Installing used cams

boosted79 · 03-11-2016, 09:14 AM

I've got a set of used SC cams and am considering installing them in my '79 930 I'm in the process of rebuilding. The cams are in good shape with no pitting. Am I asking for trouble with rocker/lobe wear? I am planning on getting the rockers resurfaced and rebushed. I know on pushrod engines it's frowned upon to install a used cam without the lifters that came with it and mated to the original lobe. A little different with these engines but am I asking for similar problems?

Alan L · Alan L's Garage

If the rockers are being re done,that is giving you a fresh surface to mate with the cam lobe. That is better than having two 'worn' surfaces mated together.
IMHO you should be OK if the cams have no unusual wear patterns.
But then I'm not an engine builder and I told you the scratch on the wrist pin was OK. (And still think so).
Alan

Tippy · 05:08 AM

Well, on old school pushrod engines, half the lobe is touching the lifter so the lifter would spin. Also, due to having a pushrod and lifter, spring pressures are many times higher than the 911.

The 911 rocker rides the cam lobe completely and uses light springs.

VFR750 · 03-11-2016, 04:35 PM

Getting the two cams reground is only about $350-400.

boosted79 · 03-12-2016, 03:27 AM

Yeah, that's the right way to do it. I'm still not sure I want to put these in, I may just keep the car all original except for headers and maybe a turbo and IC. Decisions, decisions..

VFR750 · 03-12-2016, 03:46 AM

One thing to consider, is after you rebuild the engine, get it installed, and checked out you know pretty much what's needed to do it again (and possibly again and again)

For me, the thought of later swapping a cam is not that big of a deal. A lot of work, but not particularly difficult.

As a point of perspective, you could swap in the sc cam now, and over the next few years get the original cam recut. Have it ready. Then, when originality matters more,

boosted79 · 03-12-2016, 04:26 AM

That is an option I've thought of. If I go that route and at some point put the 930's back in I'd have to get the rockers resurfaced again. That would be the 2nd time on them, I'm just wondering how many times you can resurface these rockers before the surface hardening is gone?

michael lang · michael lang's Garage

I went the route of upgrading the cams in my car's engine. I sent a stock pair of 964 cams to Dema Elgin and had him resurface and polish them before I put them in. I'm not regretting having the upgrade done or the work he did especially since we had several conversations about what I wanted and what my expectations were. A bit more than the previously mentioned estimate costs but worth the extra money based on the results that I got. Resurfacing the rockers is an excellent idea but the real results will be most noticeable in resurfacing of the cams. Just my $.02

Oheggem · 03-18-2016, 03:11 PM

This is another post i just learned something. When i hear people saying "ill install sc cams" bla bla bla i didn`t realize they did this much to run them. I have a set lying around waiting to install. Now i`m not so sure if so much is involved.

Henry Schmidt · Henry Schmidt's Garage

SC cams in a stock 930 is my favorite upgrade. Well worth the effort. I've done many over the years. My favorites even in a track car.
Have them freshened up and enjoy the piece of mind.
Cheers
BTW: In order to use SC cams in a 930 you have to add a drive boss on the left hand cam to drive the turbo scavenge pump. This is best performed by a cam specialist so while he doing this modification you might just as well freshen them up.