Seized chainsaw

[alexinPA]

You had me fooled there for a bit. "No compression" means the piston moves but you get no pressure at the top of the stroke. You actually mean you could not even move the piston, right?

Nope. My neighbor and I are the kings of dull-chain sawing and we, also, have never seized an engine. Sooted up the mufflers, seized chains to bars, threw chains.......... but never seized an engine.

That's right. Piston moves but little pressure at the top-30 psi

 

[MossRoad]

That's right. Piston moves but little pressure at the top-30 psi

Rings
Cracked piston
blown head gasket
reed valves

 

[etpm]

For years I have used Opti-2 oil mixed at 100:1. It's not any cheaper but my plugs don't foul as fast. I am kind of amazed that the pistons don't stick to the cylinders. I am not at all surprised that the needle bearings are fine with it though. They really need hardly any oil.
Eric

 

[fishdrivel]

I have never seen a saw overheat and seize up if running the correct 2 cycle mix. And I’ve been around chainsaws my whole career.

Saws can overheat and seize.
Causes? Wrong fuel air mixture, blocked cooling fins or cover, air leak, bad carb, etc.
Saws that are overheating should be complaining before they seize. If they just quit, likely oil.
What you look for is on the piston, did it score on the skirt? Oil. did it score at the top of the piston, heat. Wrong sperkplug can cause overheating but usually burns a hole in top of piston before seizing.

Oil seizure:

heat seizure:

 

[MossRoad]

That's right. Piston moves but little pressure at the top-30 psi

Did you pull the muffler and look in at the cylinder and piston with a flashlight yet?

 

[fishdrivel]

I wouldn't think so. A dull chain will just cut like crap.

My buddy siezed his Husky by grabbing the wrong red gas can. Another friend's wife did the same to the leaf blower. Maybe you forgot to add the 2 stroke oil to the gas, or not enough. FWIW I always put the 2s oil in the 1 gal jug and then put in 1 gal at the pump, always 93 octane. And I started using Star Tron in small engines. And the only jugs for gas/oil mix are 1 gallon and all other red jugs are 5 gallon.

Here's an idea for all us 2 stroke users; maybe spray paint the red jug w/ mix in it half flat black. No more mix-ups.

I had a hard-working employee that was not too bright.
Anyway, I had bought a 2-sided jug that put mix in one side and bar oil in the other. While at the gas station, I told Brian, "put this can of oil in the gas can and put exactly one gallon of gas in it." I gave him exact change for the gallon. He brought me the receipt. On the job I seized up a saw. I asked him if he put the oil in the can. He showed me the empty can. I started up another saw and seized it. I went to the gas can and poured out clear gas! Brian could see my anger. I asked him to show me where he put the oil. He pointed to the bar oil side of the gas can.

I fired Brian, threw away the too complex can, and rebuilt the saws. Later I hired him back but was more careful with tasks that I assigned!

 

[fishdrivel]

After 40 years of working around loggers I have never seen or heard of such a thing. Everyone starts and runs full throttle during cold or warm weather. The only saw motors I’ve ever seen seized was due to lubricant failure.

I raced 2 stroke motorcycles professionally.
I have seen a lot of different seizures first hand.
My ear is trained to hear the conditions of the engine.
I was usually able to stop before it blows up.
There were notable exceptions! Exceptions cost money. Most people learn the expensive way.

 

[fishdrivel]

I drag raced a Yamaha RD400 2-stroke twin for about 10 years. Did all of my own engine and carb work. Pretty heavily modified bike. I had an occasion where I pulled it out of the garage, Gave it a kick to start it, the throttle cable did not return and got stuck full open, and it went from zero to a billion RPMs in about half a second, then PINNNG! It stopped. Seized solid. Upon dissection, the cylinders were scored heavily. It wasn't from no fuel or improper lubrication. It was from cold start to high RPMs instantly.

I can guarantee you that the loggers you know never do that to a cold saw. They give it a pull, it fires up to an idle speed, they pop the throttle a few times, wait a couple seconds, pop it again a few times, then go off to work. Those few seconds of warming it up make a huge difference.

Loggers and racers.
Weekend warriors I have often witnessed setting the bar on the log and pulling the rope. It takes very little waiting to warm up but grab that throttle with a death grip immediately, and you won't like the results.

Love to get my hands on an RD400 stock. Collectors item now!

 

[fishdrivel]

More oil is good to a point, then it creates problems. More oil means more carbon. More carbon, especially on the exhaust port, means more scoring on a piston.

50:1 with modern oils is fine. Hell, I have a couple of old mccullochs that say 32:1. I just dump in my stihl premix in the can @ 50:1 and go.

Chainsaw bearings need just a good oil film. Any type of modern synthetic oil provides this...

Stanford? did a study on 2 cycle oil ratio. It showed in laboratory tests that a richer oil mixture produced more horsepower. They got the highest hp at 12:1
That was in a laboratory setting. On the racetrack, I found that 20:1 was best results. I used pure synthetic.
An air-cooled 2 stroke engine loses 30% of its power when it arrives at operating temperature. Whatever friction you can remove creates less heat and more power.
There is a difference between performance and environmental politics. We are at risk of losing 2 stroke entirely if EPA gets there way. All 2 stroke manufacturers will recommend a lean mixture to prevent losing there markets. A quality machine and quality synthetic oil can run fine at 50: but they will not last as long as a richer mixture.
Note that you will have to breathe what you burn and absolutely will have to jet the machine with the ratio you choose.

 

[ericm979]

You may be thinking of Gordon Jenning's two stroke oil ratio test: http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf


For motorcycles I scale the amount of oil to the riding use: road race engines get more than MX or enduro engines, which get more than observed trials engines. On my trials bikes I ran 75:1. Trials engines are mildly tuned and don't spend much time at WFO but you want them to run cleanly and never load up.

Chain saws are industrial engines that are even more mildly tuned than trials engines. A trials 250 is about 10hp per 100cc while a 92cc MS660 is 7hp. And the saw is fan cooled. But on the other hand, it spends a lot of time at WFO. 75:1 is a little light for that. I have been successful using high quality synthetic oil at 50:1. Exactly zero lubrication related problems in 24 years of running saws. But if you want to run 32:1 or 40:1 that's fine too.

I don't think oil ratio caused the OP's problem unless it was 0:1.