Seized chainsaw

[RandyT]

The more I look at it, the more I think you're right. Those two ports are on the exhaust port side from the pictures of the 570 that I've seen. Would love to see the other side of the inside of the cylinder and the piston.

If that is the exhaust port and that side of the cylinder scoring lines up with the side of the piston that is shown, the piston has been installed backwards which could cause the ring gap to snag on the exhaust port.

 

[RandyT]

A foreign object could be anything. Especially if it was ever started with the air filter off. Or a broken part. Tip of something. Unless you find it, it's all a guess.

Was the piston scored all the way around, or just on that one side?

The foreign object is the ring anti-rotation pin that came loose from its location in the ring groove, opened up a area in the side of the piston and then jammed between the side of the piston, and the cylinder wall which is the reason for the deep gall mark down the side of the piston.

 

[dodge man]

On mine the piston and cylinder were scored on the exhaust side, which was most likely from straight gas.

 

[ericm979]

For seizures caused by overheating, insufficient oil or detonation (which is most of them), the damage is always on the exhaust side. It's because that side of the piston is hottest. So the oil film fails there first, or the ring get stuck first and then overheats the piston and the oil film fails.

If the piston was installed backwards causing a ring to snag in a port it would have failed immediately. From the pics you can see the engine has been run a number of hours.

 

[Jac65]

Well, I'm no professional but it looks like that piston may have an issue.

 

[Billrog]

This is the result of running the saw less than 5 min. with a loose muffler. I knew better when the saw started racing as I'd had it come loose before only this time I never stopped to fix it. This is a 30 yr. old saw with hundreds maybe thousands of hrs. as it's bucked over 100 cords of firewood for my use and bucked logs on a landing 12 hrs a day for 3 winters when I was logging as well as fell and cut all the logs for my mill over the last 20 yrs. The ring seized right in line with the exhaust port and stopped the saw dead. I could have got away with just replacing the piston but for $65 the price of cylinder and piston I went for it. This can also be caused by running the saw to lean when when adjusting the carb to exceed the rpm the saw is rated for.

 

[alexinPA]

Just got OEM cylinder kit. It came with some parts... On the picture: metal plug is for decompression. What is this rubber plug for?
Anybody?

 

[Rockbadchild]

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.

sick bike for the years and the sound

i agree with your warm up procedure

 

[Rockbadchild]

https://www.cycletrader.com/listing/1976-Yamaha-RD400+European+Grey-Market-5013880560

i had a 350 it’s glory days was well pass tho but holy that thing was a power house

 

[Jstpssng]

A friend used to drag an RD400. I remember seeing him riding it to work the Monday after race day, with the wheelie bar still hooked up to the back.

You had to either love or hate those old bikes, especially with a can on them. There was one parked underneath my dorm window for the entire third semester, not only was it loud but that 2 stroke racing oil wafting up through the window was a real treat. He'd sit there revving the engine for about five minutes warming it up and I know that a lot of people were complaining about it. The owner flunked out but the bike came back the next semester... he'd sold it to one of his friends. The last time I saw it the bike wouldn't start and several people spent a couple of days trying unsuccessfully to get it running. I've always wondered if somebody got tired of listening to it and sabotaged something.