Check this out

[Phizzer]

So I got a motor the other day that I was going to tear down and rebuild because I was told it was blown up. When I got it, the head had already been pulled off and you can see where what looks like a chunk of ring maybe? skirt? slammed up into the dome of the head. But the cylinder it came out of looks nearly perfect. In fact, all three cylinders look nearly perfect. How the hell is this possible? Every single 2 stroke motor I've seen thats blown up with these marks has had a piston failure. The motor rolls over fine, I can use my palm to create suction on the down stroke. I am tempted to put the head and gasket back on just to get a compression reading, but I am worried about something being broken on the bottom side of the piston I can't see. Any ideas?

 

[bnorth]

Interesting that it's only in the squish band I would expect to see marking in the dome as well if something was bouncing around in there. Looks a bit like when a locator pin comes out.

 

[PJ-Hunter]

Prolly best to pull the jugs and look. Specially since it's out and half way pulled apart.

You don't wanna damage a cylinder that's not damaged now, just on a compression check. That would piss ya off, right???

 

[Twostroke]

I've had a jet ski motor lose a ring and destroy the head and top of piston without damaging the cylinder, new piston & head and I was back up and running.

 

[Phizzer]

I'd be absolutely pissed off if I damaged something else while rolling it over. The motor is still in the sled, I am wondering if I can just pull the jugs off and do everything without removing the block. The cylinders didn't appear to be Nikasil so I think ill just have them honed out with fresh rings.

 

[PJ-Hunter]

Probably. Just wrap the pistons with a soft cloth and make sure to cover the crank area so random crap doesn't find it's way in there.

Every sled I have ever worked on, I have been able to pull the jugs and leave the case.

Even the REVs and the XPs

 

[Woodsrider]

It is possible that it ingested something. I once had a motor that broke a piece of the wrist pin bearing cage got on top of piston. I would never put a motor back together without exhausting all causes of damage.

 

[Hardass]

Guarenteed something is coming apart could be a ring or piston or crank and bearing.

 

[Phizzer]

Guarenteed something is coming apart could be a ring or piston or crank and bearing.

Well I pulled the cylinders off...There is some very LIGHT scarring on one of the cylinders, easily removed with a hone, all piston skirts are in tact, all rings and pins, motor rolls over easy. I was able to swab the bottom of the crankcase where oil had been pooling and it was clean. I just don't see anything in the bottom end coming apart, making its way into the cylinder, damage the head and nothing else, then exit!!

The guy I got the motor from, said it was at the dealership for a regular tune up, and they ended up calling him and telling him it was blown up. Like is I said, the head was already off when I got it. And I know this a long shot, but do you think its possible the dealership swapped heads off another blown jet ski to screw this guy over? Once I get to the bottom of it, I will begin making a parts list, but I need to know how far to go before that.

I'd like to not split the cases, I cannot see any debris that made its way into there. Honestly, at this point, I want to hone the block, throw in some fresh rings ( the old ones still look new) and head gasket and try getting some compression numbers.

I held a magnet to the cylinder wall and it stuck, so I am assuming these are steel and I can hone them no problem. My M sled is tore down too so I brought the magnet to it and it would not stick, Nikasil.

Anyways..I've got some thinking to do...just not positive on how I want to approach it. Thanks for all the feedback.

 

[Woodsrider]

The marks in head look like they are sharp edged if it was a needle bearing they would have a more of a round look to they. The motor that I had with the broken wrist pin cage also had sharp edged marks. I could not tell that the cage was broken until I pulled the pin. I would stuff some clean rags in the crank and pull the wrist pin on that bad cylinder snap rings are cheap.

 

[m8magicandmystery]

the foreign object could have come in the intake stream..so you may never know..

 

[LoudHandle]

The electrode from the spark plug, most likely. I had one fail in a similar fashion last winter. It separated the porcelain from the threaded portion and the small end and the electrode dropped into the cylinder and the the upper portion blew out with the compression force. The engine kept running on the one cylinder until I got it shut off. The porcelain got smashed up and ejected out the exhaust port and the electrode followed it shortly thereafter. The marks were similar, sharp fairly minor dents in the dome and piston.

If there are no dents in the piston (pic is not good enough to see top of piston) I would expect some foul play at the dealership, and stay away from them and their shady business practices.

