Bad weekend at VIR.... snapped the crank in the car.

[Cobra4B]

Just got done unloading the car at my dad's place... fought the car all day yesterday at the UTCC and got no laps in... car snapped a belt in the warm-up session. Thinking it was a bad PS pump I ran all over Danville getting parts and got it all fixed, then on the first lap of the last session it snapped another belt. Then testing it in the paddock it snapped a 3rd. The car has an odd accessory layout and has a long run of belt (a little over 2') accross the top from the PS pulley to the alternator pulley... this can get jump at higher RPMs and there's a belt slop limiter rigged to keep it from chucking belts. That limiter had broken off so I fabbed up a new one and thought I had it fixed.

Car was vibrating more than usual and oil temps were high... but it was 102 today and 100ish yesterday.... car was doing this yesterday as well. So I look down and see it was 287 (the car had never been over 272 before even in full boogie in 100 degree weather)... I'm coming down the front straight and think "If this hits 290 I'm quitting". Well as I lay down the power coming out of 2... "CLANK!!! ching ching ching...." Car shut-off and since I was tracking out I just turned left and drove right off.... here's the resultant carnage.





Funny thing is the car just made 341 rwhp w/ a 12.8:1 tune and reduced timing at Sneed's Speed Shop and was running better than ever. The bottom end was never touched and is the original stuff the car has had since being built in '97 or '98. Oh well it was only a matter of time spinning a stock 2-bolt bottom north of 6000 rpms.

-Brian

[eric1h]

Damn that sucks! Just pull the ls6 out of your new vette toy! Lol

Ok not funny, but an odd pattern for us panoz owners lately!

I guess I wont ask how you did in the UTCC then ;-)

[Cobra4B]

So would the thrust bearings have worn out first to allow the crank to start walking? On Friday, the few laps I made before belt chucked, the car was vibrating more than normal and I was having trouble shifting which I never have... mostly upshifting. So Im thinking that under acceleration the crank (and flywheel that is of course attached to it) would walk back and prevent the clutch from 100% disengaging.

In the pits the crank pulley wasnt wobbling and belt allignment was fine... Im near certain that all the issues I was chasing Friday were just symptoms of the crank walking on its way to snapping. I guess the walk induced vibration and the harmonics snapped the crank... not the RPM or use/stress.

Thoughts?

[NZGTRA17]

Originally Posted by Cobra4B

So would the thrust bearings have worn out first to allow the crank to start walking? On Friday, the few laps I made before belt chucked, the car was vibrating more than normal and I was having trouble shifting which I never have... mostly upshifting. So Im thinking that under acceleration the crank (and flywheel that is of course attached to it) would walk back and prevent the clutch from 100% disengaging.

In the pits the crank pulley wasnt wobbling and belt allignment was fine... Im near certain that all the issues I was chasing Friday were just symptoms of the crank walking on its way to snapping. I guess the walk induced vibration and the harmonics snapped the crank... not the RPM or use/stress.

Thoughts?

Brian, sad to see another work horse bite the dust!!

I have raced on an absolutely worn out crank thrust bearing, with no adverse issues whatsoever in a 6500rpm engine. It would be unlikely that this caused the shifting issue as the airgap on a single plate clutch is usually pretty generous.

It may well be that the block cracked first (common with the std block as discussed in numerous posts) and/or the crank had started cracking but not completely failed and that either of these caused the vibe. Either way it will be difficult to seperate the "cart from the horse" now I suspect due to collateral damage.

I am pretty sure that I have previously posted that Ford put out a memo on the 5.0 in 50oz balance state advising that continuous rpm over 6000 would cause crank failure due to cyclic fatigue. This is the reason we chose to build 36" long primary tubes into the headers and keep peak torque and hp rpm below 6000.

Regards the front serpetine belt, not sure about other 5.0 pedallers, but we have not had any issues with this as yet. I always fit a new (pre stretched) belt prior to an endurance race and make sure that the tensioner has some take up for additional stretch as the race progresses.

Will be interested to see what engine option you pursue now Brian. Trust the AFR heads etc have survived the engine failure and live to see another days racing.

Kel.

[Cobra4B]

Thanks for the reply Kel.... I believe you are right that it will be near impossible to figure out what failed first in this case. I knew something was wrong from the get-go w/ the vibrations and higher oil temps on Friday. Wish I hadnt spent so much time replacing PS pumps thinging the shaft play was excessive when all the new pumps had the exact same thing. I thought the in-out 1/16 inch play was what caused it to chuck the belt so I attacked that first. Even during all of that I kept asking myself what was vibrating and what was causing the high oil temps.... I figured the PS pulley may be causing the vibe. At the end of the day you have to start somewhere w/ the most obvious (or what I assumed obvious) problem and work off of that.

Leaning toward a Dart 4-bolt main iron block 306 w/ the existing stuff we have now. The car made all the power were allowed to make.

My apostrophe key is broken

[eric1h]

Brian, I had similar issues with my m3 race car... And it was the pressure plate that worked loose and would cause a NASTY vibration.... Luckily I caught it in time and didn't damage the motor, but the symptoms sound very familiar! Sorry to hear the bad news!!!

[Cobra4B]

Clutch was my first thought and in the back of my head I hoped that if it was the clutch, and it did fail, that Id be able to keep my feet!

I think the crank was partially cracked or something like that was causing the vibrations. Clutch works perfectly in the pits and it shifts into all gears w/o issue.

[Rich F]

Brian,
Sorry you broke this weekend. Never any fun with it happens. Sounds like you got the most you could have out of the lower end on this one. Good luck with the rebuild and repair.

I'm a couple of months ahead of you after an April explosion. It's a long couple of months while your pulling it together.
Hope your back together soon,
Rich

[eric1h]

Man I am starting to think these car are cursed!

Brian when my pressure plate backed out the car would run fine in the pit also but it would shift HARD into 3/4 under load... So you never know... Be interesting to see what's going on.

[Blue Streak 21]

Brian;
What a bummer!!! Sorry to hear of your motor's demise. Thanks for sharing your experience as it may help us if we face similar problems on t he track.
I thinking that we are pushing these mostly stock blocks past their intended envelops. I've had issues with a stock block, and wonder if I should have gone with a Dart block or Ford Racing block this last time to get a 4 bolt main. I stayed with the stock block (cost reasons), and time will tell if I should have changed. I don't spin it over 6000 rpm, and have gone with an internally balanced rotating components. THis may help reliability some, but I think my use is pushing the limits of the stresses these blocks can take. Going to an LS motor might be better, or maybe you just get another set of problems/issues. Not sure.

[Panoz26]

Brian, sorry to hear. Never a good time. Keep us posted.

[Ed Curtis]

Hey Brian - Just got the link from dad...

I'm sure we can come up with a bullet-proof short block combination. I'll get the info back to you guys later today on a few ideas...

Ed