Stihl MS500i cylinder and piston

[Moparmyway]

I haven’t had the chance to get the saw from the dealer or tear mine down. I was running the stihl orange 50:1. Just went to the grey bottle a month ago.

Good bit of information here. Do you believe in coincidences ?

Not to mention my fuel/oil mix is used in the 261’s 251’s and 201’s more than the 500’s so why am I only seeing a supposed failure in these “pro saws?” .

In my experience, smaller 2 cycle motors need less oil than larger ones.

Yup working long hours can certainly limit your chainsaw rebuilding ability .
Scoring on the cylinder can say alot about what happened also ,so everything else is speculation about said saws.

Exactly !!
Pictures of this/these will help greatly

Can you explain what a four corner seizure is?

Scoring/siezing marks on 4 opposing sides of a piston. Usually caused from not warming up the motor, more commonly seen with 2 cycle use in colder weather.

OEM cylinders are worth every penny spent, but the best way for us to help you is for you to tear down your saw and get us some good pictures of the piston & cylinder. We’re also interested in seeing how much, or how little, oil is in the bottom end.

@TINYHULK
I’ll make you an offer here:
Send me your saw, I’ll tear it down, posting pictures of the process, we can usually save the cylinder, but most likely you’ll need new piston & rings. I’ll port your good cylinder (new if necessary, the original one if possible), customize a muffler mod for your liking and send it back to you. I’ll pressure and vac test before and after, also posting pictures of the process. You pay for parts and shipping only. You’re a hard working tree guy, and don’t have much time for saw repairs, you can follow along, learning as we go. I’ll turn the saw around and get her finished and back on her way home to you within a week of having the necessary parts. Sound fair ???

 

[Wonkydonkey]

Can you explain what a four corner seizure is? I’m still learning to navigate these forums, which is why I haven’t posted much but I’m lurking and reading almost every day.

good afternoon. I found a pic of what we call four corner seizure, Essentially it’s where the piston expands quicker than the cylinder because of the way the piston is made expands unevenly hence the four corners seizure. in this picture you can see the flywheel side is been cooled and that there’s no point of seizure on that side.

i beleave this can happen to any saw in any climate warm or cold if not allowed to warn up before being ran hard at wot cutting/sneding or in this case on this blower.
Others may/do have slightly different ideas

btw this pic came from here page 88
https://s3.amazonaws.com/com.bryane...chnical-reference-guide_final_interactive.pdf

 

[Maintenance Chief]

Good bit of information here. Do you believe in coincidences ?


In my experience, smaller 2 cycle motors need less oil than larger ones.


Exactly !!
Pictures of this/these will help greatly


Scoring/siezing marks on 4 opposing sides of a piston. Usually caused from not warming up the motor, more commonly seen with 2 cycle use in colder weather.

OEM cylinders are worth every penny spent, but the best way for us to help you is for you to tear down your saw and get us some good pictures of the piston & cylinder. We’re also interested in seeing how much, or how little, oil is in the bottom end.

@TINYHULK
I’ll make you an offer here:
Send me your saw, I’ll tear it down, posting pictures of the process, we can usually save the cylinder, but most likely you’ll need new piston & rings. I’ll port your good cylinder (new if necessary, the original one if possible), customize a muffler mod for your liking and send it back to you. I’ll pressure and vac test before and after, also posting pictures of the process. You pay for parts and shipping only. You’re a hard working tree guy, and don’t have much time for saw repairs, you can follow along, learning as we go. I’ll turn the saw around and get her finished and back on her way home to you within a week of having the necessary parts. Sound fair ???

Thats extremely Generous! I'm half tempted to run out and buy one ,write Tiny Hulk on it and send it to you! Lol

 

[TINYHULK]

@Moparmyway that would be absolutely amazing! DM me your address and I will get my saw sent to you this week. While you work on my personal saw I will also tear down my bosses 500i and join the journey in these repairs. I have the desires mityvac pressure vac tool I want. What adapters do y’all recommend for doing the pre/vac tests on the saws? Ofcourse I don’t want to spend $500 in adapters but at the same time I want a reliable way to test stihl saws from a 201 to a 661.

