Help with Yamaha yzf250

[Logan77]

My friend gave me a 2001 Yamaha yzf250 a few weeks ago. The whole top end of the motor is torn apart and laying in a box on the floor. He said that when he was haulin balls across his field, that it just quit and locked up. So he brought it home and tore it apart. And he couldnt find the problem. He said that a bearing fell down in the crank case or something? But what would be the best way to go about this? Should I try to rebuild it myself? Should I take it to someone else? Or could I just buy a whole new engine?

Thanks in advance,
Logan

 

[Cabot]

If a bearing fell down into the crank case, your going to have to split the cases to find it. Or else it will mess everything up when you try to start it. Whether you want to do the work yourself is up to you. How mechanically inclined are you? Buy a shop manuel for it (i have good luck with Clymer manuals) and get started if you want, but there are special tools needed to split the cases apart.

Also, if the valves and piston and all that is in spec, no damage, then chances are the problem is in the cases. Locked up main bearing? messed up gear in the tranny? who knows.

But even if you do take it into the shop to get it fixed, you will be getting a YZF250 for really cheap! I wish my friends gave me their bikes when they locked up!

 

[Logan77]

Im pretty good at stuff like this. I have never really torn into a small engine like this, but I have built several chevy V8's. The piston and valves seem to be fine. Where do I get a tool for splitting the case?

 

[slodad]

If the bearing made its way to the bottom of the crankcase, you may be able to remove it by draining the oil and removing the clutch side cover. There is a relatively large passage between the clutch area and the crankcase, and with a flashlight you can see a bit of the inside. Use an extendable magnet to poke around and see what comes out. You may also see debris that will help diagnose the nature of the failure.

 

[Logan77]

Thanks slodad, I will go try that.

 

[Cabot]

Yes^ that is true. If there is alot of metal shavings in the oil, you know something is wrong and needs investigation. Did the engine turn over before your friend tore it apart? How does the crank feel? Does the rod move freely? any up and down play? or side to side play? Can you spin the crank? (check the manual for proper clearences, etc.)

It sounds like you should be able to do this yourself no problem, once you get down in there its less complicated then it looks. But DO get a shop manual for it, and in the shop manual (Clymer manuals do anways) it will have all the part numbers for the tools you will need. You can then get these tools at a Yamaha shop, internet, etc.

But it Might also be cheaper to just take the engine to the shop when you need the special tools, have them do just these steps instead of you buying the tools you will probably only use once. Depending on the shop, you might be able to get what you need done for around $20.

 

[Rich Rohrich]

The piston and valves seem to be fine. Where do I get a tool for splitting the case?

Until you pull all the valves out of the head and inspect the seats and valve faces, you can't tell the condition of the valves. These are titanium valves and when they are run too long the valve heads break off and fall into the engine, destroying everything in their path. Guessing that they are OK has destroyed a lot of engines over the years.

There is no special tool to split the cases, light tapping with a plastic dead shot hammer is all it takes to split them. The only special tools you will need are a flywheel puller (about $15 at any bike shop) and a VERY ACCURATE 1/4 drive torque wrench to use when putting the cam caps back on. The cam caps are the bearing surfaces on these engines and need to accurately torqued.

The Yamaha service is really well done and easy to follow. This is a simple motor that anyone can work on.

 

[Logan77]

I figured out that the rod is not turning on the crank. What would be the cheapest way to go about fixing this?

 

[Rich Rohrich]

I figured out that the rod is not turning on the crank. What would be the cheapest way to go about fixing this?

You'll likely need to replace the entire crank assembly and the main bearings, but you might want to investigate WHY this happened first. This isn't a common failure.

 

[Logan77]

The only thing I can come up with is, that he ran it out of oil. The guy I got it from is one of the stupidest people I know. When I was looking at it before I got it, I asked how often he changed the oil, and he said never. He just puts gas in it and rides it. So Im guessing thats what happened.

