valve clearance

[dmite]

how tight can you have your valve clearances?, 018" looks very lose.

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[MaddMart]

That's correct for a Sprint (cold). Standard cam.

<p><!--EZCODE LINK START--><a href="http://www.aqpd91.dsl.pipex.com/" target="top">Mad Mart's Website</a><!--EZCODE LINK END--></p><i>Edited by: <A HREF=http://pub52.ezboard.com/bthetriumphdol ... addMart</A> at: 24/2/04 11:44 am<br></i>

[dmite]

Can they be set tighter?

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[speedracer]

Yes they can be set tighter, but your valves will run hotter.<br>
Although i believe valve clearances for warm cams can be as low as 10 thou...<br>
<br>
speedracer

<p><!--EZCODE LINK START--><a href="http://www.triumphowners.com/2">1975 Dolly Sprint</a><!--EZCODE LINK END--></p><i></i>

[dmite]

Thats a good point speedracer, The valve spends less time on the seat therefore less time to cool down, but why is it ok to set the warm cams at 010"?

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[alun n]

I believe it is to do with the angle of the peak of the cam - a standard cam has a peak that is almost ninety degrees, quite 'sharp' in appearance and therefore as the rocker/bucket is passed by the high point it is quite a violent change of direction. On hotter cams where the duration is extended the peak is much more rounded and gentle so a closer clearance can be achieved without the same potential for wear of the components....

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[Chris Field]

Smaller clearance will create more "valve overlap" .. ie one valve starting to open as the other is closing. Valve overlap helps breathing at high revs but has an adverse effect at low revs. <br>
<br>
Performance cams are designed to create more overlap as well as staying fully open for longer - hence improving performance at high rpm at the expense of poor low speed performance and often needing an much higher idle speed. The effect of 'coming on the cam' is the point at which the benefit of this increased overlap is felt.<br>
<br>
Reducing the valve clearance with a standard cam will serve only to cause the rough running at low rpm without the benefits at high rpm.

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[MaddMart]

This is why the Honda VTEC engine is such a clever piece of engineering. You get the best of both worlds so to speak.

<p><!--EZCODE LINK START--><a href="http://www.aqpd91.dsl.pipex.com/" target="top">Mad Mart's Website</a><!--EZCODE LINK END--></p><i></i>

[John Skinner]

Had a good link for the vtec engine but it's dead. Anyway the written explanation in this link is quite good even if the crude drawings are lacking...<br>
<br>
<!--EZCODE AUTOLINK START--><a href="http://www.leecao.com/honda/vtec/dohcvt ... <!--EZCODE AUTOLINK END--><br>
<br>
So simple I wish i'd thought of it<!--EZCODE EMOTICON START :lol --><img src=http://www.ezboard.com/intl/aenglish/im ... /laugh.gif ALT=":lol"><!--EZCODE EMOTICON END--> <br>
<br>
Performance cams for engines with solid lifters tend to have bigger valve clearances. You want the valve to lift quickly from the seat and this is done by having a larger clearance. The cam effectively has a 'run up' to opening the valve so it's far more aggressive and shortens the life of your valve gear. <br>
<br>
Closing the valve clearance on the std cam is going to have little beneficial effect. Say you close it by 5 thou, you will get virtually no more full lift, and the valve will start to slowly move off the seat earlier, achieving nothing worth while - perhaps a little less rattle.

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