Jump to content
Sign in to follow this  

09 yz250F -top end rebuild?

Recommended Posts

Picked this up last spring for my son with 8hrs on it.

This is our first 4 stroke and had only had 2strokes in the past.

It's not got about 78 hrs and the valves are out of spec.

Instead of shimming, I was thinking of having the valves just replaced.

I've been reading some good things about the stainless steel valves(lasting longer etc etc)

Anyone have any experience on this?

I do not want to do this part. Does anyone have any experience with

having this type of work done by a shop?

ALso, were planning on replacing he timing chain also.

Is it necessary to replace the piston/rings?

How do you know when it's time.

I've read general recommendations of doing this after 'x' hours (and the 'x' varies. Is there a measurement of the piston or something?

I want the bike to be solid, but at the same time I don't want to dump

unnecessary money into it either

(wish the heck we'd of stayed with the 2 smoke)

Thx in advance

Share this post


Link to post
Share on other sites

You can not keep the valves adjusted? Or it just needs a valve shiming ,adjustment?

Edited by RoscoeJ

Share this post


Link to post
Share on other sites

It needs to be shimmed. We have never shimmed them.

I"d love tojsut shim them but, I"ve kind of ruled this out because:

1- I've been told (and read) by numerous sources that the shims will only last about 10-15 hrs if I'm lucky. So, If we're going to end up in this spot anyway in early spring, what's the point?

2-I've read that the Yamaha's weak point in the valve train is the timing chain and it's time to replace it to prevent even worse things from happening :bonk:

Just this part is expensive enough.. I don't want to grenade the whole motor

3-THen there is the issue of the piston and should it be changed.

If I have to do all this anyway....

Share this post


Link to post
Share on other sites

most people will shim them twice then put new valves in the bike, i have just done the piston and cam chain on my bike, i brought the bike used and i have done over 30 hours on the bike easy and has never let me down, i just did them to be on the safe side, i would just do a piston change every year and i race every weekend and practice on the day before my race, i have ran a yamaha piston for 2 years without a problem,

Share this post


Link to post
Share on other sites

I only ride offroad so my bike does not see the revs that a mxers bike would see. For my type of riding when the shims have shifted .012" it is time to replace the valves. The exhaust valve usually do not shift for quite a while. Your piston and rings should go atleast a 100 hours with my type of riding. Yes you do want to change the timing chain. A shop will charge you around a $100 to shim the valves. It is not that diffcult to do, the manual almost tells you everything. If you decide to do it yourself there some tips that will make it easier.

Share this post


Link to post
Share on other sites

depending on your wallet and how much you rev the bike: for cheap and low rev's I'd shim, new timing chain, and new rings but I'd check the piston skirt for wear and if it's in spec. For high rev's I'd shim, change the valve springs, change piston and rings, change timing chain.

The OEM shims on the intake tend to be close to the minimums from the start so any movement gets them out of spec. If you're keeping the air filter clean not allowing any dirt into the intake, you should be good to go with this 1st shim.

Share this post


Link to post
Share on other sites

Did you check the valves when you bought the bike? There is a very good chance they were out of spec from day one off the assembly line! Every new yz250f I have checked clearance on was always at the very bottom of the spec, if not slightly past it.

I can't tell you that your valves are not going to fail next summer, but if this is your first time having to shim those valves then the odds of them failing in the next up coming year are pretty slim.

If you are hell bent on getting new valves though, SS is not the way to go unless your kid rides this bike like a Honda XR and does zero maintenance. This motor was designed around the light Ti valve train, so it's not as simple as just changing the valves to SS, the valve springs need to be replaced with much stiffer springs as well, which all costs more than the stock light, reliable Ti valves.

http://www.ebay.com/itm/YZ250F-oem-yamaha-Valve-Kit-w-springs-seals-01-09-/300638119814?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item45ff6da786

And yes, at 78 hours, it would be a good idea to do a rebuild like said above.

Share this post


Link to post
Share on other sites
Did you check the valves when you bought the bike? There is a very good chance they were out of spec from day one off the assembly line! Every new yz250f I have checked clearance on was always at the very bottom of the spec, if not slightly past it.

