New problem with 3.6 case

[Henry Schmidt]

Well the 3.6 has a new problem that we have not seen in previous 911s. We have 2 3.6 engines M64/01 and M64/50 in the shop right now. The 5 step in house process we used to identify these cracks is Zyglo.
Step 1: cleaning
Step 2: apply penetrant
Step 3: remove penetrant
Step 4: apply developer (in this case dry developer)
Step 5: inspect with black light
Here are the results.



TWO THOUGHTS :
1) I HATE 3.6 ENGINES
2) SHUFFLE PIN 3.6 CASES FOR RACING

[blue82coupe]

Henry.. is that from an engine that was raced? Or was it from normal usage.Dan

[blue72s]

Originally posted by Henry Schmidt
I HATE 3.6 ENGINES

including 3.8 Varioram?

[Shuie]

damn the luck. What do the two motors have in common? Any more details or thoughts on the cause?

[Henry Schmidt]

Originally posted by blue72s
including 3.8 Varioram?

I guess hate is a very strong world. What I should say is I just like the older 911s. Old School or something.

[HawgRyder]

Henry...we used dye penetrant all the time on aircraft.
It is a great way to find faults...however...some of the cracks found were not all the way through.
Dye penetrant will also find surface cracks or lesions (sp?)...the type of surface abnormality that is not bad and will not run or expand to become a "bad" crack.
Bob

[Henry Schmidt]

HawgRyder thanks for the input. I believe that these cracks so all the way through.
See pix.

[Henry Schmidt]

Originally posted by blue82coupe
Henry.. is that from an engine that was raced? Or was it from normal usage.Dan

Hi Dan
My feeling is that racing only shows us week features of a specific design faster than we might see under normal use. In other words " a weak design is weak whether you stress it or not."
It appears to me that the webs at the through bolt holes are too thin.
Possible stresses not see in other Porsches are excess vibration from a crank imbalance exacerbated by the removal of the harmonic balancer and dual mass flywheel, too much low end torque, too much twisting in the crank? Who knows?

[blue72s]

Henry,

You didn't answer my question. Do the 3.8 Varioram suffer from the same cracks as the 3.6?

[Henry Schmidt]

How would I know?
I guess I miss understood your question. It was after all ambiguous at best. We build primarily pre 89 engines. Perhaps your question should be directed to someone who builds the type of engines your question deals with.

[Speedster94]

I dont think you will see that on the 993 Engines as they have a different Crank and they dont need a balancer . The Doublemass Flywheel is not a balancer for the crank but for the main shaft in the Gearbox . The 964 /965 Engines have a balancer on the Beltside and some People take them off , sometimes the cranks did brake , obviously sometimes the case too .
harald

[Henry Schmidt]

The dual mass flywheel is definitely a balancer for the crank. It was designed to help the engine run smoother at lower RPMs.
The flywheel is not indexed to the transmission mainshaft so it can have no effect as a balancer for the mainshaft.

Of corse this is just my opion. Perhaps you could explain (to me) how a flywheel can balance the mainshaft.

[blue82coupe]

Hey Fellas.. according to dear old Bruce Anderson.. the double mass flywheels purpose was to dampen engine vibration,that was causing the transmission to rattle. This info was pulled his 911 Performance Handbook. Dan

[Tyson Schmidt]

The dual mass flywheel was used to dampen the noise that the G-50 trans is famous for. It really isn't about dampening frquencies related to crankshaft longevity.

The front pulley on the 964 served that purpose. The 993 didn't need it due to the stiffer crank and lighter rods.

So in effect, you're both right. Harald likely meant what I posted rather than "balance". Substitute "dampen" input shaft noise for "balance" input shaft. Close enough in my book for a guy who speaks English as a second language.


In regard to the cracked case, It makes me see why they switched to a much higher torque spec for the through-bolts on the 964/993 case. Things obviously move around quite a bit more with the extra torque output and longer stroke.


Thanks for the heads-up Henry!

[Tim Walsh]

Hmm.. interesting, and I belive porsche is still using that case for their higher end motors, the twin turbos and GT3's. I wonder if they're encountering this as well.

[Henry Schmidt]

The problem seems to be definition not function.
A harmonic balancer is a vibration damper.
A dual mass flywheel is a vibration damper.
Can we call a dual mass flywheel a harmonic balancer?
I believe we can , but opinions will vary. It seems that before the DMF, harmonic balancers were only mounted on the front. This was done for convieniece not because that was the only place it would function. Now we know it will work at either end.

The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.

When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.

A dual mass flywheel, or DMF, is made up of a primary and secondary flywheel with a series of torsion springs and cushions. There is a friction ring located between the inner and outer flywheel that allows the 2 flywheels to slip. This feature saves the transmission from damage when torque loads exceed the vehicle rating of the transmission.

The function of the DMF is to isolate the torsional crankshaft spikes created by high compression ratios. The DMF isolates the frequency below the normal engine operating rpm's during startup, acceleration and shutdown.

[Speedster94]

Hallo
Yes , exactly , the DMF has nothing to do with the Torsion of the Crank . That is the Job of the Harmonic Balancer on the beltside . The Damage you see on the Case is most likely from a defect or not mounted Balancer on the older 3.6 crank .
In the newer Engines you dont have a balancer , even not in the 996 Cup- Cars with 12.8 CR and 450 HP in a NA Engine and i did not hear of any Damage on the case yet ,nor on the Crankshaft . So i think the newer crank makes a big Difference .
Harald

[stevepaa]

So will you weld these cracks as a repair? Or is it too far gone. I had Ray Litz weld up some heads with cracks and they worked well.

[Henry Schmidt]

Originally posted by Henry Schmidt
.............The function of the DMF is to isolate the torsional crankshaft spikes created by high compression ratios. The DMF isolates the frequency below the normal engine operating rpm's during startup, acceleration and shutdown.

Quoted directly from :

Motor Age, June, 2005 by Eric Bakke

[Henry Schmidt]

[QUOTE]Originally posted by stevepaa
So will you weld these cracks as a repair? Or is it too far gone. I had Ray Litz weld up some heads with cracks and they worked well. [/QUOTE

Weld and shuffle pins??
Not certain.
What is certain, these will not be used in a Turbo or race engine.