Cam specs, dumb question.

[Mogman]

I am trying to spec my cam before tearing down my engine. I have zero lash on the valve I am testing.
SO I get 300 deg total duration and 230 deg @.050 both ways opening and closing, is this the correct way or should I only count the first .050 when opening?
I am only getting .365 total lift at the valve.
The total vs .050 duration does not look comparable to cams I have found online so I think I am doing something wrong.

[Dan Ruddock]

Best to get your specs at the lifter and not at the valve. Most grinders do it that way. Eliminates tolerances in upper train parts and the deflections involved.

Dan

[Mogman]

I am unable to get a good reading at the push rod because of the angle of the rocker, it has VW rockers, if I only count the .050 at the opening of the valve I get 260deg which seems to be more in line with other cams.
OK I will remove the push rods and try at the lifter.

[Dan Ruddock]

You just glue a bolt into the lifter long enough to pop up out of the case.

[modok]

If you want to measure at the valve, that's ok with me, but I would do that differently.
Set the "lash" so the valve is slightly open, say .010 off the seat, that will eliminate flex.
Then check at .050 and .015

Or if you want to know what the duration is AT the cam then multiply by the rocker ratio.
so for 1.1 rockers you'd measure at .055 and .016
What Running duration is measured varies depending on the cam but .015 is a good guess.

[Floating VW]

Here's how I clocked mine. All you need is a degree wheel and a dial indicator. Pretty simple, really:

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[modok]

YES, or as above, thanks for the pic.
That works GOOD if the pushrod is vertical or 45 degrees but it might be problematic if the engine can't be tilted, without gravity helping may need a bit more spring than the indicator alone. Maybe.... worth a try anyway.

[Floating VW]

Yeah, tilting the engine to get the push rod vertical would probably be the ideal way to do it. I put a little pre-load on the dial indicator and that was more than enough to hold the push rod in place.
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works."

[67rustavenger]

Another dumb question.

The @50 as mentioned on every cam card I have and read.
Does it mean 50°, 050" past TDC?

Can one of you smart guy's explain this, like I'm a 5yo?
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[Floating VW]

You mean the "at 0.050"? That means 0.050 inches of lift. At 0.050" of lift is approximately where the air actually starts to flow past the valve, so this reference point is often used to give a more "useful" value for cam duration.

Kind of like static compression vs dynamic compression.
_________________
"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works."

[67rustavenger]