How much is too much

Tom,
If it is true that you can't grind the same profile onto a worn, stock cam, then there must be tons of info out there to prove all those cam grinders wrong who are doing it. There shouldn't be just one diagram from one guy as the only evidence that it can't be done.

I can't find any documentation that it can't be done. In fact I find just the opposite while looking for evidence to disprove those cam grinders. They all do it and some explain how they do it.

Give it a try. Do a few google searches.
 
I've flip-plopped on this so many times my neck hurts. Then I thought of a picture of a cam profile being shrunk. All the proportions remain the same. Then it hit me - lift is absolute. You can shrink the base circle so the lift remains the same and "fatten" the bottom of the lobe so the duration is the same. What has to give is the ramp from base to tip.

And maybe that's why many don't like them. May they strain the other components.

So both sides were right.
 
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!"
 
bwaii64 said:
I've flip-plopped on this so many times my neck hurts. Then I thought of a picture of a cam profile being shrunk. All the proportions remain the same. Then it hit me - lift is absolute. You can shrink the base circle so the lift remains the same and "fatten" the bottom of the lobe so the duration is the same. What has to give is the ramp from base to tip.

And maybe that's why many don't like them. May they strain the other components.

So both sides were right.
Click to expand...

If that's your theory, dig a little for support of that theory. It it is true, there must be at least a couple of cam grinders who will not grind stock cams back to stock specs because it will "strain the other components" (or for any other negative impact on the engine or its performance).

A theory or opinion is interesting and worth developing...but doesn't go too far to convince.
 
H. L. Chauvin said:
...I've never seen a regrind with as much lift as original...

...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...
Click to expand...

Shame on all those name cam grinders out there regrinding cams to stock lift (and better when desired) and with the ability to duplicate the original profile (or higher performance when desired) WITHOUT adding material. Someone needs to tell them it can't be done. ;)
 
I am sorry to see that Pete's posting was deleted.
Not to say though that the people who could benefit would pay any attention or learn anything....
 
Dick Steinkamp said:
Shame on all those name cam grinders out there regrinding cams to stock lift (and better when desired) and with the ability to duplicate the original profile (or higher performance when desired) WITHOUT adding material. Someone needs to tell them it can't be done. ;)
Click to expand...

It is just geometry. Lay the regrind profile over an original profile, then use a degree wheel to check opening, lift and closing at each degree.

______________________________________________________________

Time for me to get back to my roadside stand. I'm selling dirt by the yard.

New dirt $10 per cubic yard
Used dirt $7 per cubic yard
 
Mitch//pa said:
Tom at least selling ur dirt is more productive than this thread. SMH
Click to expand...

When the road in front of my house was redone about 10 years ago they pilled all the extra dirt into a huge pile in the middle of the small park to make a sledding hill for the kids. My neighbor was talking about it this afternoon, and I asked him if they used NEW or USED dirt. He thought about it for about 10 seconds, then replied "it was used dirt".:D
 
Tom Wesenberg said:
When the road in front of my house was redone about 10 years ago they pilled all the extra dirt into a huge pile in the middle of the small park to make a sledding hill for the kids. My neighbor was talking about it this afternoon, and I asked him if they used NEW or USED dirt. He thought about it for about 10 seconds, then replied "it was used dirt".:D
Click to expand...

Ask your neighbor if Reground dirt is the same before and after the process :rolleyes: :D
 
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If some one shorten the road where you live and there were 10 house in lets say a mile. They shorten it to 3/4 of a mile. You could still have ten house in the 3/4 mile but they would be closer to gather. Now you might get to hear that loud neighbor better. Same with a cam, but some thing had to change. the time the valve is open, how far it opens, how fast you open it, how long it stays open, and so on. There is no free lunch, some one had to pay.
 
George Miller said:
If some one shorten the road where you live and there were 10 house in lets say a mile. They shorten it to 3/4 of a mile. You could still have ten house in the 3/4 mile but they would be closer to gather. Now you might get to hear that loud neighbor better. Same with a cam, but some thing had to change. the time the valve is open, how far it opens, how fast you open it, how long it stays open, and so on. There is no free lunch, some one had to pay.
Click to expand...

There is a problem with that analogy. The road is measured from one end to the other (one mile). The cam lift is measured from the center of the shaft to the top of the lobe minus the measurement from the center of the shaft to the heel or the end opposite the lobe.

You can shorten one and then shorten the other and still have the same lift. The "free lunch" you speak of in a reground cam is the length of the push rod or in our case the valve stem has to be longer because the "road is shorter.

By using the formula (Center of shaft to tip of of the nose) - (center of shaft to the bottom or heel)= lift. Take off from the top and then the same from the bottom and the lift is the same.

Duration does not "start" until the valve is 0.05" off the seat and is measured until the valve is 0.05" from the seat.

I noticed that no information from re-grinder I can find on the net, say they grind the same profile. The do say the same specs.

So what exactly is called out in the specs of a cam, I have only heard of two here lift, and duration?
 
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Pete agreed that something has to change.
You can NOT grind a cam and have the same specs.
The specs include lift, duration, and how far the valve is open in relation to piston position.
 
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