I agree with Ricard for the most part, but I would set the valve lash a
few thousandths tighter than. I've got a couple of pages on degreeing a
cam and determining valve lash at my website -
http://www.tildentechnologies.com/Cams/Tips_Takes.html There is also a
spreadsheet you can download.
Larry Young
On 1/25/2012 12:45 PM, Richard Good wrote:
> Marty,
>
> Cam lobes are generally ground with a gentle ramp leading up to the
> actual lobe so that the valve clearance is taken up at a fairly low
> velocity. If you slowly turn the cam while watching a dial indicator
> on the push rod, you should see the dial indicator start to move
> slowly as the lobe approaches and then speed up rather abruptly. The
> point when it starts to speed up is when the valve should start to
> open. To accomplish this you should set the valve clearance at
> whatever the tappet lift was at that point times the rocker ratio. So
> if the tappet was moving slowly up to .010" then started accelerating,
> and your rocker ratio is 1.45:1, you would set the valve clearance at
> .0145". Check the degrees at that point then continue on past full
> lift until the indicator is back down to the same point. The number
> of crankshaft degrees between points is your seat to seat duration.
> If you were checking degrees on the cam itself multiply times two.
>
> If it is hard to determine the point where the velocity starts to
> increase rapidly, plot the lift at each degree of rotation on a graph.
>
> Cam timing specs are generally given at .020" or .050" tappet lift
> just because timing can be more accurate at a point where the tappet
> velocity is higher.
>
> Regards,
> Richard
>
> ----- Original Message ----- From: "marty sukey" <trmarty@hotmail.com>
> To: "FOT" <fot@autox.team.net>
> Sent: Wednesday, January 25, 2012 10:29 AM
> Subject: [Fot] Camshaft Duration
>
>
>> Question, at what lift is camshaft duration measured at for the values
>> typically published? I am currently checking the cam that came in
>> the Spit,
>> no outside info available on it so I am trying to get an idea what I am
>> dealing with. It is a Reed re-grind and they are out of business.
>> Lobe lift is
>> .290, duration is where ever I measure at :)
>>
>> Thanks,
>> Marty
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