asking the guy I bought it from if it was internally balanced and he told me yeah...but I lost his number to confirm it.

so with that,,,,can someone point me to the correct dampner with the correct timing marks that I need or can use? I dont want to use a stock one...

AlkyIROC

From looking at that third picture again, I'd have to say it's internally balanced also. Right behind the #2 main is an extra counterweight. That isn't normally there on a factory crankshaft internal or externally balanced. My BBC stroker crank is the same way except it's behind the #3 main.

As for balancer size, the accuracy of the timing marks will depend on the pointer. An 8" balancer will need timing marks slightly wider apart than a 6.75" balancer. If you use an adjustable timing light and line the mark on the balancer to the TDC mark on the pointer then it doesn't matter what size the balancer is. If you buy a balancer that has degree marks around it, then you line them up to the TDC mark on the pointer and again, balancer size doesn't matter.

I use an adjustable pointer. When I put an engine together, TDC is located with a degree wheel and a piston stop then the pointer is adjusted to exactly TDC. Factory pointers can be very inaccurate.

CamarosRUS

Defenitly go with an aftermarket pointer.

Tombowman89

They make different timing pointers for different dia balancers. Also ATI dampers can be tuned per the rpm range you want to run to or through. I’ll also add that the weight of the balancer needs to be chosen correctly to the cubic inch that you plan to have a displacement of. Just because you use a 3.750 stroke crank doesn’t mean you have a 400 crank or have the need for a 400 cubic inch balancer, there is a difference of at least 0.125” just in the bore which means the weight of the rotating assembly will be heavier than what you will be required to use in your 4.000”, 4.030”, 4.040” and 4.060” bore small blocks .
Also the crank journals are a larger diameter on a 400 cubic inch 3.750 stroke crankshaft vs a 350 cubic inch 3.480 stroke crankshaft.
Also six counterweights are normal on all SBC cranks, out of the ordinary and higher performance are considered to be fully counterweighted which has 8 counterweights.
I know this isn’t about one mfr brand of balancers but the same can be applied.

Yes I know this is an old thread