Slant Six Forum :: Regrind Cam?

now I am really confoosed.

the base circle is where the valve is closed right? If so, how can the valve get any more "closed"?

Does this change the opening and closing times of the valve too?

Still wondering how this helps and what niche it fills.

Thanks

and I think its harder to some degree

A regrind is great if your milling some off the block or head because you can zero out the effect and still keep the same push rods and geometry.

I still can't for the life of me see how taking material off could increase the lift

Yeah I know I am a little dense:)

Is there a laymans way to explain this or do i need to go buy $100 worth of Amazon books

Quote:

I still can't for the life of me see how taking material off could increase the lift

Yeah I know I am a little dense:)

Is there a laymans way to explain this or do i need to go buy $100 worth of Amazon books

If you dig a hole next to a hill you have to go farther up to reach the top.

A picture is worth 1000 words...

Grind the base circle of the cam smaller (the inner red line) and the remaining lobe becomes bigger... as far as what the lifter sees.
DD

Author:	ValiantOne [ Thu Sep 06, 2007 11:21 am ]
Post subject:	Regrind Cam?
So what is a regrinded cam? I've been reading abou it in the "twiggy" build up thread. Obviously a cam is being ground in some fashion, but what I am wondering is how material is added to the cam to get the right specs. Is this done because it is cheaper / better product / no blanks available? Thanks, Chris

Author:	dakight [ Thu Sep 06, 2007 11:26 am ]
Post subject:
In a regrind, no material is added to the cam; it is simply ground to a new contour which usually lowers the base circle of the lobes.

Author:	ValiantOne [ Thu Sep 06, 2007 1:33 pm ]
Post subject:
now I am really confoosed. the base circle is where the valve is closed right? If so, how can the valve get any more "closed"? Does this change the opening and closing times of the valve too? Still wondering how this helps and what niche it fills. Thanks

Author:	slantvaliant [ Thu Sep 06, 2007 1:45 pm ]
Post subject:
Quote: now I am really confoosed. the base circle is where the valve is closed right? If so, how can the valve get any more "closed"? Does this change the opening and closing times of the valve too? Still wondering how this helps and what niche it fills. Thanks The base circle can be reduced in diameter, with the lobe peak left or reduced. Reground cams help when good cam blanks are hard to come by, as with the slant six.

Author:	BigBlockBanjo [ Thu Sep 06, 2007 1:48 pm ]
Post subject:
The valve doesn't really get "more closed".... the rocker arm just tilts a little more to reach the base circle. Taking metal off the base circle only would increase lift only. If you take some paper, and draw a rough pic of a cam lobe, you can sort of visualize it. They can do some amazing things by just taking off metal in the right spots, Its deep stuff, doing a search on the subject would give you alot of info. I personally believe a reground cam is better because it woul dbe near as likely to have problems with the oil gear(like some of the new blanks do) and I think its harder to some degree.

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Author:	68barracuda [ Thu Sep 06, 2007 2:00 pm ]
Post subject:
Quote: and I think its harder to some degree ans since it has been around the block a couple of times- the stresses will be out of it - nicely seasoned

Author:	Dart270 [ Thu Sep 06, 2007 2:23 pm ]
Post subject:
I have two regrinds that work great. The highest HP NA Slant on earth only uses regrinds... Lou

Author:	Aggressive Ted [ Thu Sep 06, 2007 6:06 pm ]
Post subject:
A regrind is great if your milling some off the block or head because you can zero out the effect and still keep the same push rods and geometry. I recently did this on my rebuild and it worked out well for me! Doctor Dodge had made a strong recommendation to do it so I had Delta Cams in Tacoma, WA. do the regrind. Cost was $35.00.

Author:	ValiantOne [ Thu Sep 06, 2007 6:49 pm ]
Post subject:
Quote: A regrind is great if your milling some off the block or head because you can zero out the effect and still keep the same push rods and geometry. Now that makes total sense to me, and seems intuitive. I still can't for the life of me see how taking material off could increase the lift Yeah I know I am a little dense:) Is there a laymans way to explain this or do i need to go buy $100 worth of Amazon books

Author:	Joshie225 [ Thu Sep 06, 2007 7:18 pm ]
Post subject:
Quote: I still can't for the life of me see how taking material off could increase the lift Yeah I know I am a little dense:) Is there a laymans way to explain this or do i need to go buy $100 worth of Amazon books If you dig a hole next to a hill you have to go farther up to reach the top.

Author:	Aggressive Ted [ Thu Sep 06, 2007 8:39 pm ]
Post subject:
Think of an egg shaped cam lobe. Visualize the fat part at the bottom and the pointy end at the top. They grind off the bottom only. This gives you a smaller base where the lifter has to follow. So the pointy end is effectively longer as you grind more and more off the bottom. The centerline through the cam lobe moves up as you grind the bottom. Try to draw a picture on paper of a stock cam and original center line of the bottom radius. Then grind some off and redraw the centerline to correspond with the new shape. Watch what happens as you keep rinding more off. Think of the lifter following that shape and arc. The more you grind the bottom off the taller the lift. Hope that helps. It really does work and you get a proven cam as a result.

Author:	slantasaurus [ Thu Sep 06, 2007 8:41 pm ]
Post subject:
Quote: Quote: I still can't for the life of me see how taking material off could increase the lift Yeah I know I am a little dense:) Is there a laymans way to explain this or do i need to go buy $100 worth of Amazon books If you dig a hole next to a hill you have to go farther up to reach the top. Another example, you can't make the nose (tall part of the lobe) too tall to fit through the cam bore/bearings...so you take metal away from the other side. I learned this years ago while a friend was doing a cam swap, he put a caliper on the old cam and then on the new cam...the new cam was smaller...then we figured out what was going on.

Author:	Doctor Dodge [ Thu Sep 06, 2007 11:30 pm ]
Post subject:
A picture is worth 1000 words... Grind the base circle of the cam smaller (the inner red line) and the remaining lobe becomes bigger... as far as what the lifter sees. DD

Author:	ValiantOne [ Fri Sep 07, 2007 6:18 am ]
Post subject:
Ok, now I feel extra stupid I'm still not seeing it. In the pic, assuming the centerline of the cam stays the same in the block, it looks like the lifter would just drop down on to the base circle more, and the lobe would be the same height. Please, please bear with me I really want to understand this If the lifter drops down lower in its bore and you adjust the rocker to that base level, is that where the extra lift comes from? This is really sad. I wored as a general tech and a jeep/eagle tech back in the late 80's and early 90's!!!!! Quote: A picture is worth 1000 words... Grind the base circle of the cam smaller (the inner red line) and the remaining lobe becomes bigger... as far as what the lifter sees. DD

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Author:	CARS [ Fri Sep 07, 2007 6:44 am ]
Post subject:
Let me see if my understanding helps (or if I am just as confused) When you make the base smaller in diameter you need to set the rockers down lower to keep the geometry correct. When the lifter goes up the ramp it needs to climb higher than before, i.e., more lift. So if you take .100 off a head the rocker geometry is going to be off. Since everyone replaces their cam anyway, by re-grinding the cam you can off-set the shave by taking off a calculated amount off the cam. (or buy shorter pushrods) Right??? How would one calculate how much to take off or is this done offen enough that any of the previously mentioned cam grinders can figure out in a few minutes?