Micahdogg wrote:

On a stock 2002 YZ250F that I'm rebuilding, I am wondering if anyone can tell me if the stock titanium valve and stock valve guide both expand at the same rate with heat? I'm basically wondering if the stem to guide tolerance will get looser or tighter when the engine is warm?

The stock valve guide is brass and the valve is TI so no they won't expand at the same rate. The tolerance would get tighter when warm. But, the amount of expansion when warm will be minimal and will not solve any excessive clearance issues. With the bike being an 02 it probably needs new guides and valves. Im not familiar with that model but for some the service manual will give a I.D. measurement for the inside of the guide. They make special gauges for measuring them.

I like your thinking but youre overthinking it lol. Your service manual will give you the size and tolerance for room temp size. The engineers already calculated the thermal expansion when they specified the tolerance. Theres no reason to worry about that kind of thing.

It wouldnt make sense to have a thou of clearance when the valve expands a thou. Otherwise it would seize in the guide. Make sense?

I'm specifically asking because I installed a guide in the center intake valve. It got deformed just a smidge...I mean just a freaking smidge. I've got a starett gauge and I can feel just a hair of drag at the end. I'm using a used valve and it does seem to have a little slight catch, but only at the end not far from the keepers. When seated, under the normal range of movement, it "seems" fine.

I don't have any way to hone the guide, and I think it'll be fine. But I was just wondering because if the clearance gets looser with heat, then I feel fine about it. If it gets tighter with heat...I don't know. Then again, now that I think about it, if the intake valves get a steady shot of fuel on them, it should help alleviate my concerns about.

If its right at the end you might be able to deburr the end but if It did get deformed then it will create excessive wear on the valve and guide. Best to replace the guide or take to a qualified shop and have them hone the guide.

Its not at the tip, but inside about 1/8th inch. The guide is like 1 inch long, and its only this one little snag 1/8th inch inside where you can feel that it got deformed a smidge. I'm using a starrett small bore gauge and it feels fine the entire length except that on little patch 1/8th inch inside from the tip.

I'm pretty sure this is an iron guide too....right outta the Yamaha parts bag. All of the guides in this head look iron to me.

Micahdogg wrote:

Its not at the tip, but inside about 1/8th inch. The guide is like 1 inch long, and its only this one little snag 1/8th inch inside where you can feel that it got deformed a smidge. I'm using a starrett small bore gauge and it feels fine the entire length except that on little patch 1/8th inch inside from the tip.

I'm pretty sure this is an iron guide too....right outta the Yamaha parts bag. All of the guides in this head look iron to me.

So look up the valve guide standard size in the service manual, buy a valve guide reamer in that size and run it through. Problem solved

If the guide is damaged, then replace it.

Paw Paw

When you press fit the guide in to the head the guide collapses a little bit. You will need to hone the guide don't ream it get a ball hone from kbc tool 5mm or what ever size it is hone the guide till the valve is a slip fit .001 valve to stem Clarence. but when you replace the guide you will need the valve seat cut

krgperformance wrote:

When you press fit the guide in to the head the guide collapses a little bit. You will need to hone the guide don't ream it get a ball hone from kbc tool 5mm or what ever size it is hone the guide till the valve is a slip fit .001 valve to stem Clarence. but when you replace the guide you will need the valve seat cut

Thanks. Is there a valve guide material that is more resistant to collapsing? I heated the cylinder head and installed the guide frozen, trying to avoid this. Also do you use those hones dry, or spray wd40 or something on the guide?

there is no way to avoid it you will always have to hone the guide because of the press fit and always always have to re cut the seat so the valve will seal proper. use wd40 is fine.

FYI, to answer your original question:

The coefficient of thermal expansion for titanium is 8.5x10^-6 per degree Celsius at room temp up to 100C (temp of boiling water.) This appears to be the best temperature range to use.
Brass has a coefficient of 19x10^-6 for the same temperature range.

