Degreed the cam, weird results..

fastsc92

Registered User
Ok, I finally got around to degreeing the cam, after i was done x-mas prep. I made a piston stop, and found true top dead center. Then i used a dial indicator on the intake lifter ( the one closest to the front, right?). I brought the intake lifter to max lift, then set the dial indicator to zero. Then i went opposite engine rotatation about .100. Then i when in the dirrection of rotating to .050 before max lift, took a reading on the wheel (62), then kept going to max lift, then back down the other side of the lobe to .050 again, and got a reading of 148. I added the two together(210) and divided by two for a final intake center line of 105. This seems very strange because the cam should be installed at 112, and i thought most cams would be retarded after the grind, not advanced 7 degrees! Anyways, I checked this about 4 times with the same results. My question is, why is it so advanced? Maybe i have the timing marks off by one tooth. The dots were lined up the best i could see, but maybe its off a little. And my final question is, could i just keep the timing marks off by one tooth in order to correct the cam timing, instead of cutting a new keyway in the crank gear, or am i forced to get a keyway machined? It seems like either way would/should work. Because thats what i'm doing with a new keyway, or in a SBC case, offset bushings. Moving it one tooth should do the same thing right?? I'm going to check it all after the holiday and make sure the timing dots are lined up, but if they are correct...what should i do???
 
You could get a double roller timing chain from Morana which enables you to retard or advance the timing 4 degrees each way, the lower sprocket has 3 keyways on it. :)
 
i understand that, but wouldn't moving the sproket one tooth achieve the same results?? And its 105 right now, i would need 7 degrees retard, and the adjustable bottom peice wouldn't give me enough.
 
I'm not sure I follow exactly what you did, but I assume the cam has 112 deg LS? If so, Comp Cams always grinds 4 deg advance into their cams. That being the case, you are looking for an intake CL of 108. That being the case you are advanced an additional 3 deg. Expect this to generate about 5ftlbs more torque below 3500 and cost about the same above 5200. In other words, I would not worry about it if I were you. I feel that you are certainly close enough. Make sense?
 
it just seems weird that its 7 degrees advanced and not retarded. There is no way to add an advance in after a grind...thats what comp told me. I'm going to check the timing marks tonight. The cam card says a LS of 112 and an ICL of 112. I'm at 105. I need to retard it 7 degrees. It almost seems that the timing marks are one tooth off. But if thats not the case...can i achieve correct cam timing by moving the cam gear one tooth?
 
ok, the timing marks were correct, and its still at 105 ICL. I moved the cam gear one tooth and now im at 121 ICL. A keyway will have to be machined, but how do i know where to make a new keyway?, and more importantly..how do i make a keyway correctly? OR......could i get a crank gear off something else, and use that instead of the stock peice? Maybe switching timing sets would yeild different results.
 
You are taking your measurements on the camshaft lobes which are turning at half the speed of the crankshaft, so if you get a new keyway cut into the crank gear you would divide the amount of gerees you're off on the cam by 2 and that tells you how much to move the keyway in the crank gear.
Example: You're 7 deg advanced at the cam so you need a new keyway cut 3-3.5 degs retarded in the crankgear. Have your machinist put a new timing mark opposite the factory mark on the crankgear then have him cut a keyway 3.5 deg retarded indexing off his new timing mark. Make sure he marks the new keyway so you can tell which one is what. Thats all there is to it. :)
 
mike, i just figured that out about 5 min before i read that. I'm using the center line of a tooth and making a keyway 3 degrees off of that. Basically, exactly what you said. Now i just need to find someone to do it for me...
 
fastsc92 said:
... I made a piston stop, and found true top dead center. Then i used a dial indicator on the intake lifter ( the one closest to the front, right?). I brought the intake lifter to max lift, then set the dial indicator to zero. Then i went opposite engine rotatation about .100. Then i when in the dirrection of rotating to .050 before max lift, took a reading on the wheel (62), then kept going to max lift, then back down the other side of the lobe to .050 again, and got a reading of 148. I added the two together(210) and divided by two for a final intake center line of 105. This seems very strange because the cam should be installed at 112, and i thought most cams would be retarded after the grind, not advanced 7 degrees! .

Before you go crazy ruining parts, you might wanna try checking it again. Your procedure above is a little wrong.

Here's how it is supposed to be done:

1.) Set piston to TDC (on compression stroke i.e. both valves closed)
2.) Set pointer on the degree wheel to TDC.
3.) Set dial indicator to zero on the SHELL of the lifter!!! Using the plunger of the lifter will net erroneous results because of the spring loaded lifter design.
4.) Spin crank in direction of rotation (CW I think, but don't quote me) until you see .050" lift on the dial.
5.) Record reading, this is Intake opening
6.) Continue spinning crank to max lift on dial (somewhere around .300" probably)
7.) Record reading, this is the Intake centerline (almost every cam lobe is symmetrical, so max lift is also the centerline)
8.) Continue rotating crank until dial reads .050" again
9.) This is the Intake closing.

You're measuring points before max lift when it's really points from closed (basecircle) that you should be measuring. It's also important to note BTDC or ADTC or BBDC or ABDC on your readings.

You should get something around -5* ATDC (For calculating, it's spec'd in ATDC, it's actually BTDC on many cams, thus the negative number) for the Intake opening and 30* ABDC for the Intake closing.

Int duration = Int opening (don't forget it may be a negative) + Int closing + 180

Int Centerline = (Int duration/2) - Int opening

For reference, here's my intake cam specs

Int open = -4* ATDC
Int close = 34 ABDC
Int duration = (-4*) + 34* + 180* = 210* which matches what it's supposed to be
Int Centerline = (210*/2) - (-4*) = 105* + 4* = 109* which matches the card

When I measured mine, it came up 1 degree off, big deal.
 
Blackbird...let me add to that as well. I am using the shell of the lifter, and not the plunger part. According to Comp. cams i should us the intake center line method, which you take a reading .050" before and after MAX lift. The method you stated is what crane cam recomends, and you take a reading before and after the closing on the intake and exhaust valves. I have a video and instructions from Comp, and i did it exactly like that. You can take a look on their site and see the method they used...as well as me. There are two ways to do this. The method i used is the intake center line method, and the method you used. Both will work, according to your cam card.

This is what i used:
Comp. Cams Degreeing Instructions
 
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ok, here is the update. I had a hard time finding someone who will cut this keyway for me. I finally found two people who can and will cut it, but they both ran into a snag. The machine they use to cut the keyway, uses a center peice which fits in the center of whatever you are cutting. The catch is that with the inside diameter of the crank gear, the machine must use a 1/4" keyway. I need a 3/16" keyway. I hope everyone understands what the problem is. So here is my new question. Can i cut a keyway in the CAM gear instead? I think the cam gear has a smaller ID which will allow the machine to cut a 3/16" keyway, instead of a 1/4". Can i do this?
 
I dont see why not..Shouldnt matter where you adjust the cam timimg from so long as the strenght of the part is compramised
 
Yes you can do that but remember the posistion will be different at the cam than at the crank because of the gear reduction of the timing gears.
Maybe a better solution for you would be to have offset keys made for the crank gear and cam gear, any machinist can make them pretty easy and even Coy does that.
 
to my knowledge, an offset key wouldn't give me the amount of change that i need. I also found out some cool info from the local engine shop about a new timing set for our cars, which i'll post in another thread. Oh and i am aware of the change....which is a 2:1 ratio. I would need a key 3* difference in the crank and 6* in the cam gear.
 
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OK a final update about all this mess. I finally cut the keyway in the cam gear. Actually, even though its a 2:1 ratio....you still only cut the keyway 3*, and it equals 6 camshaft degrees. Its hard to explain but the engine shop i've been dealing with told me that, and it makes perfect sense. Anywho....I cut the key by hand with a broach tool. It degreed in at 105 before hand, and the target was 112. After i cut the keyway, i got it to read 113.5. Which means i was only about 1*(2 degrees camshaft) off from my target degree. Thats pretty damn good for doing it myself. I think it'll be close enough. I got the motor sealed up, with the heads bolted on. And i ordered my pushrods which will be in tommorrow...hopefully i'll get it together by friday and running.

The engine shop actually contacted Cloyes and they made them a proto-type stock style timing set for the 3.8l, which will be adjustable. They will be the first people to try this set out, and if it works, it'll go on the market. They offered to order another set for me, but i couldn't wait, and decided to do it myself.
 
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