08 yz 250 -- Wow, Really?? Flywheel issue...

GeorgiePorgie

GeorgiePorgie

PR Founding Father
So tonight, I took my handy dandy impact wrench and took the flywheel cover off--only to find a very minute flaw in the engineering. (Unless of course this was put here on purpose I'm not sure why the Japs that designed this bike could of let this slip through the ringer...)

photo.jpg
Ok, picture 1 above you see my aftermarket flywheel. (Which I want to remove because I want the snap out of corners that people oh so desire to rid themselves of...) Evidently I need a special tool for that process. Which I don't have...No big dealf ?i'll acquire the tool and remove it another day, but I look closer...and I see that dirt and mud has gotten into my case somehow...

My first thought: Oh bad gasket, ok easy fix. **Wrong.

I closely examine my gasket and gasket cover only to see this:

photo(1).jpg

Where you see a collection of mud there is small round gap between the gasket and case. This is a factory gasket and as I can see this is not a tear, but specifically in the design. Which lets mud in, water, dirt and whatever else I decide to run through...

My question is, Why? I'm going to post now to see if the pictures come out right. I will follow up with a response with a few other of my concerns...
 
Alright, so those pictures work great:

To further my argument:

photo(2).jpg

Above you can see that I have taken a close up shot of the gasket flushly in line with the case. The lettering you see if the lettering from the factory on the flywheel, Thus proving there is an opening... again, is this like a drain or something? I can't see why the inside of the case would be left so ill-protected from the enemy of engines: dirt.

Here is a picture I took to allow you to see the flywheel lettering and the gasket on the flywheel case side as a whole:

photo(3).jpg


Issue #2:
photo(5).jpg

Above as you can see there are phillips screws behind the flywheel, a total of 4. I only have 3 in mine. There is an area with threads that looks as though it is missing a phillips screw. I'm wondering if there is not one from factory in this thread as I did buy this bike used...I'm thinking that perhaps the first guy that owned this bike was a moron when doing maintenance. I think when he put the aftermarket flywheel on he forgot to put the 4th phillips screw back in...? (I dont know why he would of touched those screws in the first place) Is this about right in my thinking? Or is that thread left empty (phillips screwless) purposefully from the factory?? (The last owner: overtightened every bolt on my bike for one...so bad as to bend up my stop blocks on the swingarm for chain adjusting.)

photo(6).jpg
photo(6).jpg
 
Ok answer to own question issue 2:

I lifted the cover off my buddies 2011 yz 250: There is no phillips screw in the thread which I was concerned about. Not only does my bike have a gap in the gasket his does too. And as you can see he only has bout 5 hours on his bike and dirt is accumulating in the same spot in the case as mine... Which leads me back to my first question? Why the Heck would you leave a gap in the gasket to let dirt inside the flywheel cover???That seems beyond stupid to me....!??!?!
photo(7).jpg

Although, Now i'm wondering where my flywheel nut is, because the guy who owned the bike before me didn't give me the nut, but so I've heard that the aftermarket flywheel will just go overtop of the stock flywheel. (does this mean the nut as well?) I don't want to take the thing off to only realize I need to go get the nut. Does the stock nut stay or does it get replaced?
 
The only thing I could guess, is that Yamaha left a small gap to vent the area so condensation doesn't build up and rust the electrical components. I would review the owners manual and see if there is anything in there about periodically removing the cover and cleaning out inside there.
 
Is that in your suzuki manuals? I can't find anything in mine....?

do your bikes have that slight gap in the gasket on the flywheel side?
 
George….. Please!, Put the tools down, turn around and slowly back way from the motorcycle…….this way know-one will get hurt…..
</O:p
Yes! That's the way the gasket is supposed to be. It a condensation vent hole!

And the open threaded hole is supposed to be that way too!!!!!

Yamaha Motor Corp. has designed and engineered hundreds of different internal combustion engines types over the last few decades and I’m sure the YZ250 is nothing new to them (like it is to you).

Also, you don’t need a special tool to take off the Stealthy Flywheel.
There are set screws on the outside diameter of the flywheel. Crack them loose and back them off one full turn at minimum. Then take off the nut that holds the flywheel / magneto on. (it should be the stock Yamaha nut). Unscrew the flywheel from the crankshaft. (righty-tighty, lefty-loosey). That’s it!!!!

