Two Stroke Seized- Questions

[Mek-a-nik]

A good friend has a Stihl MS260. He cuts a lot, and he takes very good care of his equipment. A couple weeks back, it started dying out on him after it ran long enough to get thoroughly warmed up. No seizing, it just wouldn't start until it cooled off.
He took it to his local shop (he doesn't live close to me, otherwise I would've looked at it). He was told that the piston was scored, and the cylinder was okay. They said that it was probably water in his gas. He told them that he has used that same gas in other equipment with no issues. The shop agreed that it wasn't the gas.
The shop installed a new piston, and they honed the cylinder. I don't know if the cylinder was mic'd. I don't know if new rings were used. (When my buddy called me, he didn't have the invoice handy.)
He has now run 6 tanks of fuel through it and it shut off and is seized tight. He called the shop, they asked about the gas again. He reminded them that they said it was okay. He's taking it back tomorrow. I told him to have them pull the muffler while he was there.

Is there a way to check the mix for the proper amount of oil?

I told him to shake the mix and pour some into the largest glass container he has and see if it seperates. -Just to be sure about the water. I told him if there was water in it, it wouldn't run right (nor would the other equipment he runs it in).

Bottom line- What seized it?

I can get more info from him.

[bgsengine]

I think he needs to take it to another shop that knows what they are doing.. if they honed the cylinder they already ruined it before they ever put it back together. Those are plated cylinders, NEVER hone them.

Water in gas can cause a lean seize - if it phase separates you'll pretty much be running on an alcohol/water mix with no oil in it.

Proper diagnostics of a seized 2 stroke isn't rocket science, but if what you posted here is verbatim what the shop said, they are not gonna be able to do it...

There are tests to check the mix ratio (B3C solutions) but it is not an exact science..

[Mek-a-nik]

Last night, he let some of the mix sit in a large glass jar for an hour or so, no water apparent. If by "Phase Seperates", you mean it's gone bad, that's not an issue here.

It sounds like the shop owes him a new cyl, piston, and ring. He was told when he took it for repair that a new cyl and piston would cost more than the saw was worth. I think that's why they used the old cyl. Would it have worked to use the old cyl without honing, if it sized okay?

My buddy has known the shop owner since high school, (he's 63) so it could be interesting. He is a Stihl dealer, too.

I thought there was a definitive test for oil ratio. Something that would be used in warranty work. But I sure don't know. I guess it's done by looking for evidence of oil on the bottom of the piston, etc. But how could it be known if the ratio and type were correct? This is all a bit extraneous, as my buddy says that the shop owner knows he takes care of his stuff. -He has an old Homelite saw that he bought in the early 70's that just gave up this year, and the shop owner knows that.

[KE4AVB]

Last night, he let some of the mix sit in a large glass jar for an hour or so, no water apparent. If by "Phase Seperates", you mean it's gone bad, that's not an issue here.

Usually it the separation of the water from the fuel. Water is more dense than fuel and oil mixture.

It sounds like the shop owes him a new cyl, piston, and ring. He was told when he took it for repair that a new cyl and piston would cost more than the saw was worth. I think that's why they used the old cyl. Would it have worked to use the old cyl without honing, if it sized okay?

Could go either way depends what cylinder condition would have been. Depending on exactly which MS260 model he has the cylinder and piston kit are not that bad though some the Fleabay sources but got get the right one. Some these cylinder kits are aftermarket so they cost less. There is three different cylinder versions that could fit and really depends on which model he has.

Here is a list of the different models (1) MS 260, (2) MS 260 W, (3) MS 260 C, (4) MS 260 PRO, (5) MS 260 WVH, (6) MS 260 Arctic

My buddy has known the shop owner since high school, (he's 63) so it could be interesting. He is a Stihl dealer, too.

Even dealers can make mistakes sometimes.

I thought there was a definitive test for oil ratio. Something that would be used in warranty work. But I sure don't know. I guess it's done by looking for evidence of oil on the bottom of the piston, etc. But how could it be known if the ratio and type were correct? This is all a bit extraneous, as my buddy says that the shop owner knows he takes care of his stuff. -He has an old Homelite saw that he bought in the early 70's that just gave up this year, and the shop owner knows that.

