C2 SB Timing mark check

[Steve D.]

63 SB, LT1 cam

When I degreed the cam, it showed to be about two and a half degrees Advanced and I left it that way. With the timing cover in place, I checked TDC using a piston stop. At TDC, the timing mark on the balancer will align with approximately two and one half degrees Retarded on the timing cover scale. Is this as it should be, or is something amiss?

Steve

[Clem Z.]

Re: C2 SB Timing mark check

with the piston stop installed turn the engine CW till it stops,mark the damper in line the "0" mark on the timing tab,turn the engine CCW to the stop,mark the damper in line with the "0" mark on the timing tab,half way between these 2 marks is TDC of the damper

[Duke W.]

Re: C2 SB Timing mark check

"Degreeing" a LT-1 cam can be tricky because the points of maximum lift DO NOT correspond to the center of the lobe. The points of maximum lift are 110ATC, inlet and 122 BTC, exhaust.

The lobe is asymmetrical below about .165" on the inlet side and .135" on the exhaust side, so if you try to determine the points of maximum lift by taking the halfway point of lifts below these values, you're not going to get a correct answer.

So what process did you use and what were the results?

Duke

[Steve D.]

Re: C2 SB Timing mark check

Duke

I located TDC with the piston stop and degree wheel, removed piston stop, rotated to TDC, zeroed the degree wheel, rotated to locate maximum lift of #1 intake lifter with dial indicator, rotated to move lifter 50/1000s either side of maximum lift, calculated position of max lift relative to TDC. I was following instructions on a CompCams video; they referred to it as the "intake centerline method".

Steve

[Steve D.]

Question rephrased

I should have phrased the question like this; Does cam timing have any effect on the position (at TDC) of the mark on the balancer relative to the A..0..R scale on the timing cover? It doesn't seem like it should. Then the second question would be, what would cause the miscalibration of the balancer mark/timing scale, ie. to read 2 1/2 degrees off? I previously checked the cover to make sure it was compatible with the balancer.

I guess I will put a new mark on the balancer that will be positioned at zero on the cover scale when #1 is at TDC.

Steve

[G B.]

Re: Question rephrased

Does cam timing have any effect on the position (at TDC) of the mark on the balancer relative to the A..0..R scale on the timing cover?

No.

What would cause the miscalibration of the balancer mark/timing scale, ie. to read 2 1/2 degrees off?

Normal production tolerances on the cover tab placement and the balancer scribe mark position would allow for + or - 2 degree error in my experience. Or you could believe that crap about the balancer outer ring "slipping". Riiiiiiight.

[Duke W.]

Re: C2 SB Timing mark check

If you computed the point of maximum lift as the average of the crank angle .050" down from max lift, that should yield an accurate value since that portion of the lobe is symmetrical, and if you used a piston stop to locate TDC as your reference rather than the balancer and tab, then any error in the balancer and tab will not be a factor.

Unless you do this type of measurement regularly, it's best to do it at least two to three times and look for all values to be within about a thou of each other. Such consistency usually is proof that your technique is accurate.

So what did you measure for points of max lift?

Duke

[Steve D.]

Re: C2 SB Timing mark check

I must reluctantly admit that I did not record lift measurement, just noted max point for determining centerline. I did however mic the cam when I received it, to make sure base circle and lobes were at given specs; which they were.

Steve