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How the hell does regrinding a cam work?

Discussion in 'The Hokey Ass Message Board' started by Brad54, Nov 30, 2004.

  1. Brad54
    Joined: Apr 15, 2004
    Posts: 6,021

    Brad54
    Member
    from Atl Ga

    This has bugged me for a long time. If you have a cam reground to new specs, but it's all built off existing cam lobe profiles, where do they "steal" the extra material from? Something has to change. My thinking is that the total lift would have to be affected, but what else? Or do they weld up the lobes and then regrind from there, keeping the original Lobe Seperation Angle but putting new lifts/ramps on the lobes?
    I think I'm getting a '57-'59 Chevy Truck/Buick 322 cam, and the guy says it's a regrind. I'm getting it to use for a "someday" Nailhead portable electric generator, and want the low-end torque the truck engine produced. From what I've read, all I can see that's different from car engines is cam and compression. The truck has less CR, and falls flat on it's face at upper RPM, yet makes more low-end torque than the car, so this cam is the choice.
    But again, it's a regrind--what am I going to give up? For $20, I can live with a lot. Or a lot less, as the case may be.
    -Brad
     
  2. 50dodge4x4
    Joined: Aug 7, 2004
    Posts: 3,534

    50dodge4x4
    Member

    Post deleted by 50dodge4x4
     
  3. Wish I still had all four peices of the last MELLINGS reground camshaft I had [​IMG]...Id show you....
     
  4. A cam is a bump on a circle. When the lifter is riding on the circle, it's at zero lift. as the cam rotates, the lifter sides over the bump. Regrinding a cam is making the circle smaller, in order to make the bump bigger so it can be reshaped. David
     
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  5. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,254

    Hackerbilt
    Member

    Yeah...your basicly grinding down the radius of the ass end of the lobe to effectively give more lift without adding metal. That allows some freedom to alter the profile as well for duration changes etc.
     
    Hemi Joel likes this.
  6. Like the guys have already said, the base circle has it's radius reduced. This can cause some issues depending on whether the engine has the ability to adjust the rockers.

    I had a cam reground for my hemi since new blanks were not available. The stock rockers are not adjustable. Since the base circle was smaller the lifters would have too much gap. I had the choice of getting some custom pushrods to take up the slack, getting some adjustable pushrods (Have you ever tried to adjust valves with adjutable pushrods??? [​IMG] ), finding some expensive oem adjustable rockers, or converting my stock rockers to adjustable. I had the rocker conversion done and did have to order some special pushrods to go with them but I'm very happy with the setup. None of this applies to a SBC but there are plenty of other engines with non adjustable rockers where it will.
     
  7. Jim Marlett
    Joined: Aug 12, 2003
    Posts: 867

    Jim Marlett
    Member

    Just to restate what others have said, lift and duration are increased by grinding away the "base circle" of the cam. The lobe doesn't have material added to it, but the non-lobe part is ground away making the difference between highest part of the lobe and the lowest part of the base circle a greater distance. If you grind away enough of the base circle, you can flatten the top of the lobe and still increase the lift while changing the duration profile substantially. There is a bit more to it than that, but I hope you get the idea. Some extreme flathead cams actually grind the base circle right down to the shaft.
     
  8. Brad54
    Joined: Apr 15, 2004
    Posts: 6,021

    Brad54
    Member
    from Atl Ga

    Thank you very much guys! That made it a lot clearer. I was kinda dancing around the answer in my mind, but was never able to really get there. I'm there now--thanks. [​IMG]
    -Brad
     
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  9. yalc
    Joined: Apr 27, 2009
    Posts: 2

    yalc
    Member

    When we regrind a cam, we just put the same profile (or a different one if you're changing something) back on it, only at a slightly smaller size. We have to check the cam for hardness when we're finished to make sure we didn't grind through the hardness layer. There are some pictures of the regrinding equipment at this website: Kams, Inc. camshaft and cam follower manufacture and regrinding.
     
  10. Mark P
    Joined: Jul 29, 2015
    Posts: 1

    Mark P

    I always wondered how a cam shaft could possibly be reground. Of all the websites I checked this one explains it the best.

    Does anyone know if its possible to repair a crack in a cam? I found a company that is local to me that claims they can weld the cam! They are Cams Northeast.... a small business, not sure if anyone has used them but I've heard some good things about them. My major concern is that the camshaft is not an easy part to replace if this goes wrong. I definitely don't want to being doing this twice if I can help it. Anyone else ever had a camshaft welded?
     
  11. I am by no means a cam grinding expert but one way that I know that the create more lift if to steal a little bit off the heal of the cam. you adjust your valves when the lifter is on the heal of the cam so if you remove some of the heal it makes the nose farther away in relationship to the heal and your valves will open more from the extra adjustment that you can now throw in there.
     
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  12. 19Fordy
    Joined: May 17, 2003
    Posts: 8,096

    19Fordy
    Member

    Just Google" "Cam Grinding Video" and you will see how cams are ground.
    Pretty neat.
     
  13. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,233

    sunbeam
    Member

    One other option ask the cam grinder how much he reduced the base circle and cut the heads the same amount.
     
  14. Something I'll add, the lift on the lobe is limited by the diameter if the cam bearing.so yes it is reground as others have commented.
     