As Brian says there is a kit out there but it not as accurate as we need it to be. It only the present oil and requires some experience in using it to get close ratio estimate. It takes a lab to determine exactly what it is and what type oil was used to produce that mix. That one of the reason I suggest that my customers stick to a good 2 cycle multi-mix oil that is pre-measured for either 1 gallon or 2-1/2 gallons and contains an ethanol treatment. That takes out a lot of the guess work in mixing the fuel.

[bgsengine]

Last night, he let some of the mix sit in a large glass jar for an hour or so, no water apparent. If by "Phase Seperates", you mean it's gone bad, that's not an issue here.

Phase Separation: that is when the ethanol blended fuel absorbs moisture from the environment, until it reaches as little as 0.5% (half a percent) water and then the water/ethanol mixture (along with its octane boost to the fuel) drops to the bottom of the tank with fuel/oil mix floating on top - when that happens, the fuel filter is typically immersed in a mix of alcohol and water (which WILL burn much like straight gas, but not well) which not only is highly corrosive to aluminum, but *very quickly* (in a matter of seconds to minutes) can destroy the jug & piston and bearings on a hot running saw. I wrote an article a while back about "motor moonshine" : http://bgsengineclinic.com/motor-moonshine.html

Would it have worked to use the old cyl without honing, if it sized okay?

Depends on the jug - But, I have "rescued" (with no guarantees whatsoever) old saws by cleaning up piston grooves and slapping in new rings as long as the cylinder bore has no severe grooves to it (Piston can be scored, but have to clean up the ridges from the scoring) and had them last anywhere from 6 months more , to a couple that are still running to this day 3 years later... BUT, it was not a quality repair and was only done as a favor to a special customer on hard times (and only had wood stove for heat)

My buddy has known the shop owner since high school, (he's 63) so it could be interesting. He is a Stihl dealer, too.

Doesn't mean the tech (if an employee) knows what they are doing. Just had an MS170 in that Stihl dealer put a carb on it the day before and handed it off to the customer as "fixed", and came to us with the same problem it had before.. the adjustment screws on the new carb were broken off, and fuel tank vent was plugged, customer is taking it back to dealer for new carb (again, so they can re-adjust after fixing the tank vent), and my suggestion to check everything else FIRST before condemning the carb.

I thought there was a definitive test for oil ratio. Something that would be used in warranty work. But I sure don't know. I guess it's done by looking for evidence of oil on the bottom of the piston, etc.

That is the general rule during a failure analysis - checking the oil residue that is present in the machine, on the bearings, and the condition and quantity of same. If oil is present and not deemed excessive , and not all gunked up, then generally it's assumed to be the correct mix and quality. It takes quite a bit of tear down and analysis over several machines both new, used good, and failed, to be able to effectively spot the differences.. Most factory service schools and seminars will go over that in some detail with the techs/owners (service schools are a requirement of being a warranty dealer.)

But how could it be known if the ratio and type were correct?

Only a laboratory can tell that. If mix oil is present, and the basic mix ratio test as I mentioned before shows it as "close enough", only other checks that can be done is the bound water and phase separation tests to see how much moisture the fuel has absorbed.

[Mek-a-nik]

This is wrapped up.

My buddy and the shop owner looked at it this morning. Piston, ring and cyl damaged.
When asked about the plating, the guy had to be pushed, but said that Stihl doesn't recommend it. He said he only did it lightly. -So what? He ruined it, in my opinion.
He said he'd repair it if my buddy paid for a new cyl, the shop would eat the piston, rings, labor. -If it were me, I'd eat the whole job, embarrassed that I screwed it up in the first place.
Bottom line: He bought a new MS261C, with the shop crediting him the repair bill towards the purchase price. I think he was too nice about it. He's dealt with this guy for years and I think the guy took advantage of their relationship. My friend is a great guy, and as in this case, to a fault.

Thanks for the detailed replies, gentlemen.

[bgsengine]

He said he only did it lightly. -So what? He ruined it, in my opinion.

Mine too. Nikasil plated should NEVER Be honed in any fashion. Lightly or otherwise.

He said he'd repair it if my buddy paid for a new cyl, the shop would eat the piston, rings, labor.

-If it were me, I'd eat the whole job, embarrassed that I screwed it up in the first place.

I agree 100%.. but then I'd never have honed it in the first place.. LOL!

Bottom line: He bought a new MS261C, with the shop crediting him the repair bill towards the purchase price. I think he was too nice about it.

Much too nice. Shop should have given him a new saw or rebuilt the old one, whichever cost them the least, but your friend should not have had to pay one more red cent. Period.