964 Crankshaft mods

NoEardGoat · 10-15-2008, 07:14 PM

I am rebuilding a 964 motor. I know the 993 motor's crank doesn't need a balancer like the 964 crank. Is there something I can have done like balance, etc. so that I don't need the balancer anymore?

Any other things I should do to it while I am in there? Ball park prices would be very helpful.

turbobrat930 · 10-15-2008, 08:08 PM

I think that the 964 crank is internally balanced....meaning there is no balancer to get rid of. The balance is in the counterweights... not on an external pulley. If I am reading your post right. I could also be wrong.. But when people use the 964 crank in the older crankcases, they dont need to put a balancer on.

Cupcar · Cupcar's Garage

A synopis of the Porsche literature on this topic, make what you wish of it:

The 993 crank is stiffer since the crank webs were increased in size from 7.9 to 9.4 mm, thus the 993 crank is 2.2 pounds heavier.

The above stiffer crankshaft plus lightening the pistons by 55 gms each and the rods by 112 gms each allowed the elimination of the vibration dampener.

sten gr · 10-19-2008, 04:20 AM

Hello I to have a couple of questions regarding this.

Does this mean that if you chose to use lighter pistons and lighter con-rods, you can skip the balancer?

And if we want to use the engine for racing, is there any need of mods to the oiling system on the crankshaft?

Thanks
Sten

turbobrat930 · 10-19-2008, 10:21 AM

Quote:

Originally Posted by sten gr

Hello I to have a couple of questions regarding this.

Does this mean that if you chose to use lighter pistons and lighter con-rods, you can skip the balancer?

And if we want to use the engine for racing, is there any need of mods to the oiling system on the crankshaft?

Thanks
Sten

Sten, What balancer are you referring to?? There is no balancer on a 964 or 993 crank. The crank is balanced as an assy by shaving metal off of the counterweights.

As far as any oiling mods go, there is a center main bearing mod that you can do as well as cross drill the crank. Use the search button, and you will find several post about it....

sten gr · 10-19-2008, 10:55 AM

Hello, I believe the pulley for the power-steering/AC compressor is a sort of balancer?
My 92 RS got no AC or power-steering, but still it has the pulley, I Haw been told its there for damping resonance in the crankshaft.

BURN-BROS · 10-19-2008, 11:50 AM

Quote:

Originally Posted by turbobrat930

Sten, What balancer are you referring to?? There is no balancer on a 964 or 993 crank. The crank is balanced as an assy by shaving metal off of the counterweights.

It is a harmonic damper, not balancer and was used on the 964's .The crank is balanced by itself and rods, pistons, pins within a specified weight are used to minimize imbalance.

I would crossdrill #4 main, have the main bearing modified and possibly knifedge the crank.

Henry Schmidt · Henry Schmidt's Garage

The 964 crank is a POS. I would sell the stock 964 crank to an end user with a dead crank ($1500-$2,000) and install a GT3 crank. ($1,880)
Stronger, full counterweights and uses stock 3.0 SCC rods. ($200 on Ebay)
The only issue will be deck height and that can be cured with a special piston design.( JE about $1000)
You will also need a GT3 front pulley.
As suggested by Aaron I would advise cross drilling even the GT3 crank.

sten gr · 10-20-2008, 08:07 AM

Thanks.

safe · safe's Garage

Quote:

Originally Posted by Henry Schmidt

The 964 crank is a POS. I would sell the stock 964 crank to an end user with a dead crank ($1500-$2,000) and install a GT3 crank. ($1,880)
Stronger, full counterweights and uses stock 3.0 SCC rods. ($200 on Ebay)
The only issue will be deck height and that can be cured with a special piston design.( JE about $1000)
You will also need a GT3 front pulley.
As suggested by Aaron I would advise cross drilling even the GT3 crank.

1,880 for a new GT3 crank?? That's surprisingly cheap.

Correct me if I'm wrong, but that crank would also fit in 3.2 case? What displacement would you end up with?

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by safe

1,880 for a new GT3 crank?? That's surprisingly cheap.

Correct me if I'm wrong, but that crank would also fit in 3.2 case? What displacement would you end up with?

The current price of the GT3 is remarkably cheap. The thing to remember is that Porsche is notorious for offering new part numbers at a reasonable price then jack the price to the moon.
The GT3 oil pumps were selling for under $ 1,000 a year ago and now they are almost $2,000.

Yes the GT3 crank will fit the 3.0-3.2 cases just like the 964 and 993 cranks. The main issue is oil pump clearance so caution is needed.
The GT3 crank (76.4 mm ) in conjunction with a 95 mm bore would yield a 3250 cc 98mm bore is 3450 cc 100mm bore 3600 cc 101.5 mm bore 3700 cc.

jpahemi · 03:47 PM

Henry:
That $1800 price, is new OEM dealer price?? 996 & 997 is the same part?? Reading your thread about dropping this crank in a 3.2 case with 98 mm pistons is very tempting. Is the oil pump clearance isolated to each application? Is there any rod clearance issue with the cylinder bases on the 3.2 case ?
Regards,
jp

PS. as for the deck height, I'm guessing you can't use off the shelf 98 mm Mahle pistons; is this due to the wrist pin location on the piston?