Combat 2S camshaft in 1971 Commando cases

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Trying to stuff a Combat cam into a set of '71 cases results in negative clearance particularly on the intake lobes. Pretty sure this has already been done by others. Looks like the 72 cases don't have the "hoop" around the camshaft on the drive side cases. Additional clearance can be cut out of the cam tunnel but that's getting very close to the 1/4" stud at the front of the cases.

Should I fire up the hacksaw and die grinder or take a big step back?
 
I used a woodcutter mounted on a vertical mill.

Combat 2S camshaft in 1971 Commando cases


Combat 2S camshaft in 1971 Commando cases
 
Was done a lot in the olden days, I would imagine. I had it done on '67 P11 cases in the late 1980's. Of course, the first time I mentioned I had a 2S cam in a P11 engine here, I was told it wasn't possible to put a 2S cam in a Atlas motor. Gotta be careful who you listen to on the interweb.

I had the machine work done by people in the know. They told me I was nuts, but I wanted the motor to pull much harder above 4500 RPM, and it was either the 2S or something much larger back then. I didn't want a drag bike, I just wanted to chase Ducatis in the canyons of California. Only thing I did was shim the cam when I assembled the motor. It was a bit sloppy on the timing side in an Atlas case. One of the bushes may have had to be replaced as well. And the timed breather stuff was pulled, since the 2S cam did not support a timed breather then.

Have fun with it. Some tuning may be required, and you may need a better breather set up. Crank case pressure will kill the top end with that cam.

If you already know all that, oops. I do tend to rattle on.
 
Was done a lot in the olden days, I would imagine. I had it done on '67 P11 cases in the late 1980's. Of course, the first time I mentioned I had a 2S cam in a P11 engine here, I was told it wasn't possible to put a 2S cam in a Atlas motor. Gotta be careful who you listen to on the interweb.

I had the machine work done by people in the know. They told me I was nuts, but I wanted the motor to pull much harder above 4500 RPM, and it was either the 2S or something much larger back then. I didn't want a drag bike, I just wanted to chase Ducatis in the canyons of California. Only thing I did was shim the cam when I assembled the motor. It was a bit sloppy on the timing side in an Atlas case. One of the bushes may have had to be replaced as well. And the timed breather stuff was pulled, since the 2S cam did not support a timed breather then.

Have fun with it. Some tuning may be required, and you may need a better breather set up. Crank case pressure will kill the top end with that cam.

If you already know all that, oops. I do tend to rattle on.
Good point on the breathing - the '70 engine that I built was switched to 850-style breathing while I had it apart, the timed breather port was capped. I believe that the owner stuck with the 30mm carbs, and I do not remember if he ever re-jetted them (was over 15 years ago), but it was a strong, smooth runner.
 
Hi
Was done a lot in the olden days, I would imagine. I had it done on '67 P11 cases in the late 1980's. Of course, the first time I mentioned I had a 2S cam in a P11 engine here, I was told it wasn't possible to put a 2S cam in a Atlas motor. Gotta be careful who you listen to on the interweb.

I had the machine work done by people in the know. They told me I was nuts, but I wanted the motor to pull much harder above 4500 RPM, and it was either the 2S or something much larger back then. I didn't want a drag bike, I just wanted to chase Ducatis in the canyons of California. Only thing I did was shim the cam when I assembled the motor. It was a bit sloppy on the timing side in an Atlas case. One of the bushes may have had to be replaced as well. And the timed breather stuff was pulled, since the 2S cam did not support a timed breather then.

Have fun with it. Some tuning may be required, and you may need a better breather set up. Crank case pressure will kill the top end with that cam.

If you already know all that, oops. I do tend to rattle on.
Hi,
Excuse the basic question but what has a cam got to do with crankcase pressure?
al
 
I used a woodcutter mounted on a vertical mill.

Combat 2S camshaft in 1971 Commando cases


Combat 2S camshaft in 1971 Commando cases
Thanks, what dia did you machine to if you can recall? Didn't think of Forstner bits. I'm thinking 1.75" dia or maybe step up to 45mm.
My drill press is starting to look a bit like a mill.
 
Was done a lot in the olden days, I would imagine. I had it done on '67 P11 cases in the late 1980's. Of course, the first time I mentioned I had a 2S cam in a P11 engine here, I was told it wasn't possible to put a 2S cam in a Atlas motor. Gotta be careful who you listen to on the interweb.

I had the machine work done by people in the know. They told me I was nuts, but I wanted the motor to pull much harder above 4500 RPM, and it was either the 2S or something much larger back then. I didn't want a drag bike, I just wanted to chase Ducatis in the canyons of California. Only thing I did was shim the cam when I assembled the motor. It was a bit sloppy on the timing side in an Atlas case. One of the bushes may have had to be replaced as well. And the timed breather stuff was pulled, since the 2S cam did not support a timed breather then.

