View single post by Esprit2
 Posted: 10-10-2016 06:57 am
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289
The second file, the camshaft drawing, is pretty illegible. I've reversed the color bias so that it has a white background, but the resolution is still low, fuzzy. Can you re-write the notes in a message here?

What cams are installed in the engine? Can you confirm what MOP pulleys are used. From what I can see, I presume they're the standard Lotus dual MOP pulleys, 110 red dot and 100 blue dot. But it's not good to guess when timing cams, so please confirm the starting point... what cams and pulleys are installed?

For the sake of conversation, let's say the pulleys are the 110 MOP (red)/ 100 MOP (blue). In that case, the first thing for you to understand is that there were separate single-MOP pulleys that were true 110 MOP (red) and 100 MOP (blue). But 110 and 100 do not fit on the same pulley, so the 110/100 dual MOP pulley cheats, and the blue dots are really 97 MOP, not 100. If your father had tried to reverse engineer the pulley's math based on 110 and 100 being 4 teeth apart and the pulley flipped over, it would have driven him nutz... it doesn't work.

Also, there are 40 teeth on the pulley, and 360 degrees in a circle, so 9 degrees per tooth. However, cams are timed in 'crankshaft degrees', and there's a 2:1 ratio in crank & cam speeds. Therefore, each tooth is 18 crankshaft degrees. One tooth beyond the red dot 110 MOP advances the cam timing 18 degrees, or 92 MOP, which is not a useful value with the OEM cams.

The white marks in your first photo have no value in timing the stock J-H 907 cams.

If the cams are stock C-cams, and the pulleys are 110/100 (97), then the best cam timing to use is 110 IN and 110 EX. The Lotus 100 (97) and JH 115 MOPs were emissions settings, and results in a loss of power compared to 110 IN/110 EX.

The photo shows the pulleys to be installed the correct way around. The raised bump on one spoke faces forward on the exhaust pulley, and backward on the intake pulley. That's correct.

Now, rotate the crank until it's at TDC. Then the red dot next the the IN mark on the intake pulley should align with the red dot next to the EX mark on the exhaust pulley. That will give the design-correct 110/110 MOP.

The original JH 115/115 MOP reduces power output about 10 Hp. If you want to use that setting (why ??) it's also on the 110/100 (97) pulley, just not marked.

In your first attachment, the photo of the pulleys, refer to the intake pulley... it's the most straight-on shot, and the easiest to read.

The timing dot farthest to the left/ counter-clockwise (nearest the white mark) is red, or 110 MOP. The alternative blue timing dot is 4 teeth clockwise, and is 100 (97) MOP... EXCEPT it's next to an EX mark. Follow that tooth to the back side of the pulley, and you'll find a second blue dot next to an IN mark. To time the cam to 100 (97) MOP, the pulley must first be removed, flipped over front-to-back, and re-installed (ie, raised bump facing forward on the intake pulley, or facing backward on the exhaust pulley). Then rotate the INtake pulley until the blue dot next to the alternate IN mark aligns with the dot next to the EX mark on the EXhaust pulley.

Similarly, the missing 115 MOP dot would be three teeth to the right/ clockwise from the red dot, on the tooth next to the tooth with the blue dot... next to the EX mark. Again, follow that tooth to the back side, and that's where the 115 dot would be next, to the IN mark.

So you have your choice of three MOPs with the pulleys shown in the photo. But, IMHO, unless local emissions inspections will not allow the OEM cam timing to be altered, there's no desireable reason to use either of the alternative MOPs, 100 (97), or 115. The engine will run it's best if you time the stock cams to 110 red IN / 110 red EX.

But before taking all that to the bank, first confirm what cams are installed in the engine, and look for any marks stamped on the pulleys that indicate the MOP. Normally, the MOP would be stamped on at least one side.

Good luck,
Tim Engel

Attachment: JH Cam Timing for qwerty - White Background.JPG (Downloaded 65 times)

Last edited on 10-10-2016 06:52 pm by Esprit2