383 harmonic balancer help.

crazypurgatory · 04-13-2006, 05:21 AM

In my 1971 Camaro that I just bought the guy told me that it has a 383.
I think I have a bad balancer not sure yet have to look at it this weekend.
How can I tell what kind of balancer I have on there 350 or a 400?
What should be on it?
I'm not sure how he got the 383 cubic inches.
Either by just replacing the rods or just the crank.
Thanks for any help.

Chris G.

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Z28SORR · 04-13-2006, 12:33 PM

A 383 is normally a 350 bored .030 over with a 400 crank. So you shoud have a 400ci harmonic balancer. 383's like 400's are externally ballanced so if you replace the balancer you "should" get the engine rebalanced. The thing about the balancers is they all look the same.

angel71rs · 04-13-2006, 05:43 PM

400 balancers look like a portion of the outer ring is scalloped, very easy to tell the difference from a regular internal balance balancer with a complete outer ring. Unless the guy payed big $$$ to have the 383 internally balanced, it should still be externally balanced and have a 400 balancer on there.

So if you look at balancer and part of outer ring is cut out, I'd believe the claim that it's a 383. If it has a complete outer ring either 1. it's a 383 that had $$$ spent on it for internal balancing (doubt it) 2. it's a 383 with the wrong balancer on there 3. it's a 350.

One way to tell if it's a 383 is to measure the the piston travel. 350 crank would have ~ 3 1/2" of travel, 400 ~ 3 3/4".

Why do you believe you have a bad balancer?

Stephen 87 IROC · 04-13-2006, 08:40 PM

Quote:

Originally Posted by Z28SORR

383's like 400's are externally ballanced so if you replace the balancer you "should" get the engine rebalanced.

Don't think of them as balancers. They're vibration dampeners. Replacing a dampener has nothing to do with the rotating assembly balance so replacing a bad dampener doesn't need a rebalance. When mix and matching internal parts such as pistons, rods etc, from anything other than stock, you should have an engine balanced. Using 400 crank and rods with 350 pistons to make a 383 is not stock.

The reason the 400's were externally balanced is that there wasn't enough room inside the engine for the extra counterweight so GM added the weight on the outside. The 400 has an externally balanced damperer and flexplate/flywheel. A neutral balanced dampener on an externally balanced crankshaft will have an extreme vibration.

I agree with the above that the chances of the 383 being internally balanced are slim. Looking at the dampener to see the cutout weight is the easiest way to tell if it's a 383/400. If the dampener is smooth all the way around then you don't have a 383 or have the wrong dampener installed. By checking the casting number on the block to see if the block is a 4" bore or not, you can find out if the block is from a 350 or just a 305.

Also by building a 383 with a 400 crank as mentioned above, the mains need to be turned down to fit into a 350 block.

crazypurgatory · 04-13-2006, 09:45 PM

Quote:

Originally Posted by angel71rs

400 balancers look like a portion of the outer ring is scalloped, very easy to tell the difference from a regular internal balance balancer with a complete outer ring. Unless the guy payed big $$$ to have the 383 internally balanced, it should still be externally balanced and have a 400 balancer on there.

So if you look at balancer and part of outer ring is cut out, I'd believe the claim that it's a 383. If it has a complete outer ring either 1. it's a 383 that had $$$ spent on it for internal balancing (doubt it) 2. it's a 383 with the wrong balancer on there 3. it's a 350.

One way to tell if it's a 383 is to measure the the piston travel. 350 crank would have ~ 3 1/2" of travel, 400 ~ 3 3/4".

Why do you believe you have a bad balancer?

It looks like the balancer is wobbling on the crank.
I have not been able to to look at it close yet.
I'm going to look at it this weekend.
I have never seen a 400 balancer so maybe it just looks like it's wobbling.

I had one go bad on my 1997 Z28's LT1.
My friend who looked at it when he helped me tow it to my house said it had the 400 balancer.
But the car had been sitting for 2 years so I had some prep to do to the engine before I got her started so he did not see the engine run.
So like I said maybe it just looks like it's wobbling.
But if it's bad what car can I use to order the 400 balancer from?
Thanks,

Chris G.

Stephen 87 IROC · 04-13-2006, 11:54 PM

The "wobble" you see is probably the cutout.

The last 400 was produced in 1979. If you can even find one in the junk yard, your best chances are in pickup trucks or vans. Even then, you're looking for a 25+ year old balancer. Go buy a new factory replacement one. They're cheap. Just tell your parts supplier you need a balancer for a 400 SBC.

Check your flexplate to see if the balance weight is still on it. They've been known to fall off.

Z28SORR · 04-14-2006, 10:45 AM

Also the LT1 is more prone to crank shaft snout failure then the older style SBC's. A lot of times it's the crank pully that is broken and wobbling and not the balancer.

crazypurgatory · 04-14-2006, 05:03 PM

Quote:

Originally Posted by Z28SORR

Also the LT1 is more prone to crank shaft snout failure then the older style SBC's. A lot of times it's the crank pully that is broken and wobbling and not the balancer.

Yea my LT1 just came apart 2 pices.

I don't know why they made the balancer into a pulley too.

O well I'm going to check it out tomarrow.
Thanks for all the info guys.

Chris G.

crazypurgatory · 04-14-2006, 05:04 PM

Quote:

Originally Posted by Stephen 87 IROC

The "wobble" you see is probably the cutout.

The last 400 was produced in 1979. If you can even find one in the junk yard, your best chances are in pickup trucks or vans. Even then, you're looking for a 25+ year old balancer. Go buy a new factory replacement one. They're cheap. Just tell your parts supplier you need a balancer for a 400 SBC.

Check your flexplate to see if the balance weight is still on it. They've been known to fall off.

I will check the flexplate too he told me he had a new one put on.
Thanks,

Chris G.

bestracing · 04-17-2006, 05:48 PM

Summit has aftermarket ones for a reasonable price but you would have to get it balanced to work for your engine.

Also with more and more companies getting into engine kits the internal balance assy has become a lot cheapier than what it once was. I have looked at a kit from Ohio Crankshaft and the price wasn't too much more then the external kit. Well worth the extra cash IMHO.

Stephen 87 IROC · 04-17-2006, 06:01 PM

When I bought a new BBC stroker crank from Eagle, it was internally balanced. I needed to buy a new flexplate and dampener because the ones I had were for an externally balanced crank. Normally 454+ BBC engines are all externally balanced.

You look at the dampener on my engine and can see it's for internal balance. I can say I've got a 396 or a 427 instead of the 540 which it is

Nobody could know the difference by just looking at the engine.