This means that a rod of Ti will grow by .0000085, or .00085% of its length for every 1 degree celsius it gets hotter.
Brass will do the same by .000019, or .0019%.

It doesn't seem like much, but multiply those values by a 100-degree change in temp and it gets significant. Like Acidreamer said above, however, the engineers have already thought about this for you.

krgperformance wrote:

When you press fit the guide in to the head the guide collapses a little bit. You will need to hone the guide don't ream it get a ball hone from kbc tool 5mm or what ever size it is hone the guide till the valve is a slip fit .001 valve to stem Clarence. but when you replace the guide you will need the valve seat cut

Are you really suggesting the little diamond deburring brushes KBC sells? Yes you can do it, but then you're into small hole guages, and a high degree of skill, both at keeping the hone straight, and reading the small hole guages. Look at the factory recommended valve guide installation method...it'll tell you that after the valve guide is installed, you have to ream the guides to the correct size. If you have the factory service manual, it'll also generally give you the part number for the correct valve guide reamer. And yes, If you replace valve guides, the seats must be recut.

In my opinion it's better to hone I use a sunnen hone with arbors. The kbc ball hone isn't best honing option but best cheapest way get you back going instead of sending head out to a machine shop. When trying to ream it's also hard to keep it Straight and making sure you don't ream it over size.

Thanks for the replies everyone. You'll probably flame away, but this is what I ended up doing.

I found out that 5/32 is nearly identical to 4mm. And I happened to have a harbor freight drill bit in that size that I simply could not believe how well it fit into the guide. I could also feel the snag in the guide that I installed, but the drill bit passed through the other two intake guides. So a friend held the head, and I chucked the bit into my hand drill and gave it a spin. After checking with the gauge, the snag remained, so I hit it again, and again, and again with some oil. After a few passes, I was able to remove that snag about 80% and the intake valve is now much happier in that guide.

However, I still had a problem from before and after my awesome harbor freight drill bit clearancing, and that was the intake valve wasn't hitting the seat square. You could clearly see where it was hitting 1/4 of the seat first. So I grabbed an old intake valve and lapped it into the seat. I know this is something you usually do to match a valve to a seat, but I was trying to match the direction of the valve to the seat. After several passes with a hand drill hooked up to it, I was able to refinish the offending part of the seat and now my "good" valve sits nice and square in there. I installed the spring and shined a light in the intake port and it looks to be sealing as good, if not better than the other valves.

I know none of this is the right way to do this, but I'm trying to do this restoration (http://www.vitalmx.com/forums/Bike-Builds,46/2002-YZ250F-Restoration,1316154) on a budget and I don't need it to be perfect, I just need it to be good.

P.S. The Yamaha manual does say to ream, and it offers a Yamaha part number for said ream. But the manual also says to lap the valves into the seats, so I'm taking their instructions with a grain of salt.

krgperformance wrote:

In my opinion it's better to hone I use a sunnen hone with arbors. The kbc ball hone isn't best honing option but best cheapest way get you back going instead of sending head out to a machine shop. When trying to ream it's also hard to keep it Straight and making sure you don't ream it over size.

A Sunnen hone with arbors is a bit different than a micro ball hone. I get that the ball hone is the most expedient, least expensive method, and that it can be difficult to use a reamer correctly. I'm an old school guy...I use Neway cutters with a T-handle driver, I hand ream valve guides, and I don't typically have problems. It does take a fine touch though.

Micahdogg, Yes the factory manual says to lap the valves. However, I'm certain it also says to grind or recut the valve seats, then lap the valves. After replacing valve guides and reaming to the correct ID, you would then recut the seats to make the valve contact patch concentric with the guide, set the contact patch to the correct width (typically .5mm-1mm), and set the contact patch to the correct area on the valve face. Lapping can be done as you did, to correct alignment issues, but the contact area will be too wide. This can result in removing too much material from the valve seat, and moves the valve too far back in the head, limiting your ability to adjust valve clearances. The factory manual specifies lapping as the final step to obtain a perfect seal.

