lightweignt flywheel failure

[Robert Shafer]

This flywheel was a modified stock unit purchased from Patrick Motorsports for a 1969 911 with a 901 transmission. While accelerating in third gear, I had a drive line failure. When I pulled the engine/transmission, I found the center part of the flywheel pulled out.

The break came at the edge of the washer, used under the G bolts to attach the flywheel to the crank. The washer with the bolts tight and the center of the flywheel were still attached to the crank. The engine is a 2.5 short stroke, probably putting out about 225 HP, 901 transmission with the clutch, pressure plate and flywheel from Patricks. While the flywheel is three years old, it had less than 30 track hours on it.

James, at Patrick Motorsports stated he had not seen a failure like that and had no idea what caused it. When questioned further, he expressed no interest in trying to determine a cause. The little research I have been able to do had come up with one other failure of this type flywheel which was also from Patrick Motorsports. However, that failure was in a slightly different area. It was through the 12 holes just outside the mounting area. James attributed that failure to an unsound workmanship problem when someone drilled 12 holes rather than 9. The funny thing is that my flywheel has 12 holes which I believe contributed to my failure. I wonder how many more of those units are out there.

The flywheel is a lightened version of the stock flywheel and if you are running one, I would be cautious. I am very surprised that Patrick Motorsports has taken such a disinterested approach to this failure.

Buyer beware! Bob Shafer

[SXSMAN]

I've toyed with the idea of replacing the stock flywheel with a light one while the engine is out . Will do a little more homework on it first . Thanks for sharing your problem/story .

Before it failed , did you like how the lightened wheel felt and preformed ?

SxS

[ErVikingo]

Bob,

My Patrick unit (also on a 901 box) failed exactly like yours. I have it here and can take photos for you if interested. Quite scary for my (yours looks the same) as mine blew up at the end of the main straight at Daytona and I had a flash over of magnesium dust (from the case) in the bell housing. It was like an old style flash from a camera. I had a white powdery ash covering alot of parts afterwards.

I did not even try to contact them for a replacement as the last thing I want is a similar problem. Which other one did you hear of (mine?).

Cheers from So. Florida

[Jim Sims]

Looks like a classic stress concentration/fatigue failure. There is an abrupt change in stiffness at the washer edge; perhaps drilling the circle of holes was an attempt to address this. However, this seems opposite of what should have been done to better match the joint compliance. Also, unlike steel, aluminum doesn't have a fatigue endurance limit (stress below which there is essentially infinite fatigue life). I wonder if stress, fatigue and vibration analyses were done during the design of these modified flywheels.

[ErVikingo]

Here's some pics from the day it happened:

[ErVikingo]

[racing97]

I believe that Pelican sells a Aluminum 901 unit that will accept a 215mm disc and has been proven in VARA

regards

[kucharskimb]

I have the 915 version which has 6 drilled holes and the scalloped edges. Was the construction of the flywheel all that different structurally in the area that yours failed compared to a 915 225mm? I can see they look different.

[RWebb]

what parts of your flywheel are Al?

I _have_ heard reports of the Patrick 915 style flywheels failing...

[shbop]

signing up

[wastintime]

You know the other thing to consider is the 911 (pre 964) flywheel was pretty damn close to a racing flywheel, certainly for a stock car. It's HUGE advantage on a 964 or later, and then you just have to worry about overcoming idle issues. With really light early ones though, unless you're racing they're hard to drive and maybe the 901 flyhweels just really can't take the lightening? What was the final weight on that flywheel? It didn't look that light, by that I mean it didn't look like a race wheel.

[JohnJL]

I have a Patrick G50 lightweight flywheel/clutch about to install...lets hope it likes 450hp...

[javadog]

I'm sorry to hear that they didn't take much interest in looking at this problem. I don't think the failure had anything to do with the 12 holes. What kind of radius is present on the flywheel where the outer edge of the washer sits? Does Patrick do any machining in that area? What radius is there on the outer edge of the washer, where it contacts the flywheel?

JR

[mgibrace]

subsribed

[Elombard]

Do they take any thickness out of the area where it broke? Was the lightening performed on a new or used flywheel?

The holes are not part of the break so I dont understand why they had anything to do with it? Maybe because they allow more flexing in the area?

[Shoepop]

[QUOTE=wastintime;4003672]You know the other thing to consider is the 911 (pre 964) flywheel was pretty damn close to a racing flywheel, certainly for a stock car. [/QUOTE./]

That's why I prefer 70-71 901's. They use the latter design 225 MM flywheel.

[ErVikingo]

These are brand new made from scratch (not machined from a regular flywheel) and made of aluminum. The shop found me a better solution and, even with more power and much more use (time) we have not had any issues whatsoever (with the new one).

[Shoepop]

Originally Posted by ErVikingo

These are brand new made from scratch (not machined from a regular flywheel) and made of aluminum. The shop a better solution for me and with more power and much more use we had not had any issues whatsoever.

Juan, you lost me on this one

[ErVikingo]

Try now (I edited my post), keyboard went wacky and a couple of words were skipped (perhaps my brain too!)

[aws]

The early 6 bolt flywheel is famous for the bolts coming loose if the engine is rev-ed over 8000 on a regular basis. I remember a quote where the factory had to call Brumos to remove a flywheel they had installed a certain way to keep it from coming loose. There were no details as to HOW Brumos attached it. I have for years used new bolts, gone 5lbs heavy on the torque setting and used red loctite. In that time I had one lightened 6 bolt flywheel come loose. I have never seen a failure like these. My opinion is that the problem is the harmonics, not the component and I feel the later model 9 bolt flywheel was the factory's attempt to address the problems. Patrick has told me they are very careful how they attach flywheels, chase all the threads and clean with carb cleaner, use new bolts and loctite, use the roll pin on the later 9 bolt cranks, torque 2 bolts and then start loctiting the other bolts, then remove the original bolts and loctite them to keep loctite from getting between the flywheel and the crank. I have used these methods but I know they are no guarantee the bolts won't come loose.
Tilton quit making aluminum flywheels because the metal would yield at the mounting point and they had too many problems with the bolts coming loose.
One thing I will say is that from now on all the used early flywheels I use are going to be magnafluxed!!!