Vilhuer

944 S2 pistons would need quite heavy mods to clear block also. Notice how low piston comes at BDC. Lowest part of skirt is some 13-14mm below block cylinder wall. Now check Adam's piston pic in #36. Wide skirt below wrist pin hole in S2 piston needs to go almost totally I think for piston to clear part of the block which is sticking out into cylinder bore. The one where squirter is in early '87 block. 968 piston barely clears this as there is nothing in it on the sides of skirts. 968 piston is only factory part I know which don't need serious mods.

After trying rod and piston into all cylinders I'm thinking I need to get 1 or 2 mm metal taken of from crank counterweights or from pistons below wrist pins. Piston goes so close to weight that there isn't any room between them at BDC. 1 or 2 mm's empty space would be good I think. Also pistons come 0.3mm above deck on TDC. Might need thicker head gasket and/or little larger cuts for valves on piston tops. And rod upper end could have little more clearance sideways too. On closer inspection there are many small details which need to be taken care off which simply would not be issue with stock parts.

Mike Simard

Stan, the basic bobweight formula is:
Bob weight = (1 x rotating stuff) + (.5 x reciprocating stuff)

Your shop's hand written paper must be confusing to anyone but the guy who wrote it, they wrote one entry for a piston etc and two entries for rod big end, it's just their way of adding it up but looks correct.

svp928

AH! Stan, now I see what you are after- If the shop says you need to add 500 grams of heavy metal to the counterweight, that is about 3.3 inches of heavy metal. (ours was 1.5 times heavier than steel) Steel is 101 grams per inch at 1inch diameter, heavy metal is 150 grams per inch at 1" diameter. So, he would drill into the counterweight 3.3 inches, removing about 333 grams, and put in 500 grams of heavy metal. This is a bob weight difference of 167 grams, and thats how much weight you need to lose out of the bob weight for your crank to not need heavy metal.
I am assuming (bad word) he doesn't mean 500 grams TOTAL weight out-of-balance- this would mean nearly 10 inches of heavy metal to make up that amount. Most cranks don't have enough area to put 10 inches of holes into!

So, 167 grams is probably do-able with Carrillo rods and lighter pistons.
500 grams is probably out of the question.

Hope that helps

Steve

Stan.Shaw@Excell.Net

Thanks Steve,

My understanding is that it needs 500g of weight added, but I will confirm.

Fastest928

Stan, just call Whitey and ask him what the crank is balanced for....

Hi Steve!!

Marc

Stan.Shaw@Excell.Net

Thanks Marc, Would I reach him at the main number listed on the website: 310 370 5501 ?

You wouldn't happen to have an email address for him, would you?

Vilhuer

Isn't Whitey working at Moldex, not in Scat?

atb

Here are my component weights.

I don't have the hanging rig to measure the ends of the rods separately, so I just used Stan's numbers since I believe we have the same Oliver rods.

Rod Rotating 466
Rod Rotating 466
Rod Recip 175.5
Piston 473.5
Pin 124
Rings 33.6
Rod Bearing 96
Locks 1.5
Oil 6.0
Total: 1842.1

So, what does it all mean? How much Mallory will I need?

Stan.Shaw@Excell.Net

I hope to get there tomorrow and fnd out more. If you look back at my first post, you see they subtract the bob weight from 2870.2g then divide by 2 to arrive at the mallory required. I don't know where 2870.2 came from, but for now presume it comes from the dynamic balance machine.

Until I know more, a reduced bob weight doesn't help (mine could be @1819.3), since subtracting it from 2870.2 and diving by 2 will give a larger amount of mallory needed.

svp928

Stan, I don't know where that 2870 number came from, either, but I know the balance weight and position are determined by the machine, not a hand calculation. At least on the Stewart-Warner type of machines... I would talk to your man at Scat and ask him what they used as a target bobweight for that crank. I don't recall ever seeing that large an imbalance, even on an old 454 Chev when changing it over to internal balance from external... Your bobweight is not high compared to stock components, in fact its lighter, so you shouldn't be needing that much weight... and I don't recall seeing any other posts about this crank requiring huge balance weight..
Something is not right here...???

Stan.Shaw@Excell.Net

Thanks, I was hoping for a calculation I could replicate to determine what I needed for bob weight. I guess the premise of a hand calculation is contrary to a dynamic balance.

Unfortunately, I don't have a contact at Scat.

My local machine shop did say this is the most out of balance they have seen in 17 years of business...

I haven't found anyone yet with this same crank in balance. If you do, let me know!

Thanks for the thoughts.

John Veninger

Ask our highly skilled Sales Staff anything
you need to know about Crankshafts, Rods and Pistons.

Drop us a line at Cranktech@ScatEnterprises.com
SCAT Enterprises, Inc.
1400 Kingsdale Avenue
Redondo Beach, CA 90278

Phone: 310 370 5501
Fax: 310 214 2285

Fastest928

Sorry, I thought it was a moldex crank. Whitey works at Moldex.

It is a Scat 6 cwt crank??? Call the folks you bought it from and ask for their rep.

Marc

Stan.Shaw@Excell.Net

It was purchased from a person, not a company.

svp928

Stan, give the number in Johns post a call and see if you can find out more about the crank's build specs