If you find your valve clearance is too tight for the factory adjustment shims, Kibblewhite makes them down to 1.2mm thick

Micahdogg wrote:

Thanks for the replies everyone. You'll probably flame away, but this is what I ended up doing.

I found out that 5/32 is nearly identical to 4mm. And I happened to have a harbor freight drill bit in that size that I simply could not believe how well it fit into the guide. I could also feel the snag in the guide that I installed, but the drill bit passed through the other two intake guides. So a friend held the head, and I chucked the bit into my hand drill and gave it a spin. After checking with the gauge, the snag remained, so I hit it again, and again, and again with some oil. After a few passes, I was able to remove that snag about 80% and the intake valve is now much happier in that guide.

However, I still had a problem from before and after my awesome harbor freight drill bit clearancing, and that was the intake valve wasn't hitting the seat square. You could clearly see where it was hitting 1/4 of the seat first. So I grabbed an old intake valve and lapped it into the seat. I know this is something you usually do to match a valve to a seat, but I was trying to match the direction of the valve to the seat. After several passes with a hand drill hooked up to it, I was able to refinish the offending part of the seat and now my "good" valve sits nice and square in there. I installed the spring and shined a light in the intake port and it looks to be sealing as good, if not better than the other valves.

I know none of this is the right way to do this, but I'm trying to do this restoration (http://www.vitalmx.com/forums/Bike-Builds,46/2002-YZ250F-Restoration,1316154) on a budget and I don't need it to be perfect, I just need it to be good.

P.S. The Yamaha manual does say to ream, and it offers a Yamaha part number for said ream. But the manual also says to lap the valves into the seats, so I'm taking their instructions with a grain of salt.

The proper tool for that job is not a drill bit. You either ream it out or hone it. Theres a very good chance you drilled crooked and thats why its not square. Brass is extremely soft. Maybe someone else has done it and it worked out ok but from my tool and die experience hand drilling something like that sounds like a bad idea.

Acidreamer wrote:

The proper tool for that job is not a drill bit. You either ream it out or hone it. Theres a very good chance you drilled crooked and thats why its not square. Brass is extremely soft. Maybe someone else has done it and it worked out ok but from my tool and die experience hand drilling something like that sounds like a bad idea.

X2. By the way...Acidreamer...are you a member at Mansfield M/C club?

Micahdogg wrote:

Thanks for the replies everyone. You'll probably flame away, but this is what I ended up doing.

I found out that 5/32 is nearly identical to 4mm. And I happened to have a harbor freight drill bit in that size that I simply could not believe how well it fit into the guide. I could also feel the snag in the guide that I installed, but the drill bit passed through the other two intake guides. So a friend held the head, and I chucked the bit into my hand drill and gave it a spin. After checking with the gauge, the snag remained, so I hit it again, and again, and again with some oil. After a few passes, I was able to remove that snag about 80% and the intake valve is now much happier in that guide.

However, I still had a problem from before and after my awesome harbor freight drill bit clearancing, and that was the intake valve wasn't hitting the seat square. You could clearly see where it was hitting 1/4 of the seat first. So I grabbed an old intake valve and lapped it into the seat. I know this is something you usually do to match a valve to a seat, but I was trying to match the direction of the valve to the seat. After several passes with a hand drill hooked up to it, I was able to refinish the offending part of the seat and now my "good" valve sits nice and square in there. I installed the spring and shined a light in the intake port and it looks to be sealing as good, if not better than the other valves.

I know none of this is the right way to do this, but I'm trying to do this restoration (http://www.vitalmx.com/forums/Bike-Builds,46/2002-YZ250F-Restoration,1316154) on a budget and I don't need it to be perfect, I just need it to be good.

P.S. The Yamaha manual does say to ream, and it offers a Yamaha part number for said ream. But the manual also says to lap the valves into the seats, so I'm taking their instructions with a grain of salt.