Have fun with it. Some tuning may be required, and you may need a better breather set up. Crank case pressure will kill the top end with that cam.

If you already know all that, oops. I do tend to rattle on.
Thanks, I figured that plenty of folks have put a "cam" in an Atlas or early Commando before Combat cases. I have a friend that also has a '71 Commando with some sort of hot cam in it. Never saw what had to be done to make it fit.

The breather will be much like this. https://www.accessnorton.com/NortonCommando/1972-oil-breather-problems.30211/post-488762
 
Hi

Hi,
Excuse the basic question but what has a cam got to do with crankcase pressure?
al
Atlas relied on a timed breather on the drive side case. The 2S cam I used did not support a timed breather, because it is not machined for it. When the breather function is removed, the pressure in the crankcase has nowhere to go.
 
This is what Paul Dunstall said in his tuning guide back in the late '60s or early '70s (no date on the document) about fitting a higher lift cam to the early cases.

Combat 2S camshaft in 1971 Commando cases


And his photo of the process.

Combat 2S camshaft in 1971 Commando cases


Ken
 
Thanks, what dia did you machine to if you can recall? Didn't think of Forstner bits. I'm thinking 1.75" dia or maybe step up to 45mm.
My drill press is starting to look a bit like a mill.
I measured a set of Combat cases at 42mm so used a 42mm carbide wood boring tool and check fitted the cam which rotated with no clash unlike before.
 
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I bored out an Atlas case to accept a PW3 cam. I used a mill with an adjustable boring head. I can't recall how much material I removed, but it wasn't a lot. I think the job could be done with a die grinder and a sharp burr.
 
Thanks all, with a little die grinder action the Combat cam now rotates freely in '71 cases. Didn't take much to make it fit. I'll do a final cleanup and wrap the lobes in tape for some extra deflection type clearance and check again.
 
A final followup in case anyone actually uses this thread for guidance in the future. For '71 barrels, you would be well advised to take a 0.060" bite out of the bottom of the lifter bores. The intake lobes in particular clashed with the bottom of the lifter bores but the exhaust lobes also needed a little extra clearance.
 
Before you fit the Combat cam, are you sure you have got the most out of the standard cam ? The 850 cam is later than the Combat cam and is still relatively hot for a street bike. I have the Paul Dunstall tuning notes and some of his stuff seems to be very dated. Especially when it comes to exhaust systems. Dunstall has got a name, but he raced a long time ago. In my background, I did a bit with Triumph 650s - the 850 cam is almost as hot as a Triumph E3134 race cam. The cam in my 850 motor has slightly more lift, but it is optimised to suit the 2 into 1 exhaust system. There are three keyways in my cam sprocket. I had the extra two broached in at random.
Fitting the Combat cam might be theoretically good, but it is what happens in practice which is more important.
 
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Before you fit the Combat cam, are you sure you have got the most out of the standard cam ? The 850 cam is later than the Combat cam and is still relatively hot for a street bike. I have the Paul Dunstall tuning notes and some of his stuff seems to be very dated. Especially when it comes to exhaust systems. Dunstall has got a name, but he raced a long time ago. In my background, I did a bit with Triumph 650s - the 850 cam is almost as hot as a Triumph E3134 race cam. The cam in my 850 motor has slightly more lift, but it is optimised to suit the 2 into 1 exhaust system. There are three keyways in my cam sprocket. I had the extra two broached in at random.
Fitting the Combat cam might be theoretically good, but it is what happens in practice which is more important.
The new 2S cam is not only fitted, but broke in so it's too late to go back now. I'm sure I could have gotten something more out of a bog stock 1971 750 Commando, but this fool just had to try and make a Combat outa it. Jeltz doesn't know anything about 850 Commandos. Never owned one nor ridden one either.
 
The new 2S cam is not only fitted, but broke in so it's too late to go back now. I'm sure I could have gotten something more out of a bog stock 1971 750 Commando, but this fool just had to try and make a Combat outa it. Jeltz doesn't know anything about 850 Commandos. Never owned one nor ridden one either.
The 2S is a good cam. Probably not the best, but definitely better than a stock cam if you want some upper end power. Mine seems to get happy above 4500RPM on my 750 Norton, but my motor is set up like it belongs on a 1 mile flat track, so I'm not sure that would be accurate for a stock engine. Anyway, enjoy it.
 
Before you fit the Combat cam, are you sure you have got the most out of the standard cam ?
Gotta come back and give this un a like. There are in fact performance improvements to be had and those were part of the plan. I've finished removing the single Mikuni VM34 and gione back to twin Amals. Next up could be the Boyer. Yeah the old Mk III/IV black boxes work, but these days there are much better options for an ignition. Who knows, maybe even a ham can.
 
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