Cam type?

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Wonky

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How can I identify what type of cam I have installed? I want to set the timing correctly but don't know what's inside?
 
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Thread 'Identifying a Combat motor'

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...
 
Wonky said:
How can I identify what type of cam I have installed? I want to set the timing correctly but don't know what's inside?
Click to expand...
Do you mean you want to set the cam timing?

Unless your racing I'd just set the cam timing as per the book.

Are you concerned about what tappet clearances to use ?

If it's ignition timing your worried about the CR is more important for that. But Commandos are pretty insensitive to ignition timing unless your using exotic fuels. So again I'd set it up at the standard.

If you really are concerned about what cam is installed then you could try using a dial guage on the valve retainer and a degree disc on the crank and measuring the lift curve. That's a bit messy but can be done. You would need to back out the 1.13 rocker ratio on the inlet. Can't remember the ratio for the exhaust. 1.1 ?

Here's a photo doing this on an AJS 7 R motor to give you the general idea about how to do it.
 

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If the possibly is only standard cam or combat an exact measurement of intake versus exhaust lift isn’t needed. Only if the intake is more than exhaust to indicate combat profile. The rocker ratio for both intake and exhaust is the same at 1 to 1.3.
 
If I did not know what cam I had in a road bike, I would set the exhaust valve opening point to be about 78 degrees before bottom dead centre. A racing cam usually opens there but it gives an earlier inlet valve opening point than for a road cam. The valve closing points are less significant. All that happens if the cam is too advanced is the power band might shift slightly and fuel consumption might change a bit.
 
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ILLF8ED said:
If the possibly is only standard cam or combat an exact measurement of intake versus exhaust lift isn’t needed. Only if the intake is more than exhaust to indicate combat profile. The rocker ratio for both intake and exhaust is the same at 1 to 1.3.
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With respect I'm pretty sure your wrong.

I'm almost certain it's 1.13. Ie 13 % extra on the inlet due to the lenght of the rocker arm asymmetry

And I'm almost certain the exhaust is different. 1.1. Ie 10 % extra due to the asymmetry.

Pleased to get confirmation from someone who has actually measured it.
 
johnm said:
With respect I'm pretty sure your wrong.

I'm almost certain it's 1.13. Ie 13 % extra on the inlet due to the lenght of the rocker arm asymmetry

And I'm almost certain the exhaust is different. 1.1. Ie 10 % extra due to the asymmetry.

Pleased to get confirmation from someone who has actually measured it.
Click to expand...
Cam type?


Workshop manual.
 
I do remember the 1.1 ratio for the exhaust so I searched my old files and found it in my copy of the Dunstall tuning guide, camshaft design - 1.1 exhaust and 1.13 to 1 for the inlet - as the valves lift.
 
hybridracer said:
I do remember the 1.1 ratio for the exhaust so I searched my old files and found it in my copy of the Dunstall tuning guide, camshaft design - 1.1 exhaust and 1.13 to 1 for the inlet - as the valves lift.
Click to expand...
Are you saying that the workshop manuals (both 00-4224 and 065146) are wrong or that Dunstall had something different or that the Dunstall tuning guide is wrong?
 
marshg246 said:
Are you saying that the workshop manuals (both 00-4224 and 065146) are wrong or that Dunstall had something different or that the Dunstall tuning guide is wrong?
Click to expand...
andover-norton.co.uk

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

4 different rocker arms of two different lengths is what I have always believed. Right or wrong.
 
I'm going to have to dig some out and measure them. But I can't do it in the next couple of days.
 
SteveA said:
andover-norton.co.uk

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

4 different rocker arms of two different lengths is what I have always believed. Right or wrong.
Click to expand...
Yes, all four are different. What's being discussed is the ratio of the length of the short arm verses the long arm of them.
 
marshg246 said:
Yes, all four are different. What's being discussed is the ratio of the length of the short arm verses the long arm of them.
Click to expand...
Exactly. I'm going to have to dig some out and check.