 

[Hardass]

The side of the piston or cylinder wall may not take a beating at all it happens alot. And yes it could be something from out side the motor but probably not and if not will you be upset you didnt tare it down and save it at the point its at? If so run it compression may not show any thing. i have seen many cranks fail and it looked just like that. Im not trying to argue but you have a issue and it does not cost alot to take it apart and save your self. i know i would Its your call.

 

[PJ-Hunter]

I cannot see the piston well, but I don't see anything weird other than none of them have consistant wash, leads me to think it was running a wee bit lean, but that's just me. Are there marks on the piston dome? If not, I'd really question the "dealer"

 

[Phizzer]

No marks on top of piston at all what so ever. Not missing circlips, pins, skirts, etc. Which leads me to come to these conclusions:

1: The ski was brought to a SHI#@$Y dealership, and tore apart a perfect good motor to try and screw the customer? Maybe offer hime $400 bucks for the whole works because it is "blown up." This seems friggin crazy, but it's definitely a possiblity. Are heads serial numbered to match the block? I found some casting numbers but nothing that matches. Is there anyway to determine if this is even the proper head for the motor.
(1997 Yamaha GP1200)

2: A main bearing cage, rod bearing, piece of casting, managed to make its way from the bottom end, up into the cylinder where it was mashed into the cylinder head without causing any damage to piston or cylinder.

3: Something was sucked in through the intake, and shot right back out.

Even with these possiblities, one thing just doesn't make sense to me. If the head was damaged that bad, something forcing chunks of metal into the dome, then where is the force doing that work? It simply does not add up to me.

 

[PJ-Hunter]

No marks on top of piston at all what so ever. Not missing circlips, pins, skirts, etc. Which leads me to come to these conclusions:

1: The ski was brought to a SHI#@$Y dealership, and tore apart a perfect good motor to try and screw the customer? Maybe offer hime $400 bucks for the whole works because it is "blown up." This seems friggin crazy, but it's definitely a possiblity. Are heads serial numbered to match the block? I found some casting numbers but nothing that matches. Is there anyway to determine if this is even the proper head for the motor.
(1997 Yamaha GP1200)

I don't think heads match the block. Is there a part number stamped on the head? A quick search within an online parts site for Yammie would answer that question.

2: A main bearing cage, rod bearing, piece of casting, managed to make its way from the bottom end, up into the cylinder where it was mashed into the cylinder head without causing any damage to piston or cylinder.

With that much damage to the head there WOULD be damage to the piston Dome. No if's and's or but's. The scoring you found on the cylinder wall could be water scoring (quite possible since it was a jetski motor) and that would explain why a hone would fix that.

3: Something was sucked in through the intake, and shot right back out.

Not likely. There was too much damage to the head to just be sucked out into the exhuast that quick. What ever it was bounced around a while before being either burnt to nothing or sent out the exhaust port.

Even with these possiblities, one thing just doesn't make sense to me. If the head was damaged that bad, something forcing chunks of metal into the dome, then where is the force doing that work? It simply does not add up to me.

I'm under the idea that the dealer has played a little game with the original owner. That is not the original head to that motor, IMO. With the damage to one part and not the other...

 

[Phizzer]

there is no way this could happen and have the top of the piston look like this...

 

[Bowfisher]

I agree. Two years ago on a buddies M1000 the ground electrode bunt/broke off by the ceramic and the tip bounced around inside that cylinder and the piston was as hammered as the head. If there's something bouncing around in there and the head is getting that much damage the piston is going to have some too. What's the chances that the motor has been rebuilt once before? If it has maybe they thought the head wasn't bad enough to warrant replacing.

 

[Blu Du]

damage probably done on a prior burndown

 

[Phizzer]

haha, so I was staring at the cylinder head in my garage before I got back on here, and started thinking along the same lines. That is the only reasonable explanation aside from the dealer being a total rip. It makes more sense it was possibly done earlier in time. The guy said he brought the sled in for a tune up, and when he got it back, they told him it looked like a "rock" had been bouncing around inside....but why the hell would they have pulled the head to look at this? That is definitely not a tune procedure. Maybe it was low on compression on that cylinder maybe?? I don't know. Im ordering rings, pins, bearings, head gasket a few other things and putting this thing together. I cleaned the block up already and it looks brand new. SWEETTTT!