MS440 top end rebuild

Keepfixin · December 24, 2023, 05:22:18 AM

Tearing apart a project ms440 because a no run condition. To find out it had a scuffed piston/cylinder and a brittle fuel line that couldn't keep the filter in the tank! Completely fell out when dumping fuel out. My diagnosis was the saw had obstructed cooling fins (at least 40% blocked) which led to overheating and a breaking apart fuel line which led to an air leak to cause a lean running fuel mix. So I ordered a farmer tec piston kit from ebay to run in my old 044 cylinder that I have laying around. The old 044 cylinder had a lot less scoring than the original ms440 cylinder on the exhaust side. But I honed the cylinder and believe that there is bare aluminium showing by the port :-/. Will still use it to see what happens with a few tanks ran through the saw. So a hone can eat through the nikasil! Also wanted to replace the rings with the nwp 50mm x 1.2mm ductile split grooved rings but Bailey's is the only place that I could find them. Problem is that they want over $19 shipping for a $12 part to Alaska! So I'm at a standstill till hopefully I can find some reasonably. Heard a lot of good reviews and also that they break in fast so thought they would be a perfect fit for this experiment.

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Keepfixin · February 01, 2024, 01:38:57 AM

Got the saw back together last week. Compression wasnt the best at first. But started it, then warmed it up, shut off, and then repeat. Did that a few times and compression seemed to feel more on the pull cord. Even started it up cold at -36°F!! Stayed running on the 6th pull. Sorry I only got one picture to compare the underside of the farmer tec piston vs the oem piston in its cylinder. Will check compression later after break in.

Keepfixin · February 21, 2024, 03:16:09 AM

Just checked the compression on the MS440 with the cheap aftermarket piston. It came up to 142 psi compression. It also had .009" ring end gap on top ring and .012" ring end gap on bottom ring. So now lets see how long it runs for!!!

Al_Smith · February 21, 2024, 07:37:26 AM

Normally a low spot on a cylinder doesn't hurt that much unless it's a giant scalp because the rings will span it .On the other hand a high spot will break the suface tension of the oil film .If you keep it tuned just a wee bit rich and don't get stingy with the oil ratio it could run for a long time with no problems .
140 PSI on an old cylinder in time will rise as the piston rings "wear " in .If not 140 is not that bad .Things don't have to be perfect nor do you need to run high priced premixed gasoline nor some high priced mix oil to get good service out of a rebuild .Might run forever .
You might think about doing a little work on the muffler so it can breathe better .BTW keep a good sharp chain on that thing and don't crowd it .It's not always a race like some think .If you listen to that engine it will tell you where it wants to run .

Keepfixin · February 21, 2024, 07:13:41 PM

Thanks for the insight. I put new caber rings on an old 10mm pin 044 about 11 years ago. To what i could remember I honed it then put it together for only 120psi compression. Never did run right so sold it on ebay. Yes I will run it a little rich for sure! I'm using Amsoil Saber in my saws at about 60:1. At 50:1 they smoke like crazy and foul plugs. Also use Stihl oil at about 45:1. Saws run good at 50:1 but engine life expectancy is quite a bit longer with more oil! I'll try to do the muffler work here soon. A good running ms440/044 or ms360/036 is a good noise to hear!

Keepfixin · April 18, 2024, 03:51:02 PM

Well got the saw cutting wood and there seems to be a leaning out problem that thats becoming more prominent. It would run great, slightly lean but the limiter caps limited adjustment, then would just all of a sudden just lean out. Sometimes I could save it by feathering the trigger. But yesterday it was just dying then I would have to full choke it then it would run only a few seconds then die again. So I took the carb apart and it looked good. Also decided to change the crank seals because I thought that could be it since it was a leaned out and burnt up piston and cylinder. But no change. Still was dying. The crankcase passed a pressure and vacuum test so I'm thinking carb. So last night I pulled off those limiter caps and adjusted a little more richer and I haven't heard any leaning out! But we'll see after some cutting. When I pressure tested I noticed that the piston skirts had light scratches on it so maybe those limiter caps set improper are to blame for the leaning out and the burnt up condition it was in before I fixed it? One good thing is I made a flywheel side seal puller. Worked like a dream!!

