Just took the heads and cyl's off my 82 930 engine and the #1 piston was pretty chewed up. Few pics below... Everything stock in pics along with head studs.

1. Is this a result of detonation?
2. Is the cyl still good? Can it be fixed by machining surface down a little and adding gaskets at base of cyl? Note there is a rub mark inside cyl which can be seen in pic.
3. Are those black radial lines on the head/cyl interface the result of head lifting and gas escaping? Saw on one or two other cyls in exact same place.
4. Is the head still good? If not can it be fixed?

...gotta love those digital camera's. Can see more detail than you can see with naked eye.

Thanks!!

 

Joe,

Yes, detonation
Cylinder junk - you've lost the squish area
Piston junk
Head can most likely be used again. Measure the head height at all 4 corners as well as the middle to see if it is warped. Most likely you can remachine them assuming there is enough material.

 

Joe, you definately have blow-bye, the exhaust gases have breached the sealing surface of the head and cylinder. Have you looked at your rod bearings, to see if they are pounded.. The damage could have been worse.

 

ouch!

 

Looks like the three motors we just tore down and completed. You are very fortunate that they didn't blow apart. The pistons that is.

The heads can be reused. Send them out to be checked. They more than likely will need guides, seals and valves. Depending on how long and how hot these got the seats may be gone as well. You will know once you tear them down and can start measuring. Also be proactive. Tear the rest of it down and check the rods and bearings. That is a lot of abuse on the lower end. Not to mention the metal fragments that can be floating around.

The common quote after something like this is "but I didn't hear anything" correct, you didn't. This is sub denotation which occurs before audible. This is the most dangerous because the owner doesn't hear it nor knows it is occurring until it is too late

 

That's exactly what my engine looked like when I took it apart last year! That's when I decided to go EFI.

Good luck Joe!

Brian

 

Ok, thanks, as I suspected... Don't know what rods look like as I haven't gotten that far. Now have case with pistons hanging out of it.

Now to make sure I get the correct parts.

1. Piston -- My piston's have a "1" and a "+" on the top of them. Figured out the "+" is the weight class but not sure of the "1". Do I need to find a piston with both a + and 1?
2. Cylinder -- What should I be looking for there? Recall reading something about 5 and 6 in a triangle as height. Anything else?

Few other questions:
1. What does detonation sound like? Stephen's right, I didn't hear anything unusual.
2. Is the #1 cyl the most prone to this on CIS cars? When I was taking intake system off the fuel line that goes to the #1 injector really has a pretty sharp 90 bend to it right as it goes into the injector and the others loop around and give a much straighter shot.

 

...Not really sure when detonation started, but in the last year and a half I changed park plugs after every race and I never noticed anything unusual on them.

I've also been monitoring a/f with innovate system last season. At what A/F should I be concerned at in on track driving? I've read to shoot for 12.2, but really wasn't sure at what number I should be concerned at as it starts to lean out more at higher rpm.

 

What kind of gas are you running?

Brian

 

Joe,
The number 1 refers to the diameter group. 1 means 96.967-96.977 according to the spec I got.
On the cylinders, 5/6 is the height group and there's the same diameter group
HTHs...

 

Brian -- Just this year I started running straight 110. Prior years mixed 50/50 93 oct and 110.

 

That looks like some of my kart pistons with detonation problems.

I'd shoot for a lower AFR for track events, like 11.6 at full boost.