I can't tell you that your valves are not going to fail next summer, but if this is your first time having to shim those valves then the odds of them failing in the next up coming year are pretty slim.

If you are hell bent on getting new valves though, SS is not the way to go unless your kid rides this bike like a Honda XR and does zero maintenance. This motor was designed around the light Ti valve train, so it's not as simple as just changing the valves to SS, the valve springs need to be replaced with much stiffer springs as well, which all costs more than the stock light, reliable Ti valves.

http://www.ebay.com/itm/YZ250F-oem-yamaha-Valve-Kit-w-springs-seals-01-09-/300638119814?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item45ff6da786

And yes, at 78 hours, it would be a good idea to do a rebuild with new piston/rings, and timing chain.

Just about every one I've checked (250F's and 450F's) have the valve clearance set right in the middle of the tolerance range when they are unpacked from the crate but after 30min to an hour of running they'll close up about .001 on the intake valves. This usually puts them, as you have observed, right at the low limit. I wont adjust valves unless they are close to .001 under the low limit. The valves will stay at the low limit for a very long time and they usually last longer if you keep the clearance on the tight side. Obviously, if the valves won't stay in adjustment, it's time for a new set of valves. My wifes 2007 WR250 gets ridden 2000-3000 miles a year and the valve clearance has never been adjusted. It has been sitting right at the low limit on the intakes since right after the first ride in 2007.

Share this post


Link to post
Share on other sites

Right now they are at the botom limit on both exhaust and intake. We checked the clearances on the valves after we had the bike at about 20 hrs and they were near the high end. At 50 hrs they were in the middle of the range. Now at 78 they are at the bottom. So, the valves are wearing. He has been pretty good with his maintenance

changing the oil every 2- 3 hrs, and the filter after every ride.

Alot of the riding is at the local mx track on practice nights, usually once a week.

ONly a couple actual races. THen, he usually rides around where we live(in the country), as many of the local boys have built hare scramble tracks through the woods etc.

I'm not sure how much he's hitting the rev limiter. I don't hear it, but I imagine he is hitting in once in awhile

Share this post


Link to post
Share on other sites
Right now they are at the botom limit on both exhaust and intake. We checked the clearances on the valves after we had the bike at about 20 hrs and they were near the high end. At 50 hrs they were in the middle of the range. Now at 78 they are at the bottom. So, the valves are wearing. He has been pretty good with his maintenance

changing the oil every 2- 3 hrs, and the filter after every ride.

Alot of the riding is at the local mx track on practice nights, usually once a week.

ONly a couple actual races. THen, he usually rides around where we live(in the country), as many of the local boys have built hare scramble tracks through the woods etc.

I'm not sure how much he's hitting the rev limiter. I don't hear it, but I imagine he is hitting in once in awhile

78 hours is a lot for abike if it has regular racing. You are probably due for a top end complete with valves and piston (and a timing chain too).

Share this post


Link to post
Share on other sites
Right now they are at the botom limit on both exhaust and intake. We checked the clearances on the valves after we had the bike at about 20 hrs and they were near the high end. At 50 hrs they were in the middle of the range. Now at 78 they are at the bottom. So, the valves are wearing. He has been pretty good with his maintenance

changing the oil every 2- 3 hrs, and the filter after every ride.

Alot of the riding is at the local mx track on practice nights, usually once a week.

ONly a couple actual races. THen, he usually rides around where we live(in the country), as many of the local boys have built hare scramble tracks through the woods etc.

I'm not sure how much he's hitting the rev limiter. I don't hear it, but I imagine he is hitting in once in awhile

Based on the above, I'm with 2grimmjim on this one. Minimum you need piston/rings and cam chain plus a shimming. You are also a candidate for new valves and springs but you may be able to stretch those 2 till the next rebuild in 60 hrs.

Share this post


Link to post
Share on other sites

you dont see many of these engines blow-up,but the one that i personally witnessed was a bike with almost 100hrs,that was well overdue for a rebuild.the piston pin had excessive wear and ended up breaking the piston,which inturn totally destroyed the engine.if your goona do something,do it rght or you will be sorry.

Share this post


Link to post
Share on other sites

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
Sign in to follow this  

×