Web Camshafts Experience

Mark McClure · 02-28-2006, 11:15 PM

Hi,

Has anyone used Web Cam camshafts. I have been timing the cams and found that the intake opening degree and overlap apprear to be slightly different. The instructions are open @ 32 BTDC with zero lash or 4.8-5.2 with .1mm lash @ TDC.

With zero valve lash I can time the cam at 32 BTDC with 1.27mmm lift ( .05"). When I have .1mm lash the overlap at TDC is 4.85mm. The range at TDC is 4.8-5.2mm. I was aiming for 5 but this will change the opening degree to something like 29 or 30 degrees.

Any thoughts or experience with these cams would be much appreciated.......

Mark........

2.7RACER · 03-01-2006, 05:42 AM

Mark,
Let's assume your measured numbers are accurate.
At 32 degrees BTDC you measured 1.27mm (0.050") with zero lash.
You are using a nice big degree wheel for accuracy right?
So now you go to TDC and measure 4.85mm with 0.1mm lash.
This means in 32 degrees crankshaft rotation the valve went from 1.27mm to 4.85mm plus 0.1mm lash.
Or to state it another way the cam moved the valve 3.68mm (4.85+0.10-1.27), in 32 degrees crankshaft rotation.
This translates to 0.115mm per degree. (3.68/32=.11500).
Again assuming 5.0mm is optimum and you are measuring 4.85mm, the difference is 0.150mm.
This is 1.3 degrees error.
Now either the cam isn't spec'd correctly or your measurements have a 0.150mm (0.0059") error. Maybe a little bit of both.
If you set the cam to 5.0mm with your measurements, you would be advancing the cam 1.3 degrees. The degree wheel should read 33.3 degrees BTDC.
Bottom line, the measurement at TDC crossover is a derived number. That is, once the cam is timed correctly with a degree wheel, 5.0mm is what you should measure at TDC with 0.1mm lash.
My view is if you have a large, accurate degree wheel, set the cam to 1.27mm (0.050") at 32 degrees. That is the spec.
Then check the intake valve at closing, the same 1.27mm, the degree wheel should agree with Web cams number.
Once this checks out, the cam is timed according to Web's spec.
A 1.3 degree error isn't much at all, so make sure you are doing everything as accurately as possible.
A simpler method would be to set the cam to 1.27mm at 32 degrees with zero lash as specified.
Then simply rotate the crank to TDC. You should read 5.1mm with zero lash.
Then go back to 32 degrees BTDC and you should be back to 1.27mm, then back to TDC and you should see 5.1mm.
If this checks out, the cam is perfect. Then set the lash to 0.10mm.
This business of checking one position at zero and the other position at 0.10mm lash just makes a greater chance for error.
I hope I haven't muddied the water to badly.

Mark McClure · 03-01-2006, 01:46 PM

Doug,

No mud.......just wanted to see what peoples thoughts where on the degree wheel againt the crossover point. I have not checked the cross over with 0 lash. Will try that again tonight. The degree wheel is about 30 cm in diameter big enought to be acurate. a 1.3 degree difference is acceptable considering the movement of the caams/chain.

If the cross over is a derived number! that makes sence and obviously why a range rather than a definitive number aka open/close degrees.

Thanks for you input

Mark......

2.7RACER · 03-01-2006, 09:22 PM

Mark,
As you may know, relatively new 993's with low mileage have been found to have the cams as much as 3 degrees retarded from factory specs.
Some of this is from chain stretch, but even the factory cam timing has some tolerance.
From SC's thru Carrera's the same cam profile was moved around from 7 degrees BTDC to 1 degree BTDC to 4 degrees BTDC.
My point being we sweat a one degree accuracy, I think as we should, but it, in most cases, is undetectable.
I keep asking myself when timing a cam, whether I should put in a little advance and then let the timing chain stretch thru the the tolerance range. I'm talking maybe one degree.
Porsche could be doing this without saying anything.
Just food for thought. I'm not an expert.
Have fun,

Mark McClure · 03-01-2006, 09:41 PM

Doug,

You are right looking at the pressure tensioners and the amount of slack in the chain I am suprised that the cam timing could remain anywhere near the spec.

I will contiune with the degree wheel timing since that is a given rather than a range, that must be more accurate?

I have concentrated hard on getting everything as right as possible....don't tell me now that the factory has a larger tolerance......my face is already lined with concentration.

This engine has set be back th's $ and at least 15 years!

Cheers

Mark......

bkreigsr · 03-02-2006, 04:47 AM

I had Web Cam redo my 73T cams to 906 spec and ran 8 years with them, no problems... then took them to Elgin for my second rebuild and had them redo the same cams to a custom grind suited to my second rebuild. Elgin also agreed WebCam did a decent job.