How can smaller be bigger? Cam regrind?

[7.3workhorse]

Had to rebuild 99.5 7.3. All stock. Didn't get a good, understandable answer to my question else where, so I joined here. My 370K cam had wear ridges on some of the lobes. Bought used cam from salvage yard. They sent me older oil pan and cam with fuel pump lobe, supposed to be out of 2000 F250, apparently and old block with new heads? This is what I posted on other forum.

The first thing I noticed is that some of the non friction surfaces seemed to be polished? Especially between the end bearing surfaces, and closest lobes. On my old cam they are dark gray and rough. I do not have a mic, and I am certainly not a pro with a caliper but I am consistently getting measurements of the lobes on my old cam of 1.828 - 1.831''. And remember I have wear ridges on some of my lobes. On the used cam I bought, I am getting measurements from 1.819 -1.824'' I am sure my measurements leave something to be desired, but the point is that the purchased cam, even though it LOOKS to be in much better shape? The lobes are consistently measuring as much as .009'' smaller? Know I am wondering if this cam had work prior to being installed in a 2000 F250 2000 F250
with old block, and newer heads?
So did I buy a cam that is more worn, even though it has no wear ridges? Ugh!

Can someone tell me what the lobes on a good cam should measure? From measuring my old cam, I'm guessing 1.830''

I am only measuring the max diameter of the lobe, common sense tells me that if the lobe is .009 smaller, then modifications would have to be made to something else to get enough valve lift? I assume longer push rods? I am not into mods?

It was suggested that it probably was reground and would be OK to use. Trying not to make my book any longer, the explanations of how grinding the back side/ small side of the lobe gives more lift were given.

My final question was - even though I worked a late long sat. night, I am still up googling what I am missing here, I had finally decided that it must be the valve action of the hydraulic lifter taking up the slack when not under pressure, then due to the smaller back side of the lobe the lifter locks into a solid state sooner thus starting the lift earlier??????? But if due to the smaller back side of the lobe the lifter valve locks solid later this wouldn't work??? Well at this point I am so tired that I'm not sure I even understand what I am saying myself? Goodnight!

So can somebody here explain to me how grinding down the small side of a cam lobe where the valve would be fully closed/ seated is going to result in more valve lift??? Hopefully in english! Sorry about the length

 

[IDIoit]

when regrinding the cam, grinding the "base lobe" basically resets your "zero"
using as much of the metal on the top of the lobe to give you more lift is whats going on.
lifters and pushrods dont care how much lift, or the dimension of the base lobe you have.

but...
this can upset your rocker arm geometry.
so sometimes longer pushrods will be needed to keep the rocker where you want it to be on the valve stem.
ive never been a fan of regrind cams.
but on a roller application its not that big of an issue.

i have a few 7.3 DI's but i have never gotten past the point of the heads, which are the same casting from 97 to 2001.
im guessing the fuel pump lobe is on all of the 7.3's in order to save money on re engineering a engine that was going to be obsolete anyways.

 

[OLDBULL8]

The cam fuel pump eccentric was eliminated on the 99 cams when the electric fuel pump was added.

I have the Adobe pdf for the 99 and pdf for the 99.5 updates, but adobe won't let me copy or print them, or at least I don't know how to do it.

 

[7.3workhorse]

I guess here is what is troubling my limited brain power, Is not the valve fully seated when the lifter is riding on the back/ base of the lobe? This is what the purpose of hydraulic lifters are for, to eliminate lash? So with a solid lifter, the regrind removing base lobe metal, especially .009'' would create a lot of lash? While leaving the valve fully seated/closed? This hasn't affected the valve lift if the valve remains seated while the lifter runs around the base of the lobe? The lifter oil valve wont lock the lifter solid until pressure from the valve spring compresses the lifter enough to close the lifter valve. I can't picture how increased lash is going to close the lifter valve any earlier? That doesn't mean it isn't so! I just don't see it? I guess if the lifter has more oil in it due to the increased lash it MIGHT lock in a longer position? But can a lifter even lock solid in a longer position?

I haven't tore an engine completely down since I was 20 yrs. old, that was over 30 yrs ago! I barely have the energy left to keep up with the grass in the summer time! All I am saying is that this is really stressing me out. I AM NOT TRYING TO BE DIFFICULT. Just desperate to understand before I put this cam in my block, if I ever get it back from the machine shop. Still haven't heard about the pressure check from the head shop in Nashville either. The machine shop had to take my block to another shop they work with because their machine was about 1/8'' from being able to do the bore.

So, should I have the heads and block milled down more if I am going to use this cam? Thanks guys!