yamaha 300 - Snowmobile Forum: Your #1 Snowmobile Forum

dietschek · 09-02-2008, 12:29 PM

Hi,
I'm working on an 83 Yamaha 300. It runs great for 10 minutes and then the motor freezes up. What do you think it is? I was thinking maybe a bearing on the crankshaft is going out. I would be interested to hear different experieces people have had with this and what the problem is. Thanks!

JheLrey · 09-02-2008, 01:33 PM

What do you mean freezes up? It locks up tight after ten mins. of use?

**RJ Gleason** · 09-02-2008, 01:36 PM

Or just quits and won't restart until it cools?

dietschek · 09-02-2008, 03:10 PM

yep, it runs really good and then it freezes up. can't turn it over, then once it cools and you breack it free, it will start right back up and repeat the process

JheLrey · 09-02-2008, 08:25 PM

Overheating?

dietschek · 09-02-2008, 11:11 PM

ok, i took the bottom of the crankcase apart to get a better look at the bearings. heres what i found. a lot of grime and chunks of who knows what. however, i held the chunks to a magnet and they didn't stick to it. but what i can't figure out is how all of that stuff got in there. it almost looks like sand. the bearings look to be in good shape but they are just full of this stuff. hopefully i can figure out a way to clean them out real good and i'm thinking that might fix the problem...but then again the question remains....where did this stuff come from? could really old fuel turn into something like this? is there something that got chewed up in there? hmmm, this will take more time

JheLrey · 09-03-2008, 01:24 PM

Maybe it's Twizzlers....

Much more funny if you know the post I am referring too.

**RJ Gleason** · 09-03-2008, 01:57 PM

Old gas that evaporated and became varnish.
Clean all that out, should solve the problem then.

Skligmund · 09-03-2008, 02:42 PM

Are you running it with mixed gas? I assume these are not oil injected. I've seen this happen with pistons melting down enough to lock it up then break free after cooling.

Also, if the top end was rebuilt, the pistons and/or rings might be too big (not enough ring gap).

dietschek · 09-03-2008, 04:32 PM

it is oil injected...i believe the oil and gas are mixed in the carb, from there it circulates through the block and then it is injected into the intake manifold in each cylindar. i think the old cat rider is right about it being old gas

is there a solvent i should use that would disolve this stuff so i wouldn't have to take the bearings off of the crank to clean it?

**RJ Gleason** · 09-04-2008, 07:39 AM

Yeah, just put some gas soaked rags into the case and put it into a plastic garbage bag and let it sit a few days. This will loosen up any of the gunk and then it can be flushed out with brake cleaner. Then put a little oil into the base and work it into the bearings before re assembly.

dietschek · 09-22-2008, 03:02 PM

I took the engine apart a little farther...meaning I took apart the top end to see how that looked. One of the rod bearings seems to be bad and the piston is a little charred (black) and the rings are froze into the piston. I don't know much about these motors so I have a few questions. Is this a more likely cause for the freezing up of the motor? I'm assuming that I should replace the rod bearings and pistons. Is that a good idea? Are there sleeves in these motors? Where is the best place to get an overhaul kit, gaskets etc. I appreciate your help, Thanks.

kccats · 09-22-2008, 08:17 PM

You need anothermotor! I got one!

JheLrey · 09-23-2008, 03:49 PM

Quote:

Originally Posted by kccats

You need anothermotor! I got one!

Trying to make a sale, ehh?

dietschek · 09-24-2008, 10:11 PM

nah, i don't need another motor, i just gotta fix the one i got!! thanks though!