One for all you engine experts...

[Jon Tilson]

Friend has a hot smal vauxhall engined grass trackk racer...<br>
<br>
Having rebuilt the lump....familly one 8v ohc 1300 with hydraulic tappets I think....he is now finding after upping the CR by machining the head that he hits heavy misfiring at about 4500 rpm...<br>
<br>
He suspects valve lifters pumping up too much. What do you guys reckon? I would have thought hydraulic lifters would cope up to about 6500 rpm?<br>
<br>
Jonners

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[KLJ895W]

How are the ignition timing and fuelling controlled? Higher compression would give a faster burn which would need less advance. Also the mixture may be harder to ignite, requiring a higher power ignition system, wider plug gap. Or the fuel requirements may have changed. Or the valve timing has changed due to the reduced distance between cam and crank? Does he have a vernier cam pulley to allow this to be checked and set correctly?<br>
<br>
David

<p><!--EZCODE LINK START--><a href="http://www.triumphowners.com/570" target="top">1980 Sprint</a><!--EZCODE LINK END--><br>
<!--EZCODE LINK START--><a href="http://www.triumphowners.com/569" target="top">1980 1850HL with Sprint gearbox, propshaft and axle</a><!--EZCODE LINK END--><br>
1972 VW Camper Van</p><i></i>

[george]

the valve spring height is in correct causing the lifters to jack out leaving the valves slightly open causing a missfire

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[george]

what i meant was the valve is either sitting down in the seat to much (seat has been cut to deep?)result is the <br>
rocker is up higher than normal (which if correct should set the lifter at about midway down)and allows the lifter to jack up causing misfire<br>
there is a mesurement for this but can't rember the height of the valve above the head but i'm sure a good engine shop would have the info at hand

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