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96 XP PTO PISTON in peices , WHY? Pics inside
- Thread starter Rosie2514
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Austrian Rotax
Active Member
Ive seen similiar cases and this looks to be a lean issue, did you clean your fuel filters/ internal carb filters? did you replace your oil filter often? most people say the oil pump is bullet proof.
Skidoodle
Member
Looks like a lean condition and the piston was in the process of MELTING from excessive heat caused by too lean of a mixture for that cylinder. You will probably find some aluminum on your spark plug too, (which by the way, is a very good early indicator of leanness, IF your lucky enough to find it early)
Strizzo
Well-Known Member
I'd suggest you test your oil pump while you have everything apart. the 787 has check valves on the rotary cover that, if they fail, won't reliably move oil into the cylinder. make sure they hold back a little bit of pressure from flowing in, 2-3 psi, and lock down tight on vacuum.
I don't see lack of oil evidence here. When that happens everything looks grey and dusty. Is the rave valve chipped?
I'm thinking detonation possibly, lean on fuel since the oil was there? That's the exhaust side of the piston so it would get hotter and possibly detonate the ring land. Just make sure you go thru everything. I know you not starting the debate but pre mix wouldn't have stopped that just because the oil is there, the fuel is what would cool the crown.
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Raves are fine so we are going with lean. Here are a couple common culprits:
1) The fuel selector is faulty. Change it regardless it's $25
2) loose fuel line connections or bad O-ring on the top of your screw on filter bowl.
If your carbs were done correctly then it is a fuel supply issue. Any air leak in the system and it's like trying to suck a soda up a cracked straw.
1) The fuel selector is faulty. Change it regardless it's $25
2) loose fuel line connections or bad O-ring on the top of your screw on filter bowl.
If your carbs were done correctly then it is a fuel supply issue. Any air leak in the system and it's like trying to suck a soda up a cracked straw.
Then you went lean from plugging up the little filters in the carbs.
Rosie2514
Active Member
I want to say your right . I hadn't cleaned then in over a year 
Looks like this happened because of my laziness lol
Live and learn !
But I always thought you could have signs of them being clogged such as hesitation, bogging and so on . My ski didn't have that . My ski HATED hot restarts though . Especially after 10 mins or so .
The only time it bogged was the last 5 minutes before she finally called it quits .
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Looks like this happened because of my laziness lol
Live and learn !
But I always thought you could have signs of them being clogged such as hesitation, bogging and so on . My ski didn't have that . My ski HATED hot restarts though . Especially after 10 mins or so .
The only time it bogged was the last 5 minutes before she finally called it quits .
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68ragtop
Well-Known Member
I am on board with the lean fuel answer. I have rebuilt several snowmobile engines that had this same exact destruction. Piston gets hot & expands larger than it should be & the hottest spot is right in front of the exhaust port. clearances get the tightest in front of the exhaust port & the land breaks off from the binding.
As far as color, the color of a scattered piston means nothing. they all turn grey once they grenade & you can't tell spit from it anymore.
As far as color, the color of a scattered piston means nothing. they all turn grey once they grenade & you can't tell spit from it anymore.
68ragtop
Well-Known Member
Here's a picture of a piston from an engine I rebuilt a few years ago. This was the good side. When I pulled it apart, I found the crown had no piston wash at all, evidence that it was running lean & hot. If you look close at the pictures, you can see where the ring groove is pinched tighter. basically the land is mushroomed & fatigued right in front of the exhaust port only. This piston was headed for sure destruction just like the one in your pictures.
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Just take one small line and hook it to both nipples. If you buy the kit it comes with two little caps to plug those fittings and a cover for where your oil pump was
68ragtop
Well-Known Member
I have never seen the kit, but does it have some sort of breather for the RV case? just curious.
No prob, I have no issues with Pre-Mix. My Speedster is set up for pre-mix, it's easy. I did it when I kept gagging the MAG piston on the one engine in the Speedster and swore it was oil related, came to find out it was an air leak killing the engine. But now, I'm done with pre-mix and switching back to injection. Just looking to get back to simplifying and cutting back on the gallons of oil I would go through every season. @ 40:1 I use a full jug of oil to a fill up of gas (40 gallons), so I constantly have to have XPS-II on tap. I don't mind the cost but some days I look at the $120 fill up(about a 1/2 tank) just to go for a ride and scratch my head.
Most just just leave the tank hooked up, plug the line going to the pump and install the kit pictured. race guys will ditch the tank and loop the RV from one side to the other.
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I would just leave the tank, much easier to keep an eye on the level. Fill tank 1/2 way, mark the level with a sharpie. Check before you ride, easy. Don't forget, you'll need to mod the filler cap.
If you want to remove it here you go, get one of these. Just use the "T"
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