Thread: Burned up a piston
11-17-2009, 03:42 PM #1
Burned up a piston
My last day on the lake got cut short. My '97 SLTX with 1050 started running real bad. Anyway, it looks like i burned up the mag piston. I'm guessing she was running lean? Would you all agree?
Also, I haven't had to do this repair before, but i'm guessing a new cylinder, cylinder head, piston and rings. Does that sound about right?
Any thoughts on best place to purchase these parts?
Also, besides addressing the lack of fuel issue (i believe i need bigger jets, as i recently o/h the carbs) is there anything else i should look at? The other cylinders, the crank?
11-17-2009, 03:54 PM #2
My first impression is that debris in the cylinder has caused that damage. Maybe a ring broke, or one of the bearings has come apart. It's kind of hard to say without taking the cylinder off and inspecting the piston and crankshaft for further damage.
11-17-2009, 04:09 PM #3
Looks like it went lean, burned the piston ring land off, ring broke, and got loose in the motor. No need for a new cylinder, just have that one bored and honed to the next over sized piston. Head will probably need to be replaced, just be sure you get one from a 96-97 1050 or a 96-97 700. The newer 1050/700 domes are lower compression. Also, you will need to inspect the crank to be sure the rod bearing is ok. You shouldn't need larger than stock jets. There is probably an air leak somewhere. What do the other pistons look like? Post pics
11-17-2009, 04:23 PM #4
Thanks guys. I've been searching the forum for info but there isn't a whole lot on these red engines (a lot on the blue ones though).
Earlier in the summer i overhauled the carbs and replaced all the fuel lines because i felt she was running lean...poor piston wash. And when I finished with the carbs there was little to no difference (they were really clean when i tore into them). Anyway, my carbs do not have the adjustment screw for the upper end mixture, so I assumed i would have to install bigger jets.
Where can i find the procedure for checking for an air leak?
Also, is it okay to mix an oversized piston with two others that are standard?
11-17-2009, 07:03 PM #5
11-17-2009, 10:03 PM #6
When you said earlier, I redid the carbs because I felt they were running lean...Why would you think that? Just the look of the piston wash? Maybe the carbs where they connect have a air leak at the mag carb possibly? Was the Mag hot before you rebuilt the carbs or did you feel excessive heat from all 3 or just the one or didn't look really? . Just trying to do a little investigating into what actually happened. Did the ski have a lot of hours on it.......the rings wore out and broke possibly? maybe a jet got clogged in the mag carb and it started to go lean. Sounds like it happened pretty quickly,, Just cruising around and pow, falls apart for no reason..Were you a WOT when it failed? That would definely cause a lean condition with debris caught in the jet while cruising fast. Mere seconds probably. Are the filters clean? What about the fuel separator? any junk floating in there or is a screen broke in that? That doesnt look lean really, It has black burn bubbles on it. Lean is smooth and black looking. Anyone know what the black bubbles mean?
11-17-2009, 10:39 PM #7
11-17-2009, 10:55 PM #8
Probably is lean all black like that ...Hard to tell from the pics if the bubbles are parts of the piston breaking up or if it's bubbles like from bad gas or oil ...On my pistons that are lean, there are no bubbles like that on mine.. take a look at these. far right has parts in it, middle has has almost a hole in it and one the left is lean. See what I mean? Yours looks bubbled but lean.. Not sure what caused that.
looks like the exhaust side got real hot on yours.
11-18-2009, 09:50 AM #9
Its lean, no doubt. It was debris that marked the piston all up. Not all lean pistons will look exactly the same. Depends on if it was a part throttle burn down, full throttle burn down, if serious detonation played a role, oil type, etc.
To the original poster: Yes it's ok to mix different sized pistons, that will be fine. As for where a possible leak is...either the intake manifold to reed cage gaskets, carb to intake gasket, or the cylinder base gasket. Could be the front crank seal, but doubtful. Also need to be sure that the carbs are in 100% good condition...seals, jets, fuel pumps, filters, lines, etc. Again, post pics of the CEN and PTO pistons.
11-19-2009, 12:12 AM #10
I'm out of town for a couple of days, but when i return i'll pull the heads off the other 2 cyls and post pics.
I'm not sure what you are refering to as "black bubbles", but the piston and head do have many pock marks from, i'm assuming as someone mentioned; a broken piston ring bouncing around.
This ski has about 130 hours on it. I've owned it for the last year (about 30 hours) and it's always had a problem at 3/4 throttle. If you run 3/4 throttle for five or six minutes the rpms would start to fall off. You could either apply full throttle and fix it, or back to idle, and then bring the throttle back in and it would be good to go. Later, someone here suggested adding a little choke when this happens, and that did seem to help. So, between that and the lack of descent piston wash i concluded that she was running lean. I o/h the carbs and replaced all fuel lines but it didn't make much difference.
On the day of the failure i did notice another problem that i hadn't expeirienced before. I was running her hard, ~6500 rpm (nearly WOT), and after about two or three minutes of this she just died. I could restart her an she'd run good again, until i ran her hard, and then the same thing.
Sorry for the long post, but i do appreciate everyone's input. Thanks!
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