Help diagnose toasted piston

[specialk6r]

This is the PTO side piston of my 04' King Cat. The sled has 550 miles on it and has 360 mains (way too rich.) I've only put a couple miles on it but the guy I bought it from was riding from 6-9000 ft.

The scoring is on the front of the piston where some of the top edge was falling apart. The little bit of scuffing is on the back of the piston, but a little to the rider's right.

The cylinder damage feels like aluminum deposits, as the rough areas feel higher. I'll know after I hit it with some muriatic acid. There is a little black junk in the bottom of the cases but nothing shiny.

So what do the experts think?

 

[76FOMOCO]

cant get a good look at the top or the other side of the cydr, but i think you cold sized it.

 

[spring snow hero]

have you been losing coolant? does the coolant show any dark/carbon color?

my guess is either a leaky head gasket or a oil related problem.

 

[specialk6r]

Haven't lost a noteable amount of coolant. The wear is exclusive to the front and back. It doesn't have the classic 4-corner cold seize marks, but I'm no expert.

Do you fellas suppose it would be alright to leave the bottom end alone and just do new pistons and gaskets? On that note, what are your opinions on just doing one side if the mag side looks good?

 

[spring snow hero]

I would want to ID the cause before I gave it my blessing. Oil related burn downs will some times scuff front and back, especially if you have a bigger clearance (like on the bigger bores) I asked about the coolant because one of the pics the domes edge looked like it could have been a coolant leak....too fuzzy for my eyes. if it turns out to be a head gasket than I would just clean and leave the bottom alone, if it was oil.......well, case by case there.

you blow any belts recently?

 

[bullfrog123]

If you already have it torn down, do both sides. I have never been a fan of one piston rebuilds. If one side puked, the other side deserves the same attention as well. Just my opinion.

 

[specialk6r]

I've only put a few miles on the sled, but the previous owner said it's blown one belt.

What would you do as far as "cleaning" the bottom end?

What's the technique for checking the operation of my oiling system? Thanks for the help guys.

 

[mattymac]

I've only put a few miles on the sled, but the previous owner said it's blown one belt.

What would you do as far as "cleaning" the bottom end?

What's the technique for checking the operation of my oiling system? Thanks for the help guys.

PTO seal if the other cyl looks good. The blown belt can easily mess up a PTO crank seal causing an air leak which will cause a lean condition like your seeing here. JMO though.

I take a heavy soulution of gas and oil and wash out the bottom end getttin all the junk out, usually about 5 rinses. But if your seal is bad (pop the clutch and the seal retainer off and look, though it may not be visible) then it will be the perfect time to clean it anyway!

There should be some alignment marks on the oil pump's arm, check idle and WOT to see if they line up correctly. Make sure thats theres no air in the supply line, theres a screw with a sealing washer to bleed it, DO IT TO BE SURE! they wont pump if theres air in the pump.

 

[JayO]

It is VERY possible that the crank is out of index if it blew a belt. My 04 KK went through 5 seizes, (I know, I'm a slow learner) always within a few hundred yards of the truck and I had 420 mains and 55 pilots just to try to be safe. They all looked like cold seizes. It was common for me to warm it up for several minutes and it would still stick as soon as the choke was turned off. I cleaned carbs, re-built the floats, upped the jets, you name it. Checked the oiler with a drill motor, checked the fuel pump, even ran extra oil in the gas, nada. I later learned that the 900 cat was/is prone to twisting the cranks. It is claimed that the bearing on which ever side is affected will get abnormally hot and attract the oil/fuel to it thus robbing the top end of the fuel it needs....? If it seizes more then once within a short distance and you have eliminated the other things , check the runout of the crank. my.02

 

[spring snow hero]

PTO seal if the other cyl looks good. The blown belt can easily mess up a PTO crank seal causing an air leak which will cause a lean condition like your seeing here. JMO though.

I take a heavy soulution of gas and oil and wash out the bottom end getttin all the junk out, usually about 5 rinses. But if your seal is bad (pop the clutch and the seal retainer off and look, though it may not be visible) then it will be the perfect time to clean it anyway!

There should be some alignment marks on the oil pump's arm, check idle and WOT to see if they line up correctly. Make sure thats theres no air in the supply line, theres a screw with a sealing washer to bleed it, DO IT TO BE SURE! they wont pump if theres air in the pump.

that is exactly where I was going

 

[CATSLEDMAN1]

If you don't have 1/2 or better of wash on the piston that didn't go down, you are just running too lean. Check with shop's that fool with this motor. Two 800s and a 900 king kat I often ride with are running 420/440 range, and yes they came with mid 300's jetting out of the box. Keith siezed his lightly @ 8000 ft altitude this spring with this jetting. The flat slides carbs on your motor are very difficult to tune the lean spot out of, takes some dilligence to be able to ride these twins at modest mid range throttle openings without smoking a piston. Add an egt gauge, water temp gauge, you'll be shocked at some of the high temps you see on this motor at very modest throttle openings.

