Burnt piston ouch!

[K-DAWG XB 2003]

Just wonder what the masses think may have caused this. These are the big pics didnt want to down size them and kill detail, Thanks.
You can see its eroded at the bottom of the exhaust port.

The spot on the left side of the piston is hard gooey burnt oil built up.

Close up of the burnt spot on the piston. You can also see the aluminum transfered to the cylinder wall here.

A look at some more of the cylinder. More aluminum transfer.

 

[K-DAWG XB 2003]

The head
The head.

 

[Myron]

easy just pure old detonation, now you have to find out what caused it, could be one of many things,what motor is it?

 

[mtolley]

id say a 150 or 175 by the comp relief slots. a friend has a 200 that looks alot worse. his has done it twice now, same hole both times. good luck! mt

 

[suicidealli]

that isn't to bad lookin....... when i burn them it looks like somebody took a torch to it!!!!!!!!!!!!!!!!!


what is your timing set at?
what oct gas r u running?

 

[K-DAWG XB 2003]

Its a 1991 carbed 200. I just put a set of 35cc heads on it. They were all 138 to 140 on that side. I checked it 3 times in the last few months. I guess moving the compression up you always take that chance for problems. But, I think I had a head gasket leaking. The cylinder above this one had some piston scuff in it and it was only 120# on compression. The one pictured was at 95#. I am hoping I can pull it apart hone the scuffs out of the cylinder and re-ring it. There is a slight scratch I can hang a nail on but, it is small.

 

[K-DAWG XB 2003]

Heres a picture of the cylinder above number 6 (the burnt one). This is #4. The flash from the camera makes it look burnt to, it is a optical illusion. The flash made a shadow. I looked at his pic and said what the ...... and ran back to look again but it is just carbon/oil deposits. Although it may have been on the verg of melt down. There are scuff marks on the bottom of this cylinder to.

 

[Myron]

what gas were you running? It has been a log time since I messed with those motors, but I remember something about the carbs for the 91 for some reason, this is a 7 peedle motor right?

 

[K-DAWG XB 2003]

Yea, 7 peddle motor running 93 octane. Pumper carbs.

 

[GFinch]

First guess head gasket or sleeve dropping down into block. In the first pic I can see what looks to be exaust soot beyond the fire ring of the head gasket. Gently blot the oil from the surface of the sleeve/block and look. Take your finger nail and pull it across the junction of the sleeve/block.
If it is a exaust leak into the cooling system, the exaust pressure during combustion will pressurize the cooling system and the water wont be there to cool the rest of the cylinders in that bank.
I had a set of cast aftermarket heads that had a porosity passage between the combustion chamber and the water jacket aera.

Looks like a good excuse to yank the sleeves and put some in that don't have that exaust relief. MORE POWER, YES!!!!!!!!!!!!!!

 

[K-DAWG XB 2003]

That exhaust soot is just where it ran out of the cylinder when I pulled the head of. I had the motor tilted way down so I could reach the top head bolts easier. My water psi was at 15 pounds at 4000 rpm and 2-3 at idle. Water temp was at 150 when motor shut of at 6000 rpm. Knid of bogged out then shut off. But fired right back up.

 

[Myron]

could just be gas, I have stuck way to many motors, some I could say yes that was the problem, some not so sure, the gas we have today just sucks, it makes it hard to mod a motor for pump gas. While you have it apart I would top pin the pistons if you have not already

 

[fasteddie]

Looks like a call to hotprop is in order.

 

[HO]

As Myron said it could be the gas. One step further is to check your carb that feeds #6 for trash (and possibly #4). Obviously the cylinder expanded (heated) to the point where it transferred to the sleeve so it was running lean. Also, did you change the jetting with the change in compression? If you had a bad head gasket your problems should have been worse (i.e. water in cylinder, broken pistons). Appears to be a gas delivery deficiency causing it to run lean...

If you are running 140psi and you are concerned about fuel quality then splash some higher octane to be safe. Your engine is at the cusp.

$0.02

John

 

[mtolley]

its hard to get accurate compression readings with sleeves with the relief slots. was your compression at 140 at cranking speed? if so it would be higher once the engine was running and the slot stayed covered more(rpm) so i wouldnt rule out detonation. i am wondering if my buddy's motor didnt have the same problem on that one hole. too lean mt

 

[patches]

i didn't know any of the 200's had the relief slots. another thing to consider that i will always do now is check compression with more than one gauge. especially if your running on the edge

 

[Myron]

the 91 7 peedle motors had the relief slots

 

[K-DAWG XB 2003]

Well I reckon I just had a lean condition. Runnin to close to the edge on compression. Brian sorry 'bout destroying a great motor. Thanks for all the input fellas.

 

[Myron]

were those the stock heads that were cut down?

 

[chad202]

When you put the cut heads on, did you rejet the motor? You are not on the edge of compression.