Hey everyone,
I'm in the midst of a 2.5 8 valve na rebuild that involves forged pistons and molnar lightweight rods as opposed to the pca legal rods along with using a fidanza aluminum flywheel.
The engine has a 272/272 custom grind cam as well. I won't go into everything, but my question here is, can anyone think of a reason not to use a S2 harmonic balancer on the crank?
I have one on the shelf and I'm having the rotating assembly balanced. I figure it can't hurt, but don't know if I should source an S harmonic balancer instead.

Thanks in advance for everyone's input!

MG

 

Hi MG,
I cannot offer a comment on using a harmonic damper.
I would recommend balancing the fidanza aluminum flywheel with the pressure plate. The fidanza's are notoriously out-of-balance. I am assuming you had the crankshaft balanced along and the new piston and rods are balanced from,the supplier.
Tom

 

Can't hurt. Only downside is that an S/S2 unit are 30+ years old...RS Barn makes a new production one though.

 

Tom,
The shop that is doing my balancing wants to balance everything from the pressure plate forward to the harmonic damper including requiring the rings for the pistons.

I will weigh each rod and piston tomorrow to verify that the set is equal in weight.

V2,
I like the idea of the RS barn one, but this S2 harmonic damper has been staring me in the face for four years…

 

I apologize for the wait.
Part weights are as follows:
Yes, I weighed every part and they were all equal by golly!

CP Carrillo forged pistons as designed for the 944 spec class NASA-944-3937
537 grams each.

Matching wrist pins
144 grams each.

Molnar lightweight forged rods PRH5906MNB4-A
681 grams each.

This is a 668 gram reduction of the rotating assembly.

I have an S2 harmonic balancer on the shelf, but it’s rubber is cracked all the way around.

I can source a 944S harmonic balancer, but is there anything newer available?

It looks like RS Barn is out of business…

 

My opinion is that lack of the harmonic balancer is not a deal breaker in the 2.5L 8 valve NA. I run a race engine w/o a harmonic balancer, rpm range 4000 -6500, without any issues. The inner valve spring is not a Porsche OEM 951.

 

Give these guys a shout if you want a replacement or possibly get yours rebuilt.

http://bhjproducts.com

FWIW - they built them for RSBarn IIRC.

 

I copied this paragraph from the bhjproducts website, technical section on why a harmonic balancer is needed. This is the reason Porsche installed a harmonic balancer on the 944S, 944 S2, and 968. All these engines have chain driven dual overhead camshafts.

• Cam Chains #8212; Cam chains can take a beating from the torsion peaks. Same for cam gear drives. The vibration motion tries to make the cam drive do the same motion and jerks the chain back and forth. If this motion gets through to the cam, it doesn't help cam dynamics and can also show up in the spark scatter with cam driven distributors.

 

The 968 didn't get one of those dampers, because the 968 got a dual-mass flywheel instead.

However I think it's just as likely the 16v models got the dampers because of the expected higher RPM use than the 8v tractor engines.

 

Technically they are, but Pete Fitzpatrick has three (3) dampers left in stock as of today. When those are sold then BHJ Products will sell direct, but the lead time could be 90 days or more. Price is $511 plus $39 shipping. Contact rsbarnpete@gmail.com. I bought one today.