Rebuilt RH4 head with Black Diamonds and flow tested. What is a reasonable price to pay?

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Fast Eddie said:
Below 3,000rpm it was difficult to judge either way, so my assumption is, backed up by riding it, that below that there really wasn’t much change. Hard to tell in reality of course, as when the throttle is opened, even from a standstill, 3,000 is past so quickly.

Above that there were substantial gains in torque and power everywhere. Biggest gains in torque were in the 4,000-5,000 region and the biggest gains in power were above 4,500. But there was more everywhere. Peak power was still same figure of around 6,250rpm which I found as a pleasant surprise as I had expected the point of peak power to increase up the rpm scale.

What was most interesting was to ride it back to back against my mates near stock mk111 (ham can, peashooters and EI being the only mods). There was just no comparison.
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You can get substantial gains just by cutting the valve seats properly. The port SHAPE and down angle is important, what happens on a flow bench, might not be directly replicated when the motor is running. Norton was involved in racing developing single cylinder four strokes for about 3 decades. So the port shape in the Commando engine is probably already very near the optimum. If you modified it and it became better, you would probably be very lucky. - Joe Craig was probably not simple-minded.
Do you think more down angle would be better, or is flow through both valves across the top, from inlet into exhaust at TDC, important ? It is on a two-stroke.
 
I don't believe there are any naturally fast riders - only fast motorcycles. The rider adjusts to the bike. If you got on Agostini's MV3, you would probably become nearly as fast, very quickly., as long as you were reasonably intelligent. It is always one step backwards and two steps forward. Agostini shaped the MV3 as he raced and stayed ahead of it. If you got on it you would adjust to the mould.
 
acotrel said:
I don't believe there are any naturally fast riders - only fast motorcycles. The rider adjusts to the bike.
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I'm going to join everyone that says that couldn't be further from the truth than almost any other statement I've ever seen made on this or any other forum.

Some people (myself included) can only be taught a certain amount of information that their brain and body cannot advance past. Even with a fast bike and a solid YEAR of intensive training, I don't believe I can ever get anywhere near even a back-marker pro rider.
 
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grandpaul said:
I'm going to join everyone that says that couldn't be further from the truth than almost any other statement I've ever seen made on this or any other forum.

Some people (myself included) can only be taught a certain amount of information that their brain and body cannot advance past. Even with a fast bike and a sold YEAR of intensive training, I don't believe I can ever get anywhere near even a back-marker pro rider.
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You could not be more correct there GP!

And I doubt it could have been put better.
 
acotrel said:
You can get substantial gains just by cutting the valve seats properly. The port SHAPE and down angle is important, what happens on a flow bench, might not be directly replicated when the motor is running. Norton was involved in racing developing single cylinder four strokes for about 3 decades. So the port shape in the Commando engine is probably already very near the optimum. If you modified it and it became better, you would probably be very lucky. - Joe Craig was probably not simple-minded.
Do you think more down angle would be better, or is flow through both valves across the top, from inlet into exhaust at TDC, important ? It is on a two-stroke.
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Joe obviously never went any where near a Commando.

I’m not sure how much port design is transferable from a cammy 500cc single cylinder GP race bike and a 750/850 road going twin, but I’m gonna guess it ain’t a lot.

The fact Norton had such different approaches to port design during the life of the Commando shows that whilst they definitely performed well, especially by the standard of the day, they certainly had no golden formula.

To suggest that a Commando head cannot be improved by any one of our current Commando specialist is staggeringly and factually proven to be WRONG.
 
grandpaul said:
I'm going to join everyone that says that couldn't be further from the truth than almost any other statement I've ever seen made on this or any other forum.

Some people (myself included) can only be taught a certain amount of information that their brain and body cannot advance past. Even with a fast bike and a sold YEAR of intensive training, I don't believe I can ever get anywhere near even a back-marker pro rider.
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Most learning depends on having a genuine interest in the subject matter. When you have that, learning is usually easier. My whole world view has been shaped by motorcycles. I am a scientist, but in everything I ever learned at tertiary level, there is a connection to motorcycles. As a scientist, I usually worked with engineering materials and processes. My whole approach to life is about development and progress. My motorcycle racing is a minor part of that. During my working life I was always studying, and and improving my competence. I never put limitations on my own ability to learn. Sometimes learning takes a bit of patience. If you can fix you own Commando, you probably do not have brain damage. So you cam learn anything which takes your fancy.
If you can ride your Commando and was handed Ago's MV3, you would probably learn to ride it very well, provided you had the interest. A big mistake which I made was in riding a shitter when I first started racing. I have got the brains to out-think a lot of guys during a road race, but if the bike crashes you - where are you ?
 
My Seeley 850 has become a very easy ride in recent years. The danger is that when you out- ride the fast guys on an old dunger, the danger is they start pulling desperates. IF you do it with something respectable the other guys are more likely to become resigned to their fate.
 
Seeley920 said:
And yet another thread gets derailed onto "my crappy Triton" and "My Seeley" :mad:
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Sorry to hijack the thread but the head was done by an old fella in Brisbane as a favour. He worked in the heads off the world's fastest na knucklehead. As I said, it was a favour and the guy who rebuilt my engine owns the knucklehead. I believe HD and S&S paid for him to go to the states to drag it just so they could see it. When I was kicking round the shop he was still holder of the title but no idea what know. I heard the thing fire up and it was really mean. Like black shadow with straight pipe mean.
From memory it was road registered so he road it to the drags. That should get me an extra hundred yeah?
 
acotrel said:
My Seeley 850 has become a very easy ride in recent years.
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I have been on this forum since 2013.

Have you ridden your Seeley more than 100m since then?

I ask this seriously because I cannot recall a single post of yours that isn't a "back in the day my Seeley" recollection.
 
acotrel said:
Flow testing is not usually done under sonic conditions. When the motor is running, there are standing waves in inlet ports and exhausts - you can hear them, so they are sonic.
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1. Flow in an intake port is for the largest part not at all supersonic but in the range of 0,5-0,6 (mean number) mach.
2. one can very well calculate the theoretical speed of gas in a port using the coefficient of discharge/flow
and if one would be very motivated could even take into accounts the pressure waves out of a P-V diagram.
3. over and over during the last 20years i hear that same old gospel that flow in an intake port is not static etc etc.
and the funny thing is for already 20-30years that are numerous SAE papers (i will refrain from quoting even older NACA papers) stating the exact opposite.
4. any serious head porter would definitely take into consideration Port flow area regarding cam events (Ivc).
So thats my 10 cents considering for the past +15years i have been porting mostly classic bike heads as well as the one or other Gixxer, KTM (being austrian myself) or Cossy.
5. Increase in gas velocity according to flow increase in regard to verifiable port area changes considering "pseudo static" flow can be calculated already by means of undergraduate text books on fluid mechanics.


All the best and kind regards

Christian
 
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EstuaryBoy said:
No (with proviso.. and apologies to OP for thread deviation) How many of us will ever NEED a new head? Yes, guides wear but if you have a running bike all is good, no?
Those wishing to 'upgrade'.... different story...
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I fitted new guides to a Commando head once. And A65s and Tridents, the latter two distort the guides a bit with the crush on them. Norton's may be similar, so I only ever remove them if I'm doing the ports and need to get tools in there to cut. And by preference I put the old guides back in and have them K-lined because they last so much better, are precise and can be tighter fitting with nitrided valves. So if you wear guides and are not doing ports just K-lining is a good repair plus should you wear them out just replace the liner. It's also cheaper.
 
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