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WTF caused this????

Here's some pics. to start with.I can do most of the work myself and send out the machine work but need some used stuff as I dont have the dough for new P&C's.Any info and help with this would be greatly appreciated.Thanks.








Old 06-10-2010, 03:31 PM
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Old 06-10-2010, 03:32 PM
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Old 06-10-2010, 03:36 PM
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Regarding the picture of the distributor, Does that happen to be the cylinder that split open?

It looks as if there was some arcing there on that terminal.

that would explain a lot.

Last edited by nocarrier; 06-10-2010 at 03:39 PM..
Old 06-10-2010, 03:36 PM
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Did you jump on the accel when you had a cold motor? I had two cylinders burn and blow a hole (actually crack) just like that. Detonation due to incorrect deck height and flooring it when cold.
Old 06-10-2010, 05:56 PM
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+1 on why the terminal on the dizzy cap is bad.

Also I was told once to never use anywhere near full throttle until operating temperature is reached. Now I know why!
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Old 06-10-2010, 09:49 PM
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If you were effectively a twin plug on 5 cylinders and a single plug for one and it was properly timed for a twin plug it would probably detonate a bunch on the single plug cylinder.

That is one of the challenges of a twin. I think a number of people lost 3.6 motors to detonation when the belt that drove the second rotor failed.

Might want to check you injectors and do a balance test to be sure you do not have a cylinder or two running lean. I do not know if it is just the lighting but on the header pic it looks like the two center cylinders might be running lean.
Old 06-11-2010, 07:25 AM
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D E T O N A T I O N

Now to puzzle out the cause. The above posts are great starting points. Since it is a single cylinder, it has to be one of the following:

Missing spark: one of your plugs, contacts, wires is wonky
Fuel: An injector is misbehaving, leading to lean conditions

As mentioned above, it looks like lack of spark due to the buggered contact. Yeesh, this is ugly:


Not sure if the contact is the cause or a symptom of another issue manifested on the cap, but in case it is just operational corrosion, this is why dielectric grease is a nice addition to these contacts to keep moisture/air away from highly charged parts. It provides a barrier from the atmosphere that decreases the liklihood of accelerated oxidation due to the electrical charge passing through the part.
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Old 06-11-2010, 07:59 AM
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Quote:
Originally Posted by 911st View Post
If you were effectively a twin plug on 5 cylinders and a single plug for one and it was properly timed for a twin plug it would probably detonate a bunch on the single plug cylinder.

That is one of the challenges of a twin. I think a number of people lost 3.6 motors to detonation when the belt that drove the second rotor failed.

Might want to check you injectors and do a balance test to be sure you do not have a cylinder or two running lean. I do not know if it is just the lighting but on the header pic it looks like the two center cylinders might be running lean.
This is one driver on why I am going to run knock control. One, you get some margin, two knock gets logged, so if the EMS sees a single cylinder banging its brains out, you know it.

Even with knock control, many a 3.6 went TU due to the "ozonated belt" issue in the 964 distributors killing the second plug bank. I am not sure if the CEL on these cars was set to notify owners there was an issue.

This risk comes with the territory, I guess.
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Old 06-11-2010, 08:07 AM
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Wondering what's with the valve reliefs on the exhaust side of the pistons? My stock pistons don't have that.

Probably not hard to find a used replacement cylinder. I have a set, though I haven't measured them yet.
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Old 06-11-2010, 10:37 AM
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Yeah 911st I noticed the center two cyls. look lean as well,it's not the lighting.I dissasembled the left bank and found all compression rings broken as they were on the right side as well. Some scuffing from that in the cylinders that you can catch with your fingernail so I'm wodering if they are no longer usable because of this.The engine was hot and up to temp when I got on it so that was not an issue.Anyone with parts just PM me,thanks.
Old 06-11-2010, 03:59 PM
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Injectors and or the Fuel Distributor can cause uneven fuel to the cylinders.

Part of the reason CIS should run richer than an EFI Turbo.

There is a great post about verifying your balance at the injectors here somewhere.
Old 06-11-2010, 04:29 PM
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Quote:
Originally Posted by kenikh View Post
This is one driver on why I am going to run knock control. One, you get some margin, two knock gets logged, so if the EMS sees a single cylinder banging its brains out, you know it.

Even with knock control, many a 3.6 went TU due to the "ozonated belt" issue in the 964 distributors killing the second plug bank. I am not sure if the CEL on these cars was set to notify owners there was an issue.

This risk comes with the territory, I guess.
I have a Bosch knock sensor on mine and cannot get reliable readings from it since this motor is already noisy (valve train, air cooled). So the threshold to start counter-measures is kind of a guess. Too low, and you loose performance - too high and loose pistons.
Old 06-11-2010, 05:38 PM
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Don, what system is picking up the knock?
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Old 06-11-2010, 05:45 PM
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Great pictures...the damaged piston tops, cylinders and shattered rings are clearly visible, I agree that detonation is the culprit. Have you found any of the broken ring bits yet?
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Last edited by William930t; 06-12-2010 at 10:29 AM..
Old 06-12-2010, 10:24 AM
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The ring bits all came out and on to the ground.I tilted the engine on the stand so they would hit the ground and not enter the case.A lot I had to pick out of the piston that were still there.It's been determined that the cause was in fact the bad dist. contact which did coincide with No.6 cyl.I hooked up with a race engine builder who's going to help me get it back on the road( with EFI,997 turbo injectors etc.)
Old 06-12-2010, 04:00 PM
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