General Motors 168 Tooth Flywheel

[mfgenggear]

any one know what the unbalance weight is for a chevy 400 block 168 Tooth externally balance flywheel is?

what the unbalance weight for the matching damper.

trying fix my 383 stroker.

I have search and can not find this anywhere.

 

[ornerynorsk]

A good speed shop or engine machine shop might have this info on hand.

 

[mfgenggear]

thanks for your reply.

unfortunately it was an auto. machine shop that ruined my fly wheel.

I need to know what a stock flywheel unbalance is?

 

[Tmoose]

I think I've seen it somewhere, maybe in the older chevy power books.

Some companies offered a counterweight plate to bolt on along with a zero balanced flexplate.
If the engine was "right" with a stock flywheel (most unlikely if the engine assembly was precision balanced externally counterweighted) then matching a stock flywheel or flexplate would get you close. Any shop Could do that statically with decent tooling.

 

[mfgenggear]

just so you know
I had an other balancing company verify an external weight.
I was advised it was 125 Grams.

 

[IceStationZebra]

Why do you want the balance weight for a 400 to fix your 383? The correct balance weights on the flywheel and damper are dependent on your piston mass, a portion of the rod mass, stroke and the counterweights on the crank. A good shop should have no problem with this.

ISZ

 

[mfgenggear]

I am familiar with balancing. “Rotating Assemblies” an so on
I purchased 1953 Belair with a 383 stroker. Which had a little vibration but It was tolerable no major issue.

I was replacing the clutch & so in the process I had my pressure plate & flywheel balanced. (No Big deal right)
The shop balance my flywheel by adding heavy metal
I reassembled the drive train now my engine vibrates worse.

So what I should have done is left alone and been done with it.

Now I have to drop the Pan & visually verify there is no heavy metal install onto the crankshaft. Then buy a new flywheel with the standard Imbalance and hope for the best.

This is what was reported
fly wheel was drilled to remove metal to an imbalanced of 76 Grams
Shop added Heavy Metal to Increase Imbalance to 96 Grams.

An other shop advised it should be 125 Grams.

A Mcleod Flywheel Weights Brochure is as follows

GM 1 Piece seal configuration Crank 1986-97 305 350 CID 125.5 Grams (23.44 In-Oz)

Chev. (GM ) cranks 383 stroker 1970-86 383 400 CID 156.1 Grams (24.45 In-Oz)

See there that’s why I want to be informed on what is required.
Even the second shop had it wrong.

The error was on me for allowing this shop to screw up my flywheel. Even thou you expect the experts to know not screw with it unless that have all the facts .

He was told it is was for 1981 chevy 383 stroker .

 

[Tmoose]

Sorry you're having problems.
I'm surprised heavy metal was needed to "balance"/unbalance a typical steel flywheel There's lots of places to drill.

The values you provided have me a bit confused.
Simple Unbalance results from a weight (mass, really) at a radius. For the 125.5/156.1 gram "unbalances" the radius of application should be known. If either weight was applied exactly on the crank centerline the radius would be zero, and unbalance would be zero, too.

23.44 oz-in ~ 665 g-in..........divide by 125.5 gram = 5.298 radius.

24.45 oz-in ~ 693 gr-in ........divide by 156.1 gram = 4.443 inch radius

In addition to weight and radius, angular position is important. early Chevy cranks and flywheels had a dowel to enforce a particular installation orientation. If your dowel is missing, it is possible to put the flywheel on 5 wrong ways and 1 correct way. Or, If the balance shop created the "right" unbalance in the "wrong" angular position, it could be real bad. Way more than a shivering rear view mirror. More like a circus ride at 3000 rpm and getting worse with revs.

Are the new drilled holes opposite the "heavy metal", making a REAl heavy spot on the flywheel? That heavy spot should be installed oriented inline with the back counterweight. Approximately inline with the front rod journal ( 1 and 2)

http://www.adperformance.com/images/scat_chevy_cast.jpg

 

[IceStationZebra]

Sorry to hear about your mess. ISZ

 

[patprimmer]

The SBC never came from the factory in 383 configuration so there is no right figure.

The best starting point would be a std 400 CI SBC damper and flywheel if it is in fact a std 400 crank as it came from GM.

Once an engine has been hotrodded, it is a braver man than me who would just guess that the std parts from another configuration will suffice.

If it where mine, I would disassemble it and have the entire rotating assembly balanced without heavy metal being added.

If the crank already has heavy metal, a std 350 flywheel and damper should work., but it still requires re balancing to get correct piston and rod weights.

I would not use any of the people you have been talking to.

There are aftermarket steel 400 cranks that are internally balanced without need for heavy metal.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[mfgenggear]

Tmoose

I think you’re on the right track. I on the other hand I am
Confused also.

If the weight is in grams the what is C/B weight in Grams.
vs. weight in-oz


There is a dowel on my crankshaft.

IceStation Zebra

Thanks

Patprimmer

Yes & No

I had correspondence with an aftermarket Crankshaft Manufacturer and they do use GM's standard Damper & Flywheel specs. Yes they are standard.

No because some People get lazy, do a hack job of balancing.
Thats why there are standards those standards should be followed.

Yes I am Brave ; >/

Yes I do realize rotating assembly requires all the details for balancing.

I was hoping to avoid tearing apart my engine.
it is worth trying to solve it.
if not possible to solve then it's time to rebuild it.
That way I know what I’am dealing with.

Thanks

One Pist Off Engineer

 

[LionelHutz]

It should cost less than $50 to buy a cheap new 400 weighted flexplate. Then bolt it to the crank and see how much the engine vibrates. If that works, then buy a new flywheel or get the flywheel balanced (unbalanced) to match the flexplate.

 

[GregLocock]

Thiis how it is done in production, on two engines with which I am familiar, one is a ford, one a GM, one an I6, one a V8

The machined crank is dynamically 2 plane balanced

The flywheel assy is static balanced

The conrods are selected to be the same big end weight (to within a tolerance)

The pistons are selected to be in the same weight (to within a tolerance)

The harmonic balancer is single plane balanced

The engine is assembled.

The whole engine is then single or to plane balanced, dynamically.

Now, you want your engine to be as good as a production one? Then that is pretty much what you have to do.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

The way I do it is to put the heaviest pin with the lightest piston etc then balance all the piston pin assembly to the lightest one, or maybe even reduce the weight of all of them to a common weight.

I then get the rods balanced end for end. I sometimes lighten them as well before balancing.

I then get the crank dynamically balanced to the rods and pistons. I then individually dynamically balance flywheel, balancer and pulleys.

That way if I need to replace an individual component I can. This might be excessive for some, but I only work on engines that I expect to use at well over OEM performance levels.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules