We just looked at the motor in Fritz. We found the belt in the dual distributor broken and one of the disty caps had evidence of arcing. Leakdown shows cylinders 4 and 5 have 100% leakage. You can hear the air rushing past the exhaust valves!

In a word....fuck... (Sorry for the language, I'm a little sad and more than a bit frustrated).

It would appear that I either have bent valves in cylinders 4 and 5 or broken rings and / or pistons.

Can a distributor failure in one of the two disty's lead to such a top end failure? I was driving very well at Thunderhill when this happened. I did not miss a shift or over rev the motor. The funny thing was that I was actually feeling smooth about everything.

I cannot describe how bad I feel.

We're having another cup of coffee and the motor will be dropped in about 2 hours. We will tear down the top end over the next few weeks and fix it.

Major bummer.

Bill P.

From what I've read, yes. With only one plug firing, you can get detonation.

The 'dead' distributor was probably firing one or two cylinders (4 & 5 I'd wager). So you would be getting extreme detonation in those cylinders. I haven't heard of detonation bending valves, but I suppose it's possible. Or the detonation caused the timing chain to skip or stretch to the point where the piston contacted the valves.

If it's just leaking out the exhaust valve, there's a chance your pistons are okay and it'll only need some head rebuilding. :pray:

The second dizzy head ran by the belt runs the bottom plugs. There is something like 5deg timing difference between the two rotors. If the belt breaks.. the computer cannot compensate enough with the timing (knock sensors cant keep up) and you get severe detonation. Porsche has reported MULTIPLE broken cranks!! because of this issue. This is why the updated breather setup from the fan was SOO important. They added a line from the fan shroud to help evacuate what amounted to "ozone" breakdown of the small drive belt.

This SUCKs.

This could be worse than thought.


B

The motor was idling smooth and we just cut open the filter and found not metal. Can I still have a broken crank?

Bill P.

Engine shot...dropped in one hour and 15 minutes....drinking coffee...

another engine shot...

What the hell...my G50....

On the plus side, the lightened flywheel and 4 puck clutch setup looks great. No wear issues. Even AXing it all season on top of the track events.

I may put a new 4 puck back in and keep the used one as a spare...you know...DWD...

And maybe some solid lifters? More things to think about.

Bill P.

dang sorry about that bill.

my understanding of the broken dist belt, is that the detonation often holes a coupld of pistons.

on your 100%leakdown test, where was the leaking sound going (intake, exhaust, oil sump?)

you can put a rubber disposable glove over the intake/exhaust/vent and easily see where the leak is going.

hoping for the best!

brant

Hi Brant,

It appears to be coming from the exhaust valves on both 4 and 5.

I'm hoping it's top end only.

So far, finding no metal in the oil or filter is a positive.

Bill P.

The engine will run fine on one belt. I know several 993 owners who drove around for years with one broken belt. They always ran premium and never drove the car hard. They ignored the dash light. The computer will log mis-fires.

I dont know how else the valves would have bent unless a piston or 3 came apart and hit the valves.

Brant nailed the test with the plastic gloves. Factory techs are trained to use a glove on the oil filler of a Boxster or 996 to check for a broken Air/Oil seperator. If the seperator is broken.. then the glove gets sucked into the oil filler neck!


B

Might consider "Crank-Fire" ingition when you rebuild.

Ken

got clewwit on speed dial ?

sounds like a good idea

Cheaper to replace the little belt once a year.

I'm curious now to know whether or not the car has a "check engine light" This would have quickly triggered the light when the belt broke. I'm kinda doubting it had a light since the gauges are probably early 911 and not 993.

I suggest a Boxster




B

The tub is a 1980 SC with only oil temp and pressure and tach left. No warning lights.

With my luck regarding race cars, I fully expect to blow the Boxster motor when I start it up to pull it out of the trailer at the first event.

Really.

Bill P.

I'll be watching this.

I have bad dreams about that distributor belt cutting loose on the RS.

No metal in the oil filter is a good sign.

If the crank was gone there would have been lots of noise and metal everywhere.

Air blowing into the header says a valve is bent, or I guess in the case of extreme detonation part of a valve could be missing?

Do you have a scope to look into the cylinder? You might learn a lot.

Still hoping it is confined to the top end.

Hi Randal,

I was going to take it easy this weekend and just pick off the honeydo list before the big build weekend. It looks like we'll pull the motor apart this weekend instead. I'll take pics of our findings.

Bill P.

Missed shift =mechanical overrev= bent exhaust valves

I missed a shift in my 914-6 with the 2.8 on July 4th, 2004 weekend at Buttonwillow. I know what that does to a motor.