 

[TINYHULK]

@Wonkydonkey thanks for that reference! Lots of good info in there for me to study over. I wish the dealer was open tomorrow so I could go get the other saws and do some work on them tomorrow. Off topic but I also have a 440 and 460 barn finds that I plan on rebuilding. When I have time for that I’ll make a thread to bring everyone on that journey

 

[TINYHULK]

@Moparmyway can you send me some examples of your work? My saw has the west coast bark box, suspension kit, felling spikes, and an 8 pin sprocket. Should I change any of these back to factory so it can be built to match your desired airflow for the performance of the porting

 

[Moparmyway]

Just click on my name, hit “profile page”, then hit “postings” and start your search. I’ve ported quite a bunch of saws for guys on this forum, and lots of members who go to GTG’s have ran saws I’ve ported. I’ve got my own MS500i that I ported that’s pretty impressive too.

Some of these guys might be willing to vouch for my work ….
@SOS Ridgerider
@sawmikaze
@drf256
@Onan18

No need to remove anything except the fuel, oil, & sawdust from your saw.

 

[Wonkydonkey]

To add something to this thread, so thoughts and questions!?
This/these pics are from a friends saw (171) who said it didn’t start or run well and then became impossible to start.

when I came around to his place he insisted on trying to start the saw. I just said let me look at the exhaust first.

so I eventually did get to look … well you can see the piston pic I saw through the exh,

so my questions are what you think what happened to the saw ,, see pics…
but I will be honestly and say he already fućked a ms151 a day or two before…
I"m not trying to be smart. It’s just to point out that *s-word happened and I had to fathom out what he done wrong
So here’s the pics for you or anyone else to decide, although I don’t have the other pics of the 151.. but really the only difference is/was the intake side was different.

i will add my thoughts of why later… but it’s not cold here when this happened..20\25c*

Edited to add another pic, as I miss uploaded the intake side

 

[TINYHULK]

Just from the brief reading in the book and what y’all have said it looks like the four corner seizure with the exception that the flywheel side of the intake isn’t seized. I feel like there is something else going on here but I need to study it more

 

[Moparmyway]

I’d say there is a very good likelihood that saw was ran hard immediately after it started, 4 corner siezed and the exhaust started chewing itself up, coupled with it being a strato, there probably wasn’t much oil between the piston and the cylinder

Doesn’t matter if it’s warm outside, different metals expand at different rates. Gotta give it a little time to get some heat into the cylinder before going at it

 

[Nutball]

@Moparmyway can you send me some examples of your work? My saw has the west coast bark box, suspension kit, felling spikes, and an 8 pin sprocket. Should I change any of these back to factory so it can be built to match your desired airflow for the performance of the porting

He machined more compression into a 660 cylinder I have, and it is a strong runner. Just send it.

Today I go get my 500i to start bucking some trees on a clearing job, my guys were using it end of day yesterday and it was fine for them.

Now you know not to let other people use your saw.

 

[TINYHULK]

Thanks guys! I knew to let a saw warm up some before running it but never realized how critical that was. We’re not working tomorrow so I’m going to go get my saw from the yard and get it ready for shipment. My guys will be required to read those failure pages in that stihl book and I’m going to be implementing some new policies real soon. Nice to see you here nutball!

 

[Wonkydonkey]

Just from the brief reading in the book and what y’all have said it looks like the four corner seizure with the exception that the flywheel side of the intake isn’t seized. I feel like there is something else going on here but I need to study it more

I’d say there is a very good likelihood that saw was ran hard immediately after it started, 4 corner siezed and the exhaust started chewing itself up, coupled with it being a strato, there probably wasn’t much oil between the piston and the cylinder

Doesn’t matter if it’s warm outside, different metals expand at different rates. Gotta give it a little time to get some heat into the cylinder before going at it

i went and took those pics yesterday as I kept the p&c.
Yes absolutely correct, although I was not expecting it when I was taking it apart.

