How do I measure cam specs?

[John Fitzpatrick]

I’ve got a Moon solid-lifter cam in my SBF that I bought in ’79 or so, and I’ve lost the spec. sheet that came with it. Actually, it's not technically lost, it's just not findable at the moment. At any rate, the engine is out of the car and on a stand, and while it’s out I’d like to determine what the revelant specs are. Can someone explain how to do that or provide a link? I’ve got a degree wheel and a dial indicator with a magnetic base.
Thanks
John

 

[Sandy]

Do a search on google for 'degreeing your cam' you will find loads of info. You will need a degree wheel and a dial gauge to get most of the info. OR you could give Moon a call if you have the Grind number maybe they have some old catalogs that would have it.

HTH

Sandy

 

[John Fitzpatrick]

Thanks Sandy-perhaps I used the wrong terminology. I degreed in the cam when I assembled the engine. What I'd like to do is to determine how to measure the cam lobe specifications: E&I valve open & close, duration and overlap. I suppose I could start at TDC, rotate the crank one degree at a time for two revolutions and plot the valve lifts, but that's 1,440 measurements and I'm hoping there is a better way.
John

 

[Sandy]

I don't think there is another way, but if you do have the cam out it is really easy as most hipo machine shops have a tool that can do the, or you can take a look at this -

http://www.performancetrends.com/ca20.htm

Might be just what you need. But you might be able to just get a new cam and lifters for the cost (Not really sure how much it is for just the software).

HTH

Sandy

 

[Jac Mac]

Hi John,
Just check the readings off the degree wheel at the following amounts of Cam Follower Lift both opening and closing :: 0.050", 0.100", 0.200". The 0.050"/0.200" readings will allow you to compare the grind with most modern cam manufacturers spec sheets while the 0.100" readings will enable comparison with Ford factory grinds at that lift (the second set of figures given with ford cam spec's). Im assuming you know the basics of doing this, if not just say so and I will run thru the procedure for you, hope you can understand KIWI english !!!
Cheers Jack.

 

[John Fitzpatrick]

Jack
Is duration measured from 0.050" lift (at the tappet)after opening to 0.050" before closing or 0.006"? I've seen both figures used and I seem to remember reading that not all manufacturers use the same reference point. Also, would overlap be measured using the same lift point as used for duration? I'm assuming lobe setaration angle is simply taken from the maximum lift points, and that all angles are referenced to TDC on the intake/exhaust stroke.


Sorry if this is all very elementary, but I never really gave valve timing much thought. Back then I just told the guys at Moon compression ratio, where I wanted the power band to be, and how the car would be used (SCCA Solo II), and bought what they recommended.
John

 

[Jac Mac]

Hi John,
Use the 0.006 as an indication for total advertised duration only (treat it as an indication only. Dont take it as absolute , due to the open/close ramps of the cam lobe there is a lot of variation in measurements taken at this point and the reason most checking is done at the 0.050" point. So for advertised duration go from 0.006" to 0.006".
When checking the 0.050" duration take the readings from the degree wheel @ 0.050"after opening and 0.050" before closing on each lobe (1 intake/ 1 exhaust).
Check your overlap at 0.006" lifter rise. Take the readings of the degree wheel on the intake lobe as it starts to rise and the exhaust lobe as it just about to close. Add these readings together to get the overlap in degrees.
Lobe centre angle: Take readings from the degree wheel as follows- Let's assume your cam has a lobe lift of 0.300", On the Inlet Lobe turn the crank until your dial gauge reads 0.280" note the reading on the degree wheel, continue turning the crank over past the full lift point until the dial gauge reads 0.280" again, note this reading as well. Now add both these readings together and divide by two, this gives the centerline angle of the lobe you have just checked in relation to TDC. ( the two readings you just took would have been something like 85deg+131deg=216x0.5= 108deg) Now repeat the process for the Exhaust lobe.( The readings might now come out like 135deg+89deg=224x0.5=112deg). You can now calculate that the cam has been ground on 110deg lobe centres [(108+112)x0.5] and the cam is installed in a 2deg advanced position.
Take all readings while turning the crank in the clockwise direction, if you miss a point turn back at least a 1/4 turn and come back to take the reading.
If doing these checks with remainder of valve train installed ensure that bolt holding damper is installed on crankshaft to prevent shearing keway in crank timing gear/sprocket. Ditto with cam gear bolt.
You obviously have a Hyd cam to use the 0.006" check dimension, If the cam was a solid lifter you can play with the valve lash by about 0.004" to reduce/ increase the duration& overlap :eg Lash=0.020"+/-0.002". On the Hyd cam you can use Hi- Bleed Lifters to reduce the duration at low rpm only (Oil pressure related).
Advance your cam for bottom end / retard for top end.
Shorter duration for bottom end / longer for top.
Tight lobe centers for bottom end/ wider for top end.

DONT forget to check your valve to piston clearance!! & most important have fun.
Cheers Jack..ps- if it was elementary everyone would be doing it, you will now be able to help your mates out.(FORDS ONLY- them chevy guys are beyond help)

 

[Jac Mac]

John < I just reread your first note, your cam being solid should be checked at the manufacturers lash setting divided by the rocker arm ratio { example 0.022" divided by 1.6 rocker ratio = 0.0135" } to give the advertised duration(not @0.006").

Cheers Jack.

 

[John Fitzpatrick]

Jack-
I was right with you ‘till your last post. You said earlier to measure overlap at .006” lifter rise, but revised it to be lash divided by rocker arm ratio. I’m not understanding how the rocker arm ratio comes into play if the measurement is taken at the lifter end? It would seem the lifter (pushrod) would rise the lash distance before the heel of the rocker arm would move at all.
Would it simplify things to just pull the intake manifold and take the measurements directly at the lifters?
John

 

[Jac Mac]

John,
When you set valve lash you measure it at the valve end of the rocker arm. Lets say you set the lash at 0.016" for example, now with out changing the setting set your dial gauge up on the pushrod end of the rocker arm and check the clearance at this point, It will read approx 0.010", this is the ratio of the rocker arm coming into the picture. You are partly correct in stating that the lifter would rise, but using the above example it will only rise 0.010" to take up the lash distance before the valve opens, but you need to know the amount the LIFTER rises for checking purposes to accurately calculate the effective duration and overlap as the motor see's it.
You dont need to remove the intake manifold , just take all your readings off the end of the pushrod, ensure that the telescopic shaft on the dial gauge is parallel to the pushrod and that the pushrod does not bind on the guide plate or slot during the checking procedure.

Cheers Jack.

 

[John Fitzpatrick]

Aha--the lash is measured at the valve end of the rocker so you divide by the rocker arm ratio to get the gap at the pushrod end.
*sound of forehead slap*
Thanks for your forbearance—I am ordinarily not this thick!
John

 

[Jac Mac]

John,
I have an old chev block and sledgehammer just outside my shop door for moments like that, does not hurt as much as your method, in fact it makes me feel much better!!!

Cheers Jack.