Rotating Assembly balance???

88-378 · May 20, 2009

Just got my block and rotating assembly back and balanced. Machinist said he almost has it to a zero balance ( or closest he could get with a Ford) He took weight off of the crank, flywheel, pressure plate and the balancer! does this seem right?

It was a scat crank and he said it was out.????

88-378 · May 21, 2009

Anyone???

stykthyn · May 21, 2009

every set up will be different, I personally believe that a balanced rotating assembly should be at the core of every build.

347HO · May 21, 2009

What was your bob weight before balancing?
What is the combined weight of your rods, pistons, bearings, pins, keepers and rings?
What crankshaft?

My first thought is that your rotating assy is lighter than your "bob", very common IMO.

I'm interested to know what damper and flywheel you have that needed weight removed?
Depending how much... I would have opted to return them for defect as they should be extremely close to zero balance out of the box. Now it's too late, and if they break... no warranty.

Rick 91GT · May 21, 2009

347HO said:
What was your bob weight before balancing?
What is the combined weight of your rods, pistons, bearings, pins, keepers and rings?
What crankshaft?

My first thought is that your rotating assy is lighter than your "bob", very common IMO.

I'm interested to know what damper and flywheel you have that needed weight removed?
Depending how much... I would have opted to return them for defect as they should be extremely close to zero balance out of the box. Now it's too late, and if they break... no warranty.

I agree...

just want to add these questions/comments. Was this a cast crank or a forged crank? A cast series 900 crank is made to go 28oz external balance, and most of the 4340 require Mallory to go internal but it all depends on your bob weight.

88-378 · May 21, 2009

It is a cast 9000 series Scat crank. I saw where he drilled holes into the balancer, flywheel weight and pressure plate and the grind markes on the crank.

Don dixon Hi perfomance machine did it. He does a lot of work around here in GA including my friend who owns a performance european car repair business.

i also checked with my wifes stepfather who races comp eliminator and his buddy Bobby lagana who also races.. they said the cosest you can get to a zero balance the lighter the mass and thus it revs quicker and less strain???

i just never seen this before, but it is the first engine i am assembling.

also, i have no idea of the the specs before i dropped it off..nor did i get anything from him except clearance measurements for main and rods.

Rick 91GT · May 21, 2009

Do you know what piston and rod it has? Can you get a copy of a balance sheet?

I just did a 333 (.040) over piston and the bob weight was a little over 1600, SCAT I-beam rod, Probe SRS piston and the SCAT 9000 crank.

Personally it was a bad decision to take that rotating assembly of yours to "0" by drilling and griding on every component you had...IMO

What was the weight of the balancer and flywheel you supplied him? Now if you ever have any issues those components will need to be matched. I typically do not balance assemblies with the clutch and pp on, I know some prefer to do that.

88-378 · May 21, 2009

it was the scat I beam and probe SRS flat tops.

I guess If i ever need a new component, I should weigh them before assembly so i can match it up.

347HO · May 21, 2009

You should receive a computer generated result of before and after weighting.
If the machinist uses old school equipment, the results should be given to you hand written on some sort of excel type document.

The crank should not be ground down. The throws and counters should be drilled, drilled and filled.

28oz balancing averages about 200.00 to do
0 balancing can range from 350.00 to 1000.00 depending on mallory and time spent making holes and filling.

I've only seen two handful of 0 balanced assemblies and I can't remember one that didn't have mallory installed and zero had the crank ground on. On the rods... yes.
The only reason I can think of grinding on a crank would be to lop the throws for knife edging on a lathe.

Rick 91GT · May 22, 2009

Do you have any pics of the internals??

88-378 · Jun 5, 2009

347HO said:
You should receive a computer generated result of before and after weighting.
If the machinist uses old school equipment, the results should be given to you hand written on some sort of excel type document.

The crank should not be ground down. The throws and counters should be drilled, drilled and filled.

28oz balancing averages about 200.00 to do
0 balancing can range from 350.00 to 1000.00 depending on mallory and time spent making holes and filling.

I've only seen two handful of 0 balanced assemblies and I can't remember one that didn't have mallory installed and zero had the crank ground on. On the rods... yes.
The only reason I can think of grinding on a crank would be to lop the throws for knife edging on a lathe.

Yep, that's what he did. He did drill some holes in it too, to balance.

Rotating Assembly balance???

88-378

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stykthyn

I want to measure mine. It doesn't look that tall.

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Rotating Assembly balance???

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I want to measure mine. It doesn't look that tall.

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