H.P mods ?

myjota said:

don’t worry too much about porting, the early heads flow just as well as the later 32mm ports. 32mm Amal’s on tapered manifolds.

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FWIW
At the 92 INOA rally , on dynoday shootout, My combat out performed every declared stock bike including other combats. I did 47RWHP over stock 750s 38-42 hp and 85s about 40-45. I was actually(cheating) running a RH1 28.5mm port head with my combat carb setup 32X32 manifolds.

K
Actually a megacycle 560NR or web 132 is probably a bit gentlier on the intake valve springs than a 2S combat cam.
You can see them all on my website library http://atlanticgreen.com/

Remember that these engines were pushed out to well beyond the original design of the late 1940's. Expecting noticeably more power AND (street) reliability is not realistic. Don't pay any attention to what race motors can do. Race motors can blow up a foot beyond the finish line... In fact, a famous drag racer once said that's how he knew he was making the maximum possible power - when the engine blew just after the car went through the traps.

Knucles said:

MYJOTA , what is the difference between the stock cam and the combat cam ?
what differences do they make ?

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Standard cam is a great cam and was really a race cam for 650 engines, the 2s has a tiny bit more lift on exhaust and a lot more lift on inlet but duration is similar to standard. This cam gets a bad rap as it’s associated with the ill fated combat engine that was only really let down by its main bearings and poor attention to engine porting. Combat engine with properly dialled in cam and standard head is the way to go.

Thanks , I will check around and see where I can get the 2s cam ?

Knucles said:

MYJOTA , what is the difference between the stock cam and the combat cam ?
what differences do they make ?

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On the first page of the thread there is a graph with the stock and combat cams overlaid.

Knucles said:

Thanks , I will check around and see where I can get the 2s cam ?

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It's a very high lift Combat cam and makes the sound of the old Norton motor real angry. It's hot rod stuff.
Sold mine at Burlington Ont. C.V.M.G. Swapmeet for $80 to a very interested buyer. Then fitted the Std. cam.

Knucles, it would be beneficial to you if before you attemt to do any engine tuning, to run your bike on a rolling road and obtaining a digital printed readout . Then after you have reassembled the engine back together, repeat and see just how successful you had made it.

Ok , I will slow down till motor is at apart .

If I had to make a list of the top 10 items to make a Commando a quicker and overall better performing road bike, more HP would not be in the top 5.
A hotter cam wouldn't even make the list..

SteveA said:

Well over 40 years ago a Mr John Hudson wrote a series of tuning notes.

Doing what he recommended will go a long way to building a reliable motor able to deliver the performance available from the basic configuration.

Somewhere, possibly Dyno Dave had them, there is a copy of these notes online.

That will go some way to answering your questions, but....you would still be best placed to commit something to a list of requirements....what you want to achieve....targeted at the riding experience, not the build or bragging experience.

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Since no one else has, I'm providing a link to the most legible version of the above mentioned document I've found on the web.

http://www.billymegawatt.com/uploads/6/8/4/6/6846461/norton_750cc_service_notes.pdf

35 years ago, I owned both a Mk II 850 and a 72 Combat. My first Mk III I kept the engine stock, other than peashooter silencers, re-jetted carbs & balancing the engine. What say the gray beards, regarding installing a 2S cam in a Mk III engine? I ask, as I suspect when I Rockwell hardness test the cam on my 2nd Mk III, I may be in the market for a new camshaft. Andover Norton prices the standard cam & the 2S the same.

chaztuna said:

Since no one else has, I'm providing a link to the most legible version of the above mentioned document I've found on the web.

http://www.billymegawatt.com/uploads/6/8/4/6/6846461/norton_750cc_service_notes.pdf

35 years ago, I owned both a Mk II 850 and a 72 Combat. My first Mk III I kept the engine stock, other than peashooter silencers, re-jetted carbs & balancing the engine. What say the gray beards, regarding installing a 2S cam in a Mk III engine? I ask, as I suspect when I Rockwell hardness test the cam on my 2nd Mk III, I may be in the market for a new camshaft. Andover Norton prices the standard cam & the 2S the same.

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I had downloaded a copy of that set of notes. I think John Hudson's wisdom was carried over, but of course there is editing involved.

What I have is just John Hudson originated material with no editor I am aware of. I have seen somewhere online a copy of Johns notes exactly as I recall them in '75. I did download them, but they were lost in a typical home computer catastrophe! My wife typed them up on a small portable typewriter from a simple 1970s Roneo type spirit copier, there were no graphics at all, just text, and no photocopiers at work let alone home in those days!

Perhaps what I should do is cross-check the words attributed to Mr Hudson, at first glance, the main issue is ordering of comments, obviously the editor has applied what he sees as a logical order, why not when aligning material from various sources.

Regarding your cam, the choice is of course yours. Many will tell you what an excellent cam the standard item is (including John Hudson). Having both raced and toured a 750 with small ports and a standard cam I can only agree with those comments. If your MkIII cam has lasted this long there is hope for it continuing.

I would go back to what I said earlier, clearly state your requirements and be brutally honest with yourself! Why would a 2S cam improve your riding experience 35 years on? It clearly works for some as they tell us about it.

When selecting cams for circuit race bikes it comes down to variations on two themes, PW3 or 2S! Bearing in mind that 4S is a variant of 2S, as are several of the cams mentioned here over the years I have been a member.

In my current race motor I have run an actual PW3 and two variants on the 2S theme. I enjoyed the PW3 most and want to go back that way, but I have no doubt the 2S and variants work well!

