Guess, what did I break?
 

I was autocrossing my sons project 944, I blew a shift badly. I go into the braking zone touching redline 4th gear, after braking you need to be in 2nd. I was having a hard time smoothly transitioning from 4-3-2 so I decided to go from 4 directly to 2 and just stay on the brakes to settle the car and then go to 2, well my brain let the clutch out early. I left a skid mark in the turn. The car was down a touch on power then 4 corners later when you are completely off the gas the car stalled. When I try to start the car the starter is not engaging the ring gear, the starter just spins. I bet I broke the crank...Whats your guess?

Unfortunately for my son the car gets moved to storage as I have other 'car' projects to finish before I look at it. So it will be a while before I know whats broke. But its going to haunt me all winter.

First off I don't know how you broke the crank and the car still ran. Second that's kinda dick to beat on your "sons" car even if technically not his...

He is 12, the car has sat 2 years so I decided to knock some of the rust off the rotors and use up the gas that was in it. He is playing video games instead of working on the car anyways....But I will fix it for him. Im sure when he gets a drivers license he is going to beat up on my gear. I have a few ice racers and track cars for him to drive.

No smoke, no kocking, no loud bang, no fluids on the track the cars rpm dropped and it stalled.

When I got off the gas it stalled, doesnt the flywheel keep the engine turning by the rotating mass helping out? With the starter not enganging the ring gear I figure the flywheel might have shifted due to a crank failure. I cant explain the 4 corners down on power, the stall AND the starter issue without guessing its the crank\flywheel.

Anyways, open to guesses as to whats wrong.

You racing son's car and now needs fixing=moves up list. Usually if if broke, it was going to brake.

no autocross course would have a 944 in 4th gear at redline. I call BS!

impossible that u broke the crank. I call BS!

The autocross is at CFB Namao that used to have the Hercules transporter planes. Its a wide open track on several airstrips. Top of 4th is 98 MPH or 160KPH. My track car runs 220KPH on the same straight. So top of 4th gear in a autocross isnt a issue. They run Races and DE's at the same facility.

My guess is the crank, Im not saying it must be. Take a guess as to what broke with how I described it please.

i'm so jealous of autoX at airstrips heh



if starter is spinning but not cranking the engine over....possible sheared ring teeth or fractured flywheel? or possible that the starter solenoid is busted and it just doesn't push the starter forward.

did the tach ever go overrev beyond 6?

I dont know what the tach went up to, I was looking at the track not the tach when I was braking for the corner as I was really pushing the car to its limits ( I ran 110 seconds, the viper and 993 turbo were 103 and some boxsters were 120 seconds ) This car has some suspension and engine mods......I see the skid mark I left behind when I walked the track. Going from redline 4th to 2 I could really overrev it and I know I screwed up by letting the clutch out early, I heel\toed the car and I heard the revs go up from whatever the engine was spinning when I let the clutch out.

I wasnt having any starter issue prior to the incident and the car was running great. If I sheared ring teeth I dont know how. The car stalled, I rolled to the side of the track incase I was dropping fluids. Then I tried to start the car and the engine isnt turning over, first try on the starter and I heard it spin, no crunch or anything like that.....Im thinking the starter issue is related to the stall issue....Broken flywheel is along my same thoughts of a broken crank.

Here is the previous owners video of him in his new M3, same track. Just before the start of lap 2 is where I screwed up.

BMW M3 Autocross PCA Polar 1040.mp4 - YouTube

I guess they don't call you aftermath for nothing!

I'm going to qualify this suggestion by saying it's simply a suggestion - others here are a lot more experienced than me:

Does the engine turn over from the crank bolt? Just wondering whether revving it high could have made the engine seize, and the starter making a noise but not actually spinning.

Again, I'm not that experienced but I reckon you're on the right track with something in the clutch area - maybe the flywheel bolts have sheared.

Good luck with it.

Mike

I would suspect the flywheel if the engine contiinued to run but lost power. I would also suspect possible head damage maybe a valve trashed

Have you tried turning the crank by hand?

If you let the clutch out too soon then you over revved the engine and bent some valves.

I do not have a clue why it will not turn over. Let us know what you find.

Nice to see an Edmontonian on the board... I used to run on namao quite frequently but got busy with other hobbies.

If you been running autox at Namao you know justin. This is how the 944turbos spank the locals. :) 97.9 on that same course.

944 turbo S at Edmonton PCA autocross - YouTube

I doubt you broke the crank (have you seen one of these monters)... maybe floated a valve and bent one thus it ran weird after over revving.

No clue why the starter would have failed at the same time (coincidence).... but I have seen these cars do some really strange things...

Yup I know Justin. Its Justin's old car that I broke :)
Justin also pit crews for my LS1 944 at the Indy event and he just picked up his own track car, oh....that means he probably wont be on my pit crew next year :(

My guess is that the valves floated and the engine ate one & locked up.

Namao sounds like a lot of fun. Too bad it's so far away.

We have 2 runway autocross courses out here, one at the now closed Marine Corps Air Station El Toro, and one at the closed Onard Air Force Base....both have VERY long straights or straights with a kink or dogleg. Yes, winding out in 4th is possible in an auto-x.

1) No you didnt break the crank. The block / rods / pistons would have died long before the crank (FWIW the crank accounts for almost 50% of the weight of these motors)

2) possible you floated the valves, bending them in the process and now the engine while turning over is making zero compression.. which would be why you think it is just spinning.. try cranking it over while someone watches the belts... or watch the tach.. if you see the tach needle moving while you are cranking the motor is spinning just with no compression.

Crank the car while having someone watch the pulleys on the front of the motor.. if it is spinning you need a head rebuild.

These cars in stock form (stock valves and valve springs) are good for about 7000 RPM... much higher and the spring pressures won't close the valve all the way before the piston reaches TDC!

You say a 4-2 shift release the clutch and overspeed the motor.. I would look to the valves!

Al, sorry I missed you running, I saw you at the event before when you had your V8 944 there, I was in the black 944 Turbo. 109 is so fast for an NA, I struggle to get to 115 in my Turbo, I'm a slow bastard.

My vote goes with the others above, I really think you floated valves. Maybe you'll get lucky and just get away with some head work.

You need to come up north, the Polar PCA does an "autocross" correctly.

I checked out Justin's new track car on the weekend, its very cool.

Simon, we have to get you out there!

Time for a comeback Alex!