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What Goes into a Valve Job?

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Hey! I recently bought a seized up 2009 YZ250F planning to rebuild it. The cylinder was rehoned and I replaced the crankshaft, most of the bearings, piston, timing chain, and some other smaller parts. Everything was working okay until I got to checking the valve clearances. The guy I bought the bike from (a mechanic) had taken apart the top end before he sold me it so I hadn't seen the valve clearances until now.

The exhaust valves were fine, running at .20mm on the left and .18mm on the right with 1.70mm shims (the printed number). The leftand right intake valves were slightly out of spec at .08mm and .09mm. I was able to get the left clr. to .13mm on a 1.40mm shim and the right clr. to .10mm on a 1.55mm shim. Once again, these were the printed sizes, but it still seems weird to me that I had to go down two shim sizes for that small clearance change. I'll get back to that later. The real problem was the middle intake, which was zeroed out on a 1.40mm shim. I switched it with the smallest shim I have (1.20mm) and I still couldn't fit the .005mm feeler underneath the lobe.

My question is what do I need to do when the valve can't be shimmer any further? Will I need to have the seat recut? What all goes into replacing valves. I've never seen it fully explained.

And on the left and right intake valves, I've heard that once your shims are under 1.70mm you need to look at working on your valves. Is that true and would anything be done differently than on the the mid intake valve?

I'd really appreciate it if someone could tell me what goes into a valve job and if my valves should be replaced. I've been looking around online for a couple hours and found only bit's and pieces. If someone has already answered these questions, please, point me over there. And if I'm asking the wrong questions, just let me know, I'm not here to be spoon-fed answers, but just couldnot find a full explanation.

Sorry about the long post. It's my first time (probably) replacing valves,  and I thought more people might want a good idea of what goes into a valve job.

Thanks in advance!

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A lot of variables, none are fast and true.

It is incorrect about once a shim size is 'X' you must do the valves. In reality, right from the factory, shim size can vary greatly. Typically, they strive to enable at least two shim job before you must do the valves. Now, once the valves need to be adjusted ONCE, it is a warning that you need to get ready to do them. As the valve face wears, the valve cups and recede into the head. Once the wearing starts, it tends to get worse fast. Many guys report no clearance changes for 100's of hours and then all of a sudden, a valve is out, it gets shimmed and five out later, it has tightened again. A few ignore the warning signs, keep shimming (even 'sanding' shims or other monkey biz) to 'ride one more time' only to end up with a broken valve, ruined head, damaged barrel, piston, bent rod and possibly worse.

If one valve is going bad, do them all. A good shop will use a SERDI cutter to get a precise cut and centered valve seat. If the seats are too worn, they may need to be replaced. If the seats are cut, the stems of the valves often need to me milled/ground to account for the cut seat.

Shims size marking are not absolute, they are just where in the range that shim falls into. A .177 shim would be marked as a .175. A .173 would also be marked as a .175. So... to be sure, always use a micrometer to get the actual shim thickness.

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24 minutes ago, William1 said:

A lot of variables, none are fast and true.

It is incorrect about once a shim size is 'X' you must do the valves. In reality, right from the factory, shim size can vary greatly. Typically, they strive to enable at least two shim job before you must do the valves. Now, once the valves need to be adjusted ONCE, it is a warning that you need to get ready to do them. As the valve face wears, the valve cups and recede into the head. Once the wearing starts, it tends to get worse fast. Many guys report no clearance changes for 100's of hours and then all of a sudden, a valve is out, it gets shimmed and five out later, it has tightened again. A few ignore the warning signs, keep shimming (even 'sanding' shims or other monkey biz) to 'ride one more time' only to end up with a broken valve, ruined head, damaged barrel, piston, bent rod and possibly worse.

If one valve is going bad, do them all. A good shop will use a SERDI cutter to get a precise cut and centered valve seat. If the seats are too worn, they may need to be replaced. If the seats are cut, the stems of the valves often need to me milled/ground to account for the cut seat.

Shims size marking are not absolute, they are just where in the range that shim falls into. A .177 shim would be marked as a .175. A .173 would also be marked as a .175. So... to be sure, always use a micrometer to get the actual shim thickness.

 Okay, thanks man! Yeah I definitely need to pick up a micrometer.

When you said if the seats are too worn, they may need to be replaced do you mean I might need to replace the head or am I not understanding?

The thing about this bike is I got it for a good price and figured I would probably sell it after a good ride or two. When I saw the exhaust clearances were fine I was thinking I might only need to replace the intake valves. I don't want to hand off a time bomb but would rather not mess with the exhast valves. I know they have been shimmed before (aftermarket shims in the bike), but couldn't they still hold up for a while since they're still in spec?

When replacing valves do the spring seats, springs, retainers, and buckets need to be replaced too?

 

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1 hour ago, DeAndrae Loewen said:

 Okay, thanks man! Yeah I definitely need to pick up a micrometer.

When you said if the seats are too worn, they may need to be replaced do you mean I might need to replace the head or am I not understanding?

The thing about this bike is I got it for a good price and figured I would probably sell it after a good ride or two. When I saw the exhaust clearances were fine I was thinking I might only need to replace the intake valves. I don't want to hand off a time bomb but would rather not mess with the exhast valves. I know they have been shimmed before (aftermarket shims in the bike), but couldn't they still hold up for a while since they're still in spec?

