I just bought a used 2007 yz250f that looked to be in great shape. Since its my first 4 stroke, I really wanted to check valve clearances just be safe. I have replaced the timing chain as well with an OEM one.

2 of my intake valves and both of my exhaust valves were kinda tight.. about .001" too tight. Nothing major, but I want them to be back towards the middle of the spec range. When I measured the shims, the exhaust shims were .075" and the intake shims were a bit bigger, more like .080". Since I needed more clearance, I got some sandpaper and went to work sanding the .001" I need off every shim. I sanded for at least an hour and am missing a few fingernails and my fingers are down to nubs, but the shims didnt seem to measure much different.

Frustrated, I decided to just throw it back together and measure my clearances to see if anything changed. I decided to do this without the cam chain on, I was planning to put the exhaust/intake cams back in, and then put the chain on as thats how the manual instructs. Exhaust cam goes in, torque it down with my new cheapo harbor freight wrench, turns over smooth as glass by hand until the lobes hit the lifter buckets of course.

Then I go to try the intake cam.. torque it down (evenly as the manual suggests) and it turns by hand, but with quite a bit of resistance. Doesnt feel anywhere near the other side, and I dont feel like this is normal. Undo everything, clean it all, reinstall, do this about 3 more times to no avail. Tried a few different methods.. seating cam into cap first then installing, then tried seating cam into head first, then fitting cap.. no change. Even with the bolts finger tight, it still doesnt turn great.

What is going on here? I did notice when installing it, I feel like one (or more) of the valves is being compressed a little bit, but why would this happen and what could cause it? Could my shims I "made" cause it? First thing Im trying is going to a dealer and buying new shims (correct way) and lightly sanding the journals with 2000 grit sandpaper. Any other suggestions??

"I sanded for at least an hour and am missing a few fingernails and my fingers are down to nubs, but the shims didnt seem to measure much different."

You don't sand down shims, you just don't do it. pack up the bike and parts and go drop it off at a shop and let them put it back together.. I'm not looking to be a bitch but it's easy to see your over your head with this one..

Tammy63, on 28 April 2012 - 05:12 AM, said:

I am no where near over my head. I have all the tools needed for this.. micrometers, torque wrenches, flywheel puller, etc. I got the chain swapped out in 15 minutes or so, but this is my first time doing valves.

I got that advice to sand down the shims on another forum. I am not going to name the forum. I will go buy some various shims and put it back together. Hopefully that is the problem.

Assuming the cams were not tight prior to dismantling, sanding the shims is not your problem.  Put the cams in without buckets/shims and start from there.
BTW...you can remove a small amount of material from a shim.  Remember they are case hardened, so anything more will render them useless.

Make sure the shims are tight down in the valve keepers and not just sitting on top. They should almost "snap" down in there then put the buckets on. Chances are the shims are sticking up a bit. It's easy to do. Sanding the shims is not recommended but you gotta do what you gotta do. You should replace them as soon as possible tho. You can buy individual shims online at some places.

I kinda agree with Tammy. I personally would never sand a shim down. With the tolerance having been within a thou you didn't really need to reshim it unless the bike was hard to start.

Sorry I did not say it to upset you in any way. Tho in my 24 yrs as a Tech any time someone would pull a move like sanding down a shim it was a sign..

The net has a lot of good info and a lot of people that know what they are talking about but t the same time it is also filled with shit.  You said you have the service manual go by that and if they tell you to replace something it's a good bet they know what they are talking about.. Sanding shims, drilling jets, cutting wires will never save you time or money.. I will stay away from that site that told you to sand them down, TT is a good place for reall info and if someone gives you a load of BS someone will see it and call them on it so it's a safe place for help...

Do what Swede said replace the shims you sanded down and start over..

Sorry if I came off hard, I hope you get it back together and running real soon..

youve been a tech for 24 years but you had to post up on here which fork seals should you buy?  

Luke I have been a mechanic for 25 years and was wrenching on small engines when I was 10. I am a very good mechanic but even I still don't know it all. Cut her some slack.

I went to the shop today, got a bunch of random assorted shims.. came home, sanded the journals lightly with 2000 grit (no typo) and its not binding anymore. No idea what the problem was, but its fixed.

I had to take the cams on and off about 5 times and keep swapping out shims, but eventually I got it. The intakes are all around .005" tolerance, and the exhaust is .008" I believe. Not 100% sure if I am remembering those numbers correctly, but everything is in spec.

