Degreeing a cam

Nick Chelenza · #1 (**permalink**) 03-01-2002, 11:22 PM

Could any one explain how degreeing a cam with the degree wheel fine tunes the set up. I have replaced cams and had success without going throught the process. I have read the instructions on the proceedure but dont see how it makes any difference. In my way of understandingthe timing gears are only going to let the cam sit relative to the crank based on the timing marks anyway. What is this little brain of mine missing. Thanks
Nick C.

Jack21 · #2 (**permalink**) 03-02-2002, 02:51 PM

Nick, here's why. Essentially how much error are you willing to accept when you assemble your engine, particularly when you can control it by checking it? It's kind of a pay me now, or pay me later proposition.

The crank keyway notch, timing gears and chain, and cam, are all manufactured with machining tolerances. These tolerances can add together to install your cam in quite a different location than it was designed to. Using a modern replacement timing chain set, you can adjust any inconsistencies to install the cam exactly where it was designed to go. That's why the different keyways and offset keys are there. Some guys even install a cam with 2 deg advance just to allow for timing chain stretch.

With a grocery getter rebuild, you can assemble everything on the marks, and the engine will run (hopefully). You can also take the rings out of the bag, install them on the piston, and if the piston slides in the bore, the rings are fine. If the crank turns when the bearings are installed, they're fine too.

HiPo street motors need more checking. If a cam isn't dialed in, the valves could hit pistons, or the engine will perform poorly, and you'll never know why. Some guys not only degree the cam, but degree each lobe, and send the cam back if it's off.

Some guys only use file fit rings, and set each ring with the minimum gap. Some guys will send a crank back if one bearing is too loose or too tight.

And it's always the one thing thing you didn't check that haunts you later.

It's your time, your money, and your engine. If you spend the time checking the clearances on the engine while you're assembling it, and adjusting things that aren't right, it will run better and last longer, and minimize the chances of having to pull it back out again to do it over.

Hotfingrs · #3 (**permalink**) 03-02-2002, 03:23 PM

My cam is 2 degrees advanced, but it's not for chain stretch. If you advance a cam you get the power in at an earlier rpm, and conversely if you retard the cam the power comes on at a higher rpm. There are kits out there with offset bushing to adjust cam timing 4 degrees either way.....

Dave Wharran · #4 (**permalink**) 03-02-2002, 05:32 PM

I wanted to advance my cam to drop the "power band" rpm. The Cloyes timing set I have had 3 keyways in it. One was supposed to be "straight up", one advanced 2 degrees, one retarded 2 degrees. I used the 2 degrees advanced keyway but when I checked the timing with the degree wheel, it was more like 4 degrees advance. I went with that, but it is nice to know that the cam is advanced 4 degrees, not 2.

I mess with VW Beetle engines too. Yes, they hotrod the same as the V8's do, and parts for them are usually more expensive than they are for a V8 (ie $1500 for a forged CW crank). Anyway, the cams in them are gear driven from the crank. The gear can be made to attach to the cam with 3 bolts. Slot the bolt holes in the cam and the timing is now infinitely adjustable via flat washers whose OD registers in gear and whose ID is drilled with offset holes so the gear can't slip once set.

As mentioned above, if you are putting a stock cam in a stock engine, it's probably not worth the time checking. But when you start to mess with different cam profiles and lifts, advancing or retarding cam timing, different pistons, deck clearance, headgasket thickness, bigger valves, etc., Murphy's Law says that if you don't check each and every part and clearance, something that can go wrong, will. A part will be made wrong , a valve will be dangerously close to a piston, a valve retainer will bottom out on the guide because your new cam lifts higher, a 1.5 ratio rocker arm may actually be 1.55, etc, etc. Simply not worth taking the risk of damaging parts.

Nick Chelenza · #5 (**permalink**) 03-02-2002, 11:40 PM

Thanks for the explanations guys. Makes more sense to me now.
Nick C.

Cal Metal · #6 (**permalink**) 03-07-2002, 02:08 PM

Someone may have mentioned this already, but advancing the cam will increase power at a lower RPM level; that is, the engine will come on stronger at lower RPMs. Retarding it does just the opposite.

Andy Dunn · #7 (**permalink**) 03-07-2002, 06:13 PM

Here is an 8 page primer from CRANE on degreeing a cam
http://www.cranecams.com/instruction...ing/degree.htm

and here is the Holley / Lunati version of degreeing a cam
http://www.holley.com/HiOctn/TechSer...IECCTech8.html

hope this helps

Andy

Greg Dunn · #8 (**permalink**) 03-09-2002, 07:42 AM

Careful on advancing a cam to lower your power curve. Rule of thumb is every 4 degrees of advance lowers your power curve 500 rpm (so if your pc is 3000-6500, 4 degrees advance lowers it to 2500-6000). I did exactly this on a 306 with the idea that lower would be better on a "f" cam w/ 1.6 rockers (.512 lift) - the gain was more than offset by the loss of exhaust gas scavenging per a chassis dyno. I'm switching back. Lesson learned.

Andy Dunn · #9 (**permalink**) 03-09-2002, 03:35 PM

here is another view on the subject of advancing or retarding a cam. Some of the latest books on the subect consider it "nonsense" and here is why.

Desktop Dynos : Using Computers to Build and Test Engines

Page 92
If advancing or retarding the cam is such a "poor practice" why is it so popular? The answer is simple: It is just about the only "tuning" change available to the engine builder without regrinding or replacing the cam. Advancing the cam slightly improves low-speed power, while retarding the cam gives a small boost in high speed power. If advancing or retarding allows the engine to perform better, the cam profile was not optimum in the first place.

hope this info was interesting

Andy

Jack21 · #10 (**permalink**) 03-09-2002, 08:39 PM

Agreed, but timing chains do stretch after awhile. Some engine builders install a new cam 2 deg advanced to allow for this for street motors that will likely see high mileage before chain is replaced. Function of the application.

Hotfingrs · #11 (**permalink**) 03-10-2002, 05:40 AM

If your timing chain is advancing your cam 2 degrees it's time to replace that sucker. Also if you're advancing the cam to take up slack for a timing chain, it's time to replace that sucker. Also if you have the front cover off, to adjust the cam, to account for the slack in the timing chain, why not replace that sucker.....