Exhaust valve tappet clearance

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Pengze
Mechanic
Posts: 60
Joined: Tue Sep 23, 2008 8:57 pm

Exhaust valve tappet clearance

Postby Pengze » Tue Jul 03, 2012 8:18 pm

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.

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D Winsor
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Joined: Thu Nov 22, 2007 8:23 am
Currently located: Dartmouth

Re: Exhaust valve tappet clearance

Postby D Winsor » Wed Jul 04, 2012 11:34 am

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.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Big Pete
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Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

Re: Exhaust valve tappet clearance

Postby Big Pete » Wed Jul 04, 2012 1:09 pm

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
It is always better to ask a stupid question than to do a stupid thing.

Pengze
Mechanic
Posts: 60
Joined: Tue Sep 23, 2008 8:57 pm

Re: Exhaust valve tappet clearance

Postby Pengze » Wed Jul 11, 2012 7:01 pm

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


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