Also took me 2 trys to get the cam chain on correctly.. what a PITA that is. You need like 6 hands to do it, I had to have a friend help me. I think I got it. The marks all line up when Im at TDC, but the only questionable thing.. Im not sure if I am on the right stroke. I know I am supposed to be on the compression stroke with the marks line up at TDC. When my marks DO line up at TDC, when I push the kickstarter down I immediately feel resistance. This would be the compression stroke right?? I sure hope so, cause its all back together and Im going to hopefully start it up tomorrow morning

On the timing if you have the crankshaft marks Lined up correctly the camshaft lobes should point outward at about a 45 degree angle ( away from each other).

 Ktmrida4life, on 28 April 2012 - 11:39 PM, said:

If it doesn't start, after your work, pull the pistion and sand the rings...JK TDC is the time when the cams are on the base circle (no valve lift) same time you would have adjusted the valves - should have clearance between the cam and bucket.

With the cams out there is no compression stroke or exhaust stroke. It's your cams that determine that. Makemsuremthe timing marks are dead on then instal your cams so the dots line up. As long as nothing moved you're good to go.

 Ktmrida4life, on 28 April 2012 - 11:39 PM, said:

When I went to the dealer they wanted something ridiculous like 8 bucks a piece for an OEM shim That would have been $80 for 10 shims as I needed to get some small ones because the ones I had in before the rebuild were too tight, then measure and get the correct size. Just as I was about to bend over and take it, I asked. "Hey, do you happen to have one of those hot cams shim kits?" Sure enough, they did! It came with three of each size in just about every size imaginable for something like $90! Pretty good deal!

I was also scratching my head over tight cams not wanting to rotate when I first installed them with my new valves. Turns out there was no clearance with the oversized shims installed. It could have been that one or more of your shims weren't seated correctly so it was making it seem taller.

The stroke is determined by the cams so as long as you are at TDC (it's all the same with the cams off!) and you aligned the cams correctly according to the manual, then you should be good to go! I too was really struggling with getting the cam chain on and the cams timed properly... maybe there is some secret technique?

This thread is pertinent to my own situation, If its inappropriate for me to ask a question that's related but not to the gentleman's own reply, please let me know.  I am new to TT and new to dirt bikes in general.  I just purchased an 05' Yz250F 7 weeks ago.  I've put maybe 7 hours on it and have been pleased with it's performance.  In as far as I can tell, it pulls hard, runs smooth and has plenty of power to launch my 225lbs.  I've read all of the info on the YzF specific site regarding rebuilds, adjusting valve clearance and other maintenance topics.  What I don't have a handle on is what are the symptoms of needing valve adjustment or even new valves for that matter?  I understand that buildup combined with valve stem stretching may cause the clearance to lessen, so I should pull of the valve cover and check it out.
  Do yzf models have issues with this?  Is it best just to replace the valves if there is build up or if the shim(s) height needs to be lessenend.   Does a compression check / leak down check tell anything about valves or only whether the rings are good?   The manual is a good source for how to, but doesn't really give me a feel for how often replacment maintenance is likely to be needed.

Thanks in advance for any tips.  I just want to treat my bike right and keep it reliable and become self sufficient.

Eric
Hudson, Fl

Excellent questions Eric. It is always good to check the valves on a regular basis. Typically I will do one valve adjustment before replacing the valves and recutting the seats. Once the valves start to move they typically continue to do so as the coating is wearing/worn off the valves.

Depending on your level of riding and maintenance routine you should be able to get 50 to 100 hrs on the valves.

Hard starting when the bike is cold is a good indication that the valves are getting tight. This being the case with a properly jetted carb.

Forgot to say checking the valves every 10 hours is a good interval.

Thanks Charlie.  Since I don't really know the "true" history of the bike, I'll check the clearance and replace the valves if they aren't within spec, just to have confidence in the valves.  Is valve seat cutting something one can do with basiic hand tools (a hand drill with a grinding stone?) or does that need to be done by a machinist?
On a related question, what to the valve seats look like if they need to be cut?

My bike is especially hard to start sometimes when its hot. I do not have the hot start lever, so apparently it was removed.  I think my bike starting challenges when cold speak  more to my poor technique than valve or carb issues.  Normally, it starts in three kicks.  It seems sometimes I flood it, though.

I got it back together the other night, started it up yesterday morning.. it did not want to start at first. First kick it started, then died a few seconds later. Then 20 kicks later it finally started.. I assume the fuel bowl in the carb had to fill up.

It runs great. Hot starts great, but it didnt seem to like cold starting with the choke on. Choke off it starts up. I may try it again today to make sure. Also, there seems to be a lot of mechanical noise coming from the cylinder head.. and Im not sure how much noise is normal. I noticed this with my helmet off, so maybe I am going crazy. I think I might pull the head and check the clearances and the timing marks again just to make sure Im not.

 Ktmrida4life, on 30 April 2012 - 07:38 AM, said:

What jets do you have installed?