HELP, Is my engine seized?

[rpmchev]

Forgive me, I am new to 2-Stroke engines. I recently received a 96 RM 125 in partial trade for a street bike. The engine had just been completely rebuilt and wasn't even broke in yet. I properly broke the engine in and began enjoying a few rides. During one excessively long ride I got lost and ran out of gas near a highway. I walked down the highway a couple of miles with my bike and found a gas station. I dicided that I could mix some gas station 2-stroke oil (stupid,stupid) in my tank and ride back to my truck. Well, Immediately after pulling out of the gas station my plug fouled. I pulled the plug, cleaned it, put it back in, and forced the plug to work. A little choppy at first, the bike began to run strong. I pulled over one hill and began climbing a second when my engine started running sluggish and sputtering. I let the engine die and then pulled the kick start out. As I began putting weight on the kickstarter I was met with extreme resistance. assuming I had seized the engine, I spent the rest of the day trying to walk back to my truck. Anyways, long story short, I got the bike home, and pulled the engine. I put some 2 stroke oil on the piston to allow it to move. Suprisingly it moved relatively easy and began compressing as normal. I did a fairly good inspection of the piston and cylinder, and could not find any visual damage. i then reassembled the engine, bike, and kicked the engine over. The engine runs, but very rough, some slight knocking noises. Is it possible I assembled the exhaust or carb, etc., etc. wrong? Do I need to rebuild the engine again? can I get away with just a top end rebuild?

I know that nobody can be certain, but any general advice would be greatly appreciated. This is my first 2-Stroke. I dont know much about them, but i have good mechanical knowledge.

 

[biglou]

I think at the very least, you're going to have to pull the head off and check piston to cyl wall clearance and ring end gap clearance. If either of these is too small, they will swell when hot and cause the engine to seize.

 

[marcusgunby]

Sounds like maybe the crank rod bearing has worn?

 

[showtime586]

What ratio did you mix the oil at that you bought at the gas station?
I was curious if you might have purchased one of those 100:1 or 50:1 pre-measured bottles for marine engines or weed-eaters?

 

[rpmchev]

I mixed the oil 32:1 into 2 gallons of gas in the tank using the measurement table on the side of the oil bottle, and mixed as thoroughly as I could. I cant remember what brand of oil it was though. it did have a picture of a motorcycle on the front (some lawn equipment as well). I should start purchasing rebuild tools for 2-strokes, and any books or videos I can find.
Should I ask the dealer for these tools, or is there any web sites selling engine tools (case splitters, clutch holder, flywheel puller, etc.)? Any recomendations?

 

[bobkx]

A couple of points.
Drain all of the lawn mower gas/oil out of the tank and carb and pour on your weeds. Besides the questionable quality, you may have switched from synthetic to natural oil, which can cause problems when mixed.
If you removed the piston, did you replace it facing the correct direction? Is the ring gapped around the ring stop properly?
If you ran OUT of gas, you may have sucked in trash from the tank that is now blocing jets in the carb.
Did you change the plug?
32 to 1 is really rich, I know the books call for that but for woods riding, and depending on oil brand, you can go way north of that and eliminate fouling problems without endangering the engine.
Just wanted to offer some ideas for you to consider, good luck and I hope you get it running.
Bob

 

[Birken Vogt]

I can't imagine how any 2-cycle oil mixed at 32:1 would cause an engine seizure. I have even run straight 30 engine oil mixed at a "get you home" ratio that did not cause any problems. I don't think the oil would have caused it by itself.

Nevertheless it seems your engine had siezed when hot. Take the bowl off the carburetor and see what is in there. Take the top end apart. The tools required are basically some wrenches. You might have to take the engine out of the frame, I don't know. Still just wrenches. No use guessing.

Birken

 

[JasonJ]

I second the Bottom end bearings, 32:1 is plenty rich and explains the plug fouling. A better oil posibly masked the bearing issue with better lubrication.

 

[rockers109]

Check your flywheel a sheared key will do all the things you described.

 

[hunter1]

It sounds like the motor has heat seized (piston got too hot), the fact that you could kick it over after it cooled down confirms this. Piston rings and barrel are probarly scored. A RM 125 is an mx bike and shouldn't really be taken on a long ride ie: long straights with the throttle at a constant opening, an mx bike properly jetted likes to accelerate and de-accelerate as you would experience on an mx track. If you want to use it for trail rideing rejet and change sprocket combinations, smaller back, to give you better top end without over reving, also change the gearing.

 

[Bizerk]

Ah, guys...more oil to gas ratio results in a leaner mixture. Try not to confuse people by saying 32:1 is really rich mixture...quite the contrary. Please see previous posts on this topic of what to use for oil-fuel ratio. Also see Eric Gorrs site.

32=amount of gas
1=amount of oil

20:1 is a lean mixture
50:1 is a rich mixture

Fouling plugs can be also caused by too much oil and not a hot enough plug range. Not knowing what the bike was setup for previously as far as a gas->oil ratio, it might have been setup to and was running a richer mixture like 40:1. When you went to the 32:1 mix it would do two things,
1) It would lean out the mix causing the engine to run hotter which may have caused the partial seizure. The jets may have been the correct size for whatever the previous mix was but the 32:1 caused it to run too lean.
2) More oil in the mix sometimes requires a hotter spark plug range than what the bike had. Too cold of a plug with more oil can cause it to foul.

Misconception number two:
Mixing "Natural oil" with synthetic is a bad thing. (INCORRECT).

There are many "Synthetic Blends" of two stroke oil that are used and sold by many companies. I myself have gone from "natural" to synthetic and back and also have used blends for many years. The problem with synthetic vs "natural oil" is in a four stroke motor where the oil is not used in the combustion process. It is not good to go from a synth oil to natural in these type of motors. The syth penetrates the lube surfaces making it hard if not impossible to use a natural oil afterwards because the natural oil "beads" up on the lube surfaces of a previously syth oil 4-stroke engine.

OK....now, the problem that the bike had could have been some of the other things that others had mentioned here. I would take the top end off again and inspect things, drain all gas oil out of the tank and carb, clean things up. Also ask the previous owner of the bike what ratio he was running at and use that ratio seeing as I assume that it was running fine before and the carb is setup for that ratio.

 

[Kjetil]

I mixed the oil 32:1 into 2 gallons of gas in the tank using the measurement table on the side of the oil bottle,

Did you close the fuel tap on the the bike before you filled the gas in the tank. If not, the carburetor was filled with gas before you filled oil, and you ran without oil a while.

 

[rpmchev]

Quote: Did you close the fuel tap on the the bike before you filled the gas in the tank. If not, the carburetor was filled with gas before you filled oil, and you ran without oil a while.

Not sure, but i think it is more likely that I did not close the fuel tap. I considered this after the fact also.

 

[cr2504life]

The fact that you did not close the fuel tap shouldnt' affect it unless you were completely out of gas because the carb would have the already mixed gas in it and it wouldn't be letting any more feul in.

 

[Porstala F9]

Well when talking about the mixture of oil and gas:
20:1 = Rich 50:1 = Lean

With the air/fuel mixture for the carburetor that goes into the engine:
20:1 = Leaner Condition 50:1 = Richer Condition

Some people think you can go with less oil in the premix ratio to try to solve spark plug fouling problems, but this however isnt always the solution. You must find the best premix ratio, and adjust your jetting from there.