F650/800 valve clearances

Over on the ADVrider forum there is talk of new valve clearances that have been issued for the 650/800.

I inquired at my dealer and he sent me the new settings.
Intake - .23 to .33mm old settig was .18-.26
exhaust - .30-.41mm old settings was .27-.35

I'm not an expert, but I've always heard that if the valves were too tight it could lead to excessive wear on valve seats and valves. This raises the question of the long term impact on the older and/or higher mileage bikes that were run at the old settings.

There is not much difference in wear/damage for an intake valve. It might impact breathing, but they are cooled by the incoming air/fuel charge and don't run very hot. There can be wear/damage to exhaust valves that are too tight. They are cooled by contact with the seats and the seats/head carry heat away from the heads of the valves.

The certain case is where the gap is very tight so they stay closed significantly less time or don't even close tightly at all. This will burn exhaust valves quickly. Looking at the old and new specifications it seems the big end of the old range is now about in the middle of the new range. I doubt this change makes much of a difference in valve life. I always preferred to set valves at the loose end of the range but that is not always easy with fixed shim sizes. That depends on the shim size increments.

Paul:

In your experience with the vertical twins do the clearances tend to shrink or grow with mileage? I've heard the "dominant" factor is valve face/seat wear along with some stretch of the valve stem adding up to make clearances smaller over time.

This runs counter to my personal experiences on other types of vehicles, but these could be a different situation all together........

Thanks!
Jim

jimbob59 said:

Paul:

In your experience with the vertical twins do the clearances tend to shrink or grow with mileage? I've heard the "dominant" factor is valve face/seat wear along with some stretch of the valve stem adding up to make clearances smaller over time.

This runs counter to my personal experiences on other types of vehicles, but these could be a different situation all together........

Thanks!
Jim

Click to expand...

I haven't seen much change at all, but a few valve checks does not make that gospel.

Generally speaking though, I expect offsetting wear. Valve face/seat wear tends to close gaps. Camshaft, cam follower, and any rocker bearing wear (if applicable) will tend to open gaps. So things can go on a very long time with offsetting wear that doesn't show up in gap changes. Finally, something gets noisy or valves get leaky.

PGlaves said:

... Finally, something gets noisy or valves get leaky ...

Click to expand...

Yeah... that's how it goes with me

Seriously, thanks Paul!