Converting RH4 head to RH10

I'm helping someone reduce his RH4 port diameter from 32mm to 30mm with sleeves as shown below. It won't prevent cracking at the valve guide hole but with a little more finessing on both ends of the tube it should increase port velocity and flow.

The black mark is to align and butt it up against the guide because that end is shaped to fit the port (guide is removed in photo). The bottom side of the tube extends and blends to the radius near the valve seat.

Just wondering out loud. Could you have the insert sit a little proud of the manifold flange so that it projected into a 32mm heat insulator a little to reduce some of the angle changes?

marshg246 said:

Just wondering out loud. Could you have the insert sit a little proud of the manifold flange so that it projected into a 32mm heat insulator a little to reduce some of the angle changes?

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On this bike it has rubber manifold boots and the heat insulators are not needed or used.

jseng1 said:

On this bike it has rubber manifold boots and the heat insulators are not needed or used.

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What does it look like on the valve side? Just a 90 degree end?

jseng1 said:

I'm helping someone reduce his RH4 port diameter from 32mm to 30mm with sleeves as shown below. It won't prevent cracking at the valve guide hole but with a little more finessing on both ends of the tube it should increase port velocity and flow.

The black mark is to align and butt it up against the guide because that end is shaped to fit the port (guide is removed in photo). The bottom side of the tube extends and blends to the radius near the valve seat.

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The taper on the needles in the carburetor are designed to compensate for loss of vacuum. Loss of vacuum is more likely to happen in larger ports. But it depends on the cam which is used and the limit which is imposed to the top of the usable rev range. The Command crank is designed to be smooth, probably at about 4000 revs. If it is rebalanced to 70% by fitting a steel plug in the hole, it will be smooth at 7000 RPM, and you would be less likely to lose vacuum. The trouble is, the bike would be less useful for commuting.
Big ports were probably better when used in an Atlas than a Commando. An Atlas can rev regularly to 8000 RPM without cracking crankcases.
If I had a road-going Commando with that head, I would rebalance the crank and find other ways of improving torque, rather than sleeving the ports.
If you fit slower taper needles into the carbs without changing anything else, you might find the bike would be quicker. All that usualy happens if the taper on needles is too lean, is you need to exercise a bit more control as you use the throttle. When the taper is too rapid, the loss of power is often not detected, because the bike still performs OK, when the mixture is a bit rich. But when the mixture is right, the difference is significant.

t ingermanson said:

What does it look like on the valve side? Just a 90 degree end?

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Still refining the valve side. Tho photo below was the 1st attempt. The tube was chamfered on the OD on the valve end because the original RH4 port necks down a little near the valve. The port is 32mm but necks down to around 31.5 about a half inch from the valve seat. Next try I'm going to try turning down the OD on the valve end of the tube a tad so it inserts to about 1/4" from the valve seat and then chamfer the ID of the tube so it blends tighter with the port. The angle cut is so it clears the guide. Its important to raise the port floor and broaden the radius leading up to the valve seat.







Or it may work best just to cut it 90 deg and chamfer it on both ends to give a little venturi effect leading up to the guide. This is an experiment and won't prove itself until it hits the street or track.

I might be superstitious, but I believe Norton know a lot about port shapes and sizes. I might be arrogant if I ever thought I knew better. Experimentation might stuff a good head. What really amazes me about my 850 motor, is it is so right in so many ways, which I did not expect. Even the heavy crank is not stupid. With a close ratio gearbox, it works very well.
I think that with the Commando, the engine was designed by motorcyclists, the rest was designed by car guys.

You are a wild and crazy guy. I mean that with respect for somebody that thinks outside the Norton box.

What will happen at the floor where the tube ends?

What carburetion is planned for this experiment?

Schwany said:

You are a wild and crazy guy. I mean that with respect for somebody that thinks outside the Norton box.

What will happen at the floor where the tube ends?

What carburetion is planned for this experiment?

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I'm still working out the details but have something I'm pretty happy with now. Both ends are gradually chamfered on the ID so they blend with the port - same on the port floor. The floor of the sleeve extends further than the top so it reaches and blends with the curve at the valve seat. The area around the sides of the guide is not restricted by the sleeve. This bike already has a set of JS Keihin Smoothbore carbs.

The sleeve at the port floor showing the factory cut valve seat at bottom, the radius near the seat and the end of the sleeve. Difficult to photo and the depth perception is off.

acotrel said:

I might be superstitious, but I believe Norton know a lot about port shapes and sizes. I might be arrogant if I ever thought I knew better. Experimentation might stuff a good head. What really amazes me about my 850 motor, is it is so right in so many ways, which I did not expect. Even the heavy crank is not stupid. With a close ratio gearbox, it works very well.
I think that with the Commando, the engine was designed by motorcyclists, the rest was designed by car guys.

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If everyone felt that way, Al, there would be no improvements in design or development over time. There are very few designs of mechanical devices that don't have room for improvement, particularly in light of new developments in material science and technology.

Ken

If it gets any thinner, you'll be able to shape it with finger pressure.

Looks good.

What are you going to use for sleeve adhesion inside the port?

lcrken said:

If everyone felt that way, Al, there would be no improvements in design or development over time. There are very few designs of mechanical devices that don't have room for improvement, particularly in light of new developments in material science and technology.

Ken

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And the facts that Norton were woefully short on development budget at the time AND bikes were built down to a cost.

acotrel said:

I might be superstitious, but I believe Norton know a lot about port shapes and sizes. I might be arrogant if I ever thought I knew better. Experimentation might stuff a good head. What really amazes me about my 850 motor, is it is so right in so many ways, which I did not expect. Even the heavy crank is not stupid. With a close ratio gearbox, it works very well.
I think that with the Commando, the engine was designed by motorcyclists, the rest was designed by car guys.

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That’s an odd comment coming from someone with so little Norton left in his Norton !

Schwany said:

If it gets any thinner, you'll be able to shape it with finger pressure.

Looks good.

What are you going to use for sleeve adhesion inside the port?

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Only the very edge is thin, it seems fine and not subject to damage. We can just use high temp silicone to hold it in if we want it to be removable. But probably red loctite because its impervious to ethanol/gas fuel.

With the sleeve there is still room for some port work around the guide and into the bowl - to raise the roof at that point and direct the flow more directly downward around the circumference of the valve.

The left blue image of Nascar ports below is an exaggeration of the direction I'm trying to go - a venturi leading up to a "Cobra head" shape.


The black mark in the photo below shows where a small amount of metal will be removed - shaped, smoothed and blended of course. I've already applied this port shape to my 750 cafe racer with excellent results. CR Axtell used to do something similar and his motors were rockets.

Jim,

Sorry for the ignorant question, but why not use the high temp epoxy putty that's used by some to smooth out the edges, toward the valves? I'm very interested as I've got a 650 head with 32 inlets that needs to be shrunk back down to something realistic.

t ingermanson said:

Jim,

Sorry for the ignorant question, but why not use the high temp epoxy putty that's used by some to smooth out the edges, toward the valves? I'm very interested as I've got a 650 head with 32 inlets that needs to be shrunk back down to something realistic.

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Unfortunately epoxy starts to melt with ethanol.

jseng1 said:

Unfortunately epoxy starts to melt with ethanol.

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Roger.