Acidreamer wrote:

The proper tool for that job is not a drill bit. You either ream it out or hone it. Theres a very good chance you drilled crooked and thats why its not square. Brass is extremely soft. Maybe someone else has done it and it worked out ok but from my tool and die experience hand drilling something like that sounds like a bad idea.

harescrambled wrote:

X2. By the way...Acidreamer...are you a member at Mansfield M/C club?

No im not. Went to watch a harescramble there once thats about it

Acidreamer wrote:

The proper tool for that job is not a drill bit. You either ream it out or hone it. Theres a very good chance you drilled crooked and thats why its not square. Brass is extremely soft. Maybe someone else has done it and it worked out ok but from my tool and die experience hand drilling something like that sounds like a bad idea.

The guide was crooked before and crooked after my ghetto reaming.  It was crooked in the same fashion - with the valve contacting one specific part of the seat before and after.  So the reaming didn't cause the issue, the guide install did.  Also these are iron guides.  Part number 5NL-11133-10, which was iron out of the bag, and matches the other iron guides.

I do agree though that the hand drill/harbor freight drill bit sounds like a bad idea, but everything I've been doing to this head sounds like a bad idea. 

harescrambled wrote:

A Sunnen hone with arbors is a bit different than a micro ball hone. I get that the ball hone is the most expedient, least expensive method, and that it can be difficult to use a reamer correctly. I'm an old school guy...I use Neway cutters with a T-handle driver, I hand ream valve guides, and I don't typically have problems. It does take a fine touch though.

Micahdogg, Yes the factory manual says to lap the valves. However, I'm certain it also says to grind or recut the valve seats, then lap the valves. After replacing valve guides and reaming to the correct ID, you would then recut the seats to make the valve contact patch concentric with the guide, set the contact patch to the correct width (typically .5mm-1mm), and set the contact patch to the correct area on the valve face. Lapping can be done as you did, to correct alignment issues, but the contact area will be too wide. This can result in removing too much material from the valve seat, and moves the valve too far back in the head, limiting your ability to adjust valve clearances. The factory manual specifies lapping as the final step to obtain a perfect seal.

If you find your valve clearance is too tight for the factory adjustment shims, Kibblewhite makes them down to 1.2mm thick

I thought lapping under any circumstance was a bad idea on these titanium valves as it removes the hardened finish?  I was just surprised to see Yamaha suggest it.

And I am half expecting my clearance to be too tight.  Good to know on the kibblewhite shims, but I was kinda thinking of removing a little material at the end of the valve.  My neighbor has some tools that I think will work for getting a square cut. 

The problem with removing material from the valves is you weaken the tip when you do it. I don't know if Yamaha valves use a single groove retainer, but it's even more critical not to remove material if that's the case. It would suck to do all that work and drop a valve because too much material was removed from the valve stem tip. Thing is if you take off too much material from the stem tip, the retainers might just pull the tip right off. I wouldn't recommend going that route.

As for the "hardened finish" on Ti valves, it's about .0002" thick. They're not telling you to lap the valve for gross reshaping, and the lapping compound you'd use isn't what you can buy at autozone. Clover (now owned by Loctite) makes it up to 1200 grit. I use the fine stuff when I have to.

Very good info, thanks harescrambled. Yeah it is a single groove...hopefully it the shims will work out.

Thanks for the tips everyone. Turns out I wasn't measuring correctly and my valve shim issue wasn't as bad as I thought. Most of the shims I used were in the 160 range.

Looks reasonable, although the valves are a bit on the tight side. They'll tend to tighten up as they wear. Hope it works out well for you with all the work you did. By the way...after you run it through a heat cycle..like for 30 minutes or so, let it cool down to room temp and recheck the valve clearances

Thanks. What would you set the valves at? I tried to set them on the loose side. Btw, got any oil recommendations? Im leaning toward synthetic but have no idea on weight.