MS440 - Seal Leak or Rebuild? Saw is not running.

Easy E

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Hi. I have a friend's MS440 to repair that I believe needs an engine overhaul. He owns a professional tree service and I suspect the saw is at the end of life on the current motor. I tested compression and got 60-65 psi which is know is well below what is required for it to start. It raised to 60 PSI quickly during the test but struggled to get above 65 PSI while cranking the crap out of it and I gave up after about a dozen pulls and it not going higher than 65. The engine was not running when he gave it to me for repair.

I'm wondering, is it possible there's a seal leak (or leaks) that are so bad it can cause that much compression loss or is it definitely time for an overhaul kit? To my mind, seals are cheaper and easier than complete overhauls and I'm trying to keep costs down. I have not done a leakdown test, I don't have the tools to do one (I could probably borrow or buy them if it's worth doing). However, with compression that bad I don't know if it's worth doing a leakdown test. All the threads I've seen on leakdown tests are with folks who have running saws that are having problems, not a no start condition like I have.

If it is time for an overhaul kit has anyone had experience with the Chinesium ones off Amazon? I know the general consensus is Stihl OEM or Meteor and I've already ruled out a Stihl kit based on cost. I mainly just want to be sure if I put the money and effort into an overhaul kit that it'll run when I'm done. I've already done a carb rebuild kit and a new ignition coil. All other consumables appear like-new.

It's also worth mentioning prior to this the saw caught fire and was professionally repaired after the fire. It ran for about 4 days after that and hasn't run since. It has no visible fire damage and I would not have known had he not told me.

Thanks in advance for any help.
 

Bob Hedgecutter

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Clarify- the guy gave you a 440 as a gift and you now own it, will run again if you can repair it and you will own a running saw?
Or guy gave you a saw to repair and charge him X amount to repair it so he can continue to use it as a pro tree service tool?
 

Easy E

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Clarify- the guy gave you a 440 as a gift and you now own it, will run again if you can repair it and you will own a running saw?
Or guy gave you a saw to repair and charge him X amount to repair it so he can continue to use it as a pro tree service tool?
2nd one.

I'm not a professional mechanic and the saw has been down for a long time so there's no rush on it. He's trying to save some money by having me do it and I'm trying to make a little side money because I'm mechanically inclined.
 

Bob Hedgecutter

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I am a bit loath to advise people way out of their depth to repair saws for others and for profit.

Low compression is subjective unless using a specific small engine tester- if using a box store automotive tester- 65 might be as good a reading as you ever get.

You need correct air/fuel mixture entering the combustion chamber, compression, spark and timing of that spark relevant to the piston position- thats all it takes for a simple 2 stroke to run- you are missing at least one of those "needs".

Seal leaks- could be some or part of your issues- sure. If the saw has done enough to have thoroughly worn the engine, seals being needed to be replace is just about a matter of course- along with the main bearings- which means a full crank removal case splitting adventure.

If you are going to repair saws for others for profit and to be put back into pro tree service use- you need basic diagnostic tools and enough knowledge to put a tool back in the owners hands you can warranty as good to go for the next year or two.
Not just get a non running saw running and have it eat a new top end for the same reason it ate the first.
You have to figure out why it became a non runner, repair that and any other wear items past their use by date- not just hit the forums in a hope someone else will diagnose for you.
Mityvac 8500 kit is almost a must have for what you are expecting to do- tools cost money, money is recouped in the price charged for repairs.

You need to pull the muffler and inspect the piston face through the exhaust port of the cylinder- put up some photos- it can help confirm low compression and give some hint as to what caused the condition (if indeed it is low).

OEM Stihl top ends, then Meteor/Hyway are pretty much on par for second place- after that it is an absolute crap shoot of Asian knock off crap.
But there is NO point slapping a new top end on a faulty saw unless the fault that took out the old top end is repaired- or it will tear that one up as well and you loose a friend over a crook repair, he looses money and still has a useless saw.