 

[specialk6r]

Well I took the MAG side apart and found some very light scaring there too, as well as a dome with almost no wash, so the problem isn't isolated to the PTO side. I believe this rules out a bad PTO seal. I'm also doubting a double coolant leak, especially since my coolant looked new when I drained it, but I'll be safe and do new gaskets anyhow. The intake boots look new. This leaves me with the fuel system unless anyone has some other ideas.

Do these pumps ever fail?

Does anyone have some jetting specs for the same sled? What size pilots and where is your fuel mixture screw set (if that's what it's called on this sled.)

 

[sledmasterr]

Just a heads up, I run a 03 900 with SLP twins and reed spacers, ride from 5 to 9000'. I run a 420/430 with ZR needles to help with the mids. The 420/430 may be a size to rich but we ride up some damn cold draws heading up bright and early in the morning. You might be a little lean where your at with your jetting..good luck.

 

[squarehead55]

My 04' king cat 900 has a gutted airbox and that calls for a little different jetting, I have a 390 on the mag side an a 380 on the other, runs great, from 6,000 to 9,000 have a hard time getting egt's over 1180, a little rich but a little insurance as well, hope this helps,

 

[Rixster]

I burned down twice this winter on my king. Finally found the problem. there is a check valve where the oil comes out of the pump. It has to have 4-5 pounds of pressure to let the oil through. If it goes bad you get no oil. No oil = 2 burned down motors. My pistons looked EXACTLY like yours. The valve wasnt actully bad, just a bad smash washer on it so it leaked a tiny bit and didnt have enough pressure to push the oil through. After rebuilding I was premixing my tank at 100-1 so that got me through 2 rides before the gas was deluted to about 200-1 and I burned down again.

I would recomend SPI pistons, I have hadc great luck with them, plus the are forged not billet so they hold up to heat better then weisco pistons. As for cleaning out your bottom end, just run paper towles through it, you stuff 2 down and rotate the crank around, the crank will push them through. You can do that tell they come out clean. Even dump some solvant down there and clean it all out, works great.

 

[specialk6r]

When your motor went down due to no oil were your domes also black w/ carbon? I did notice on my first 2 rides that my sled wasn't drinking as much oil as some of my old sleds used to.

Can anyone tell me the best/easiest (at home w/o special tools) way to check the operation of the oil pump?

As far as jetting, does anyone have any safe suggestions for a stock sled? Are many of you using ZR900 needles? What clip and what size pilots?

 

[spring snow hero]

I would premix the first tank at 50-70 to 1 and see what the oil level does after checking all the above. cheap to buy a couple plugs....at least cheaper then pistons.

 

[specialk6r]

After all the suggestions I recieved, I found a fuel filter that looked to be about half full with sand and/or rust flakes and a bit of debris in the tank. I could still blow air through the filter as well as through the new one I replaced it with, but I was hoping that was my problem.

So I rebuilt the engine with new pistions and one new jug and all new gaskets, flushed the tank, raised the needle a notch, went one size bigger on the pilots, and put 390/380 mains in. I premixed it 50-1 and fired it up. As soon as it was idling I sprayed starting fluid behind the clutch and around the intake boots, and had no reaction from the engine, so I hope the PTO seal and boots are good. Once it was warm I feathered the throttle around the parking lot a few times then gave it a couple 100 foot pulls at full throttle (it ran great) and pulled it into the garage.

The MAG side plug was still whitish and wet, but the PTO side (the one that went) looked black and pretty dry, and the electrode had a whitish appearance. I pulled the power valves (both had equal mess inside) and saw that the PTO piston had some very minor scratches, that I could just BARELY feel when running a paper clip over them.

What do you guys think? Take it for a ride or keep looking for problems?

 

[spring snow hero]

how was the chamfer on the ports? you should not feel any scratching.....that takes a mechanical interference to cause a scrtatch....there is still a problem. perhaps someting was in the case and got picked up at start up. it sure sounds like you need to get your oil system checked out or you are gonna be here again.....I know it sux.

 

[specialk6r]

I'm not sure what the chamfer in the ports is, but it's a new cylinder. You think it could be oil related if I premixed?

The one thing that I may have fouled up is that after it was first idling for a few minutes, I tried move it forward and didnt realize the parking brake was on until I'd zinged it up near 5,000 rpm. It was probably not fully warmed yet.