New problem with 3.6 case
 

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.

http://forums.pelicanparts.com/uploa...1127492875.jpg http://forums.pelicanparts.com/uploa...1127493921.jpg

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

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

Re: New problem with 3.6 case
 

including 3.8 Varioram?

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

Re: Re: New problem with 3.6 case
 

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

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

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

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?

Henry,

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

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.

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

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.

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

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!

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.

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.

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

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.

Quoted directly from :

Motor Age, June, 2005 by Eric Bakke

[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.

What doesn't make sense to me if the DMF is for dampening the crankshaft for durability, then why was it eliminated in all the racing versions of the 964 engine, and all the performance versions like the 964 Euro Carrera RS and USA 964 Cup cars? The latter of which are basically identical to the regular production 964 engines internally.

When you swap out the DMF on a 3.6 for a light weight set-up, you get rotational noise from the trans with the clutch released in neutral. The G-50 trannies are noisy in general compared to a 915. This is the main reason for the DMF on these cars. It allowed them to eliminate the dreaded rubber-centered clutch discs.

I'm not saying that a DMF isn't used for that purpose in other cars. It would surely help on a 964 motor. But clearly the front pulley is enough to take care of things without the DMF.

Who said durability ?
You are concentrating on effect not cause. Reducing vibration is the reason less noise is the result.
Eliminate the "dreaded rubber-centered disc" and replaced it with the "dreaded rubber-centered flywheel".

If it is "clearly enough", why the excess vibration causing trans noise?

This discussion is the reason I keep reading and following this site. Not only learning about important details, but the hows and whys from different points of view.
Thanks

good info here - so if you are rebuilding a 3.6 - seems it would really make sense to shuffle pin the case... Don't skimp in that area.

That crack is familar, but odd. It is familar in that it is in the thinest cross section of the web, but odd in that one would think that it would caused by longitudinal force. Applying such force would seem difficult without leaving some telltale mark...a harmonic vibration would seem plausable. The
most likely candidate (for me) is that the crack was there from
the get go....at the machine processing.....which is why we (aircraft industry) PT parts after machining.

It is also familar in having a nice sharp edge from which to propagate. Increasing the strength (or crack ressistance) could be accomplished by radiusing these edges, then shotpeening the whole works.....but cleaning the used shot would be a he!! of a challenge, but just a .03-06 radius would help.

The pictures we are looking at are two different cracks. We have two cases with two cracked webs per case totaling four cracks per case. Same webs #5, #6.
Each web is cracked at the top and bottom case through bolt.

Not likely that both cases were machined with this type of flaw.

i just read on the LUK and Sachs Website ,the reason and Function for the DMF , it is in German so i try :
The mainreason to install a DMF is to dampen the noise of thr Gearbox created by the resonance of the Crankshaft in very low speeds .
The second reason is to allow the Engine to idle in lower RPMs for lower Emissions .
Third for creating Torque in lower RPMs and keep the Engine speed while shifting .
It has nothing to do with the Torsion of the Crank but to overcome the Pauses between the Firing Cylinders in low RPMs .
I have a close Friend at Freudenberg ( producer of the DMF in 964 ) he told me the same .
And again like Tyson says , all High performance Porsches dont have DMF , the Cup Cars have 450 HP at 8500 RPMs , once a Year the overhaul the Engine and they almost never have to change the Crank or Case , the cases you show had other Problems ,who knows what happened to them .
Harald
Harald

ok so say the DMF is not involved; why does this not happen in heavily raced/modified 3.2s? torque and stroke, or a fundamental case design or manufacturing difference?

On the contrary, there is a good probability. The design & the lack of hand finish lend themselves a weakness in that area.
The only thing I can see that would tend to discount my theory is that it is a casting and durring machining, it is not subject to near the built in stresses of a billet or forging.
I'm not adamant about this, but if forced to bet, that's the way I'd go. I've been in inspection for 30 years, in NDT & out....seen more cracks than a porn .....er, nevermind.


We make thousands of complex machine parts each year.
Defects come and go in a random fashion in certain areas of a given part.....which is why we do NDT on every part.
We don't do this to waste money but to insure the reliability of a part...even then, things get by.

I just spoke with the smartest ,most experienced Porsche engine builder I know and he tells me two things.
1)993 Cup cars came with harmonic balancer and they raced with them. Some teams that removed them had cracking problems. {I tried to verify this but have not gotten a call back}
2)He has seen many of these cracks and his theory is that the crack is caused by engine vibration. Quote " these cracks are most assuredly caused by hi RPM harmonic vibration"
Andial before they were Motorsports, came up with a modification to prolong the life of the case. As of yet I don't know what that mod is.

BTW, he also said he saw these same cracks in 962s.
The factory never ran a harmonic balancer on the 962. Perhaps they should.

Apparently, if you run high enough RPMs and HP you will see this type of cracking.

same engine builder's experience with the 3.2s? Thanks for all this, Henry, it is AWESOME info.

hallo
very true , i looked it up in the Specs from my old Cup car , as you see it says at Nr. 4 :
" Schwingungstilger " in Riemenscheibe integriert
harmonic Balancer in V-belt disc integrated
here is a scan .
It is strange but the normal 993 RS didnt have one .
Haraldhttp://forums.pelicanparts.com/uploa...1127946590.jpg

Henry.. have you seen this sort of near failure in smaller displacement engines ..3.0 or smaller?. Dan

Duh... read your original post.. that answered my question. Dan

Henry,

Would you venture to guess a what RPM or horsepower level one would expect cracks to occur?

Tinker

Henry...after looking at the pix of the crack....is there a possibility that there was too much end play in the crank?
It appears that the crank may have "walked" back and forth to put pressure on the webbing.
If it did...the crack would be just where it is.
In other words...the crank "worked" the metal inside the bolt perimeter to create a time related crack.
Does this web hold the end play bearing?
Bob

Crankshaft end play has in no way contributed to the cracks we are experiencing in these cases.
The number one main bearing is used to determin crank end play. These cracks are being seen in the number five and six bearing webs.

A couple of points:

Dual mass flywheels are primarily used to isolate vibration from various sources. On the BMW side of things, the E36 318 used a dual-mass flywheel - but only on the cars with Air Conditioning installed. Presumably, the DMF helped to isolate vibration caused at low RPM from the higher compression four cylinder engine, combined with an idle load on the engine when the AC was on. Not a performance addition at all, but merely a comfort. I would think that all race cars would not have a DMF, as they are complicated, and quite heavy.

As for shufflepinning the 3.6 case, you may want to ask around about that. I remember hearing (probably from Walt at Competition Engineering) that the early aluminum cases are susceptible to cracking when they are shufflepinned. The theory behind this is that the case itself becomes too stiff, and can't relieve the stresses from both the power and the heat output. The result is that the actual aluminum metal cracks to relieve the stress. The magnesium "loosey-goosey" cases don't have this problem because they naturally bend all over the place.

I'm not sure what caused this particular crack in these 3.6 cases, but indeed perhaps the design is one of too much stiffness, rather than not enough actual strength.

-Wayne

Assuming high RPM usage (over 7k) would knife edge, lighting up, and balancing a 964 3.6 crank help workaround this problem when NOT using the harmonic Balancer?