G80CS camshafts

Hello all,
I am in the process of dialling in the camshafts on a 65 G80CS.
I have a dti set up directly on the pushrod.
At what lift should I take the reading from the degree disc?
The cam gear wheels have a dot and also a double dash mark also.
I have set up to the dots as per Ken degroome article but would like to see what the degree disc reads.
Cheers

What does the workshop manual say?

The workshop manual is unclear in regard to the very late cams, part no’s
030124, 030125.

AMC always specified valve timing for given pushrod clearance and valve .001" off its seat (note: rocker ratio!) to clear the quietening ramps at the camshafts. You need a post-1962 rocker box to dial in your CS engine accurately. Make sure you have the correct parts.


(Extract from: F.W. Neill - AJS & Matchless Single Motorcycles. Lodgemark Press Ltd.)

If you know what the valve timing should be and you have a way if fine adjustment, I would set the clearances to about 10 thou and set the cam to the specified closing point for the exhaust valve. Then rotate the crank backwards and check the inlet valve opening point. The closing point for the exhaust valve should be around 60 degrees ATDC, and the opening point for the inlet valve should be around 60 degrees BTDC. Then set your tappets to the clearances specified for running the motor and check for errors in both opening and closing points. The overlap of around 120 degrees is more important, the inlet opening point is the most important.
If the inlet and exhaust cams are independent, the job is easier. If they are on the same shaft, I would try to get the inlet points set to specification with any errors to be more advance.

If memory serves, with the timing cover off you can get a dial indicator on the tappets themselves but it sounds like you've got that work out. Plus you can also get a degree wheel on it then.

FWIW it's possible to get confused with the various dots. I was struggling to get it right one night after closing up the shop and having a couple of beers when my girlfriend who was visiting pointed out that if the cams were geared 2:1 from the crank and it fired every other revolution as I had patiently explained, then the cam lobes should be at 90 degrees to each other not 180 degrees as I had them, even though the marks lines up. Dope slap to the head! Duh! She was a Dr. who ran a molecular biology lab at the U across town. I shouldn't have let her get away. My bad. After changing it the marks still lined up.

There are several cams floating around, or were once. I have two HS, or SH depending on how you look at it, that I've run for years for scrambles and general dirt riding. They provide good torque and will spin a big knobby coming out of the corners. I have also used the CE cam, which I believe is the cam F. Neil refers to as used for sprint events. I still have one of those but it's pretty lacking in bottom end. I'd like to try the C1 cam to compare but don't have one. I once had a 57 G80cs that had been modified by the local race shop -- Pat's Top Hat Cycle in Seattle. It had C1 and CE cams and lightened valve gear with tuliped valves and coil springs with light alloy (maybe magnesium) retainers. I only ever ran it on the road. It would spin up really easily to the point it would throw the windings out of the generator.

I've never bothered to degree them as I don't know what I would do to change the timing anyway.

mdt-son said:

AMC always specified valve timing for given pushrod clearance and valve .001" off its seat (note: rocker ratio!) to clear the quietening ramps at the camshafts. You need a post-1962 rocker box to dial in your CS engine accurately. Make sure you have the correct parts.

View attachment 115531
(Extract from: F.W. Neill - AJS & Matchless Single Motorcycles. Lodgemark Press Ltd.)

Click to expand...

Thanks for the reply.
I have seen that info previously but it does not refer to the cam numbers that I have.
Certainly, if I new the rocker ratio, that would be a great help.
There is a guy on YouTube with a cut down rocker cover that allows a dti to sit on the valve. Unfortunately I don’t have this.
I’ll get there eventually.

Bigduke said:

I have seen that info previously but it does not refer to the cam numbers that I have.
Certainly, if I new the rocker ratio, that would be a great help.

Click to expand...

Here is an extract off the 1968 G80/85CS scrambler's manual. As expected, dial instructions are identical to the 1960 type engine.
That's no surprise, as the valve gear is just a worked-over version of the 1960 type valve gear referred to in Neill's workshop manual.
As for the post-62 rocker arm ratio, you may ask in the AMOC forum.

- Knut

mdt-son said:

View attachment 115550

Here is an extract off the 1968 G80/85CS scrambler's manual. As expected, dial instructions are identical to the 1960 type engine.
That's no surprise, as the valve gear is just a worked-over version of the 1960 type valve gear referred to in Neill's workshop manual.
As for the post-62 rocker arm ratio, you may ask in the AMOC forum.

- Knut

Click to expand...

Excellent.
Thanks again.

Bigduke said:

Excellent.
Thanks again.

Click to expand...

It refers to the valve timing figures in the technical section. Please can you tell what these figures are?

Here you are:



Timing hardly deviates from the SH pair of camshafts.

- Knut

Bigduke said:

Hello all,
I am in the process of dialling in the camshafts on a 65 G80CS.
I have a dti set up directly on the pushrod.
At what lift should I take the reading from the degree disc?
The cam gear wheels have a dot and also a double dash mark also.
I have set up to the dots as per Ken degroome article but would like to see what the degree disc reads.
Cheers

Click to expand...

I always use intake centreline on v8 cams and it is always provided on the cam card , it can be calculated , but here's a link to a online calculator https://www.summitracing.com/newsandevents/calcsandtools/summit-cam-timing-calculator
Once you have the centre line it's easy to set your dial indicator to max lift then backup you motor then rotate forward, use a figure like .050 before full lift take your reading then do the other side of the cam going down .050 take your reading , add them together and divide by 2 , because you have separate cams you can do the exhaust as well .
Make sure you've done your true TDC before you start . Cheers