Export thread

MS4601 Piston scarring

#1

PTmowerMech

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.


#2

Hammermechanicman

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.


#3

PTmowerMech

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.


#4

PTmowerMech

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.



#5

Hammermechanicman

Hammermechanicman

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


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


#6

PTmowerMech

PTmowerMech

Turn down your speakers.
Pull the carb and boot and look at the exhaust side of the cylinder


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?


#7

Hammermechanicman

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.



#8

StarTech

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.


#9

Hammermechanicman

Hammermechanicman

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


#10

Fish

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.


#11

Tiger Small Engine

Tiger Small Engine

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.
That piston is heavily scored. If all that damage happened in 30 seconds, I would be both surprised and concerned. As Fish said, find out cause of the damage in addition to replacing piston, rings, and cylinder. I have had good results with Meteor as well. Less than half the cost of Stihl parts and good quality.


Top