Keepfixin · April 18, 2024, 08:32:08 PM

So it still stalls and then I have to choke it to run only a few minutes. So its put up till I remedy the problem. Did put my 044 carb on it and it didn't stall but it mirrored what my 044 is doing. Which is stalling only at a certain trigger position. Let off the trigger or accelerate and it runs fine. So I might be getting two carbs..... But I'll put the 440 carb on my 044 to verify.

Keepfixin · April 18, 2024, 08:35:13 PM

Picture.

Keepfixin · April 18, 2024, 09:45:03 PM

Well the 044 died once with the ms440's carb. Not as much as the 440 but it still died. Both saws pass pressure and vacuum test so it must be the carbs.

Guydreads · April 21, 2024, 03:10:38 PM

Check for blocked impulse as well. I had a saw that gave me 5-6 hours of trouble for it to be a clogged impusle line.

DHansen · April 21, 2024, 09:54:30 PM

It sure sounds like a carburetor failure. Does that model carburetor use any check valves in the idle or high-speed circuits in the carburetor? I have had these check valves cause similar issues. I have had no luck trying to clean the check valves or restore the check valve operation. In the end after several attempts at cleaning and rebuilding, a new carburetor was the solution. Lots of wasted time, wish I had bought a new carb sooner.

Keepfixin · April 24, 2024, 03:03:37 AM

Thanks for your help and ideas! I will be looking at those impulse lines here shortly. Yes I believe those check valves are in the top just before the venturi? One carb is a Zama and the other is a Walbro. These newer carbs have so many issues. Looks like I'll be shopping for some carbs!

Al_Smith · April 24, 2024, 02:23:12 PM

Quote from: Keepfixin on February 21, 2024, 07:13:41 PMI'm using Amsoil Saber in my saws at about 60:1. At 50:1 they smoke like crazy and foul plugs. Also use Stihl oil at about 45:1. Saws run good at 50:1 but engine life expectancy is quite a bit longer with more oil! I'll try to do the muffler work here soon. A good running ms440/044 or ms360/036 is a good noise to hear!

Well it's your saw use whatever ratio of mix oil and brand you want .However that's much less oil ratio than I would be comfortable with .Now explain something to me .At 60 to one it doesn't smoke but at 50 to one it does ? After that explain something else .i run everything I have at 32 to one yet they don't smoke .Perhaps my less expensive Briggs and Statton oil is better than that high priced Amsoil

or Stihl branded stuff ? BTW I really enjoy the never ending great oil debate .Which includes engine mix oil plus bar and chain lube .Is salad oil a better choice than oil from an oil well ? Then the reverse of bar oil on a tossed salad would really be a bad choice .

Keepfixin · April 25, 2024, 02:34:45 AM

I would consider Amsoil Saber a concentrated 2 cycle oil. Just like anything concentrated you usually use less to get the same results as with using more. So Amsoil claims that its good to 100:1 right. That ratio is double that of 50:1. But the saws run pretty similar. Lean and mean! They definitely have more power but at the cost of longevity. But at 50:1 with the Saber it runs rich. So half of 50:1 would be 25:1. That's why it smokes. So my 60:1 would be about equivalent to 32:1 ,if this math is correct, which my saws and I like. But the other day I was wanting to get some fresh fuel with some non synthetic 2 cycle oil to break in a couple saws at 45:1. All the saws hardly smoked . Just my two cents. Haven't burnt a 2 cycle up yet and I've been running them and mixing gas since I got my first chain saw at 10. Just like Amsoil Dominator 2 cycle oil gives me headaches but the others oils don't. So is everyone's oil formulas are suited for different tasks and mixing ratios. And I'll pass on the bar oil covered salad!!!!! Olive oil much nicer ;-) with a sprinkle of salt. Hey I also got a digital inductive tachometer the other day. It reads pretty fast and was affordable. We'll see if it lasts :-)