DIY Cam Doctor

[tom1394racing]

I have a shelf full of serviceable cams with the only information being the casting # on the shafts.

For the most part, the casting number will give a good indication of the cam type, however, the early style Solex and L cams all have the same casting number making it difficult to tell them apart. In addition, when a cam has been reground, the casting number is meaningless and one must rely on the cam grinder's markings which are not always so reliable.

So I decided to map these cams by building my own cam doctor. I used a cam tower, cobbled degree wheel, a set of rockers and heads with valves. I used a single valve spring to lessen resistance. I measured the valve lift using my trusty dial indicator and mapped it to the degrees of camshaft rotation on the degree wheel.

I put together a simple spreadsheet to calculate the the cam parameters:

1. Lift
2. Duration at 0.05" lift
3. Lobe Center spacing

I started with a known E/L cam and a known Solex cam to see if I could reproduce known results. My data reproduced the known parameters for the E/L and Solex cams. See the attached spreadsheet. I then starting mapping the mystery cams (regrinds) and found two sets of S carb cams.

For my first two trials, I did an entire map to make sure things made sense. After that, I found it was only neceassry to establish the 0.05" lift cam positions on each side of the ramp and the max lift for the intake and exhaust valves to calculate the cam parameters.

Enjoy the pics and data and if anyone wants a copy of the spreadsheet send me your email.

[billybek]

That is pretty cool!

[304065]

. . . biggest points ever for using an ANALOG dial indicator! You KNOW what a fan of dimensional metrology I am . . . this is WAY cool.

[kenikh]

Considering most of us will do this once or twice a year...not bad!

[al lkosmal]

tom,
That is DIY at its finest. I would like a copy of your spreadsheet plz.

Regards,

al

alkosmal@hotmail.com

[356RS]

Great job Tom. I have to make one now. Like Al said, is the spreadsheet available?

[tom1394racing]

Mark

PM me your email address and I'll send a copy of the spread sheet.

[efhughes3]

Very impressive I must say.

[michael123]

hi TOM
It is very much helpful for me, and also for others,
Thanks for sharing TOM
keep it up dear,

rEGARDS

[Aurel]

Nice. Now use a numeric dial with an USB output, an electric motor to spin the cams and automate the data acquistion in Labview. And will you please make it wireless to send the data in my ipod touch too. Thanks .

[Walt Fricke]

Aurelien

Not as tongue in cheek as you suggest (wireless and ipod!!).

I thought of the USB output. My digital indicator has what looks like one, though on the model I have it may not connect to anything (none of my little USBs will plug into it, and any contacts inside are hard to see, at best.

But how might one get a digital degree reading from something you used on the crank pulley? Yes, you'd have to divide by two to get a lobe profile, but so what. Or on the end of a cam, if doing it as Tom did on the bench?

I'd like to be able to check cam lobe shapes in situ. At the race track. So I could see if a guy who should be running a stock SC cam really was, for instance. Just lift and duration won't quite do. One cam grinder/seller once advertised an SC Cheater Cam. Had a quicker ramp and fatter lobe, I believe, so lift and duration at checking height were stock, but the area under the curve, so to speak, was larger.

This can be done "manually" trackside with a degree wheel, as Tom did here so effectively on the bench. But it is slow and rather involved.

Ideas gratefully accepted.

Walt

[kenikh]

For example:
Digital Indicators, Digital Dial Gauges

How to get dial gauge data to a PC and into Excel so it can be graphed:
Interfacing a Sylvac Dial Gauge to a PC

Once you have the data points, a VB script could render it pretty easily if an in-the-box solution can't be found.

[Walt Fricke]

Kenik - thanks for the Sylvac reference. But it is rendering rotation into a digital (well, electronically recordable) format that is the area where I don't know how to begin.

If I could figure that out, I could also use it (if financially feasible) to measure gear ratios on race car transmissions faster than the more manual methods I now use. But that's far from this DIY Cam Doctor, I am afraid.

Walt

[Aurel]

Originally Posted by Walt Fricke

Kenik - thanks for the Sylvac reference. But it is rendering rotation into a digital (well, electronically recordable) format that is the area where I don't know how to begin.

If I could figure that out, I could also use it (if financially feasible) to measure gear ratios on race car transmissions faster than the more manual methods I now use. But that's far from this DIY Cam Doctor, I am afraid.

