Yz250f unsure of rebuild?

Hi all, I've been scouring the forum trying to figure out what exactly to do. I've had my 05 for 2 years now and it's trail ridden then taken to the dunes once year. Regular oil change and filter cleaning is done. I know the bike is due on checking my valve clearances which I'm going to do for the first time(instead of a shop). My question is, if it does need adjustment am I better replacing them? Should I do piston and rings? I don't ride all too often so I don't what maintenance I should do. I have no idea how much i should be expecting to spend. I've never rebuilt a top end before a day in my life so this would be all new to me.

Bike was bought from a dealer in spring '14 so I don't know what kind of life it had before me. I have this fear that it'll blow up cause I've heard of these horror stories.

I really don't feel like dropping close to $1000 in parts or whatever it would cost. Sorry for my ignorance everyone.

Check the valves, if they are out then see what shims they have in them. If you can get away with shimming and the shims you use are 170 or larger then you should be fine for a while but keep an eye on them to see how quick they are moving. If you need a shim smaller then 170 I would consider new valves. I assume you don't know how many hours are on it so i would do piston, rings and timing chain. Then put on an hour meter.

 

Piston, rings, timing chain, shims, gaskets $250-$350

What top end do you recommend? I've never done any of this before. Do I need to do both intake and exhaust valves, would it need new springs too if I replace the valves?

Which parts to use is a matter of opinion. I like OEM. You need to check all valves and base what you are doing on your measurements. If it needs valves then I would also replace the springs.

 

Start with checking everything before trying to make decisions on what you are going to do.

I picked up my 06 top end kit from on ebay, and it was legit OEM and cheap.

Cam chain is another $30 and my bike runs like a top now.  Obviously it won't last forever but new parts make engines happy.

Thanks for the help guys.

I will post what my findings are tonight, I don't have shims on hand, I was just going to check to see if they need adjustment yet. I will go from there

Check the valves, if they are out then see what shims they have in them. If you can get away with shimming and the shims you use are 170 or larger then you should be fine for a while but keep an eye on them to see how quick they are moving. If you need a shim smaller then 170 I would consider new valves. I assume you don't know how many hours are on it so i would do piston, rings and timing chain. Then put on an hour meter.

Piston, rings, timing chain, shims, gaskets $250-$350

what do you mean by 170?

guessing he means 1.70mm? I have heard that once shims go below a certain thickness, it typically means the valves are pretty much done. Not sure how accurate it is or if that is THEE number most people consider to be the thinnest.

I just checked my clearances, my exhaust clearances are within spec. However just my right side intake is out of spec, .08mm feeler gauge fits perfect. Is that normal to have just 1 be out of whack?

I don't have any shims so I'll need to order a kit.

My next question.

Do I just rebuild the top end at this point or re-shim the one valve?

Well if by the top end you mean valve job, I dunno if that is what you wanna do YET. I would re-shim it, ride 8-10hrs, check them again. So keep notes on what each one was at, especially the tight one. If its tightened up again or another one has tightened up,  then its probable you are getting close to needing new valves. At that point you CAN decide to just do the intakes if the exhausts havent moved at all. Typically exhausts will outlast the intakes by a bit. The fact it is only .02 tight and the others were fine. I personally would feel comfortable running it that 8-10hrs to get a feel for how fast the movement is taking place. When one is zero'd out, its time to be real nervous haha. You may find you shim that one valve and they last quite a bit longer. Without a full history its hard to say. I mean, if you were the original owner, knew it was the first shimming of just one valve. I would say throw a piston in it, check them periodically as normal and run it. But since you dont, it takes a little more caution. I am optimistic about your situation though since you have had it as long as you have and it hasnt become a problem (wont start cold wortha damn) and its just 1 valve and only .02 out that you may be able to get quite a bit more hours out of it as a casual rider with good maintenance including proper air filter oiling (especially if you ride sand where it gets dusty as crap sometimes) before it needs valves.

Edited by J_YZ2fittyF

Btw, since it is your first time I think you said. Stuff rags in the cam chain hole beneath or around the cam gears and lay some just over the head to the sides of the cams before you take the cams off. There are alignment pieces that sit in a groove on the cams that fit into the cam caps. They sometimes end up coming loose and fall into weird places. Rags help catch them. Next, I like to use a magnet stick to remove the buckets, makes it easy and most of the time the shim will stick inside the bucket upon removal. If it doesn't, use the magnet stick to pull it out of the retainer. Get a manual if you don't have one and follow it for re-assembly. IMO the cam cap bolts are some of the most torque critical on the entire bike.

 

I would do a cam chain (oem) now....regardless of the valves or what they may need. It is cheap and at that point a small amount of extra time to install. So, if at your next check they are still fine, its already done. 

Thank you for the help! What shim kit do your recommend? Is the hot cams kit okay? I was going to do a cam chain tensioner while I was at it as well or does that not matter?

I'm currently trying to find a pdf manual so I can get the specs.

Thank you for the help! What shim kit do your recommend? Is the hot cams kit okay? I was going to do a cam chain tensioner while I was at it as well or does that not matter?

I'm currently trying to find a pdf manual so I can get the specs.

Hot cams shims are good. Most local shops sell them as singles to save buying a whole kit.

 

I've read about the tensioner on yzf's  failing but never seen it. I would worry more about the chain.

Just a little FYI.  Shims increment in .05mm increments.  .05mm converts to .001968503937" or rounded up .002".  If a 170 is installed and you have .008" measured clearance then a 175 or 1.75mm will be almost .002 thicker than the 1.70mm.  If you increase the thickness of the shim from 1.70mm to 1.75mm it will reduce the clearance by almost .002.  The resulting clearance should be .008" minus .002" or .006".  Thicker shim less clearance.

Obviously it will be slightly more than .006 due to rounding but feeler gauges are typically only incremented in .001"'s some to .0005".  All done the .006 should be a bit loose.

I wouldn't buy at Hot Cams kit. Not worth the $$ to get a bunch of extra shims you don't need.

Pull the old shim and see what it is. Then get a couple that are smaller. There is a chart in the manual to help you figure out the size.

You can get them from a dealer in .05 increments. If you want more accuracy, Pro X and Honda sell them in .025 increments.

Pro X shims are $2.00 at Rocky Mountain.

Hi all I'm back and just finished adjusting my valves! I was waiting for a shim kit among other parts. Over all easier than I thought it would be. I tried doing a math equation and math wasn't adding up, so I did what makes sense in my head then cross checked it with the Yamaha manual and calculator. After using appropriate feeler guages it turned out all 3 were intakes were out of spec

So I'll upload my chicken scratch so you can attempt to decipher my writing. Ignore some of the writing I had decimals in the wrong place when I wrote them, example being new measured size 0.13mm not 1.3

LEFT INTAKE:

measured: .09mm

existing shim: 185(1.85mm)

New shim: 180(1.80mm)

New measurement: .13mm

MIDDLE INTAKE:

measured: .09mm

existing shim: 185(1.85mm)

New shim: 180(1.80mm)

New measurement: .13mm

RIGHT INTAKE:

measured: .08mm

existing shim 200(2.00mm)

New shim: 195(1.95mm)

New measurement: 0.127mm

I had to use two sets of feeler gauges for more accurate measurements. My shims are in increments so for example my left intake said I needed a 179, I rounded up to 180 cause that's what I had.

Left/middle intake are .003mm more play than my right intake. I tried setting as closed to the .15mm as possible but hard to do with .05mm increments.

ImageUploadedByThumper Talk1462078772.677898.jpg

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now