What Causes This?

[Mark's RMK]

Installing PERC on my son's 2002 800 RMK. The CDI has DET so figured might as well upgrade the head.

We were very surprised to see this pitting on the head from what seems like a very well running piece of equipment. The top of the pistons have some slight carbon buildup and the cylinders have no scoring whatsoever.

Do we need to do any further investigation before completing our project?

 

[Super Dave3]

Installing PERC on my son's 2002 800 RMK. The CDI has DET so figured might as well upgrade the head.

We were very surprised to see this pitting on the head from what seems like a very well running piece of equipment. The top of the pistons have some slight carbon buildup and the cylinders have no scoring whatsoever.

Do we need to do any further investigation before completing our project?

Thats not detonation. Something went through that side of the motor. Could be that rod bearing is failing or could be foreign debris.

 

[Woodsrider]

That head looks like something was banging around in the cylinder. If the piston on side with head damage is not pitted I think that it has been replaced in the past. Are you the original owner?

 

[softndeep]

If the cylinder jug looks ok and it doesn't have any marks then i'd bet its been replaced at some point. something broke off or got in that cylinder and banged around in there. like part of the piston and or maybe somehow the spark plug electrode broke off and rattled around in there. How does the crank and connecting rod look ????
Either way you need to replace that head.

 

[Hardass]

From looking at the picture it looks as tyghough some one has tryed to smooth up the rough spots. If it is something that is currently wrong the top of that piston should look the same as the head. Pistons coming apart, crank failure are some of the causes.You have stated that the pistons look fine so i would say go for it and put it back together.

 

[Mark's RMK]

He is not the original owner so it could very well be that one of the pistons was replaced.

We are replacing the head with a 2003 with the DET sensor as part of the PERC upgrade.

What harm (other than cosmetic) would that kind of pitting cause? The sled gave no indication of this condition, runs strong, very good compression.

Exhaust valves look fine but maybe we should do some more inspection there.

 

[sled_guy]

You won't ever notice any running issues with a head that looks like that. If it had high spots, they can get hot and cause detonation issues. But it looks like it got beat up, someone smoothed it off and put it back together.

As others have said, if the piston looks fine, then I don't think you have any issues.

sled_guy

 

[jgd]

I agree. "We" have seen the exact same damage caused by connect rod needle bearings not staying where they belong. Of course the pistons were toast as well. As stated, those were replaced. Good luck.

Thats not detonation. Something went through that side of the motor. Could be that rod bearing is failing or could be foreign debris.

 

[Kraven]

Installing PERC on my son's 2002 800 RMK. The CDI has DET so figured might as well upgrade the head.

We were very surprised to see this pitting on the head from what seems like a very well running piece of equipment. The top of the pistons have some slight carbon buildup and the cylinders have no scoring whatsoever.

Do we need to do any further investigation before completing our project?

Hey, that looks familiar, lol

If the piston was replaced as suspected, I'll bet the old piston broke off a part of the ring land and that's what damaged the dome.

Been there, too many times.

I have run "beat up " domes like that when we're in a rush getting ready for a trip or like the last one, changed a piston trail side with basic hand tools we had with us on a back pack trip, 200+ miles away from the truck and trailer.

I would replace that dome if it were me.

 

[xcmark]

If I recall correctly there was a differance in the 2002 and older flywheels that required changeing the flywheel to a 2003 and newer because the timeing trigger point was differant. I think the old ones are 13* and the new ones are 18* . I would also pull the jug off and see if there is a broken ring or maybe a conneting rod bearing failer .

 

[Mark's RMK]

Head

Already changed the flywheel out from 14 to 18 degree. Not sure what it does or even means but I know it's part of the PERC setup.

Put a 2003 head on with DET.

Did not pull either of the jugs.

Maybe it would be a good idea?

Actually as some have suggested the work was probably already done as it's clear someone smootheed the dome of the damaged side and the sled runs flawlessly.

 

[rmkboxer]

Already changed the flywheel out from 14 to 18 degree. Not sure what it does or even means but I know it's part of the PERC setup.

Put a 2003 head on with DET.

Did not pull either of the jugs.

Maybe it would be a good idea?

Actually as some have suggested the work was probably already done as it's clear someone smootheed the dome of the damaged side and the sled runs flawlessly.

I would think that you are ok, but for a price of a base gasket and some time cleaning the old gasket off you could pop the cylinder off. but either the motor had lost a rod bearing or a ring at some point, looks like mine did when I lost a rod bearing

 

[alankb]

looks just like mine

That is from a piston or rings failing...possibly catching the exhaust valve. (02 may not have them). I've run 1000 miles after smoothing out the high spots, but I would sure pull the jug and look things over!