do valve clearances tend to reduce or increase ?

[aSTerix]

My exhaust valve clearances on No1 engine are just below the tolerance range, this got me thinking, how did this happen ? I would have expected the clearances to increase due to wear not reduce

Is is perhaps a sign that the valve seats are wearing ?

 

[Bush]

It's opposite to what you are thinking. With wear, the valve moves closer to the cam lobe, reducing the valve lash. With a carbon buildup on the seat, the valve moves farther away from the cam lobe, increasing the lash.

Most 1100's have experienced some changes in clearances, either way, but not by much and once done the first time, most have found they stay pretty constant afterwards.

 

[beemerphile]

I've had older BMW airheads where the valves receded over time because of valve seat metallurgy problems and the clearance consistently diminished. I had a Husqvarna TE610 that had rocker arm wear because of a screwy top end design and the clearances were consistently increasing. Replacing rocker arms was SOP. Both conditions were common with each of those bikes. You have to know your machine. Once you know your machine's behavior you can adapt your maintenance process. If they tend to diminish, you can avoid the low end and set them on the high side. The opposite for a case where tolerances increase. If you are lucky, as we are in ST land, they stabilize and you can set them in the middle. But don't leave them out of tolerance. All things considered, loose is better than tight. If they tightened up, they can get tighter. Tight valves will not announce themselves like loose valve do. There is nothing to alert you that you are flying in the danger zone.
)

 

[Igofar]

Like the British say, "Loud Valves Save Lives"
Pull a plug once in a while and check the condition.
If your bike goes quite, I'd worry, otherwise, I like my engines to make a little noise.

 

[aSTerix]

Thanks for the advice, sounds like I should re-shim my No1 exhaust valves. Wish I knew what the current shim was ! probably will wait until the summer when the bike will be put away for a few months.

 

[beemerphile]

Like the British say, "Loud Valves Save Lives"

Or... "tappy valves are happy valves" same idea.

 

[Bmacleod]

Here a tip. If you have to reshim a valve on any side, lift all the buckets and make notes on the shim thicknesses on all the valves for that side. You have to remove the cams for that side anyhow and in the future, if you get a reading that requires an adjustment, you will know what shim you need without having to take it apart and then wait for parts. Also, sometimes, if you have more than one valve that needs adjustment, you may get lucky and move some shims around to other valves, negating the need to order more shims. Having this shim "layout" ahead of time makes it easier.

 

[wjbertrand]

Depends on the valve train design. Rocker arm systems with small contact areas at the tip of the valve stem and the arm or systems with push rods tend to gain clearance with mileage due to more point loading, heavier valve train and more components. Shim over bucket designs also tend to wear toward increased clearance, though much more slowly than rocker arm designs. Shim under bucket designs like our STs, have hardened buckets and large contact areas between the cam and bucket so the valve seat wear, or recession, becomes the dominant means for change which causes the valve to seat deeper into the head and reduce clearances. Again though the rate of this wear is even slower than the shim over bucket designs.