- I've been degree'ing since sometime late last year (yes Jim, your tools are getting used to hell and back!).
- Aside from having to collect mountains of data due to my not-so-off-the-shelf parts (block decked, heads decked, custom pistons, valve notches, oversized valves), I noticed that my measurements, when repeated, were off just a little bit. I could never get the intake lobe in the same exact place I wanted it to be
- if you know me, I ain't the type that says "well it's close enough, so I'll just run with it.". No sir-eee-bob.
I had gotten the degree'ing to within ~0.4° after I had found out that my cams were not going to be degree'd to the recommended intake lobe centerline (due to PTV clearances), which I was happy with considering I had set my goal to degree the left and right banks to within 0.2° of each other. But it took A LOT of trials to get that "lucky" 0.4° to be honest.
But then I purposely tore off the heads, repeated everything and I was off again! GRRR!
, leading me to ask "why?". My pointer could have moved, but it hadn't. The degree wheel said 0° at piston #1 TDC, and this was with my new dial indicator that reads down to 0.0001", instead of the traditional 0.001" dial indicator, and the pointer tip was ground down to a needle point! (sorry Jim, I owe you a new wire pointer!
Then, it dawned on me.
- I had not realized the flaw in my method that generated the errors was inclusive of the one main defect of the modular OHC timing system.
- The main area of slop leading to varying degrees of incorrect cam timing using the stock cam gears, are the cam gears themselves.
- Of course the slop could be attributed to tolerances in the keyway in the camshaft snout where the cam gear slides onto, but that is neither here nor there----point is, that "junction" is why cams are off from where they are supposed to be in the first place.
- Fast Freddie Flash-back:
So I set out to find out exactly how much slop there was to see if it corresponded to my measurements.
I set up the dial indicator as "tangent" to the cam gear teeth as possible. This is because on a small enough scale, like what we are dealing with, circular motion can be very closely approximated by linear motion; in this case, rotational slop of the cam gear is translated into the linear motion of the dial indicator plunger/tip.
This is with the slop removed "counterclockwise":
With the slop removed "clockwise":
The Cloyes cam gear center portion, just like any other cam gear, can slide around, causing the cam gear teeth to shift approximately ~ 0.026". What does this mean in terms of degree-variation at the camshaft where it matters?
Those of you good with math can see how I calculated it to be approximately ~2°! GRRR! I was so mad for not having realized it sooner! Sure enough, after looking through all my written data from countless degree'ing trials, the ICL was always falling somewhere in between, id: 107 ≤ ICL ≤ 109. 109-107= 2°. Bingo! I had not tightened down the center portion of the Cloyes adjustable cam gears in the same precise orientation each time I did a degree trial. So each time I tried to use the main feature of the Hex-a-just system to advance/retard the cam timing, the slop sometimes counteracted my efforts.
There you have it. Yet another chapter that will hopefully make that 1 extra HP to create some major ownage against racers everywhere.
Note: I checked the TFS adjustable crank gears. There is no where near as much slop with these on the crank as there is at the cam gears. With the cam gears pressed onto the crank snout by hand, there was less than 0.002" of slop on one of them---the other was even less. At the cam gear, that kind of slop translates into <0.2° in change of cam timing. So what I plan to do, is to weld the one does does have that tiny slop, with the slop taken out before I clamp them together
for the tack welding. This will eliminate the crank/crank gear junction generated slop altogether.
Final Degree centerlines:
Right Bank: 109.25°
Left Bank: 109.35°
Less than 2/10 of a degree difference, just as I had set out to accomplish.