this guy had another saw a ms151 (rear handle for wood carving) that he seized a few days before and this wasn’t a 4 corner seizure.
I thought it was his fuel mix 50:1 as I found out he was topping up the can and splashing a bit more oil in it and/or maybe forgot to add it ? So it could have been a bit of both ?
And both saws were less than a yr old


Anyhow I think he learnt his lesson 2 goofed saws in a 2 or 3 days.. well I hope he learnt…because next time I won’t be so quick to repair them for free although he is a good mate..

edit; when Ive been working with him before , I always used my own fuel… and I guess now I always will use my fuel and nobody else’s..

 

[qurotro]

To add something to this thread, so thoughts and questions!?
This/these pics are from a friends saw (171) who said it didn’t start or run well and then became impossible to start.

when I came around to his place he insisted on trying to start the saw. I just said let me look at the exhaust first.

so I eventually did get to look … well you can see the piston pic I saw through the exh,

so my questions are what you think what happened to the saw ,, see pics…
but I will be honestly and say he already fućked a ms151 a day or two before…
I"m not trying to be smart. It’s just to point out that *s-word happened and I had to fathom out what he done wrong
So here’s the pics for you or anyone else to decide, although I don’t have the other pics of the 151.. but really the only difference is/was the intake side was different.

i will add my thoughts of why later… but it’s not cold here when this happened..20\25c*
View attachment 347856 View attachment 347857 View attachment 347858
Edited to add another pic, as I miss uploaded the intake side
View attachment 347859

Scoring the whole exhaust side usually is not caused by overheating.. But not enough oil or no oil at all!

 

[Maintenance Chief]

i went and took those pics yesterday as I kept the p&c.
Yes absolutely correct, although I was not expecting it when I was taking it apart.

this guy had another saw a ms151 (rear handle for wood carving) that he seized a few days before and this wasn’t a 4 corner seizure.
I thought it was his fuel mix 50:1 as I found out he was topping up the can and splashing a bit more oil in it and/or maybe forgot to add it ? So it could have been a bit of both ?
And both saws were less than a yr old


Anyhow I think he learnt his lesson 2 goofed saws in a 2 or 3 days.. well I hope he learnt…because next time I won’t be so quick to repair them for free although he is a good mate..

edit; when Ive been working with him before , I always used my own fuel… and I guess now I always will use my fuel and nobody else’s..

This looks like a "lean seize " or not enough oil to me. I've seen similar scores of saws that have a pin hole or crack in the fuel line. Smears the piston up on the intake side or just to the sides of it.
Thing about not having oil or enough oil is that it usually smears the hole piston and you can see the dry bearings when you open the saw.
Ive see cold seize saws where the saw just stops instantly and the piston and cylinder were salvageable because the piston quit moving, if its got an air leak or not enough oil some people continue to try and run the saw which fubar's the works.

 

[Nutball]

A stihl dealer said a 029 I salvaged from their dumpster was scored all the way around, but it looked great inside as far as I could tell, 120psi compression. Maybe the rings were just worn out or stuck. Anyway, I don't trust the dealers much.

 

[TINYHULK]

Got me the idea of hitting up my stihl dealer and seeing if I can get the trash saws from them! We have a great relationship with them. I just don’t think they have a skilled service team but tbh I’ve been to every dealer in the area and have yet to find a really talented tech in this area

 

[huskihl]

Straight gas or not enough oil usually scores evenly all the way around the piston. Like the other Kevin said, I think this is a combination. Looks like he started it up and ran it without warming it up at all and stuck the rings a little bit. And then he kept running it until the exhaust side tightened up and scored that also

 

[Nutball]

That might be why I find significant scoring even in a new Echo 490. Echos have tight piston tolerances top to bottom. The piston probably warmed up too fast, and I don't like to wait around before cutting. Anyway, now I make it a point to fire up a saw asap and let it warm up on my way to the wood being cut so I don't have to wait when I get there.

 

[TINYHULK]

What would be a safe time frame to make someone wait before running a saw? I would like to give my guys specifics