If your buddy is wanting to use pro tools in a pro environment to charge folk money for tree service work- he needs reliable pro tools and should be looking at a 462 long before repairing a worn out 440.
 

Easy E

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I appreciate the reply. I usually do more with lawn mowers and power washers than I do 2 cycle engines, but I'm trying to use this just as much of a learning experience as a way to make some extra cash.

I should have made more clear, I understand top ends don't generally just burn out for no reason, there's usually a leaky seal or some other cause and I need to diagnose that too.

I've already replaced the ignition coil as that needed done and it is producing good spark on a like-new spark plug. I did a carb kit on it but haven't tuned it yet, I wanted to try to make it run before tuning it as I don't think the carb is what made it stop running. It wasn't in great shape but it also wasn't bad enough for it to not run.

Is there a way to test/check the main bearings easily?

He bought it used and supposedly the Amish rebuilt it before he bought it. What all they rebuilt, we have no idea. He used it for 4-5 years after that then it caught fire because a guy he loaned it to revved it repeatedly with the brake on. After that, he paid a pro to repair it, and it ran for 4 days and died and now it's on my workbench because the last pro wanted another 2-3 months and another $2-300 to work on it again after my buddy had ran it less than a week for it to die again.

I'm learning a lot by doing this and trying to get a start in repairing small engines including saws because there's money in it and I enjoy wrenching on stuff. I wouldn't say I'm completely out of my depth here, but I haven't been this far into a repair before either.
 

Bob Hedgecutter

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Like new spark plugs are not new NGK plugs.
You cannot tune a carb on a saw that does not run.

You check the bearings by accessing crank play, checking for noise/rumbling and checking "feel" for uneven rotation or grittyness.

Loaning a saw is a no no- the guy that broke it should have replaced it. My guess is that repair was not thorough enough and the main crank seal on the PTO side was cooked.
If indeed it got hot enough to go on fire- odds are the crank is heat blued and the bearings likely suspect to boot.

So this saw was never new to the current owner- was a rebuild when he got it, so it is now on its about 3 or 4th repair- time to stop flogging a dead horse and sinking $'s into a parts saw. Those dollars should be invested in new replacement tools.

Offer to buy it off of him and repair it for yourself, that way you get to learn, no onus on you to repair it to a warranty standard and if it craps out you can keep repairing bits and learning.

Photos will be your friend- of the burned up clutch area and the piston as viewed through the exhaust port.
 

Easy E

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I will upload photos when I get home late tonight. The plug is an NGK (iirc) with no fouling or discoloration on it, hence why I say like new. I don't call it new because I didn't put it in myself. Most of the wear parts on this saw (filters, sprocket, plug etc...) are in that condition. They look new but I didn't personally install them so I can't rightly call them brand new.

I run e3 plugs in my personal equipment and I really like them. 2 Stihl saws, one Stihl line trimmer, a Ryobi power washer, a MTD with B&S engine tiller and a Cub Cadet with Kawasaki V Twin mower all have e3 in them and run very well.

My suspicion is the guy who fixed it after the fire didn't replace or inspect the PTO side seal hence why I was asking if that could be bad enough to cause that level of compression loss.

As for repair to a warranty standard, I told him up front I'm not making any express or implied warranty or promises on it but I won't abandon him if he has problems with it either, assuming I get it fixed. He was fine with that. He's been without this saw for months at this point and he's in no rush to get it back. I don't suspect the fuel is bad. There's no varnish or anything that would suggest bad fuel.

If it does need crank bearings I assume those are a separate part not sold with the top end kit and would need to be replaced using a shop press, right? I have a 12 ton press in my basement if that is the case. I'm sure cracking the crankcase open and doing work in there is a whole different animal than a simple top end rebuild, seal replacement and pressure/vacuum check.
 

Bob Hedgecutter

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Leaking seals have no bearing on compression.
A compression tester measures the compression of vapours and air in the sealed area above any ports that would have access to the crank main bearings and seal region.

