My brother takes these to the desert with paddles on them and the kids ride in the dunes. Seized one, went back and got the other, he said it seized with in 20 minutes also. He insists he had the mix right (hmmm), and he doesn't blame the oil, but what else is a likely cause. I've only seized 1 two stroke in my life, that was about 25 years ago on a 250R three wheeler driving down a paved road in 5th gear at about half throttle and it ran lean and seized. I suspect the combination of paddles (extra load) deep sand, slow speed and maybe a lean throttle position, low air flow (although I think they are water cooled). Any other ideas?
Yamaha YZ85's seized (2)
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I'd say oil wasn't mixed properly, at least at first thought. But maybe a lean condition if they were coasting down hills or lugging the engine under load across sand or up dunes. IDK?
At first thought, I was thinking lean mixture. I saw a video of a demonstration by Stihl, with two identical chain saws. One they ran lean, the other they ran straight gas. The lean one seized in about half the time.
Originally Posted By: another Todd
At first thought, I was thinking lean mixture. I saw a video of a demonstration by Stihl, with two identical chain saws. One they ran lean, the other they ran straight gas. The lean one seized in about half the time.
An air leak will cause a lean condition exactly as you described. If the cyclinder wall and piston have deep scratches then it could be sand entering the engine.
At first thought, I was thinking lean mixture. I saw a video of a demonstration by Stihl, with two identical chain saws. One they ran lean, the other they ran straight gas. The lean one seized in about half the time.
An air leak will cause a lean condition exactly as you described. If the cyclinder wall and piston have deep scratches then it could be sand entering the engine.
what kind of oil, how old was the gas, any aftermerkat parts, how long since a rebuild, what year yz's are we talking about.
need more info.
need more info.
Extended low speed running; long periods of ildeing?
With a 2 stroke it could be a dozen things.
With a 2 stroke it could be a dozen things.
Originally Posted By: Jaybird
Can you get some digital shots of the pistons and jugs to post?
2T's give some distinct patterns with most failure types.
This is the best advice...until we see pictures of the pistons/cylinders we are only guessing. 2-strokes pistons will seize differently depending on the condition that caused it.
Post some pics if you can
Can you get some digital shots of the pistons and jugs to post?
2T's give some distinct patterns with most failure types.
This is the best advice...until we see pictures of the pistons/cylinders we are only guessing. 2-strokes pistons will seize differently depending on the condition that caused it.
Post some pics if you can
Well actually he now says one seized the other he thinks burned a hole in the piston as it turns over but no compression. Fresh gas, Amsoil racing two stroke oil at 50:1.
50:1 with a synthetic wont hurt anything, if it happened on one, Id expect a broken ring, its easy to tear down, cant ask for a simplier motor to tear the top end off, Iam sure the problem will prevent itself, if it was running that lean for that long, it would have started overheating. Unless he was dicking with the air screw or changed the pre mix ratio, he would have had to have went from a 80:1 to 50:1 to severly affect the jetting though. More oil,less gas, per same air. Iam curious, I can say from past experience jetting can be rewarding but a dangerous game to play and a pain to get right.
The other day I was at the Honda dealership here in Tucson and there was a couple of 250cc dirt bikes with paddle-tires. The mechanic came outside to get one of the bikes and wheel it in to do work. He said: "People pay a lot of money for these things then don't take care of them. The biggest problem is the air filter. Sand gets past the filter and the valves are ruined almost instantly."
My bet is on the air filter ... or, more precisely, sand in the intake and damage due to that.
My bet is on the air filter ... or, more precisely, sand in the intake and damage due to that.
its fairly common to have the crank seal leak and cause a lean condition. those can be hard to find without a leakdown tester.
Two strokes are a headache.
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Originally Posted By: Gilitar
Two strokes are a headache.
Oh, but the sound they make ... now that brings back memories from childhood.
Two strokes are a headache.
Oh, but the sound they make ... now that brings back memories from childhood.
Two strokes ROCK, twice the power and half the size. You cant beat them to death. Four strokes are for old people and lawn mowers. Oh, yeah, they will run upside down too. It was a sad day when the Greenies had theyre way and quit making them. They were the last of a affoerdable racing machine. Anybody that could play with Legos could rebuild one.
Originally Posted By: Panzerman
Two strokes ROCK, twice the power and half the size. You cant beat them to death. Four strokes are for old people and lawn mowers. Oh, yeah, they will run upside down too. It was a sad day when the Greenies had theyre way and quit making them. They were the last of a affoerdable racing machine. Anybody that could play with Legos could rebuild one.
LOL... I must be old. I've never had any luck with two stroke engines. Two stroke chainsaws, trimmers, a SeaDoo. They all gave me grief. I now only have one two stroke trimmer because two stroke trimmers are better than four stroke trimmers.
Two strokes definitely have their advantages. I guess I'm not patient enough to keep them running right.
Two strokes ROCK, twice the power and half the size. You cant beat them to death. Four strokes are for old people and lawn mowers. Oh, yeah, they will run upside down too. It was a sad day when the Greenies had theyre way and quit making them. They were the last of a affoerdable racing machine. Anybody that could play with Legos could rebuild one.
LOL... I must be old. I've never had any luck with two stroke engines. Two stroke chainsaws, trimmers, a SeaDoo. They all gave me grief. I now only have one two stroke trimmer because two stroke trimmers are better than four stroke trimmers.
Two strokes definitely have their advantages. I guess I'm not patient enough to keep them running right.
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