Crank Picture
 

Guys,

Sorry I'm so late to the party. That is a picture of my crank. It was running a Aasco LWFW with a Sachs Sport spring clutch when it broke. During the rebuild Jake balanced both assemblies and I am currently running thr DMFW with a Spec non-sprung plate. Since I am interested in longevity over ultimate 10/10ths performace, I took the safer, but by no means absolute proven route. That said the HP and TQ put out by the Flat 6 3.8 with improved X51 upgrades, makes the advantages of the LWFW a moot point in my opnion. Now if Jake could come up with something to keep my skirt from flying up at 154 at the end of the main straight at Brainerd, I could get into the 40's and be happy!

Lon

Lon,
My Wife goes that fast, actually he highest land speed record is only 153, so you have her slightly beat.. Are you wearing a Nomex skirt? Seemed to work for her. You could always couple your skirt with cloudsurfer's stiletto heels and have a true winning combination.

Anyway, the broken crank issue is being handled.. We finally decided to step up crankshaft production and have units mass produced from true forgings. The testing is going to be long and hard and we can't get it done fase enough. Most cranks we are seeing now are not passing magnaflux tests, even from bone stock street engines with DMFWs. Rebuilding without magnafluxing is like Russian Roulette with these engines. I received another X51 broken crank call last week, it was broken in 4 places, not just two.

Land Speed
 

Jake,

Yes but she does it from a standing start, I comming out of turn 10. Anyway, we'll install a new crank once you get the individual throttle body and new cams worked out! But I'm sure thats another thread.

I am looking forward to all of the tracktime I can get this year. I'll get you a fresh oil sample early May.

I know that this topic is from a few months back, but I was reminded of it while reading some of the other forums.

Are we sure that the rattling sound is coming from the engine? I have read that a lot of other vehicles with similar dual-to-lightweight flywheel conversions have similar rattling and their consensus seems to be that the sound is coming from the gears of the transmission and not the engine itself.

I tend to agree with is hypothesis as it seems to make sense: At idle, clutch out = sound. At idle, clutch in = no sound. So obviously something that changes with the clutch being pressed gets rid of the sound. That means we can narrow the problem down to something that changes when it is pressed.

What changes?

With the clutch in, the transmission and engine not connected. When the clutch is not in, the engine and transmission are connected. I believe that the dual mass flywheel dampens the engine vibrations from going to the transmission. With the light flywheel not dampening these vibrations, they travel to the transmission gears while the clutch is not in and the car is not moving.

The sound does sound like it is echoing from the transmission area and not from the engine itself.

One way to find out for sure: Have someone run an engine with the Aluminum flywheel on it without a transmission connected. :)

Anyone have any thoughts on this?

Has anyone else with the lighter flywheels noticed that the sounds seems to be coming from the transmission, and not the engine?

i never considered that since i figured my sprung clutch disk would settle it down. i'm putting it up in the air Monday to drop the tranny; i'll take a listen with it lifted & see what i think.

i always thought my release bearing was shot or something.....

I now have a 2006 Variocam Plus 3.4L from a Cayman in my 986 with the AASCO / Stage 2 Spec Sprung Clutch. I also replaced the entire arm and throwout bearing when I did the swap, so everything is good shape. Mine makes the same rattle now as it did with my 3.2L.

When I put on the RSS underdriven crank pulley Dampener, it didn't change the sound in any way at all either.

FYI, i was using the LWFW with a spring centered clutch. i'm pretty sure it wasn't a fractured crank, but i haven't opened the motor yet. the engine had 140k miles on it.

The material on the magnetic drain plug that you posted a few days ago look like rod bearing material to me.. This can be from a compromised crank that fractured at the radius of a rod journal and toasted that bearing. This is exactly what happened to Lon's engine, when he sent it to me he thought that it had lost a rod bearing, when it arrived I found the broken crank before I even disassembled it. Who knows, only a teardown will prove what the real cause is.

