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Old 01-01-2018, 04:54 PM
ragerover's Avatar
ragerover ragerover is offline
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Join Date: May 2007
Location: newcastle upon tyne
Posts: 2,983

They will always go tighter as the seat wears
That is the softest part of the valve train
That Said M cars seem to have pretty strong seats as they don’t go out much
But if you don’t check and tgere right you’ll burn the seat out
Remember to do these stone cold. Ie next day after sitting overnight
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Old 04-01-2018, 03:18 PM
Randy Forbes Randy Forbes is offline
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Join Date: Jul 2007
Location: SW Florida, USA
Posts: 103

I concur with them getting tighter with use/time, and why I feel it is important to continue with periodic checks (20k to 30k mile interval__nothing crazy, like my Healey!) for the health and longevity of the exhaust valves.

I've speculated on this with a couple of race engine builders (their claim to fame is getting 1000 to 2000 bhp from turbocharged Lamborghini V10 engines used in a powerboat race series) and concluded that along with valve seat recession, there is also elongation of the valve stems themselves taking place.

Interestingly, one of those guys just did a valve job on a S-54 head for me, and we contemplated how much to dress the tips by; he was conservative and I wound up setting the valves (whole engine rebuild) with some of the thinnest shims I've ever used (one only, was 1.96 mm, the rest were 2.00 - 2.28). I guess next time he can grind a little more off the tips!

Randy Forbes
Sports Cars Plus, LLC
Parrish, Florida, USA
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