Excesive Valve Clearance Question - NON ST

[stoc445]

NON ST, I'm doing a valve clearance check on a friends bike (04 Yam R1). This bike has about 24K miles. He told me he had a shop do the last check. Looking at his air filter, I doubt they even pulled the air box. Anyway, reason for the post is one of his valve clearance gap is huge.

All exhaust are in the middle of the range (.21-.25mm). Majority of the intake are dead center as well with one a tad tight but tolerable (.11-.20mm)

The intake valve in question is #3 cyl, facing engine left to right (closest to cam chain), valve #1 has a gap of .490 mm. I re-did the check about 6 times, same thing.

I'm not amechanic so I don't want to pull the cams and shim it down until I know if this is an indication of something major. I've personally never seen one this far out of spec.

Anyone seen this, is it serious? Any suggestions? I'm tempted to button it back up and tell him to take it into the dealership, or at least avoid the previous shop he used. Anyway, I wanted to check with someone who may know if this is a real problem.

Thanks and appreciate the time.

Denny

 

[two_wheeled]

That's really odd. Valves get tighter as they wear so I would have to guess it was messed up during the last valve adjustment.
I imagine you would be able to 'hear' a gap that large. It would click every time the lobe came around.

 

[Byron]

Sounds like they might have calculated wrong, changed a shim, and created the excess. Either that or check and see if the cam or spacer show signs of wear as if either is soft and has premature wear.

 

[Blrfl]

The difference in the clearances makes me think there might be no shim under there at all, but even that difference is much larger than the biggest shim Yamaha makes for that bike. It's also remotely possible that with no shim supporting the center, the cam lobe has pounded the bucket surface concave and has added extra clearance.

The only way you're going to learn anything more about it is to remove the cam and inspect everything from the lobe down to the valve spring retainer. Use a magnet to pull the bucket in case there are pieces of a failed shim under there. (Unlikely, but it can't hurt.)

--Mark

 

[stoc445]

Good stuff, I'll let ya know how it turns out.

Thanks!

 

[wjbertrand]

Excess carbon on the valve stem? Might try running some combustion chamber cleaner, Seafoam, or I think GM has a pretty decent one. A leaky injector at that cylinder could lead to big buildup on the back side of the intake valve.

 

[Blrfl]

We had a couple of STs here that ended up with build-up on the valves that prevented them from seating, which makes Jeff's suggestion a good one. Maybe before removing the cam, do a compression test.

--Mark

 

[stoc445]

Excess carbon on the valve stem? Might try running some combustion chamber cleaner, Seafoam, or I think GM has a pretty decent one. A leaky injector at that cylinder could lead to big buildup on the back side of the intake valve.

Jeff,
This bike has 3 intake valves per cyl. The other 2 valves have good measurements. If what you suggested is true, wouldn't the other two have the same build up?

 

[wjbertrand]

Jeff,
This bike has 3 intake valves per cyl. The other 2 valves have good measurements. If what you suggested is true, wouldn't the other two have the same build up?

I don't know. It might depend where the valves are located with respect to the injector. If the injector is leaking, the fuel may not be getting evenly distributed to all the intake valves. Seems reasonable that sticky valves could occur somewhat irregularly.

 

[Scooter]

The difference in the clearances makes me think there might be no shim under there at all, but even that difference is much larger than the biggest shim Yamaha makes for that bike. It's also remotely possible that with no shim supporting the center, the cam lobe has pounded the bucket surface concave and has added extra clearance.
--Mark

There has to be a shim in there. Assuming the standard intake clearance of 0.16mm, the difference between the measured value of 0.49mm is 0.33 mm. I don't know what Yamaha's thinnest shim is but Honda's is 1.20mm which is roughly four times the size of the gap.

Excess carbon on the valve stem? Might try running some combustion chamber cleaner, Seafoam, or I think GM has a pretty decent one. A leaky injector at that cylinder could lead to big buildup on the back side of the intake valve.

This would be my initial guess also. It might be something as simple as a small piece of carbon stuck up there in the one valve and not the others. You could ask the shop if they had changed any of the shims the last time. If they had, it's possible they might have put the wrong shim in there and didn't recheck when they were finished.

 

[Byron]

Yamaha used to use large shims on top the valve, you could tell if one was missing. They also used to make a small tool that would hold down the buckets and allow the shims to be removed without removing the cam. Without knowing more about the bike you'll have to determine what is necessary.

 

[Blrfl]

There has to be a shim in there.

I'd think that, too, but after some of the dumb stuff we've seen dealers do, you never know. If the valve isn't being held open at the seat, the extra clearance has to be at the cam end.

Yamaha used to use large shims on top the valve, you could tell if one was missing.

The R1 is shim-under-bucket like the ST. Shim-over-bucket doesn't work well in high-rev applications.

--Mark

 

[stoc445]

Well, I learned of a nugget and by the sound of it, I think Jeff nailed it. A year or so ago, there was a leaking injector causing him problems, bad gas smell when you followed him, poor mileage, etc. He didn't remember which one, but I'll bet it's #3.

Thanks for all the help.

 

[two_wheeled]

Would a gap like that eventually burn the valve?

 

[wjbertrand]

No. Excessive gap only leads to wear of the cam etc and noise. With lack of gap it can lead to the exhaust valve being held open in the combustion chamber during ignition. Thats what burns the valves. Some people run their clearlances loose on the theory that it does no harm and helps prevent tighter numbers which could prove destructive.

+1 Also, it's rare to burn an intake valve, which is the question in this case, as they get cooled by the incoming fuel charge. No such break for exhaust valves though.

 

[two_wheeled]

Oops, I knew that. I all of a sudden had it reversed in my head, thinking the valve clearance was too small instead of too large. I'm working too much.