 

[Rich Rohrich]

So Im guessing thats what happened.

Guessing isn't the same as knowing. That could prove to be a pretty expensive assumption.

 

[Ol'89r]

I figured out that the rod is not turning on the crank. What would be the cheapest way to go about fixing this?

Check with Hot Crank for a crank assembly. While you're at it you may want to check with Hot Cams (same company) for a set of cams. If the bike ran out of oil it most likely damaged the cams too. Since the cam journals run directly on the aluminum surface there is a good chance the head will have to be replaced too. The pistons in these bikes have a very short skirt and should be replaced often. You can get a piston kit from LA Sleeve.

You need to disassemble the entire engine and inspect and measure every part. If the previous owner never changed the oil there will be a lot of sludge in the engine. This sludge can clog filters cutting off oil supply to the crank and top end. The sludge carries with it a lot of metal particles. When these metal particles are run through your engine over and over they act like a grinding compound and cause excessive wear to critical parts. Unlike a chebby V8 engine, your engine has very close tolerances and can not pass large amounts of sludge or grit without destroying itself. Be sure to measure the tolerances in the oil pump and the pump itself for damage.

Take Rich's advice and get the Yamaha service manual and read it a couple of times. Also take Rich's advice when he tells you to take a close look at the seats and valves. This is the weakest part of your engine and usually to first to give trouble. If the guy never bothered to change the oil he most likely never checked or adjusted the valves. You should replace the valves and springs just to be on the safe side.

Remember, sometimes free is too much. ;)

 

[Logan77]

Ok, well I got it tore down, and I ran my finger across the bottom of the crank case. And it is terrible. The sludge looks like a grey mettalic paint with really fine metal shavings in it, and a bunch of them. Do you think it would better just to buy a whole new bottem end?

 

[slodad]

Did you notice anything on the way in? Any marks on the magneto that might indicate something gotten wedged against it and could have been grinding away for a while? If the goop on the bottom of the case is just magneto paste, there might not be the damage you fear. After splitting the case, did the crank move freely? Notice any slop in the bearings?

 

[Logan77]

Yea, the main bearings are very sloppy and hard to move. But the magneto looks fine.

 

[Ol'89r]

Ok, well I got it tore down, and I ran my finger across the bottom of the crank case. And it is terrible. The sludge looks like a grey mettalic paint with really fine metal shavings in it, and a bunch of them. Do you think it would better just to buy a whole new bottem end?

You can't buy a whole new bottom end. Unless you find a used one on one of the auction sites and then you are taking a chance of buying someone elses problem.

If you didn't pay anything for the bike, it would be worth it to rebuild what you have. Like I said you can buy a complete crankshaft assembly from Hot cranks for about the same price as rebuilding your old crank. And, some of their cranks come with new main bearings. Strip the engine down to just the cases and remove all of the bearings and seals. Heat the cases to remove and replace the bearings. Your engine shares the gearbox and engine oil so, you will also have to replace the bearings in the gearbox. Inspect your gears for excessive wear or undercutting on the teeth. Undercutting will show as a deep line across the face of the gear teeth where the matching gears mesh. Also check the dogs on the sides of the gears for wear and the shift forks for damage or wear. If the gearbox is ok then go ahead and rebuild the rest of the engine. If the gearbox is excessively worn or damaged, check the price of the individual gears needed. Replacing gears can be very expensive and may make the difference in weather or not it will be cost effective to rebuild your engine.

Clean everything very good. Use a good solvent and then hot water and degreaser and then solvent again. The fine particles in the sludge can get into the pores of the aluminum castings and unless you use HOT water to release these particles they can be released into the engine oil when you run the bike. After everything is clean, inspect and measure the parts for damage and wear. The manual shows the tolerances and specs for every part in your engine. Pay particular attention to the cams and cam journals. This is the area that will usually receive the most amount of damage when a four stroke engine is starved for oil.

Good luck. :cool: