Cam Centerline
 

Hey guys, I'm building a 12v on my engine stand, currently trying to degree my cam shaft, which I had never done prior to this. Have watched Hamilton's video a dozen times, and read many write ups. Using Hamilton's 207/220, which uses a 99-101 centerline. Mind you, at this point I have degreed this cam prob 20x now, and all numbers are consistent Everytime, and checking TDC after each try. With OEM cam gear and key, on the OEM timing marks, centerline came out to 95.5* (consistent). I bumped the gear one tooth, and came out to 90.5*( went the wrong direction). Went back to stock timing marks, +1 tooth, and now my centerline (expecting it to be at 100.5* considering each tooth of the cam gear should equal about 5 degrees) is coming out to 110.5*, consistently, several times now.

At this point, I'm thinking a 5* offset key, in the factory timing marks position should put me right where I need to be, but before doing so would like to make sure there isn't another issue at hand causing timing to jump 15* on one tooth instead of 5*.

Any input is appreciatedAttachment 70118

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I'm curious about the fact that you have the dial on the valve end of the rocker arm. I checked mine with no rocker arm installed and the dial seated in the pushrod

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The dial indicator is on the valve spring retainer, as all instruction state. I began this whole process, with the tappet cover removed and a dial indicator directly on the tappet, only because I was still p&p my cylinder head. After consistently reading a 110.5* centerline, with the dial on the tappet, I started trying different configurations... But all consistently repeated.

For tdc, I set up the dial on the piston crown, found max piston travel, rotated to .010 before/after max, marking the degree wheel, and splitting the difference for true TDC. For centerline I rotated CW to .010 before/after max lift of #1 intake lobe, mark the wheel (123* and 98*), add them together (=221) and divide by 2 (=110.5).

What could actually cause such a large spike, only on this one tooth of the gear?

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How are you finding TDC ? Hamilton cams being off that much is not common .. agree with prior post remove rocker arm and put dail in push rod

Has your crank gear slipped any , prior build high hp with a crank gear not welded

I would use the other end of the rocker or take the rocker off and use the push rod. There is a degree of inconsistency using the valves as there are tolerances and moving parts to take into account. If I'm building an engine I always degree before putting the head on so you can get absolute TDC off the Piston and use a short rod into the lifter. Also not all key ways are cut in the right spot.

The cylinder head was only put on just try a different method of measuring the lift. I used a rod in the tappet to begin with but found that the rotating of the tappet as the cam turns, was moving the rod around enough to cause inconsistent measurements.

I don't believe this to be a issue with the cam, but possibly a issue with the gear, as the timing was exactly where I suspected it would be l, on the stock timing mark. A friend running the exact same cam, in his 12v, received similar measurement at stock timing, and bumped his gear one tooth also. By rights, mine should be almost perfect , bumped one tooth, as stock timing mark was 95.5*

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I don't not believe so, this engine was totally stock prior to the build. And as I said, the timing is exactly where we suspected it to be, until I bumped it to this one tooth. I've got back to stock timing marks multiple times now, and all readings are still consistent

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Cam gear is a 10 crank degree jump per tooth. Count how many teeth. 360/number of teeth x 2 is the number is will move. Should be 10 crank degree. You should go off the pushrod not the rocker arm. His numbers are probably using .050 of lift. Here is our instructions. http://nolimitmfg.com/performance-pr...ng-a-camshaft/

All set. Got on the phone with Hamilton and figured it out.

Hamilton Cams - How To Check Cam Clearances - YouTube

Dial is not on the rocker btw, is on retainer. Got home from work and used the pushrod, and received the exact same #.

All set, centerline set at 100* now. Good to go

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So then what was the issue?