This last event I did not miss a shift or over rev the car. I have the rev light / shift point on the car set to 6K RPM, well below the 6800 RPM redline. This is a mystery to me. How can I shift 800 RPM UNDER the rev limiter and still bend valves?

Bill P.

= MONEY

Me thinks that some broken rings/ring lands is about as lucky as you're gonna get....but I've been wrong before and hope I am today.

You are right JP. My best case prayer is that it's just that and not destruction inside there...we will see this weekend.

Bill P.

I've heard the retaining clips (rings) on the valves can fail, but it sure seems to be something that has to do with the distributor failure (first).

Found the problem on the 3.6. It looks like the chain of events went like this:

1. Timing belt breaks on dual distributor. Random arcing and sparking.
2. Pre-detonation in cylinders. Cylinders 4 and 5 are the worst. They have bits blown out of them at the lip.

NO BENT VALVES. No metal bits anywhere. Heads look good but have scoring by 4 and 5.

DWD hits. While we're in there we'll send both banks to Ted at German Precision on Monday for clean up. I will need 2 new cylinders. We will re-ring the motor. And we need to fix the disty. It appear that the secondary shaft is wacked. It does not spin true. We will fix this as well.

Also, we found that this 3.6 DOES NOT have pins on the keyway. Pressure fit only. Timing looked okay, so that wasn't the issue. But there is a hole and provision for a pin already machined. WTF? Why did Porsche not pin the keyways on the camshalfts?

We will pin them.

The motor will be rebuilt and back in Fritz in 3 to 4 weeks.

Fritz will live again....

Here's a few pics.

Bill P.

Side view....

Doesn't sound so bad afterall ( $$$ )

Good news, Bill.


KT

Well, well.......I don't know much about the 3.6L destruction cycle
but it looks like a total savings of 2 pistons .....not to mention not having to clean shittage out of the botom end. A gud thing....course, I ain't paying for it.

You might want to pass what you found by Jerry W.

"It appear that the secondary shaft is wacked. It does not spin true."

How would that happen???

Might have Ted check the crank to be sure it is not bent.

Ken

Hi Ken,

The secondary disty is not wobbly, but is "sticky" compared to the primary. With a broken belt, you would think it would spin freely. We still have to pull the distributor apart.

I wasn't planning on pulling aprt the bottom end.

Bill P.

1st thing I did when I got my 3.6 was replace that $10 belt inside the distributor...car only had 70K miles on it and the belt broke when I was replacing it.....scary...

OK - the shaft I thought you were talking about was the chain/oil pump shaft.

I would still talk to Jerry about it.

Ken

Mike,

The belt will now be part of an annual maintenance schedule. It looks like the belt got brittle from heat and elements? Strange but true. This motor had 38K miles on it when I bought it from the wrecking yard.

Ken,

I guess it wouldn't hurt to talk with Jerry. He's only 5 minutes from my house.

Bill P.

Bill,

Here are a few links about the belt failure, damage looks just like yours....


belt failure

3.6 dizzy belt issues

a little more reading

If I can find my CD, I'll burn you a copy which has directions and pictures on the replacing the belt. Took me a couple of hours start to finish

I do not know of anybody that knows more than Jerry about "blown" motors - and he may have suggestions about what else to check before you put it back together.

Good Luck,

Ken

Bill,

Did your distributor have a "vent kit" installed, as outlined in Mike's documenation above?

Any way to modify the assembly to get rid of the belt?

Hi Mike,

Thanks for the links. Wow...looks just like my motor, but at least mine isn't as severe as the heads look like they will do okay. But I will need 2 cylinders. The motor problem in the link was probably from several hours of running versus mine blowing down the straight at Thunderhill.

Bill P.

Hi Randal,

My 3.6 came with a vent kit already on it. From what I understand the 964 motors did not have the venting until close to the end of their model run. The 993's have the venting provision. The venting hose on my motor is new, having been replaced by JWE. I looked through my receipts and I do not see a line item for a new disty drive belt. I haven't looked through all of them yet, but this stupid $10 part looks to be the culprit.

Bill P.

For now I'm going back in with the belt. Given The Beast and Boxster builds are underway, I don't want the cash outlay for the crankfire.

Bill P.

Suppose for a second that the sticky shaft preexisted the broken belt. It could have caused the broken belt...

That is a definite possibility. That's why we are going to rebuild the disty as well. Catastrophy from a distributor issue....

What's the world coming to....

Bill P.

Bill,

RobJ has a 3.6 dizzy sitting on cart if you want me to bring a spare with me.

Nice finding out about the "slip fit" cams huh?? Scary ??

Did you pull the codes from the computer?


B