Bad weekend at VIR... snapped my crank... thoughts?

[Cobra4B]

This is in my Panoz TTS car, but I figured Id post in here because many AI folks use SBFs. The motor was out of an Aussie Ford Falcon sedan (Panoz purchased a batch of them back in the late 90s when building the cars). The car was making 341 rwhp @ 6500 rpms w/ the following mods: AFR 165s, Ed Curtis cam, Edelbrock Performer RPM Air Gap manifold, Pro-systems Road Race carb, etc. etc. Basically we deleted the fuel injection and did heads/cam/carb.

 

 

I fought the car all day Friday 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 Saturday and 100ish Friday.... car was doing this Friday 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 14 year old track/race motor with a stock 2-bolt bottom north of 6000 rpms.

 

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, in addition to the vibrations, 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?

 

Thanks,

 

Brian

[TurboShortBus]

Assuming that your Ford block is the same as those available here, the thrust bearing (just one) is only about 1/16"-1/8" thick on the sides, so even without it, the crank won't move too far before it makes contact with the center main cap/web (where the thrust bearing is located); this is where the party would come to an immediate end. And, if the thrust bearing did happen to completely fail and allow the crank to walk, it could affect the rod bearings and related crank journals.

 

I know drag racers with automatic transmissions who have problems eating up thrust bearings while building boost at the starting line (as the converter balloons and forces the crankshaft forward). In a manual transmission application, you could kill a thrust bearing by having an input shaft that is too long; if it bottoms out in the pilot bearing before the mounting face of the transmission hits the bellhousing, then tightening the trans-to-bellhousing bolts forces the crankshaft forward and preloads the thrust bearing.

 

I personally know a couple of people who have broken 5.0L crankshafts, both while racing at the track and while just driving on the street (with there being absolutely no good reason for the latter). Both were dismissed as "one of them things," and no autopsy was performed in either case. The short blocks in both cars were bone stock.

 

I wouldn't dismiss the engine's 6000+ RPM range and resultant stress/harmonics as the cause for a bottom end failure, especially if it's an OEM short block. They simply aren't designed for that kind of use.

 

For the future, as for addressing that long portion of unsupported belt, take a look at the OEM belt routing on a 1994-1995 5.0L Mustang in that same area. I'm not sure how your "belt slop limiter" is "rigged" (not my words), but there is a possibility that it could be responsible for the broken belts.

 

Mark

[Cobra4B]

Under load the long section of belt would whip and throw itself off of the PS pulley. The belt slop limiter stopped it from being able to do that.

 

Now that I know the crank was cracked all weekend and was on its way out it could have been many things causing the belt to hit and get cut or jump off.

 

Going to most likely go w/ a 4-bolt main 306 Dart iron block... need a motor that can take 6500 rpms w/o issue.

[Trevor57]

You need a 94-95 ps bracket that has an idler pulley for the run over to the alternator. At least you won't have belt problems.

[TurboShortBus]

You need a 94-95 ps bracket that has an idler pulley for the run over to the alternator. At least you won't have belt problems.

It looks like he already has the 94-95 PS/AC bracket, based on the unused integral coil mounting bracket that I'm seeing between the distributor and the PS pulley. Somebody may have chopped off the idler pulley mount, though.

 

Mark

[Cobra4B]

Yeah an idler coming off of the PS bracket would be the ticket but I didnt have the time or parts etc. to try to fab it up at the track. I looked at a buddys AI mustang and he had the older fox body accessory setup and the tensioner came off of the alternator bracket and the tensioner was right in the middle of the top belt span... made more sense then having the tensioner down where I have it now and running a seperate idler.

 

I thought maybe my tensioner was bad and found that it was from a 94-95 and unfortunately nobody had one around Danville. I had no idea there was supposed to be an idler up there... wonder why the panoz guys removed it... or maybe it wasnt there in the Ausie Ford Falcon thing b/c the car was right hand drive and the intake manifold etc. was flipped to the other side.

 

Anyone have a picture of a 94/95 setup?

[Cobra4B]

Ok... found this picture

 

 

The PS bracket on my engine isnt cut/modified.... it simply doesnt have an idler provision. Ill make sure to get a new PS bracket to fix the problem the correct way.

[B-MAC]

You are on the right track for a remedy, i.e., Dart block, the OEM 2-bolt blocks have very thin webbing around the mains and crack. I went through three OEM blocks w/the same mild HP and results before I took the remedy.

 

MacMillan.

[Ed M.]

You should also consider Ford's BOSS 302 block:

http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=9085

 

Ed

[Cobra4B]

Thanks for the link... I was considering that one as well.... is one better than the other? (Dart vs. Boss 302).