For a road bike I am pretty sure I would install a standard cam!

I think you have a choice. Either keep your bike as near standard as possible - or do the full bit. A converted road bike is rarely ever a good race bike. And going in the opposite direction is really stupid.

I found this info from Comnoz with a search on the subject. Even if Jim is busy with other things at the moment, we can do reruns and they are still informative.

I'll try again this way- Jim Comstock said


"I have never installed a "race" cam in a Norton and experienced an increase throughout the rev range. Only an increase in it's ability to rev.
Only an increase in compression ratio ever brought the midrange back close to what is was before.

Of course the seat of the pants feeling and the dyno didn't always agree but a spirited run up a mountain pass will agree with the dyno.
Jim"

There are many paths to enlightenment...

The stock cam is a good path... However I gotta step in here before this generates into an ‘all performance cams are evil’ thread and defend the fact that there are other equally enlightened paths...

If someone were to stick a race cam into an engine (any engine) and do nothing else, the results will range from disappointing to dire. No arguments there !

But, JC also said in another thread, dynoing each individual change is a waste of time because tuning is about ‘the package’.

I‘ve ridden stock 850 Commandos, they’re bloody great, and more than enough for most owners requirements most of the time. But, my tuned 850 had more bottom end, more mid range roll on, and (way) more high rpm power than my mates low miles 850 that was stock apart from EI and peashooters. Mine just left his for dead in every scenario we tried. And it continued to do so when we swapped bikes. It produced peak power at less than 6500rpm and I seldom went over 6000rpm as the torque / power spread just didn’t warrant it.

The biggest single improvement came from having a JC head job on the RH10. But that wouldn’t have yielded the same gains on a stock bike. It enabled the carbs / cams / CR changes to actually work to their design / potential.

Do I still run this highly unsavoury engine in my bike? No, of course not. I ‘saw the light’ and swapped it out for a full race spec Maney 920 lump...

And THAT thing is a real hoot.

Fast Eddie said:

I gotta step in here before this generates into a ‘all performance cams are crap’ thread.

If someone were to stick a race cam into an engine (any engine) and do nothing else, the results will range from disappointing to dire. No arguments there !

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I believe the OP was headed in this exact direction a few posts back ( "I'll start looking for a Combat cam)
Just trying to head him off at the pass, although it looks like the other cowhands got there first.
I don't doubt that an all in engine can make more power in the midrange too, or at least as much plus give more on top. But I'm doubtful that an all in engine can hang together for high mileage, unless we toss out everything Norton and start again.
That would be cases, crankshaft, cam, lifters,rods,pistons, and transmission. About the only Norton part remaining is the head minus internals and the head at this point is highly modified.
I've been tempted to try this route but, as you know better than anyone, it's very expensive.
So if one is going to build a roadgoing Norton using mostly Norton parts, I think you logically end up back at the stock cam profile every time. You don't always have to be completely logical though!
Maybe some prefer to drop a bit in the middle in exchange for a more thrilling top end, more of an actual power band where you really feel it come on strong.

Glen

This fixation on HP and 1/4 mile ET must be typical American.
I frequently ride in the mountains with friends on bikes with 2 -3 times more HP.
My Commando is modified, but engine tune is basically std.
If occasionally I fall behind (mostly on bumpy roads ) it is not because of lack of HP, but because they have better suspension, traction control, ABS, etc.. or simply because they are better riders.
It reminds me of an event some years ago. Long story.
I won't hijack this tread, but start a new one in 'Motorcycle related'.
Maybe tomorrow..

Yes, twisty roads are a good HP equalizer, as long as your tires, suspension, and tune-up are in good shape.

ludwig said:

This fixation on HP and 1/4 mile ET must be typical American.
I frequently ride in the mountains with friends on bikes with 2 -3 times more HP.
My Commando is modified, but engine tune is basically std.
If ocasionally I fall behind (mostly on bumpy roads ) it is not because of lack of HP, but because they have better suspension, traction control, ABS, etc..
It reminds me of an event some years ago. Long story.
I won't hijack this tread, but start a new one in 'Motorcycle related'.
Maybe tomorrow..

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Increasing HP is intended to increase the power to weight ratio.

You just arrived at the same point from the opposite direction Ludwig !

(for those who don’t know, Ludwig’s bike with him on it is probably no heavier than a stock mk111)

worntorn said:

I believe the OP was headed in this exact direction a few posts back ( "I'll start looking for a Combat cam)
Just trying to head him off at the pass, although it looks like the other cowhands got there first.
I don't doubt that an all in engine can make more power in the midrange too, or at least as much plus give more on top. But I'm doubtful that an all in engine can hang together for high mileage, unless we toss out everything Norton and start again.
That would be cases, crankshaft, cam, lifters,rods,pistons, and transmission. About the only Norton part remaining is the head minus internals and the head at this point is highly modified.
I've been tempted to try this route but, as you know better than anyone, it's very expensive.
So if one is going to build a roadgoing Norton using mostly Norton parts, I think you logically end up back at the stock cam profile every time. You don't always have to be completely logical though!
Maybe some prefer to drop a bit in the middle in exchange for a more thrilling top end, more of an actual power band where you really feel it come on strong.

Glen

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You do exaggerate... only the head is still Norton

I’ll have you know that the whole, entire, complete, oil pump is too ...

But yes, I agree with most of that Glen. The 2S is a very radical cam, it was the full race cam in the day. But there are still many who swear by them.