911 sc with lsd 915- question about car moving in gear with engine off

[saxen]

hey everyone.

weird question.
lets say you have a 911 sc with stock lsd 915 transmission like me and you are in 4th or 5th gear doing down a strait away and your engine dies. (so now your moving in gear with no engine power)
what kinds of noises does your car make? loud banging from the tranny/engine?

this happened at the track today and I'm not sure if its something serious or not but my engine wont start now (no spark) but it happened right after my engine died on a a strait away at a local track.


any ideas?
thanks!

[Walt Fricke]

Yes - something important in your engine broke. That caused it to stop running (no power, no response to the gas pedal). Since you were in gear, the engine, although it would not run on its own, was still turning over as your car coasted to a stop. The noises were from broken parts inside the engine hitting other parts they aren't made to hit.

This does not sound good.

1) with clutch pedal in, what happens when you turn the starter on? Does engine turn? Make noises? I'm guessing it will turn. It might not be turning fast enough for broken parts to bang.

2) put in 1st gear (or reverse - even lower gear) and turn starter on. Will it move?

3) pull all plugs, look for damage to the plug tips.

4) since plugs are out, do compression test. Better, do that and a leakdown. If both are good, maybe it was just the ignition dying for some reason, and the noises partly your imagination.

5) pull the distributor cap, see if there is damage, does rotor move appropriately.

I've had engines stop for various reasons on the track. Running out of gas, for instance. No unusual noises other than from my mouth. No reason there should be if that's the problem, or a fuel pump quit, or the CDI box crapped out.

So there are lots of ideas. Not sure any of them are the right ones.

[saxen]

hey Walt


1 when I try to start the car the engine will turn over but will not start
1B. if I put the car in 5th gear and push it the engine will turn but also make a clunking sound every 2-3 feet

2 I did this at the track today but only for a few feet, the car did move forward


3- no damage to the plugs
-4 still need to do.

5 took it apart, everything looked to be in line.

6- drained some oil, no metal in the oil.

I'm guessing the engine let go but I would like to confirm before taking it out. I find it weird that i would have no spark after this-
thanks for the help

[Walt Fricke]

Well, the distributor was the only thing I could think of which would 1) cause the car not to start due to lack of spark, and 2) lead to a mechanical klunking sound. I was thinking maybe the distributor gear broke off, or the pin sheared, or something. Or the distributor shaft bearings are so bad that the spinning part wobbles and hits the fixed part of the reluctor.

Various things in the transmission, or clutch and TOB/release, could make noises. So could a broken rocker, or a broken rod, or other serious engine malfunctions. But usually the engine still runs unless the damage is so severe it is seized up. A friend drove his 911 100 or so miles home from a track with a broken crankshaft - our engines are exceedingly well balanced! We all thought his noises were just a collapsed chain tensioner. I've driven more of a lap than I should with a rod flailing around causing more damage.

Flywheel troubles could throw off the 3.2's Motronic sensors, but you have an SC. Hard to see connection between drivetrain and ignition.

Interestingly, in your SC one engine revolution turns the rear wheels 226 degrees in 5th gear (I don't have this kind of stuff memorized, but I do have spread sheets with it), which works out to be just shy of 4 feet if you have a 75" circumference tire. Given how the klunk seems to relate to 2-3', that sounds suspiciously like something in your engine contacting something else in your engine once per engine revolution. Or, if closer to two feet, some rotating parts of the distributor, which turns at half engine speed, hitting something.

But why wouldn't that happen when you turn the engine with the starter? Or, for that matter, when you turn it by hand. It would be good to jack up the rear end, put car in gear (5th would be fine), remove spark plugs, and hand crank engine to see how it feels turning over, and if there are any sounds you can identify, or whose locations you might be able to pin down somewhat.

[saxen]

looks like I need to take out my distributor and see if there is something wrong with it.

I cut this from another post I made today.


"I took off all 4 valve covers and everything looked ok, with that I took off the bottom drain plug surrounding plate and found no issues.
all the spark plugs look fine and so does the oil (no metal at all)
I did a compression test and all cylinders game back 120 EXCEPT for one which came back at 93-94psi"


im not sure if it will matter whats wrong with my compression being so far off, may be looking at a new engine/rebuild either way. but I will look more coming up

[saxen]

thread moved broke car at the track, now trying to figure out what broke- compression numbers off.