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-   -   427 stroked with 428 crank balance question (http://www.clubcobra.com/forums/fe-talk/68364-427-stroked-428-crank-balance-question.html)

d_ford 04-04-2006 07:53 AM
427 stroked with 428 crank balance question
 
I have a Dove aluminum 427 tunnel port that was stroked with a 428 crank and rods. It has an aluminum flywheel that I want to replace with a light weight steel unit since I'm putting it in a heavier car (mustang). My question has to do with the balance. Can I reasonably assume that it was internally balanced and therefore would use a zero balance flywheel? I didn't build the engine initially and I know there are balance differences between the 427 and 428CJ engines. The aluminum flywheel that came on the engine doesn't have counterweights cast into it but it has been drilled a number of times. (probably for different balance engines?) I don't want to have to take this thing to a shop just to find out how it's balanced just so I can buy a new flywheel for it. As far as i can determine, it was originally built by a shop called S&S engines possibly in Iowa. Any input greatly appreciated.

tpiini 04-04-2006 09:01 AM
I don't think you have any choice but to take the old & new ones in to have the balance matched.

I'm running a neutral flywheel on a 428. There's no balance weight cast in, but the machinist drilled the opposite sides to acheive a 428 balance.

If you have holes drilled in your current flywheel, you're definitely not neutral balanced.

Jeff Frigo 04-04-2006 09:30 AM
Quote:
Originally Posted by tpiini
If you have holes drilled in your current flywheel, you're definitely not neutral balanced.
Don't be so sure of that statement. Depending on how many, and how big the holes are, this could be to done to get a zero ballance.

I use to work for GM in the flywheel dept. almost every wheel had hole drilled in them.

d_ford 04-04-2006 10:55 AM
That's what I figured....or it had been drilled to balance for a variety of engines. There are numerous holes drilled in it. I guess to find out for sure I could take the existing flywheel in to check the balance on it.

Clois Harlan 04-04-2006 11:01 AM
If your 428 flywheel came from McLeod there was a small rectangular weight (28 oz) that bolted to the top of the flywheel on the clutch side. This weight can be removed to achieve zero balance. Also, your harmonic balancer will have a 28 oz weight inside for balance. I know several people that are running an aluminium flywheel in their Mustang.

Clois

ZOERA-SC7XX 04-04-2006 11:03 AM
I bought a steel flywheel for an externally balanced 428 and it has several holes drilled in one end, but no counterweights. I had a question on indexing the flywheel (down the page) that seems to be answered.

Carnut427 04-04-2006 11:07 AM
Quote:
Originally Posted by d_ford
....or it had been drilled to balance for a variety of engines. There are numerous holes drilled in it. I guess to find out for sure I could take the existing flywheel in to check the balance on it.
It's final balance (what it's balanced at now) is obviously for the engine it was run on. Take the old and new flywheels into your machine shop and have them balance the new one to match the old one.

Dan

Jeff Frigo 04-04-2006 01:02 PM
Quote:
Originally Posted by Clois Harlan
If your 428 flywheel came from McLeod there was a small rectangular weight (28 oz) that bolted to the top of the flywheel on the clutch side. This weight can be removed to achieve zero balance. Also, your harmonic balancer will have a 28 oz weight inside for balance. I know several people that are running an aluminium flywheel in their Mustang.

Clois
Not to be picky, but it is not a 28 oz. weight. What 28 oz. refers to is 28 inch ounces. At a 1 inch radius, the weight would truly weigh 28 ozs. Seeing that this weight is bolted on the end of the flywheel (about a 6" radius), the weight actually weighs 28/6 = 4.67 ozs. If you don't believe me, pick up the weight, it is nowhere near 1.5 lbs.

It is entirely possible to remove weight from the opposite side of the wheel to simulate the extra weight needed on the counter balance side (inline with the crank lugs). 4.67 ozs. = 1 cu. in. of steel or 2.85 cu. in. of aluminum. To achieve this with drilling, there would have to be about 10 .5 in. holes x .5 in. deep in steel or 28 holes of the same dims. in aluminum. These calculations are close, they do not take into account the tip of the drill point if they are not through holes.

If you need help with the calcs. reply with your number, dia., and depth of the holes and I can help you.

d_ford 04-04-2006 05:01 PM
After talking with several people here locally today, I'm wondering if just trying to match the balance between the old and new flywheels will even work. They are of the opinion that the whole rotating assembly needs to be balanced as a unit. If the new wheel is drilled like the old, just being off a small amount will affect balance and cause a vibration. I'm starting to think maybe I should just keep the old alum flywheel on this application, it might be more trouble than it's worth.

Jeff Frigo 04-04-2006 08:46 PM
I was going to say that right from the start, but I didn't think you would like that answer.

ted 04-09-2006 07:19 AM
Quote:
Originally Posted by d_ford
After talking with several people here locally today, I'm wondering if just trying to match the balance between the old and new flywheels will even work. They are of the opinion that the whole rotating assembly needs to be balanced as a unit. If the new wheel is drilled like the old, just being off a small amount will affect balance and cause a vibration. I'm starting to think maybe I should just keep the old alum flywheel on this application, it might be more trouble than it's worth.
A competent balance shop can match balance the replacement flywheel to match your old flywheel. The only nuance is if the flange on the back of the crankshaft is not exactly true with the mains, then a given amount of unbalance will occur as a result of the runout at that point.

Ted Eaton .

Jeff Frigo 04-11-2006 01:23 AM
Quote:
Originally Posted by ted
A competent balance shop can match balance the replacement flywheel to match your old flywheel. The only nuance is if the flange on the back of the crankshaft is not exactly true with the mains, then a given amount of unbalance will occur as a result of the runout at that point.

Ted Eaton .
??????????????

ted 04-11-2006 04:31 AM
Not sure what your questioning unless you don't understand how the flywheel hub at the crankshaft flange can become uncentered when the crankshaft is turned undersize. This in turn creates runout on the flywheel when installed on the crankshaft which may have been perfectly balanced on an arbor.

Jeff Frigo 04-11-2006 07:27 AM
Why would the flange become uncentered when the crank is ground under size? It is ground between centers. If that happens (never heard of it), you must be dealing with a totally incompetent machine shop.

Carnut427 04-11-2006 09:39 AM
Quote:
Originally Posted by Jeff Frigo
Why would the flange become uncentered when the crank is ground under size? It is ground between centers. If that happens (never heard of it), you must be dealing with a totally incompetent machine shop.
It happens at competent shops; the reason you've probably never heard of it is because the amount of runout, and therefore the effect on balance, is usually extremely small.

Dan


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