View single post by Esprit2
 Posted: 06-02-2019 04:04 pm
PM Quote Reply Full Topic


Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 512

In your photo of the crank position, it's a little past TDC. Not a biggie, but accuracy helps when you're trying to judge errors. On the stationary tab that overhangs the pulley, the tops/ peaks of the timing ridges are the timing marks. Not the 'notch' or base of the ridge.

The cam pulley timing marks must align "ON" the imaginary centerline between the cams. If they align, but are above or below the centerline, then the cams aren't properly timed. It would help if you were to post another wider-view photo of the cam pulleys that includes the hubs/ centers of both pulleys, if not their full front faces.

See the photo I've posted. I marked-up yours, 'guestimating' where the pulley/ cam centers are. Presuming my centerline isn't totally off, it appears that the cams are timed at 115° INtake / 97° EXhaust (ie, 100° EX). "IF" you wish to preserve the early JH 115/115 emissions timing, then yes, the exhaust pulley is one tooth off. But in my feeble little mind, that's a big "IF". For optimal performance, both cams need to be re-timed to 110° / 110°. Read on.

110° / 110° is the design correct timing for the stock JH C-cam. That timing will give the best performance... the engine feels alive.
115° / 115° is the early JH emissions cam timing. It costs about 10 Hp, and the engine feels less than energetic.
100° / 110° is the later JH emissions timing. Combined with neutered ignition and lean carbs, it's the worst, the "Torqueless Wonder".

cjwilson wrote:
Also, when rotating the crank to TDC, it looks like the exhaust cam is off by a tooth.115° / 97° is where your cams appear to be currently timed (see my mark-up of your photo). Not correct to any JH spec, and not where you want them to be for the best performance.

Not relevant to your photo, but just FYI:
With the later 100° / 110° 'emissions' timing...

100° was the intended emissions MOP... ie, the ugly goal.
On a dedicated, SINGLE MOP pulley with one blue timing dot per side, 100° is really 100°

On a multiple MOP pulley, as shown in your photo, the pulley's geometry/ math doesn't support both 110° (design correct) and 100° (emissions bodge) existing on the same pulley. So the target 100° was 'cheated' to the nearest MOP that did exist on the 110° pulley, which was 97°. Conversationally, both are referred to as, "100° MOP".

In many markets (most USA states) vintage cars older than a certain age no longer have to pass an annual emissions test. If that's the case for your car, and if you want the best performance available, then...

Go to the 110° EX timing dot on your intake pulley. Follow that tooth to the back side of the pulley, and you'll find a 110° IN timing dot. Similarly for the exhaust pulley... 110° IN on the front, and 110° EX on the back.

For both pulleys, the 110° timing marks you want are on the back sides of the pulleys. Remove the pulleys, flip them over front to back and re-install them. Then align the 110° IN dot on the front of the INtake pulley with the 110° EX on the front of the EXhaust pulley.

"IF" your priority is optimal performance (design correct cam timing), then nothing you currently see on the front of your cam pulleys will get you there. Both pulleys need to be flipped over, front to back, before timing the cams.

Whenever you plan to be rotating the cams (playing with timing, or measuring valve clearances), first set the crank to 90° BTDC. That puts all the pistons half way down their bores, far away from all the valves. Then you can rotate the cams without risk of running into pistons and bending valves. When you're done messing with the cams, first align the correct timing dots "ON" the imaginary center line between the cams, then bring the crank back up to TDC. Now the timing belt can be installed and tensioned.

Tim Engel

Attachment: cjwilson - Cam Timing - Cam Timing Marks - Notes, 94kb.jpg (Downloaded 118 times)

Last edited on 06-02-2019 07:28 pm by Esprit2