  15. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    Look at an egg to better visualize the above...it's about the shape of a cam lobe. Better use a hard-boiled one...
    Visualize the apparent center of the lower big end as the axis of rotation, the center that would exist if the big end became a full circle, as the center of the camshaft. File away some of the pointy end, and you will see that the top is now wider...a lifter going across there as your cam rotates will be at the highest part for more degrees of duration...but now the highest point has become lower, so your increased duration cut down your lift. Ooops. Now, back to the big end...file down the whole semi-circle until its radius is lessened by more that the amount ground off the pointy end... your lift has now gone up instead of down! Something now needs to get longer in the valve train, like lifter in a flathead or a pushrod in a silly modern motor.
    Now, with just that semi circle reduced, the cheeks of the curve right above it, the slopes up to the highest lift, are a bit fatter than the diameter of the base circle, so contouring there can steepen their ramping up...now the lifter going over that area has been jiggered into climbing UP a greater distance for each degree of rotation than it did stock (note that there are physical limits to that, and think about roller lifters...), meaning that you got some MORE cam, the valve is open more all around its trip, and not just at the very top! The low lift area has gotten higher faster, adding more of the same effect that you got by hacking the high lift part of the lobe back in step one.
    Now you have egg and shell crumbs all over the damn place, and you are going to be in trouble...tell your woman that this is the kind of thing Newton and Einstein did all the time, and your new egg contour is going to be BIG. Ask her to take down the phone numbers when Gates, Spielburg, and Hawking call...

    Have a beer to help the brain cells, and you will realize that the ultimate egg or the ultimate cam lobe would rapidly approach a new vision...a RECTANGLE!! Closed valve to opened valve INSTANTLY, full open to closed again INSTANTLY. ALL duration at FULL LIFT. All you need to make it work is a QUANTUM LIFTER, which will be easy to design once you finsh all the beer...
     
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  16. chrisp
    Joined: Jan 27, 2007
    Posts: 1,067

    chrisp
    Member

    I always wondered how people come up with specs to regrind a cam, I understand trial and error but there must be some basic specs to start with no?
    I'm asking because I have an oddball engine that nobody ever hoped up and thinking of having the cam reground.
     
  17. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 518

    the SCROUNGER
    Member
    from USA


    old thread, good topic. if you want to know how much lift you can add to an existing cam, just measure how far the base circle/heel is, away from the center of the stick. just checking a few the most I've seen there is .040"-.060" for a hydraulic flat tappet, meaning and it needs at least .015" or so to keep the lifters off the center stick of cam, so you can add around .045"

    a good rule of thumb is, whatever you can add going from 1.5 to 1.65 rockers, i.e. around 10% more lift, you can generally grind into the cam itself for hydro flat tappet. then if you run the same 1.65 rockers, you can add that much more again with rocker ratio. so...in case of a Pontiac V8, a .470" lift cam can become a .510" lift cam, then with 1.65 rockers a .560" lift cam- that's if it has the spring height is there, i.e. long enough valve, to not bind the springs. this is best case scenario. you can recut a hydro flat tappet, to a solid mechanical flat tappet, and the solid cams typically have as little as only .020" remaining off the base stick when brand new ! meaning you can't very well get any more lift regrinding it later.
    if you're searching for a good core to grind from, look at the nose high point of cam, if that's close to level to the cam journal height, use that. then cut the base circle/heel down to the minimum it can go, and that's all there is to gain there.
    lobe separation and duration can only be changed a few degrees either way. effective duration at .050" can be increased by just using higher ratio rocker arms.
    regrinding is really just a last resort if you can't find a replacement new cam affordably.
    there's only so much hardened surface and if they grind through, the cam will become soft and wipe out.
    staying with the original LSA will help preserve the hardness depth thickness. changing the LSA dramatically will make the hardness thin in areas because you're taking more off the sides.
     
    Last edited: Aug 2, 2021
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  18. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 4,420

    ekimneirbo

    REgrinding reduces the overall size of the lobe and while it will work, you are better off if you can locate a new camshaft that has full size lobes. Lots of people use them in lower performance engines with no problems, but lots of times regrinds don't work as well as their new counterparts. You have to remember that the interface between a flat tappet lifter and the camshaft is critical to longivity and working with a smaller lobe isn't bestus............Unless you can't get a new one, I wouldn't consider a regrind. I also would not consider a welded camshaft.....ever.
     
  19. DenverFlash
    Joined: Dec 5, 2008
    Posts: 132

    DenverFlash
    Member

    Isn't the simple answer just: longer pushrods (or milling the heads)?
     
  20. Big mike 1968
    Joined: Jul 17, 2021
    Posts: 187

    Big mike 1968
    Member

    This is good information. Ive heard the term all my life and never really considered what was involved.
     
  21. 73RR
    Joined: Jan 29, 2007
    Posts: 7,254

    73RR
    Member

    Since I only deal with EarlyHemi and related engines I can only speak of those. Trust me, no new cams for a 241 Dodge...but we do alot of regrinds. Bad lobe? Weld it up. Not a new or big deal. Welded hundreds of them.
    As Scrounger notes, many cams have very little to offer at the base circle, early Dodge/DeSoto are prime examples. I have a machine dedicated to grinding the rough center core to provide more room at the base to allow for some decent profiles. There are some 'big' cam companies that can also do the extra cutting but it slows them down so they don't advertise such.
     
  22. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,673

    Rusty O'Toole
    Member

    Isky used to make "hard face" cams by grinding a groove in the cam and filling it in by arc welding with a harder material. This gave a hardened surface where the lifter rode. Cams can be built up larger by the same welding process then ground down. But most of the time they would grind down the cam a little smaller but with a different lift and duration profile.
     
  23. TRENDZ
    Joined: Oct 16, 2018
    Posts: 386

    TRENDZ

    I think you’ll find in just about every case, that the lobe apex is as close to the cam bearing size as possible, regardless of how mild or wild the lobes are. Lift is created by diminishing the base circle.
     

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