From memory the exhaust and inlet lengths certainly look different. But thinking about it the small difference from 1.1 to 1.13 is not going to be picked up by casual inspection.

Maybe it's one of those things I read and have been carrying about in my head for 30 years.
 
The early rockers are different widths. The ratio is taken from the radius of the valve adjuster in a specific position, not that it matters much as it would only affect the ratio by 7 - 10 thou or so. Personally, it is this reason I like the Combat pushrods which are 0.040'' shorter than standard, next time my engine is apart these will be going in. A tiny change, but it will allow the rockers to 'sit back' a little and allow the adjuster to be screwed out slightly further onto the valve tip.
 
Madnorton said:
The early rockers are different widths. The ratio is taken from the radius of the valve adjuster in a specific position, not that it matters much as it would only affect the ratio by 7 - 10 thou or so. Personally, it is this reason I like the Combat pushrods which are 0.040'' shorter than standard, next time my engine is apart these will be going in. A tiny change, but it will allow the rockers to 'sit back' a little and allow the adjuster to be screwed out slightly further onto the valve tip.
Click to expand...
I thought Combat motors were fitted with standard length pushrods, hence they need shortening to maintain the correct geometry; there aren't any Combat specific pushrods listed in the parts book
 
B+Bogus said:
I thought Combat motors were fitted with standard length pushrods, hence they need shortening to maintain the correct geometry;
Click to expand...

That is correct but AN sells the shorter Combat pushrods now.
andover-norton.co.uk

Andover Norton - PUSHROD (INLET) COMMANDO COMBAT 0.040’’ SHORTER THAN STD - ORIGINAL HOLLOW TYPE - 06.7940-040

PUSHROD (INLET) COMMANDO COMBAT 0.040’’ SHORTER THAN STD - ORIGINAL HOLLOW TYPE
andover-norton.co.uk
andover-norton.co.uk

Andover Norton - PUSHROD (EXHAUST) COMMANDO COMBAT 0.040’’ SHORTER THAN STD - 06.7941-040

PUSHROD (EXHAUST) COMMANDO COMBAT 0.040’’ SHORTER THAN STD
andover-norton.co.uk
 
B+Bogus said:
I thought Combat motors were fitted with standard length pushrods, hence they need shortening to maintain the correct geometry; there aren't any Combat specific pushrods listed in the parts book
Click to expand...
They were, but "need shortening" was not a factory thing and came later by owners as best I can tell. The service release N2/03 (https://gregmarsh.com/MC/Norton/Info/SR/N2_03.aspx) talks about spring binding and using a thinner bottom cup, but AFAIK, it's the only issue with some Combat engines.

IMO, the shorter pushrods improve adjuster/valve the geometry at full open but are not required.
 
marshg246 said:
Are you saying that the workshop manuals (both 00-4224 and 065146) are wrong or that Dunstall had something different or that the Dunstall tuning guide is wrong? When I was checking my cam lift at cam lobe then rocker the ratio was as the factory manual said for both standard camshaft and combat.
Click to expand...
Greg,
Just checked the Dunstall tuning book. Page 17 does say rocker ratio 1.1 exhaust and 1.3 inlet. Either the factory manual or the Dunstall book is wrong or Dunstall used their own custom rockers.
 
ILLF8ED said:
Greg,
Just checked the Dunstall tuning book. Page 17 does say rocker ratio 1.1 exhaust and 1.3 inlet. Either the factory manual or the Dunstall book is wrong or Dunstall used their own custom rockers.
Click to expand...
If I weren't laid up, I would measure some to put an end to the question. Hopefully, I'll get back to the shop soon - I'm way behind on projects :mad:
 
B+Bogus said:
I thought Combat motors were fitted with standard length pushrods, hence they need shortening to maintain the correct geometry; there aren't any Combat specific pushrods listed in the parts book
Click to expand...
Yes, they were, but I'm sure I have read somewhere that the engine when it was an option had shorter push rods, by the time it became a standard fit then it used standard length push rods. Remember, the Combat engine was an option quite some time before it was fitted as standard.
 

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