Identifying a Combat motor

Karl Johnson · 2024-10-14T06:39:28-0600

Hi Folks. Kinda of a strange question, but here I go. A few years ago I bought a very much incomplete basket case 72 Roadster project that supposedly had a Combat motor. Hard to confirm the Combat motor, but it did come with a Combat head. Long story short, at the time I split the cases and replaced the bearings, etc. I neglected to check which camshaft was in there. Question is....are there ways to confirm whether the camshaft is a 2s without tearing down the motor? For the last couple years is been back on the road it's been really reliable with the twin Amal 932s and is happy with the valves set to .06/.08. I am aware that the Combat motor is meant to have the valves set to .10/.10. Haven't tried loosening them up to check. I'm thinking I may have a standard Commando cam in there, but thought I would see if there was a way to confirm. At the end of the day It doesn't matter to me. Just curious more than anything else. Thanks

batrider · 2024-10-14T06:49:26-0600

Combat valve specs are .008" for inlet and .010" for exhaust. You could check valve lift to see if it is the 2s cam. The rocker ratio is 1.13:1.

Karl Johnson · 2024-10-14T12:08:51-0600

batrider said:
Combat valve specs are .008" for inlet and .010" for exhaust. You could check valve lift to see if it is the 2s cam. The rocker ratio is 1.13:1.

Thanks for the info. I'll see what I can do to check that out

Stephen Hill · 2024-10-14T12:30:35-0600

The valve clearances won't help you identify the cam.
You will primarily be measuring maximum cam lift.
Details found here: http://atlanticgreen.com/camsurvey.htm
I went through this recently. Fortunately I had the head off and which meant I could disregard rocker ratios and read lifter motion directly. I still found it fiddly.

Fast Eddie · 2024-10-14T12:53:57-0600

The 2S (Combat) cam has a lot more lift on the inlet vs the exhaust, so a quick way of ruling out a standard cam, and indicating a possible 2S cam, is to check if the inlet has more lift than the exhaust.

Karl Johnson · 2024-10-14T14:56:02-0600

Stephen Hill said:
The valve clearances won't help you identify the cam.
You will primarily be measuring maximum cam lift.
Details found here: http://atlanticgreen.com/camsurvey.htm
I went through this recently. Fortunately I had the head off and which meant I could disregard rocker ratios and read lifter motion directly. I still found it fiddly.

Thanks for that. I'm thinking it may be best to simply wit until something happens or necessitates to need to pull the motor and split the cases. The mystery would be solved then.

MichaelB · 2024-10-14T18:39:43-0600

Karl Johnson said:
Thanks for that. I'm thinking it may be best to simply wit until something happens or necessitates to need to pull the motor and split the cases. The mystery would be solved then.

Why..

Fast Eddie said:
The 2S (Combat) cam has a lot more lift on the inlet vs the exhaust, so a quick way of ruling out a standard cam, and indicating a possible 2S cam, is to check if the inlet has more lift than the exhaust.

When this is fairly easy.
Set it on Center stand. Pull the tank, Plugs and valve covers.
Put it in 4th gear, rotate rear wheel observing the action.
Significantly more movement on intakes indicate a 2s, or not.
Set valve lash accordingly, done..

ILLF8ED · 2024-10-14T18:43:22-0600

Karl Johnson said:
Hi Folks. Kinda of a strange question, but here I go. A few years ago I bought a very much incomplete basket case 72 Roadster project that supposedly had a Combat motor. Hard to confirm the Combat motor, but it did come with a Combat head. Long story short, at the time I split the cases and replaced the bearings, etc. I neglected to check which camshaft was in there. Question is....are there ways to confirm whether the camshaft is a 2s without tearing down the motor? For the last couple years is been back on the road it's been really reliable with the twin Amal 932s and is happy with the valves set to .06/.08. I am aware that the Combat motor is meant to have the valves set to .10/.10. Haven't tried loosening them up to check. I'm thinking I may have a standard Commando cam in there, but thought I would see if there was a way to confirm. At the end of the day It doesn't matter to me. Just curious more than anything else. Thanks

You’re right….52 years later it doesn’t really matter. Combat was advertising hype in 1972. The combat acceleration at high rpm is somewhat breath taking however compared to the other original road tuned Commandos. My avatar is my early ‘72 combat built Dec ‘71.

B+Bogus · 2024-10-15T10:18:27-0600

One other less scientific method:
Does it take off like a scalded cat at 4k rpm?
The power delivery with a standard cam is fairly linear, whereas the Combat has a very definite surge around 4k (from memory - it may vary slightly one way or the other)

marshg246 · 2024-10-15T11:27:18-0600

If happy with bike, I would simply assume 2S, set the valves accordingly and not think more about it until you one day split the cases. As several have said it likely can be determined but you also have to consider that someone could have put in a 4S or any number of aftermarket cams so without more precise checking you still won't really know.

ashman · 2024-10-15T14:50:57-0600

If it runs well the way you been doing it I just leave it alone and ride it, enjoy it instead of worrying about it and just check the valve clearance when doing your oil changes, listen to how your motor is running, set the tappets at stock adjustments or in between stock and 2S adjustments if you are worried about it, just don't want tight clearances.

Identifying a Combat motor

Karl Johnson

batrider

Karl Johnson

Stephen Hill

Fast Eddie

Karl Johnson

MichaelB

"Sons of Arthritus"

ILLF8ED

B+Bogus

marshg246

ashman

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