MS4601 Piston scarring

[PTmowerMech]

Ooops, it's a MS460... Not a 4601.
The customer dropped this off and said it had been sitting a while and just wanted me to check it out. Said he hadn't even tried to start it. So I pulled the plug, which looked fine. Peaked at the cylinder walls, they were fine. Removed the muffler and checked the screen and the cylinder walls. (but didn't really look at the piston) Everything looked good. So I put some fresh fuel in it and pulled on it a few times and it fired up and ran. Ran it for a couple of minutes, and it was good. It was oiling the chain, so I set it aside and called the customer to pick it up.

When he got there, It fired right up, but within about 30 seconds, it fell flat on it's face. Like it was out of fuel, or not getting any.
I pulled and pulled and got nothing. Checked spark, which was good. Then did a compression test. It was below 90.
Pulled the muffler again, and this time, I had to rotate the piston up then back down, I noticed the edge of the piston was scarred bad. But the cylinder walls were still not bad.

Is this even possible? Because I've never seen this. It's usually the cylinder walls that are scarred.

 

[Hammermechanicman]

Most 2 smokes when run lean or not enough oil gets the hottest at the exhaust port and that will score the piston and cylinder on the exhaust side. The cylinder you can see may look good but piston and exhaust side scored. Ran 30 seconds???? Sounds like you straight gassed it.

 

[PTmowerMech]

Most 2 smokes when run lean or not enough oil gets the hottest at the exhaust port and that will score the piston and cylinder on the exhaust side. The cylinder you can see may look good but piston and exhaust side scored. Ran 30 seconds???? Sounds like you straight gassed it.

It was mixed fuel.

But I'll recheck the cylinder again. But I'm almost positive it wasn't scarred.

 

[PTmowerMech]

Turn down your speakers. And pay no attention to my singing. lol. I didn't even think about the music playing. Just trying to get a good shot at the cylinder and piston.

 

[Hammermechanicman]

Pull the carb and boot and look at the exhaust side of the cylinder

Meteor Cylinder Kit 52mm fits Stihl 046, MS460

Stihl 046 MS460 chainsaw cylinder and piston assembly Meteor brand Nikasil plated cylinder and piston assembly Made in Italy. Highest quality aftermarket kit. Replaces OEM: 1128 020 1217 52mm bore

www.hlsproparts.com

Nice thing about the stihl pro saws is you can do a P&C swap pretty easy.

 

[PTmowerMech]

Turn down your speakers.

Pull the carb and boot and look at the exhaust side of the cylinder

Meteor Cylinder Kit 52mm fits Stihl 046, MS460

Stihl 046 MS460 chainsaw cylinder and piston assembly Meteor brand Nikasil plated cylinder and piston assembly Made in Italy. Highest quality aftermarket kit. Replaces OEM: 1128 020 1217 52mm bore

www.hlsproparts.com

Nice thing about the stihl pro saws is you can do a P&C swap pretty easy.

I can see that side pretty good thru the spark plug hole. Obviously not as good. But from what I can see, It's not bad either. I'll definitely check further before ordering a P&C.

I'm thinking I gotta be missing something because there's no way that piston can be that bad and the cylinder not look close to the same. Right?

 

[Hammermechanicman]

Nikasil cylinder is way harder than the aluminum piston and will have some transfer from the piston. Some fine lines. You can probably cleanup the cylinder and get by with a piston and rings. Compression is down because the rings are stuck in the piston.

Meteor Piston Kit 52mm fits Stihl 046, MS460

Meteor brand piston and ring assembly Highest quality Italian made. Stihl 046, MS460 chainsaw Replaces OEM part: 1128 030 2009 52mm

www.hlsproparts.com

 

[StarTech]

Personally I would recommend going with PNC kit instead just a piston kit. And don't forget to order the cylinder and muffler gaskets.

Two different cylinder gaskets were used.

1128 029 2304 1 Cylinder gasket 0.3 mm

1128 029 2306 1 Cylinder gasket 0.8 mm low compression

Use the 0.3 mm one if the saw is using a decomp valve; otherwise, use the 0.8 mm one.

 

[Hammermechanicman]

I always go with P&C kit. Meteor the best I found so far.

 

[Fish]

Usually the "damage" to the cylinder is just pasted on metal from the piston, but you need to pull it down to see. But before that, you should try to find out what caused the failure.