Walt

Walt,

To digitally read your degrees, you need a magnetic pickup signal at zero degrees such as those used for electronic ignition. Then, the frequency f is your rpms (1Hz = 60 rpms), and the time t elapsed from the zero degree signal is your degrees: degrees=t*f*360

Example: You get a 20 Hz signal and see your max intake valve opening 0.01s after your zero degree signal.

Your rpms = 20*60=1200
Your degrees = 0.01*20*360 = 72

All the calculations and data acquisition can be done very easily with Labview.

[jcge]

Perhaps you don't need to actually measure the rotation........you could very simply drive a stepper motor to turn the cam by a known increment via a simple parallel port drive. (cam on the bench, of course)

A very simple program to turn the motor by one step, take a digital dial gauge reading, take another step, another reading etc.

Standard steppers available in 200 steps per rev, but a simple micro step drive would give plently more resolution.

John

[HKZ Bob]

Hi Tom

I have a question you might be able to answer. Could you measure the lift
directly from the cam profile insted of the valve plate.

It will reduce the complete tolerance chain.
Do I have a 1:1 projection from the rocker arm to the valve.

I just measured a rocker arm and I do have a 1:1 ratio.
does it means that I could measure the lift at the cam lobe directly?

BR
Bob

Great test setup.


I measured the valve lift using my trusty dial indicator and mapped it to the degrees of camshaft rotation on the degree wheel.


1. Lift
2. Duration at 0.05" lift
3. Lobe Center spacing


Enjoy the pics and data and if anyone wants a copy of the spreadsheet send me your email.









[/QUOTE]

[tom1394racing]

Bob

You need to factor in the rocker arm lever ratio to convert cam lift to valve lift. The ratio is around 1.45 (if my memory is correct). This ratio works to get the approximate max lift. However, the rocker arm ratio changes as the rocker moves along the cam profile because the point at which the rocker contacts the cam changes as the cam rotates. That is why I built this set up to measure the movement at the valve stem just like we do when we set cam timing.

[hcoles]

Originally Posted by tom1394racing

Bob

You need to factor in the rocker arm lever ratio to convert cam lift to valve lift. The ratio is around 1.45 (if my memory is correct). This ratio works to get the approximate max lift. However, the rocker arm ratio changes as the rocker moves along the cam profile because the point at which the rocker contacts the cam changes as the cam rotates. That is why I built this set up to measure the movement at the valve stem just like we do when we set cam timing.

I hope this is what he did.
Also, what is the typical x axis reference? Degrees from TDC not on the compression stroke?

[tom1394racing]

Originally Posted by hcoles

I hope this is what he did.
Also, what is the typical x axis reference? Degrees from TDC not on the compression stroke?

The original DIY post was done by me. I measured the valve movement and mapped it against cam rotation in degrees. The cam parameters were calculated from the data in the maps.

[HKZ Bob]

Originally Posted by tom1394racing

I have a shelf full of serviceable cams with the only information being the casting # on the shafts.

For the most part, the casting number will give a good indication of the cam type, however, the early style Solex and L cams all have the same casting number making it difficult to tell them apart. In addition, when a cam has been reground, the casting number is meaningless and one must rely on the cam grinder's markings which are not always so reliable.

So I decided to map these cams by building my own cam doctor. I used a cam tower, cobbled degree wheel, a set of rockers and heads with valves. I used a single valve spring to lessen resistance. I measured the valve lift using my trusty dial indicator and mapped it to the degrees of camshaft rotation on the degree wheel.

I put together a simple spreadsheet to calculate the the cam parameters:

1. Lift
2. Duration at 0.05" lift
3. Lobe Center spacing

I started with a known E/L cam and a known Solex cam to see if I could reproduce known results. My data reproduced the known parameters for the E/L and Solex cams. See the attached spreadsheet. I then starting mapping the mystery cams (regrinds) and found two sets of S carb cams.

For my first two trials, I did an entire map to make sure things made sense. After that, I found it was only neceassry to establish the 0.05" lift cam positions on each side of the ramp and the max lift for the intake and exhaust valves to calculate the cam parameters.

Enjoy the pics and data and if anyone wants a copy of the spreadsheet send me your email.

Hello Tom,
I am reviewing your great data and I saw on the 911L/E cam intake you close met the specification of Intake/exhaust Lift of 0.404/0.393.

Can you confirm that your mearument also met the overlap setting of 3.0/3.3mm?

Do you think the offset is caused by the wear?

Also on the Solex you are close to 0.455/0.414 inch.
Can you also confirm that your mearument also met the overlap setting of 4.2/4.6mm?

the diagramm looks yes.

Br
Bob