The sprung center disc only helps with harmonics and frequencies that are sent upstream through the input shaft from the drivetrain. The sprung center disc does nothing to aid in the harmonics generated by the engine that cannot be absorbed by the second mass of the flywheel after it has been removed and replaced with a single mass.

Jake, can the loss of the dual mass flywheel be compensated with an UDP that has a harmonic balancer built into it? like the ones offered by RSS or ATI Racing..?

http://www.atiracing.com/products/dampers/damper_tech.htm your comments will be greatly appreciated.

Gilles, across the street from El Toro base...

.

Nothing makes up for the huge second mass positioned centrally between the engine and transaxle.

Everything helps, but nothing makes up for it completely.

if you were near El Toro in the early-mid nineties I was doing my part keeping you awake at night in those big Helicopters!

Are you referring to chinooks?

CH 46 Sea Knights.. Thats what I crewed and twisted wrenches on at Tustin and El Toro in my USMC days.

Jake,
CH-46, good on ya!
I had the pleasure of flying CH-47 in Australian Army, but we did all our initial & maintenance test flight training in Ft Rucker, AL & Ft Lewis, WA.
I was VERY impressed with US Army guys & their teaching! I'm sure the Marines set just as high a standard.
I wish we had guys like you working on Porsches in Australia.
All the best,
Matt

Newb chiming in... :)

After reading all of this it seems like the safest bet is to stick with an OEM\Factory flywheel but I would still like the assembly a little more performance ready. Jake you seem like the Guru here, have you heard of any problem with the Spec clutches offered or any better brands? I haven't been able to find any other companies offering performance clutches for 2001 986.

I am having a LWFW (and new clutch) installed right now. Should be done by tomorrow.

After reading through this thread (and others), there is no way that removing the DMFW and installing a LWFW can cause crankshaft failure. No how, no way. All production engines are factory balanced to the degree necessary (along with the proper design considerations such as bearing placement and type) to ensure proper and sufficient engine balance.

No engine is in perfect balance, no matter how much time and effort you put into it. Some engines can be in better balance than others but meeting the engine balance criteria to ensure long-term engine reliability is easily met by standard design and production methods.

Harmonics are a red herring in this discusion. Harmonics have very little energy unless a forcing function is driving at one of the harmonic frequencies. Yes, this can happen to a really old bridge in high winds but can't happen in a modern engine because the only forcing function in an engine is the cylinders firing which create the primary or fudamental frequency.

Beyond that, there's nothing in an engine (analogous to the wind in the bridge example) that would drive a harmonic with sufficient energy to cause catastrophic failure of the engine.

The DMFW is meant to reduce minor engine vibration from being transmitted to the body and interior (as part of NVH control), not to keep the engine from self destructing.

What type of clutch are you going with?

You're assuming the aasco unit is balanced. I had mine done this week. The clutch / fw combo were 17g out of balance. 15g of that was the flywheel. That can break a crankshaft.

07proto - I use a sprung spec stage 1

The outer section (approximately 4 pounds (not grams)) of my DWFW was flopping around like a beached whale because the damping material was so worn. That had to create vibrations that were 100x what any LWFW might cause due to out-of-the-box unbalance and its probably been that way for several thousand miles.

Any flywheel that is several grams out of balance won't destroy an engine - or a failing DMFW (with 4 pounds wobbling around on the end of the crankshaft) would be the end of every engine.

I installed a Sachs High Performance Spring Hub Clutch, PN: 88-1861-000-017. Drove it home today, runs and shifts great.

By the way, I skipped replacing the IMS too. If it's gone 90,000 miles, I figure that there is no reason why it won't keep working. Call me an idiot if you'd like, but I'm spending the IMS replacement money on new tires and more track time. :D

How many g's do you think are exerted outward by centripetal force at the edge of a flywheel turning 7300 rpm? 100? 1000?

Try ELEVEN THOUSAND THREE HUNDRED. 11,300g at my redline. That means 17grams becomes 425 lb. Over time, that wobble can absolutely fatigue the crank. It's not forged, it's sintered.