My $50 MS440 rehab

[John Lyngdal]

So I picked up this MS440 off CL:

Stihl Chainsaw - $50 (Dallas)​

It was described as being in "salvage" condition and the owner was upfront and said the saw seized up during use.
I figured it was worth the price for the parts I could see and if i t was straight gassed the cylinder might be salvageable.
I read the service tags on the wrap, and one of them said "Needs A Tune-up" and sure enough there was a new spark plug in the cylinder.
The saw wasn't seized, but look what I saw after the muffler cover was removed:

That's right a chunk of piston between the rings is missing and my odds of being able to salvage the jug were dropping quickly.
I proceeded to remove the jug from the crankcase and look at the piston more closely. What I saw baffles me.

There is no damage to the top of the piston at all nor are there any marks at the top of the cylinder.

 

[John Lyngdal]

My next step was remove the aluminum deposits and inspect the damage to the cylinder walls.
Before:


After:

The results are a marginal cylinder, so I'm going to install a Chineesium piston and run the saw for a few tanks and see if the cylinder walls improve or degrade. That will help me decider to install a Meteor piston or a Meteor piston and cylinder.

 

[2StrokeFondler]

Nice find and good work

 

[Bearcat22lr]

nice work & nice find

 

[Mad Professor]

Worth $50 for sure even if cyl don't clean up.

Is that still some transfer left? Hard to tell from picture, if so get it all off before proceding.

In this case, I like the idea of sacrificing a chi-com piston to see what happens.

 

[John Lyngdal]

Worth $50 for sure even if cyl don't clean up.

Is that still some transfer left? Hard to tell from picture, if so get it all off before proceding.

In this case, I like the idea of sacrificing a chi-com piston to see what happens.

I couln't be sure if the off color areas are remaining transfer or just caused by a surface finish difference. I wasn't seeing any evidence of bubbling when treated with acid, but I was getting green coloration on the swabs indicating nickel chloride. So I decided to stop there and install a cheap piston and run the saw, then reinspect after a few hours of running.

 

[John Lyngdal]

I put the saw back together last night with a two port muffler.
The piston arrived weeks ago, but I didn't like the feel of the wrist pin bearing so I ordered a replacement.
It took quite a few pulls to get it started, but it ran properly.
I did some carb adjustments to help with the starting issues and cut a little firewood today.
Going to pull the muffler cover and take a quick peek at the piston when I have time.

 

[John Lyngdal]

Did a carb swap on the saw because I didn't like the plastic limiters on the OEM carb.
I put the 32" bar back on the saw and fired it up with 40:1 Saber with ethanol free premium.
Adjusted the low jet so that it didn't bog with the throttle applied and ended up at about 2700 RPM.
After a little warm up I ran the saw up to WOT. It was running rich and only 9800 RPM so I started cranking in the high jet and watching the engine RPM increase. As I was leaning it out I could hear the pitch change and the started RPMs climbing rapidly. I stopped at just shy of 15000, knowing that this was already too fast to be running it and opened up the high jet until the engine speed dropped to 14,400. The spec speed for the saw is 13,500, but if it likes running a little higher so be it. Then again, I might open the jet up further to get the 4 stoke burble.

 

[ericm979]

That's right a chunk of piston between the rings is missing and my odds of being able to salvage the jug were dropping quickly.
I proceeded to remove the jug from the crankcase and look at the piston more closely. What I saw baffles me.
View attachment 1011456
There is no damage to the top of the piston at all nor are there any marks at the top of the cylinder.

Likely it was run with insufficient oil. The piston skirts get damaged first and often the resulting piston slap is enough to get the operator to stop.

It's nice that the cylinder seems to have cleaned up ok.