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H. L. Chauvin · 01-06-2017, 04:30 PM

FWIW: Older Model A Cam Discussions by Mr. Marco:

Just one former part of one former discussion a few years ago explained by Mr. Marco and mentioned tested by Mr. Ron Kelley with a dynamometer, with Mr. Marco's BOTTOM LINE remark ...... written when we were "all" a little younger with less gray hair.

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"I have mixed feelings on this subject. To start with I would decide based on the condition and MEASUREMENT of the lobes. If I recall correctly, the lift at the lobe (height, less (-) width of heel) was originally .302" . Since the greatest wear is at the sharp tip of the lobe I'd be inclined to use the cam if all the lobes were within .002" and no less than .289" lift.
My reasons are simple. Cam regrinding seems to be more of an art than a science. Each cam grinder chooses a pattern or profile that HE deems acceptable or proper. Nobody duplicates the functional profile of the cam. I've never seen a regrind with as much lift as original. Some are close on the duration. I have even seen some with the valve timing out. I removed a "quality regrind" from a newly rebuilt short block that had a lift of .242"! That approaches a Model T cam. I traded it in on a "high speed" cam that had a lift of .282" (still short).

There does seem to be some decent ones out there, but you don't know what you have until checked with a degree wheel against an NOS cam. As I've said many times, Most restored "stock" Model A's are running around on 35 hp or less. Interestingly this was confirmed in the series of dynamometer tests by Mr. Ron Kelly.

Bottom line is if your cam has very limited, even wear, then you may be BETTER OFF than with a regrind."

AND,

"I'm not AS concerned over the indexing issue (although maybe I should be) as I am over the lobe profile. I would think that type of error isn't very common.
The original lobe profile is available but is of limited use. The only way to duplicate the original profile would be to build up the lobes and regrind. This obviously would not be feasible. Once the lobe is made smaller the shape must be totally recalculated to achieve the same results. This is WAY beyond anyone I know. The best you can realistically hope for (unless you wish to boost performance) is to have the valve begin to open at the same time, open very slightly faster, open to the same maximum height, close slightly slower, and seal at the same time.

There are other contributing factors as well. As Bob Rentz (I believe) has mentioned, the adjustable tappets commonly used today have smaller bases. Besides a slightly increased wear factor, they will slightly reduce duration. It may not be very noticeable, but it will degrade performance to some extent.

There was a short but worthwhile article on cams in the Model A News by Glen "Doc" Wishon. It was probably around 1983. He did a few very good articles relating to engines sometime between '81-'84 as I recall.

I will likely do extensive testing and logging of a couple cams (including NOS) next time I assemble an engine. Unfortunately this may be 5-6 years from now!

Going back to what began this subject, I wouldn't be so quick to jump on the bandwagon for a "NEW" grind. It's quite conceivable that if Clarence's cam has limited, even wear, it may well out perform the "NEW" one!"

01-06-2017, 04:30 PM	#44
H. L. Chauvin Senior Member Join Date: May 2010 Posts: 4,179	Re: How much is too much FWIW: Older Model A Cam Discussions by Mr. Marco: Just one former part of one former discussion a few years ago explained by Mr. Marco and mentioned tested by Mr. Ron Kelley with a dynamometer, with Mr. Marco's BOTTOM LINE remark ...... written when we were "all" a little younger with less gray hair. ------------------------------------------------------------------------------------------- "I have mixed feelings on this subject. To start with I would decide based on the condition and MEASUREMENT of the lobes. If I recall correctly, the lift at the lobe (height, less (-) width of heel) was originally .302" . Since the greatest wear is at the sharp tip of the lobe I'd be inclined to use the cam if all the lobes were within .002" and no less than .289" lift. My reasons are simple. Cam regrinding seems to be more of an art than a science. Each cam grinder chooses a pattern or profile that HE deems acceptable or proper. Nobody duplicates the functional profile of the cam. I've never seen a regrind with as much lift as original. Some are close on the duration. I have even seen some with the valve timing out. I removed a "quality regrind" from a newly rebuilt short block that had a lift of .242"! That approaches a Model T cam. I traded it in on a "high speed" cam that had a lift of .282" (still short). There does seem to be some decent ones out there, but you don't know what you have until checked with a degree wheel against an NOS cam. As I've said many times, Most restored "stock" Model A's are running around on 35 hp or less. Interestingly this was confirmed in the series of dynamometer tests by Mr. Ron Kelly. Bottom line is if your cam has very limited, even wear, then you may be BETTER OFF than with a regrind." AND, "I'm not AS concerned over the indexing issue (although maybe I should be) as I am over the lobe profile. I would think that type of error isn't very common. The original lobe profile is available but is of limited use. The only way to duplicate the original profile would be to build up the lobes and regrind. This obviously would not be feasible. Once the lobe is made smaller the shape must be totally recalculated to achieve the same results. This is WAY beyond anyone I know. The best you can realistically hope for (unless you wish to boost performance) is to have the valve begin to open at the same time, open very slightly faster, open to the same maximum height, close slightly slower, and seal at the same time. There are other contributing factors as well. As Bob Rentz (I believe) has mentioned, the adjustable tappets commonly used today have smaller bases. Besides a slightly increased wear factor, they will slightly reduce duration. It may not be very noticeable, but it will degrade performance to some extent. There was a short but worthwhile article on cams in the Model A News by Glen "Doc" Wishon. It was probably around 1983. He did a few very good articles relating to engines sometime between '81-'84 as I recall. I will likely do extensive testing and logging of a couple cams (including NOS) next time I assemble an engine. Unfortunately this may be 5-6 years from now! Going back to what began this subject, I wouldn't be so quick to jump on the bandwagon for a "NEW" grind. It's quite conceivable that if Clarence's cam has limited, even wear, it may well out perform the "NEW" one!"