2009 yz450 valves

Okay so I have a 2009 yz450 as the title says and about 12 hours ago I put a piston and new timing chain in. I bought the bike used so I have no idea of actual hours on the engine, seller said he "thought" around 50 but wasn't sure. I've put 47 hours on it since June 2012. When I bought the bike and prior to tearing into the top end I checked the valve clearance and it was fine, just a little on the minimum side but not out of spec. So in the last couple riding hours it's gotten a little harder to start and so I thought I should check the valves. The exhaust side is fine, but the intake is very tight, way out of spec. I did clean a little carbon buildup off the valves while I had the head off, but even that wasn't bad. I did not disassemble the valves. So finally to my point, I'm gonna have to adjust some valve clearance and this whole shim and bucket is new to me. I understand the concept and I believe I need to order at least a shim kit, but A) any ideas why it tightened up so much in only 12 hours? And B) what type of shim kit should I look for and from whom? I'm assuming I just need to put a smaller shim in that will get me to the correct clearance? Any advice is appreciated, thanks.

"Complete" shim kits are too expensive, and don't cover the full range you would need in order to service your YZF.  You'd need two, and they're $70-something each.  For a readjustment, buy only the shims you need after reviewing the clearances and the current shims in the bike already.  A lot of times you can shuffle the ones you have and correct one or two tight valves with shims from the other intakes.  Then you only have to buy one or two; less than $20.


For situations such as after a valve job where you don't have a good idea of what shims you'll need, and the machinist doesn't bench adjust them, I prefer buying "refill packs".   Hot Cams sells these as small packs containing 5 shims each of six sizes.  You can get two for the price of one "full" kit and have 5 shims apiece in each of .05 increments from 1.55 to 2.05mm, instead of 3 each of sevarl sizes you won't ever use.


A sudden, significant loss of valve clearance is troubling news here.  It usually indicates that the hard coating on the valve in question has worn completely through, and the valve needs immediate replacement.  Adjust it to spec, and see what the difference between the old and new shim is.  If it needs a shim .10 or more smaller than the original, the valve is probably shot.  If it takes only .05 to maybe .10 to correct the clearance, adjust it, and check it again after one ride.  If it moves measurably in under 4 hours, you need a new valve.

Thanks Gray for the info.

I just did my 450 this weekend and I learned that it is the center intake valve that wears faster. All others were perfect but center one was quite a bit off I had to go from a 1.75 to 1.5 now it starts first kick cold.

I only bought the shim I needed and next size up. Use the chart in service manual and it will save a ton of time.

Edited by dadat40

I claim no ownership of this spreadsheet - I found one online to calculate the necesarry shims for the YZ450F but it must have been made for an older model as I have an 08 and the clearance specs were different. 


I tweaked all of the data to match what was in the 08 manual.  I also added the ability to plug in the actual OEM shim value without having to do the rounding (OEMs can come in off sizes - e.g. one of my shims is a 179).  I also added a couple worksheets with tables to add service history. 




Thanks for all the great info guys. But I found a different problem when I took everything apart to check shim sizes. One of the valve keepers for the center intake valve had worked its way loose and was riding up against the shim causing a errant clearance reading. It didn't come completely out enough to go wandering around the engine (thank God!!) but it was loose enough to cause clearance interference. So the plan now is to buy a new set of valve keepers and reinstall. I inspected the valve stem and didn't see any damage and everything else looks fine. My question is why would this valve keeper come loose in the first place? I'm not a rever when I ride and typically when I come in from riding the hour meter records max rpm for that session and mine usually is around 9600 or so. I'm the type of person who isn't satisfied to just fix a problem, I'd like to know WHY something broke in order to avoid it in the future. Thanks in advance for your help.

Possibly the previous owner put valves or springs or seals in it and never verified the valve lock was seated. With any 4 stroke cylinder head service you must lightly tap on the valve tip with a punch to verify the locks are seated. If its going to come out, it will on the bench then. Just make sure the tip of the valve isn't damaged from the loose lock and you should be ok.

Edited by NitrousR1

Well replaced the valve keepers with a new set on the middle intake valve and went riding. Put 1.9 hours on the motor this past Saturday, checked the valve clearances yesterday and they were spot on where they were before riding and after repair. By the way I finally got a chance to look at that spread sheet, very nice. Great work on that. Thanks for all you guys help.

Don't know if it was mentioned but Honda has shims in half increments as well.

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