[edhunter]

Brian; I saw the Panoz getting towed in, sorry to hear of your problems. I was in TTS as well. Regarding the engine, if I was buying new I'd get the new Dart SHP block. It's priced to compete with the BOSS block but the guy that built my last engine said it wasn't much different than Dart's much higher priced block (Sportsman maybe?) He said the Dart could go all the way to 4.180 bore whereas the Boss no larger than 4.125. Also apparently the Ford people (bean counters more likely) shortened the cylinder just a hair so notching for strokers is no longer needed. Good in a way, but strokers already can experience more wear from piston rocking in the normal stock cylinder, so shortening it some more is not good. All that said, I run a BOSS block 342, zero balance SCAT forged everything rotating assembly. VIR was only it's second time out on track, and I'm very happy with how it ran. My cam is done at 5600, so I shift around 5800-6k. I built the car for AI so I wanted to keep HP low with a good torque curve. According to the dyno this weekend I got just that!

Good luck getting the car on track, hope to see you there in October.

[Cobra4B]

What about building a 351 detuned to 340ish rwhp? It'd make lots of torque.

[TurboShortBus]

What about building a 351 detuned to 340ish rwhp? It'd make lots of torque.

If you can deal with the ~50 lbs extra weight (over your stock 302 block) and either reworking your existing headers or getting new ones, then it's a good option (although a Boss or Dart 302 block will be just about as heavy as a stock 351W block, so it's a wash). Also, compared to your 302, you cannot reuse the intake manifold, distributor, or oil pan with a 351W. The SN95 accessory brackets will bolt up fine, but keep in mind that they move up and out with the heads (due to the increase in deck height), so the accessories will make the assembly a bit taller and wider (~3/4" taller and ~1 1/2" wider). Hood clearance may or may not become a problem with the air cleaner.

 

Mark

[Cobra4B]

Thanks Mark.... the Panoz GTS cars allready come w/ a 351 setup so space/parts are a non-issue.

[TurboShortBus]

Thanks Mark.... the Panoz GTS cars allready come w/ a 351 setup so space/parts are a non-issue.

So, which engine do you have now? Your mention of considering a "306 Dart iron block" had me thinking that you already had a 302 in the car, but then you mentioned building a detuned 351 that will make 340 to the tires, which could be what you already have in the car. I'm apparently having problems keeping up...

 

Mark

[UBR]

We broke a stock block 5.0 in our AI car 2 years ago. Have pictures that match yours almost exactly. The stock 5.0's are known to have thin webs and flex under load. We dyno'd the morning it broke. 319/327 so we weren't making big power.

 

Switched to the Boss 302 with a stroker crank (347) GREAT block. We bought an assembled short block and used our old heads as we only had a 3 week turn between races. The Boss blocks have incredibly thick webbings and journals compared to the stock 5.0. They are rated by Ford to over 750 hp.

[Cobra4B]

The motor in the car that broke was a stock 302 out of a Aussie Ford Falcon sedan w/ AFR 165s, cam, pro-system carb, etc. etc.

 

UBR - Any wrist pin or ring issues running the 347?

[UBR]

UBR - Any wrist pin or ring issues running the 347?

None... Sadly, we just had to put a new Boss 347 in. We sliced a lower radiator hose at Brainerd in June. Pushed all the water out and cooked the motor before we saw the gauges pegged. (Go ahead with the comments about getting lights or checking guages more often.. We've already said them all)

 

On tear down, the piston skirts had melted into the cylinder walls. Block (with a bore), rods and crank were still usable. We ordered another Boss 347 short block as our machine shop couldn't turn our parts around in time. We'll rebuild the "hot" block this winter for a spare.

 

At the end of last season we pulled the heads to replace the lifters that broke at Nationals. Cylinder walls still looked new. No indication of any ring problems.

 

j

[Cobra4B]

Thanks for the info. I put the car up for sale as is to see if there's any interest. It's my father's car and he's not sure he wants to fix it right now. He's contemplating taking a break from the hobby as he's extermely busy with work. I told him when I finished my TTA Z06 build I'd come and get it (at his place in NC) and tow it up here and tear into it, but we'll see. So if anyone is interested in a really good race car he's asking $18.5k as is w/ spare wheels, hubs, brake rotor rings, spindles, etc.

 

viewtopic.php?f=31&t=36098

 

If we decide to put a new motor in it I'll most likely go w/ a Dart block done out to a 347 w/ the existing heads/carb/manifold and shorty headers since we can only make 340 rwhp for TTS/ST2.

 

The car only weighs 2700lbs wet.