But, now will need to go out and get a new OEM Lock Washer (unless they gave you the old one with the bike).<O:p</O:p
When installing the Stealthy weight, the stock OEM Lock Washer was eliminated to make room for the thickness of the flywheel weight.

I just read all this again and will add:
If you have no Nut….that’s bad news, you should have the Nut. The stock lock washer is not used with the stealthy weight…..but the Nut most certainly is

</O:p
 
Well said. The more I tear **** apart the more I learn about them. Never really paid attention to minute details, always worked with my dad on my bikes. Shoulda paid better attention.
MarctheSharc said:
George….. Please!, Put the tools down, turn around and slowly back way from the motorcycle…….this way know-one will get hurt…..
</O:p
Yes! That's the way the gasket is supposed to be. It a condensation vent hole!

And the open threaded hole is supposed to be that way too!!!!!

Yamaha Motor Corp. has designed and engineered hundreds of different internal combustion engines types over the last few decades and I’m sure the YZ250 is nothing new to them (like it is to you).

Also, you don’t need a special tool to take off the Stealthy Flywheel.
There are set screws on the outside diameter of the flywheel. Crack them loose and back them off one full turn at minimum. Then take off the nut that holds the flywheel / magneto on. (it should be the stock Yamaha nut). Unscrew the flywheel from the crankshaft. (righty-tighty, lefty-loosey). That’s it!!!!

But, now will need to go out and get a new OEM Lock Washer (unless they gave you the old one with the bike).<O:p</O:p
When installing the Stealthy weight, the stock OEM Lock Washer was eliminated to make room for the thickness of the flywheel weight.

I just read all this again and will add:
If you have no Nut….that’s bad news, you should have the Nut. The stock lock washer is not used with the stealthy weight…..but the Nut most certainly is

</O:p
Click to expand...
 
Hold on a second George…….I may not have this 100% correct.
The “set screw” part is good ….that’s how the weight is (locked) on to the original magneto.
I do know that the washer is removed when the weight is installed.<O:p</O:p
But I’m not sure if the OEM nut is reinstalled after installing the Flywheel or if the Flywheel becomes the nut .
Let me go home and double check the instructions……I’ll get back to ya...
 
just a side note: the RM's do have a weep hole for the flywheel compartment. The venting is through the case on the bottom side and in the center of the motor where the cases come together...

I looked at a little confused when I had the 144 apart but it is obviously a designed item not a mistake on the RM. I can see where the gasket being missing would make some one scratch their head in wonder...and then go have another beer..
 
@ Georgie
Does seem strange. I mean its simply a small hole allowing moisture / water to weep out. But what about riding through a river bed or swampy bog? Seems like it could cause just as much problems to me. But it seems to work. sort of like dunking a glass under water upside down? Although maybe a little dirt may seep in, I think if you clean it once a season, should be no problems. Most people probably never service in there until an unrelated problem requires the cover to come off. I admit I don't. More dirt and water probably get in from the Wire Gromet on top of the cover during power washing than anything. I try to avoid spraying directly (or too close) around that wire.
 
Do you know what weight it is? 7oz, 9oz, 11oz? And does anyone know if that weight will bolt up in my 99 yz250?
 
BriarcliffMx said:
Do you know what weight it is? 7oz, 9oz, 11oz? And does anyone know if that weight will bolt up in my 99 yz250?
Click to expand...

Should work just fine. Not much if any difference in motor. The only significant, I know of is the swing arm gromets on back of cases are smaller from that year until 03 then the rear swing arm DIA. was increased. requiring new bushings in the cases. I think everything else was suspension and frame changes. But don't take my word for it. Contact a specialist. Don't get me wrong there are some small changes (clutch basket was modified later years and such) but you can still interchange the parts. OH! and 98 and newer are very different animals.
 
I got the original box and everything and I do believe it will fit every year since 96. It's the 11oz, but I'll re check again when I'm home to be 100%


Actually could be the 9oz...
 
so how did everything go when taking the flywheel off? You had to get another fluwheel nut? what about the washer?
 
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