When replacing valves do the spring seats, springs, retainers, and buckets need to be replaced too?

 

Seat replacement/head replacement is a matter of how worn or damaged, there is not hard and fast rule there either. Some really good head guys can tell just with a glance, other will cut the seat to see how deep it ends up being and then determine if the head is good as is, is in good enough shape to replace a seat or if a new OEM is a cheaper route.

It sounds like you got the typical used bike from another flipper, who buys a non-runner, makes it run just long enough to unload and sells it. Then the new buyer is stuck with it. If you have morals and self worth, you'll either part the bike out as is, with full disclosure or repair it properly. A couple of TT sponsors are pretty reputable, FastHeads and BigBoreThumpers.

A re-shim and a ride is a ticking time bomb with no count down timer. It might be fine for thirty hours. It might be ok for just one hour. The resulting damage can be catstrophic just out of that desire to 'get one more ride out if it'. Not worth it in my book.

 

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1 minute ago, William1 said:

Seat replacement/head replacement is a matter of how worn or damaged, there is not hard and fast rule there either. Some really good head guys can tell just with a glance, other will cut the seat to see how deep it ends up being and then determine if the head is good as is, is in good enough shape to replace a seat or if a new OEM is a cheaper route.

It sounds like you got the typical used bike from another flipper, who buys a non-runner, makes it run just long enough to unload and sells it. Then the new buyer is stuck with it. If you have morals and self worth, you'll either part the bike out as is, with full disclosure or repair it properly. A couple of TT sponsors are pretty reputable, FastHeads and BigBoreThumpers.

A re-shim and a ride is a ticking time bomb with no count down timer. It might be fine for thirty hours. It might be ok for just one hour. The resulting damage can be catstrophic just out of that desire to 'get one more ride out if it'. Not worth it in my book.

 

I don't think you understood me, I did not have to re-shim the exhaust valves. I'm not here to destroy or sell a time bomb.

And about the seller, it wasn't running when I bought it.

When your replacing valves, do the spring seats, springs, cotters, retainers, and buckets need to be replaced?

Thanks for replying though. I appreciate it.

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I was not talking about you per se 'making a worn out bike work', I just see it so often (daily) that I strongly caution people.

Yes, you replace the valve, spring seat, spring, retainer and cotters. Buckets are reused unless damaged. Re-doing valves on a race bike like a YZ is not a home garage mechanic job.

Do not lap Ti valves, you will ruin them. Really you should not lap any valve, instead cut the seat.

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8 minutes ago, William1 said:

I was not talking about you per se 'making a worn out bike work', I just see it so often (daily) that I strongly caution people.

Yes, you replace the valve, spring seat, spring, retainer and cotters. Buckets are reused unless damaged. Re-doing valves on a race bike like a YZ is not a home garage mechanic job.

Do not lap Ti valves, you will ruin them. Really you should not lap any valve, instead cut the seat.

Yeah man I get it.

I was planning on getting the seats cut but install the valves myself.

And about the buckets, a lip had kinda formed around the intake valve buckets that had to be cut out. Then to pull them out of the head I needed a plier. Would that damage the buckets? I don't think it was excessively rough.

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6 minutes ago, DeAndrae Loewen said:

Yeah man I get it.

I was planning on getting the seats cut but install the valves myself.

And about the buckets, a lip had kinda formed around the intake valve buckets that had to be cut out. Then to pull them out of the head I needed a plier. Would that damage the buckets? I don't think it was excessively rough.

Have the shop install the valves. Give them the cams, buckets and shims. A good shop will insist on it. If they cut the seats the have to have ht buckets and cams to know how much to mill  the valve stem by. They will also be able to tell you if the bucket is good or needs to be replaced.

Yeah.. pliers on a bucket is a no-no. I use high power rare earth magnets. Nary a mark.

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9 minutes ago, William1 said:

Have the shop install the valves. Give them the cams, buckets and shims. A good shop will insist on it. If they cut the seats the have to have ht buckets and cams to know how much to mill  the valve stem by. They will also be able to tell you if the bucket is good or needs to be replaced.

Yeah.. pliers on a bucket is a no-no. I use high power rare earth magnets. Nary a mark.

Okay, sorry for bothering you so much, but do you have any idea what they would charge for inspecting my cyl. head, cutting the seats, and installing the valves?

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9 hours ago, DeAndrae Loewen said:

Okay, sorry for bothering you so much, but do you have any idea what they would charge for inspecting my cyl. head, cutting the seats, and installing the valves?

No idea, varies from shop to shop. I'd call BigBore Thumpoers and FastHeads first to get what they'd charge and ask the basic steps. Any local place should price about the same and use the same steps. They MUST use a SERDI macine!!!!

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7 hours ago, William1 said:

No idea, varies from shop to shop. I'd call BigBore Thumpoers and FastHeads first to get what they'd charge and ask the basic steps. Any local place should price about the same and use the same steps. They MUST use a SERDI macine!!!!

Ill make sure of that.

3 hours ago, morphrider said:

I had big bore thumpers do mine couple years back. I bought all OEM valves, springs, everything off eBay, then sent everything to them. Jeff I think his name was, quick turn around and good pricing. 

Okay thanks guys! I'll check with a few of those shops.

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