Cam regrind - how is this possible

I often hear about cams being "reground" to change the profile. I just don't understand how this is done.

If you want smaller lobes with the same timing, I can see how you could grind down to a new profile. But when people regrind, they are usually looking for a more aggressive cam. It would seem that you have to add metal to the existing lobes to make them larger. Even if the term "regrind" is a misnomer for adding metal, I can't imagine how metal would be added to a cam lobe. How can this be?

Chuck

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'86 Cab, '77 Targa, Family Truckster

Having had no experience with this, I have wondered this too.

It seems like if you take metal off one side of a cam, the overall profile would be smaller, allowing less time that a valve is opened. For more performance, it seems that the opposite (open more or at a different time for at least the same duration) would be the goal.

Looking forward to someone explaining this.
Nick.

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Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com
PCA -- Rocky Mtn. Region

Metal is built-up/added to the lobes via welding ... then, any profile can be ground on your old 'bumpstick' ...

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Warren Hall
1973 911S Targa

I have heard the valve lift is the difference between the larger diameter of the cam minus the smaller diameter of the cam. If this were true, to give a taller lift, you would just grind off the 'sides' of the cam. Don't know if this is true, but it sounds reasonable. Escuse my terminology ignorance.

Warren

That makes sense, but would think that welding would leave a less-than-optimal surface for a cam lobe. Potential voids in the metal, etc. Is this a quality solution?

Can regrinding is common in the racing world. And yes, it does involved having a smaller "base circle" profile. Most, if not all, engines have a maximum amount of clearance that limits the max lift available for a given engine. This is usually determined by the size of the cam bearing (typical for cam-in-block arrangements.) To get more lift and duration, the heel is ground closer to the centerline of the camshaft. This becomes the baseline for the closed valve and increases the difference between the closed and max lift points. The slack is take up by either longer pushrods, lifers, or the normal adjustment method for the followers. In high bucks racing, teams may use many experimental shafts that will be reground on the way to a final profile which can be supplied by the manufacturer as a new part once the final specs are determined. Some extreme camshafts are ground from billets with no reliefs between the lobes since the smaller base circle tends to weaken the shaft and allow flexing. I never heard of any cam being welded. I suppose it's possible, but being one of the most highly stessed parts in an engine, and relatively less expensive than most of the other hardware, I don't see why anyone would. Aside from the aformentioned billet steel shafts, most are cast iron, which is VERY difficult to weld properly not to mention pricey in itself.

Hope this was helpful.

Jay

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Jay
'68 912 V8

[This message has been edited by JordonJames (edited 05-25-2001).]

[This message has been edited by JordonJames (edited 05-25-2001).]

Jordon, now that really makes sense. So you could actually increase the lift and maybe alter the lobe timing a bit by grinding the small diameter side of the cam.

But then you must compensate for this change in cam height in other parts of the valve train.

Thanks
Chuck

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'86 Cab, '77 Targa, Family Truckster

Precisely. And you can alter the duration considerably as well. Remember, the specs for camshafts are incremented in thousandths of an inch (or the corresponding metric equivilent) so small changes make a big difference in the performance of the cam and engine.

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Jay
'68 912 V8

They have been welding cams and regrinding them for years. NO BIG DEAL.

Randy Jones
1971 911

Well I never professed to be an expert, but having lived 30 miles from Crane Cams in Daytona for 25 years, and been drag racing for just as long, I never saw it or heard of it. I personally would never do it. To each his own.

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Jay
'68 912 V8

A quick search of the Net showed that there are indeed people welding cams. It looks like a service mainly for uncommon camshaft applications where obtaining a replacement is difficult.

http://www.deltacam.com/services.htm has some pics.
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Jay
'68 912 V8

[This message has been edited by JordonJames (edited 05-25-2001).]

[This message has been edited by JordonJames (edited 05-25-2001).]

Well, uh, Jay - we'll cut you some slack here.

But that V8 in the back of your Porsche, that is another story.

Chuck

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'86 Cab, '77 Targa, Family Truckster

Well I certainly appreciate it! As for my particular Porsche....we all have to start somewhere. Thanks!

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Jay
'68 912 V8

I had the need to visit the cam grinder a while back, not for the Porsche, but for my '73 Norton Commando 750 (m/c).
Many of these Brit-bikes had a bad batch of "soft" cams. Unfortunately mine was one of the unlucky ones. The shop re-profiled the worn out lobes with weld, and then hard surfaced them using plasma-arc metal spray.
Saved me a lot of trouble and money.
No magic to the process, these guys do hundreds of cams a month for everything from race cars to diesel earth-movers.

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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm