[Jim Hand]

Over the years, I accumulated various offset cam keys of unknown origin and offset value, and was curious as to what they measure. And when we are degreeing in a cam, we wondered if there might be an easier and/or quicker method of estimating the effect of an offset key before actually installing and degreeing with it.

In considering this problem, it seemed we could calculate the dimensions of each offset, and it turns out we can. (As I have only decent quality shop tools and gages, and no Laboratory stuff, don’t hold me to much more then plus or minus .002 in the following dimensions.) The diameter of the cam at the nose where the cam gear fits is 1.123" - 1.123 X 3.1416 (pi) = 3.528" circumference at the surface of the cam nose. As the circumference represents a 360 degree circle, we can then calculate the width of each degree at the surface of the cam nose. 3.528" divided by 360 = .0098" per degree. With this value of .0098" per degree, it is possible to determine how much physical offset of the key is required for any value in degrees.

The basic stock Pontiac key is .187" wide. As a basic stock key is considered as a standard, we can call it zero offset. If we want a one cam degree offset, we know that .0098" will move the center of the key one degree. So, the one degree offset key width will be .187 basic width plus .0098 offset, or a total width of .197 (rounded to a thousandth)!

With some sort of calipers, it is possible to measure the key width and closely estimate the effect it will have on the cam position in the engine before even degreeing it. Additionally, it will be obvious that many of the offset keys sold individually vary greatly from the stated value. Here is a short chart of widths of offset keys:

One degree cam key (two degrees at the crank) = .197

Two degree cam Key = .207

Three degree cam Key = .216

Four degree cam Key = .226

Again, this should not substitute for actual degreeing, but it sure makes it easier to get closer to the desired setting if the key’s affect is known before going through the entire procedure. Additionally, with the variance in some of the keys, it is occasionally possible to select an odd sized one to get the cam just where it is desired! And remember that each cam degree changes the timing events two crankshaft degrees. Also, offset keys can be used in conjunction with offset crank gears to get very close to the desired timing results.

Another tip: Occasionally, a key will not fit snugly in the cam slot. This makes it very difficult to install the gears/chain. Take a sharp punch and make several punch marks in the side of the section of the key that fits into the cam. This will create small ridges on the side effectively widening the key, and it will then stay in place (might even have to be lightly pressed in place in the cam).

Finally, MOPAR Performance sells a five key set of precision keys of 1 through 5 cam degrees that fit our Pontiacs perfectly. It is PN P4286500 and available at MOPAR Dealers only through their Performance catalog. It is also quite expensive at retail price. Straightline Performance normally tries to keep the sets in stock and are in the range of $20-25 per set. Jim Hand

Straightline Performance: http://www.straightline-perf.com/

[Jim Hand]

Over the years, I accumulated various offset cam keys of unknown origin and offset value, and was curious as to what they measure. And when we are degreeing in a cam, we wondered if there might be an easier and/or quicker method of estimating the effect of an offset key before actually installing and degreeing with it.

In considering this problem, it seemed we could calculate the dimensions of each offset, and it turns out we can. (As I have only decent quality shop tools and gages, and no Laboratory stuff, don’t hold me to much more then plus or minus .002 in the following dimensions.) The diameter of the cam at the nose where the cam gear fits is 1.123" - 1.123 X 3.1416 (pi) = 3.528" circumference at the surface of the cam nose. As the circumference represents a 360 degree circle, we can then calculate the width of each degree at the surface of the cam nose. 3.528" divided by 360 = .0098" per degree. With this value of .0098" per degree, it is possible to determine how much physical offset of the key is required for any value in degrees.

The basic stock Pontiac key is .187" wide. As a basic stock key is considered as a standard, we can call it zero offset. If we want a one cam degree offset, we know that .0098" will move the center of the key one degree. So, the one degree offset key width will be .187 basic width plus .0098 offset, or a total width of .197 (rounded to a thousandth)!

With some sort of calipers, it is possible to measure the key width and closely estimate the effect it will have on the cam position in the engine before even degreeing it. Additionally, it will be obvious that many of the offset keys sold individually vary greatly from the stated value. Here is a short chart of widths of offset keys:

One degree cam key (two degrees at the crank) = .197

Two degree cam Key = .207

Three degree cam Key = .216

Four degree cam Key = .226

Again, this should not substitute for actual degreeing, but it sure makes it easier to get closer to the desired setting if the key’s affect is known before going through the entire procedure. Additionally, with the variance in some of the keys, it is occasionally possible to select an odd sized one to get the cam just where it is desired! And remember that each cam degree changes the timing events two crankshaft degrees. Also, offset keys can be used in conjunction with offset crank gears to get very close to the desired timing results.

Another tip: Occasionally, a key will not fit snugly in the cam slot. This makes it very difficult to install the gears/chain. Take a sharp punch and make several punch marks in the side of the section of the key that fits into the cam. This will create small ridges on the side effectively widening the key, and it will then stay in place (might even have to be lightly pressed in place in the cam).

Finally, MOPAR Performance sells a five key set of precision keys of 1 through 5 cam degrees that fit our Pontiacs perfectly. It is PN P4286500 and available at MOPAR Dealers only through their Performance catalog. It is also quite expensive at retail price. Straightline Performance normally tries to keep the sets in stock and are in the range of $20-25 per set. Jim Hand

Straightline Performance: http://www.straightline-perf.com/

[Rob79]

Also available through Summit Racing in the Mopar Section. DCC-4286500. $24.95 for the set. Just ordered them today.
Rob

[Bill Boyle]

Rob--You're putting tremendous effort into getting that cam zeroed in--that's the way to do it. Work at it to get in right the first time. Very useful information from Jim on offsets for future reference too.

[Gach]

Jim, excellent job as usual. I have one question, what material are the Mopar keys made of ? I use the offset keys from Mr. Gasket that come in 2 and 4 degree offsets, and I believe there made out of Titanium for use with roller cams, are the Mopar one safe to use with roller cams ?

[Tom Hand]

Lou,
Dad is working on a set of heads and asked me to provide the information you asked for. Here is the description of the keys from the 2000 Mopar Performance sales book. "Offset Cam Key Set. For centerlining of your camshaft, these hardened keys are color coded in 1, 2, 3, 4, and 5 degree increments. Production key is used for zero offset". Here is what the MOPAR Engine manual says, page 89 in one of my mid 90s books: "The A engine offset key package (P4286500) is used to degree A engine camshafts. Most offset key packages on the market for the A engine feature only 2 and 4 degree keys. The Mopar Performance package has five hardened keys, which give the racer the option of advancing or retarding the camshaft centerlines 2, 4, 6, 8, or 10 degrees. The package will fit all 273, 318, 340, and 360 engines." If you need more information, go to WWW.mopar.com.
Tom Hand