Exhaust valve tappet clearance

[Pengze]

Dear Gentlemen,
Would like to know what are the advantages and disadvantages if we increase the tappet clearance for the exhaust valve from 0.9 mm to 1.1 mm for a 4-stroke medium speed diesel combustion engine ?
Sincere appreciate yr valuable feedback.

[D Winsor]

I can see no advantage in increasing the valve clearance unless the manufacturer has changed the design of the valve and it is necessary to increase the valve clearance to compensate for thermal expansion of the valve spindle.
If this is not the case you will end up changing the valve timing causing the exhaust valve to open later, close earlier, and not open as wide as they should, resulting in less effective clearing of exhaust gases from the cylinders during the scavenge process and introduce added stresses on the tappets, rocker arms, push rods, cam followers and cams.

[Big Pete]

I agrre with what D. Winsor says in theory, but I remember sailing with a Mirrlees Blackstone K Major engine 30 years ago and the makere increased the valve clearances by 50% to reduce the noise, and it didn't appear to cause any other problems.

BP

[Pengze]

Will this cause the exhaust valves to cut / leaking while in operation ?
Would appreciate valuable explanation.