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- 2013 ST1300 A9
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Another valve adjustment questions
- Thread starter jfheath
- Start date
wjbertrand
Ventura Highway
The reason clearances tighten with mileage is because the valves recess into their seats deeper as the seats and valve sealing surfaces wear. It's actually called valve recession. The stems themselves do not get longer.
No valve clearance gap that's out of spec error is going to cause piston-to-valve interference. The usual way something like that happens is due to a gross timing error such as a snapped timing belt/chain or improper assembly. Over-revving to the point of causing valve float can also cause piston-valve collision. These scenarios are independent of clearance gap.
Letting the clearance tighten too much for too long can still cause severe engine damage however, particularly in the case of the exhaust valves, for another reason though. The valve's only cooling opportunity is when they are resting on their seats. This allows heat transfer to the head. If clearances are too tight, the resting/cooling time will be too short or in an extreme case eliminated. The valves will accumulate heat and begin operating above their design limits, eventually burning. Again this is particularly a risk with exhaust valves as they do not have the benefit of the cool intake stream.
If you think such an occurrance unlikely, think again! Below are photos of a burnt exhaust valve from an ST1100:
No valve clearance gap that's out of spec error is going to cause piston-to-valve interference. The usual way something like that happens is due to a gross timing error such as a snapped timing belt/chain or improper assembly. Over-revving to the point of causing valve float can also cause piston-valve collision. These scenarios are independent of clearance gap.
Letting the clearance tighten too much for too long can still cause severe engine damage however, particularly in the case of the exhaust valves, for another reason though. The valve's only cooling opportunity is when they are resting on their seats. This allows heat transfer to the head. If clearances are too tight, the resting/cooling time will be too short or in an extreme case eliminated. The valves will accumulate heat and begin operating above their design limits, eventually burning. Again this is particularly a risk with exhaust valves as they do not have the benefit of the cool intake stream.
If you think such an occurrance unlikely, think again! Below are photos of a burnt exhaust valve from an ST1100:
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If you're at the limit you are still good to go. Is this the first valve check or not? If there was one performed previously, did the clearances change at all between measurements?
Jeff, I supposed you don't know how tight that valve was in order to cause that to happen?
Jeff, I supposed you don't know how tight that valve was in order to cause that to happen?
wjbertrand
Ventura Highway
In this particular case the clearance was in spec. The machinist i took the head to thought some carbon may have caught under the valve preventing it from closing. Either way the effect is the same.
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