Polaris ATV Forum banner

Bought a Not-Running Trail Boss 250, any ideas?

7K views 22 replies 5 participants last post by  army07mp 
#1 ·
Saturday evening I came across what appeared to be a good deal for a 1998 Trail Boss 250. The previous owner has had it since the showroom floor. It ran great for him from that point up until last fall. A family member was riding it down the trail and it up and died on her. Has not been able to get it to fire since. They replaced the top end, still could not get it to start. They threw it up on the local classifieds for $300. I was the first to respond, and now its mine.

Knowing the top end had been rebuilt, I brought it home thinking that it was something electrical, or fuel related. Got it home and immediately began to tear it apart. Pulled the plug out, ground it to the motor, and pulled the rope. Got spark.

Put my thumb over the spark plug hole, and turned the engine over, blowing my thumb off the spark plug hole. Appears to have enough compression to start.

Moved on to the gas tank and carb. The tank was all but empty, and the carb looked like it needed some TLC. Pulled it off, cleaned the main and pilot jets, cleaned the slide, the throat, and put it all back together. Drained the rest of the tank, cleaned it out and put fresh premium in it. Put it back together, pulled and pulled and pulled. Nothing. Hooked it up to my car to allow the starter do the work. Still nothing.

Checked the throttle cable for proper adjustment, unplugged the ETC, nothing. Key switch, and kill switch seem to work as normal.

After several minutes of holding the throttle wide open, full choke, half choke, feathering the throttle etc. I was at a loss. Pulled out the spark plug and poured a small amount of premix into the cylinder. Still nothing.

I decided to pull the pull rope for a while, one of those pulls, the engine stopped like it was seized. After a little persuasion, it finally turned freely again. It only took maybe a 1/4-1/2 rotation for it to spin freely again. I do not believe the engine to be seized because it now turns freely again.

I know this is a lot of info, but any ideas? Is it possible that a skirt or a ring is down in the bottom end banging around in there? Would that keep it from starting though? FullSizeRender (17).jpg ,
 

Attachments

See less See more
1
#4 ·
Yes. I bought an 04 trailblazer. Motor was locked. Pulled flywheel and it was all mangled. Replaced pickup coil. Stator and flywheel. Pulled it and started right up. Soon as I hit the starter it did it again. But felt no crank play. The hearing on that side was bad. Had to rebuild lower end. But those magnets like to come loose too. Pull flywheel Check everything out. Not a huge task. Like 8 bolts and flywheel puller. Car harmonic balancer puller worked.
 
#5 ·
Also, be sure to check your crankshaft seals. If they are worn or leak they will not allow the bottom end to create a vacuum to draw the fuel into the cylinder for combustion. If you replace the flywheel side seal be careful not to drive it in too far as there is no lip to stop it.

You can also do a leak-down test to check for bad seals/gaskets. To me these engines are finicky but seem very reliable once you get them right.
 
#10 · (Edited)
Pulled the recoil starter off tonight. When I pulled it off, oil came running out. It wasn't 2-Stroke oil, that I do know for sure. It appeared to be some sort of 4 stroke oil. Probably something that the PO did. To my knowledge the flywheel should be bone dry. Accurate?

When I pulled the plug initially, there was fuel on the spark plug, it appears that it is getting fuel. Will still check seals when I get it apart.

I "attempted to get the flywheel off. Broke a bolt in the process. Long story. Any tips on getting it off? Are you supposed to get the puller tight, then hit it with a hammer like with a pitman arm puller? I was cranking on it with a breaker bar tonight with no success. Any ideas would be helpful. Will be hitting it again tomorrow.
 
#13 ·
Flywheel removal can be a challenge on these. I have had better luck using an impact driver with the puller over a breaker bar if you have one. If it still won't budge, leave the puller tight and heat the flywheel around the shaft while trying to keep the heat off the shaft itself and try tapping the end of the puller with a hammer. Also, when warm, spray with penetrating fluid. Try to use grade 8 bolts with the puller as they don't tend to stretch as much.

Try not to get the flywheel too hot, you don't want it smoke'n.
 
#14 ·
Will try that tonight. Thanks for the tip.

Here's a picture of how it sits now. Is the bendix supposed to look like this? At one point the outside gear was in contact with the flywheel gear and the machine was locked up solid. It could not be turned over. Now that the bendix is not "connected" to the flywheel the engine spins freely. I cannot slide the bendix back at this point. It is stuck or lodged in its current position.
 

Attachments

#18 ·
Update, got the Bendix back in, cleaned everything up, and nothing. Finally broke down and did a compression test, 30psi. I hope to be tearing the top end down on Monday. Does anyone recommend a good place to have the cylinder bored/honed? I do not know of any reputable machine shops around here.
 
#21 · (Edited)
2 1/2 mo update: Tore the top end off, there was scarring on both the brand new Namura piston and cylinder walls. Upon further inspection of the motor, the lower rod bearing had excess play. I sent the jug to SLP in Idaho Falls, ID for a bore and hone job along with a new Wiseco piston. When they got it, they told me that the cylinder had been bored previously, not an uncommon occurrence, but found it odd that the P.O. put a stock bore piston in it. As a side note, I was surprised to see that the piston kit did not come with a new wristpin bearing.

I bought a new used crank to replace the worn out one currently in the motor, bought new crank bearings and a wristpin bearing this morning. I bought a screw extractor to remove the broken bolt in the flywheel, but broke the screw extractor in the process. Ended up getting a hard cut drill (carbide) and drilled out the screw extractor and broken bolt.

I have now come full circle, and now am working to get the flywheel off again so I can install the new crank. I have the puller, an impact wrench and a harbor freight special heat gun. I was able to crank down quite hard using the impact gun and getting the flywheel pretty warm, even tried spraying some lube between the flywheel and the crank. Still cannot get it to budge. Watching YouTube videos online, they make it look easy to remove flywheels, not my experience thus far. I am looking to try to tighten the puller and hit the puller with a hammer along with heat and more penetrating oil.

Any other suggestions?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top