Can this cam be fixed?

JoeMag · 11-26-2005, 05:25 AM

964 cam from my car ('82 930). This is right side cam #6 intake lobe. Broke a rocker 2nd to last race last year on this and repaced rocker. I was thinking it was from over-rev condition, but now I'm wondering if this may have had something to do with it...

Can this be welded up and reground?

Gunter · Gunter's Garage

Camgrinder will help you with this; I believe that it can be welded and reground. But, the hardening????
Questions: Is this a true 964-cam? Or is it an SC-cam ground to a 964-profile:
Could you, please, measure the diameter of the base-circle, and the height of a good lobe in mm?
Base-circle:
Lobe height:
Much appreciated.

edbaus · edbaus's Garage

Gunter,

I know what you are thinking. But this looks deeper than the welding breaking off. Looks like it is on the base circle too, which would not see too much build up at the time of welding.

Also, do you have lobe heights for many cams. I am interested in knowing the lobe height for the 934 cams to see if that is what these that I have are, or if they are something else.

Thanks

Ed

camgrinder · 11-26-2005, 01:49 PM

Its fixable. Its tough to be sure, but it looks like it was a welded cam to begin with?
The welding material ends up at 56-58 RC for hardness. This is close to the original chill cast material hardness. I have found the weld holds up nicely, but the rocker arm pads tend to wear out faster. To put 964 cams in a 930, I prefer to start with new billets instead of welding up used 930 camshafts.
Also, I would not use synthetic oil with welded camshafts.

JohnJL · 11-26-2005, 05:10 PM

Hi John,
Why not use syn with welded cams? Oh, while I'm asking...would a DR20 on SC cams have been welded?

camgrinder · 11-26-2005, 05:28 PM

John, my reason to not use synthetic oil is based on past experiences. Welded cams last longer using dino oils.

Your cams are not welded. Dont worry.

Gunter · Gunter's Garage

Ed: I don't have any cam specs. I don't know 934 cams?? Do you mean 964?
Joe: Please, measure a good lobe with calipers.
Base cyrcle: ? mm
Lobe height: ? mm
I would take Camgrinder's advise on welding and re-using.

JoeMag · 11-28-2005, 07:43 AM

I'll get those things measured this eve. thx.

JoeMag · 11-28-2005, 05:20 PM

Gunter -- here ya go.

Base cyrcle: 31.8 mm diameter (this is diameter measured perpendicular to max lobe height)
Lobe height: 8 mm (based on lobe diameter 39.8mm)

...now that doesn't seem right to me since 964 intakes should have have something like 0.46" valve lift. above is 0.315". so i put cam shaft back in cam holder and measured lift with dial indicator and got samething.

what am i missing here? are rocker arms different lengths (from rocker pin to valve and rocker pin to cam surface) at max lift?

...these are web cams so going to call them and ask tomorrow.

camgrinder · 11-28-2005, 06:18 PM

The 911 rocker arm ratio is on average 1.47-1 to 1.49-1 at full valve lift.

Gunter · Gunter's Garage

Thanks, Joe:
To be sure: Are these measurement from a 964-cam?
True 964-cam, or reground SC-cam?

camgrinder · 11-29-2005, 07:47 AM

The base circle on Joe's cam is slightly smaller than oem. It should be 32.1 mm The lobe lift is correct for a 964 cam.

JoeMag · 11-29-2005, 08:11 AM

Found out they're 930 cams redone to 964 profile. Other cam is fine.

I've read you need to put new rockers in if you reharden cam, and according to Web Cam the aftermarket porsche ones don't last at all. ...where can I get mine resurfaced so I don't need to buy new at $62 EACH!