Degreeing Camshafts

[Swiper the Fox]

Recently ive been asked about correctly degreeing camshafts in RB engines, this step by step guide will hopefully answer a few questions and allow others to understand how its done and use this method to set up vernier cam gears to find exact lobe centers.

Cam gears help you to adjust your cams so that it opens and closes at the correct time. It also insures that maximum lift correspond to a desired crank position. The center line or the point on the cam where maximum lift occurs is known as lobe center.

Setting the cams to zero on the cam gear means absolutely nothing as different manufacturers of cams and cam belts can cause exact position of lobe centres to be slightly incorrect.

Lobe centers on the HKS 264's are 110 for the inlet cam and 103 for the exhaust cam. Adjusting your cams too these specs will most probably bring them very close to their maximum designed performance . A lobe center of 110 on the inlet cam means that maximum valve opening will be at 110º ATDC and 103 on the exhaust will mean that maximum valve lift will be at 103º BTDC.

This is how I degree my cams

1. Use a pencil, paper and arithmetic for this procedure, to keep track of the results.

2. Make a rigid pointer from stiff wire or an old coat hanger and attach it to the engine block. This pointer locates the degrees on the degree wheel.

3. With a degree wheel installed on the crankshaft, rotate the crank to get the no 1- piston at TDC and check to ensure that the valves are fully closed then adjust the pointer to zero (0º TDC) on the degree wheel.

4. Turn the crankshaft opposite the running rotation approximately 15-20 degrees. Install a dial indicator above the spark plug hole (i use a flat metal plate ive fabricated that bolts to the coil pack bracket holes) with the rod of the gauge going down the spark plug hole to check the position of number 1 piston.

5. Continue to turn the engine in the same direction until the piston comes back up and just touches the dial indicator. Make a note of the exact number on the degree wheel that the pointer is on.

6. Rotate the engine in the other direction (running rotation) until the piston comes back up and touches the dial indicator. Again note the number where the pointer is.

7. Remove the dial indicator and rotate the crankshaft to the midpoint of the two marks. At this point the piston is at the true top dead center. Loosen the degree wheel and adjust it so it will read 0º TDC at the pointer. Don't rotate the crankshaft to do this!

8. Now, it's time to locate the lobe centerline relative to TDC. Attach the dial indicator on the top of the head. Set the tip to contact the top of the no 1-cylinder inlet valve shim/bucket. Check to make sure that the indicator plunger is parallel to the valve stem. NOTE - any variance in an angle will produce geometric errors in the lift readings.

9. Rotate the engine in the normal direction of rotation until a reading on the dial gauge of 0.040 lift is reached. (Valve will start to open) Mark the dial gauge and make a note of the reading on the degree wheel.

10. Continue to turn the engine in the normal direction past maximum lift. The valve will now return to its close position. Make a note of the degree wheel reading when the indicator reads 0.040" on the return side

11. Now add the larger of the two readings that you noted on the degree wheel to 180 subtract the smaller number and then divide the answer by two. Your answer will indicate the lobe center of the cam. Example: open reading was 4 and close reading was 43. Now add 43 to 180 = 223, subtract 4 =219 divide by 2 = 109.5. Lobe center is 109.5 degrees.

12. Continue to move the cam on the adjustable cam gear and redo steps 10 to 12 until the required lobe center is achieved.

13. Now do the same for the exhaust cam

Hope this is not too complicated to follow.

cheers

Paul

[urtwhistle]

Hi Paul,

In my situation I am running a RB30 with RB25 Neo head, but I don't trust the timing markings on my car for a variety of reasons.

going from what you have mentioned above and the specs for standard RB25DET NEO Camshaft duration 236°in, 232°ex lift: 8.4mm in, 8.7mm ex

does any 1 know what degree's in relation to TDC the intake cam is set to standard @ 0.040" of lift? or what degree's the intake cam is set to at maximum lift in standard form.

regards

[SABBAi]

Nice write up Paul.

[monty_r33]

Im running a 30/26 my exhaust cam card says at .050 should be 242 deg and intake is 253 deg at .050. does this mean in stead of

(9. Rotate the engine in the normal direction of rotation until a reading on the dial gauge of 0.040” lift is reached. (Valve will start to open) Mark the dial gauge and make a note of the reading on the degree wheel.)

I should be reading .050 and not .040

[Hanaldo]

No, the mark on the dial gauge is just a reference. Really you can use any number you like, so long as you use the same number for all your measurements. So say you choose 0.040" then you just rotate the engine forward until the gauge reads 0.040" again.

Should also note that for RB's you need to preload the dial indicator due to the lifter design in a cam on bucket setup.

[GTRNUR]

Yes, the 0.050" on the cam card and its documented lift refer to the lift you should see at a specific crank angle.

Between these two points is the crankshaft position where maximum lift occurs, which is also where the advertised duration measurement should be.

[Hanaldo]

No, the mark on the dial gauge is just a reference. Really you can use any number you like, so long as you use the same number for all your measurements. So say you choose 0.040" then you just rotate the engine forward until the gauge reads 0.040" again.

Should also note that for RB's you need to preload the dial indicator due to the lifter design in a cam on bucket setup.

Just want to correct myself here and apologise if I mislead anyone. I re-read Paul's write up and realised he was using a different method to the one I used. My bad.

So in this case, YES set the dial gauge for the valve lift indicated on the cam card.