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

[saxen]

Hey Everyone.


yesterday I had an open track day with my 911 sc.
as I was going down the strait I lost all power and the car started making some pretty loud noises (ie internal sounds) I cant remember of the car shut off or I turned it off before quickly pulling off the track (thinking I may have oil leaking out of the back)
I got well of track and started the car, no issues there, I gave it a few revs up to 4K rpm while in neutral (still no problems) I put the car in gear and drove it about 20 feet before the noises came back and the car shut its self off.

after getting a tow back to the pits I tried starting the engine with no luck. it will turn over just will not start. we did however put the car in 5th gear and gave it a push. The same loud sounds came back when pushing the car.


working on the car that night I found out I had no spark (weird because that shouldn't cause the loud sounds)


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 find 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 93-95psi.


at this point I"m not sure if its a tranny problem (rebuilt 20K miles ago) or the engine. and I"m unsure how to check the rest of the engine out- also not sure if it matters after seeing those compression test numbers...
any help greatly appreciated


itching to get back out there]

[Walt Fricke]

Saxen

You posted this on another forum also, didn't you? Autocross/Racing? Tut tut - you ought to warn readers when you do that.

Since you must live in the Denver metro area since the pictures are of High Plains, you can find some local help. I'm in Boulder and might even loan you my leakdown tester and borescope if you leave me suitable collateral (years ago I loaned something to a guy I didn't know, never got it back).

[saxen]

yes, and thank you for the help! I figured I would post something a bit more direct to my issues than a "will it make this sound post"

thanks for the offer, the car stays in a garage in Broomfield and I live in Fort Collins, I would be more than happy to leave you collateral and fully understand your point- unfortunately I think we have all had that happen in some way.

IIhave actually known you and Kathy since I was about six years old, I'm Doug Saxen's Son (Levi) if that rings any memories. I have had a few people offer a good amount of help (Dave Liddle, Martin Smith... ect)

at this point I'm just trying to figure out what went wrong more than how I am going to fix it. the car has 176K on the engine (top end only rebuild 30K ish miles ago) I'm expecting some work ahead of me..

[T77911S]

120 is low for an sc. that is what i get on my turbo. you should see more like 150 or 160
do a leak down test.
broken valve spring? (bent valve)

when was the last time you did a compression test? maybe the compression was already low and you have a gearbox problem.

as for spark start with checking for power to the CD unit.

[Goldmember]

Subscribed..... LMK How I can help.


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[Walt Fricke]

My experience with compression testing at 5,000 feet of elevation is that they show up lower than expected otherwise. I've never seen the kind of numbers I see guys post. Then again, I often forgot to make sure the throttle was wide open when cranking for the test.

However, I see one benefit, and perhaps often the main benefit, of compression testing is to find a cylinder or cylinders which are out of line with the others. Like here. For general running, I'd not worry about the 120 figure, I'd worry about why the 93-95. Gives you a cylinder to concentrate on. A leakdown will help isolate things - where is that air getting out - problem with exhaust valve? Intake - less likely. Rings - but why only that cylinder. But you will know. For that matter, just injecting compressed air, without any gauges, and listening for where it is coming out will tell you something useful.

It is possible that the ignition issue is only coincidental to the klunking issue. Seems a bit unlikely, though, but things like that often confound diagnosis.

[saxen]

thanks guys,
I had a leak down about 2 months ago- I will piece the car back together and re-due that test to see if/what changes.

I agree Walt, every car I have ever owned shows low numbers up here- but the 1 low cyl concerns me.
with that, when trying to remove the distributor, after removing vacuum lines and the adjustment nut, what do I need to do in order to remove it?
thanks again!

[T77911S]

i dont ever think about altitude since i am at sea level

[Walt Fricke]

You just pull the distributor out. You may need to pry some to get it started. Cap off, of course.

Many like to set the crank to TDC firing #1 position, and be sure to leave it there, or at least be able (not hard) to put it back there when reinstalling the distributor. I'm more casual.

I've never tried this, but with the distributor out, you could hook the cap and wires back up, and the green wire as well, put plugs in the spark plugs you removed, lay them on a ground source, turn the key to run, and twirl the distributor. See if you get sparks. If you don't, then you are apt to be looking at coil or CDI or both, though troubleshooting has you checking the coil to distributor wire especially, as well as the lower voltage wiring feeding 12V to things, and CDI voltage to the coil.

You can pull the chain box covers with the engine in (a pain, doable) to see if anything is amiss in there.

[Slider79SC]

The worse noise I ever heard come out of our SC was when the chain tensioner failed.

Sounded like all hell was breaking loose inside the engine. Ours happend at a very low RPM and there was no significant damage. If you were running full tilt and this happend you will have bent valves.

As Walt said, you can put commpressed air to each cylinder one at a time (as they are on the closed valves stroke) and listen for leaks. I could hear mine out the tailpipe when we had bent valves from a missed shift incident....