Hey all, got a question for you. What would cause a piston to burn down in a small V shape on the front side(exhaust port side) of the piston? It happened to me in March up in the U.P. goin wide open down the trail. On my older sleds, if a piston burned, it usually was in a hole right below the spark plug. Why on this sled would it burn ahead of the spark? I've never had this sled run lean, if anything it ran a little on the rich side. I'll try to post some pics later today and show what it looks like. I'm also wondering how much I can hone(sp?) out the cylinder. There is a small bit of scarring from the piston melt down, and I need to know how much can be honed out and still have good compression with a new stock oem piston and rings.

Thanks in advance


burner

A lean condition caused it, and most likely your efi boot(between efi and cylinder) has a crack in it where it drawing air from. It was common on some older sleds if the clamps were over tightened from the factory......tigger

Becareful with the hone as Cat cylinders have a thin coating on them.Did it gouge the chrome lining or is there aluminum on the surface?

That sounds like a lean burndown, the exhaust temp rises above the melting point of the piston and it shows up at the exhaust port. On an EFI machine, look for an airleak as the cause. As for the cylinder, you should have it inspected by a knowledgeable person. It needs to be well cleaned and if any aluminum is on the nicasil surface it can be washed lightly with muratic acid. The careful application of the acid and the careful use of the hone may be able to make the cylinder servicable if the plating is not gouged through to the aluminum, or flaked off. If it can't be cleaned up, then get a re-nic'd cylinder, or look for a good used one. A few vertical scratches, or scoring in the nicasil are not the end of the world and won't make for any noticable impact on performance.

I took the EFI system off and checked the intake boots but did not find any problems with the boots. Here are some pics of the cylinder and piston











Thanks for the replies

burner

Right above your exhaust bridge, there is a small bright spot with horizontal chatter marks on it. Looks like the nicasil is worn down to the aluminum there. Be sure to check it out - I pulled my pistons out after 5000 miles and on both of my cylinders the nicasil was worn down to the aluminum right above the exhaust bridge.

Defenatly caused by running lean. Could have been an air leak or could have been water in the gas. Injectors flowing water instead of gas will do the same thing.

That cylinder looks like it will be fine, just dissolve the alluminum off the walls with muracidic acid and hone it out. :div20:

I did the same thing last year to my PTO side piston. Not quite as bad as yours, but the exhaust side was knife edged. Just rebuilt it this year with a new top end and am not quite sure exactly what caused it. My throttle body flanges were cracked but not all the way through to the point that they would have caused an air leak, I think. Could have been poor quality fuel (my sled drinks 89 octane minimum) or my stator could have been cutting out fuel supply to the injectors as it was going bad at the same time. Others that I know have done the same thing due to poor fuel.

bad gas + wide open = what your pistons look like.

Thanks for all the help guys, I do appreciate it. Is there anywhere that I can send the cylinders to have them replated? Or is there a place where I can get a used/replated cylinder for a low price, or maybe core or trade in? I gotta get this thing fixed so that the wife gets off my butt about riding her sled around

Thanks again


burner

That cylinder looks like it could be cleaned up, like others have said. There are a number of places that will replate your cylinders. Millennium Technologies will send you a replacement for ~$200 US with core exchange, your dealer may be able to do it for you. http://www.mt-llc.com


You do need to find out what the problem is before running a new piston, and maybe new cylinder, to the same fate. If you can't find cracks in the intake flanges then you should look to the crank seals. A pressure test will tell you there is a leak in the engine, but you'll need to take the engine to a shop to have that done.

I would take the cylander to small engine shop and have them clean it for you, probably less than $30.00. put it back together with a new piston/ring/clips, and then check your compression. get it running and check the crank seals with some starting fluid. when the sled is running, spray the starting fluid at the base of driven clutch, if it increases idle, it is your crank seal, do the same by the stator. If it was bag gas, you wont know. but still run some dry gas thru it.

This can only test the PTO end seal. A proper pressure test is needed to check the condition of the MAG end seal as it is behind the stator and flywheel.

she got a big drink of water......
clean out tank add dry gas (alcohol based)

Cat reccomends fuel injector cleaner for there efi sleds. A dirty injector could have caused what you have. I run it in the first tank every year on my efi sleds.....tigger

if you know how to look at the pics., you will see that the exhaust port has been steam cleaned........
she got a drink of water , period........