Crank bearings are a totally different part from an Amazon top end kit and you will pay for them as one is a specific Stihl bearing not offered by any reputable aftermarket platforms.
You do not need a shop press- but it is involved and requires the two halves or the crankcase to be split and the crank removed. Will also require a gasket set and new main seals.

After the "fire" things could have been bad enough to have heat transfer damage the outer main bearing cage- or the lower big end needle bearing of the con rod to crank connection- if anything let go there, you may have had a piece of metal go up through the transfers and past the piston rings and lands- tearing the cylinder lining and damaging piston/rings. If that has happened you are looking at VERY extensive and expensive repairs.
Comes a point where you have to look at it and say, hey, you know what, by the time I put a new crank, new top end, new bearings and seals in this thing and charge the time to do it all plus the quality parts- its near the cost of a new machine.

You HAVE to diagnose, I cannot tell you what is wrong- only suggest possible causes. The saw has worked and been to the moon and back- many things are possible as to why it wont start.
You need to see if the piston is lean out scored to death first, then remove the cylinder to inspect further- go over the entire internals and assess the crank for viability of repairs.
 

Easy E

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Piston looks pretty bad. See pics. The cylinder looks ok though, definitely in better shape than the piston.

I need to get a set of T-Handle Torx before I can remove the cylinder. I don't own a set as I've always gotten by with a 1/4" driver and bits but that won't fly here due to clearance.

It is late here. I will post again once I get a T handle Torx set.
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Bob Hedgecutter

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You might as well ring your buddy and tell him the good news- he can go look for a new saw.
Remember the worst case scenario I referred to with the big end bearing loosing a needle- guess what is jammed in the face of the piston in the first photo.
 

Easy E

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I ordered a set off Amazon. They'll be here tomorrow. I'll know more once I take the top end off.
 

Easy E

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I took a closer look at it today. It doesn't feel like the needle is embedded in there. Definitely scratched up but I don't think that's the needle. We shall see tomorrow I suppose.
 

Easy E

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Crank looks ok aside from the debris that got in there when I took the cylinder off. I'll definitely clean that up before I put it back together. Interior of the cylinder also doesn't look all that bad.

I grabbed the shaft on the PTO and the flywheel side and tried to move them. I don't feel any play in them at all. I also discovered the intake boot was torn so that'll need replaced. I think the fire overheated this thing real bad and caused the failure more than anything else.

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Bob Hedgecutter

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Bottom end of con rod is blue- it has been real hot from being run lean.
I would not trust the lower rod bearing, but I am not there to inspect it either.

You rebuild what you want to rebuild- but for my money that saw has been there and done that and is due for either extensive rebuild including case split- better crank and bearings etc.
If you do decide to simply run with that crank- make sure there is zero up and down or rock side to side. Square horizontal no play movement is normal and do that to the extremes both left and right to inspect as much of the lower big end bearing you can visualise from both sides- if a bit of cage is missing- more will come if you rebuild it.
 

Easy E

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There is noticeable side to side rock, no up and down wiggle but there is enough side to side non-square play that it concerns me. Not to mention the overheated rod. He asked if the fire did it in or normal wear and tear. I told him that while the fire was probably what ultimately killed it, it had been running lean for a while and was on borrowed time to begin with. That's just my opinion on it considering the circumstances and what I can see on it.

I talked about what to do with it with him. Cost of a new crank, bearings, seals, gaskets, intake boot and top end kit is the better part of $300+ not to mention several hours of labor and a carb tuning when done.

He agreed with your opinion to just chalk it up to a loss. He's going to put it all in a box and maybe some day rebuild it but not this year.

I appreciate your help with this; I've learned a lot.
 

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If you can buy it- for under $100 as is- it might be a chance to learn a whole lot about the internals of a chainsaw.
As long as the case halves are not damaged beyond repair in any way- it is viable to rebuild it- just costly and time consuming to do so properly.

No use to him in bits in a box- not worth the time and effort for him to take it to anyone for repairs. However, it is worth it to you for a learning tool and build a respectable pro grade saw at the end of it.
 
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