DOHC Commando (2016)

I was thinking about how easy it would be to design a DOHC 4 valve cylinder head for a Commando with the cams driven by a chain up the timing side as per G50 Matchless. The next thought was how would you justify the cost ? For road use you probably would not bother, and in Australia most development occurs in historic racing classes and by nature is limited. So a DOHC 4 valve Commando would be a bird without a place to roost.
I am wondering if there are motorcycle road racing development classes in the US or the UK ? Seems to me that the way out of an economic recession is to make something which is in demand. In our town, we have a very good library, yet there are almost no technical books. You can learn manufacturing techniques such as lost wax casting off Youtube - as long as you know what you are looking for. But as far as browsing for ideas is concerned, there is little opportunity. I would have thought that with our current recession, the arts and crafts people would be more active. We have several good engineering shops around our town, however no foundries or electroplaters.
This video is interesting even if it is a bit negative :
https://vimeo.com/26251563

There was a very recent thread on here on a dohc Commando, driven by a toothed rubber belt.

Should be just down the page.
You weren't paying attention ??
Probably need to be 40+ years ago to be anything like a paying proposition.

PS Triumph have just come out with a Bonneville 8 valve motor, said to be good stuff.
Fool injected too, of course.
They were paying attention to market driven demand....

My comment was more about basic economics. Perhaps if we had more development classes for old bikes, the outcomes might be transferable to road bikes and create new demand ?

If you produced a bike similar to this Velocette in Australia today, you probably wouldn't be able to race it unless it was a very close replica. I suggest that lack of flexibility is not helping our economy :
http://www.ma.org.au/index.php?id=593

Whats the market for this though - 2 or 3 bikes, maybe ?
Brilliant though it may have been at the time - with an enormaous amount of work...

With the new Triumph 8 valve, you can buy it out of the showroom, AND it comes with a warranty.
And with 50,000 of the previous model sold, its a paying proposition for the Maker and Dealers.
If you want an up-to-date bike for competition, KTM and any number of makers can oblige.

Rohan said:

PS Triumph have just come out with a Bonneville 8 valve motor, said to be good stuff.

They were paying attention to market driven demand....

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What? again, lets hope the are abit more reliable than the TSS was

In what classes do modern KTM road bikes race competitively these days ? BOTT showed promise years ago, however became dominated by water-cooled Ducatis. I suggest everything these days is Superbikes with all the attendant expense.

KTM are entering a MotoGP team next year, our Mr Bradley Smith is a pilot.

A few years ago we had a one-make road race class for Harley 883 Sportsters which might have under different rules, been able to accommodate KTM twins and all of the other old air-cooled twins, It died very quickly through lack of interest.

As the portings very efficent anyway , and we dont want to do 10.000 rpm ( some anyway :wink: ) there wouldnt be ANY POINT .

However a free bearing 4 valve twin might have a bit of snot . But doubt a AMC would .

Hi Acotrel

What market? We have new quality heads made for Commandos, potentially a good market. Eventually Falauto will break even , then maybe make a bit of money.
The market for a 4 valve head is tiny. Ask Les Emery. As to racing, why start with a Commando? One of my race bikes started as a battle of the twins bike until they allowed Ducatis.

Chris

Chris said:

Hi Acotrel

What market? We have new quality heads made for Commandos, potentially a good market. Eventually Falauto will break even , then maybe make a bit of money.
The market for a 4 valve head is tiny. Ask Les Emery. As to racing, why start with a Commando? One of my race bikes started as a battle of the twins bike until they allowed Ducatis.

Chris

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The idea seems to be that we invent a race class that allows this cylinder head, which is not yet even made, to become desirable. Ten design it, tool up for it, and sell it...

If successful, the market will boom, up to what, 30-50 heads max (failing to recoup even a fraction of the investment...

I doing so, we rescue the economy...

The idea is so implausible as to not even qualify as an idea...

Matt Spencer said:

As the portings very efficent anyway , and we dont want to do 10.000 rpm ( some anyway :wink: ) there wouldnt be ANY POINT .

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The 8-valve head developed for the Commando in the 80's as well as the new Triumph 900 street twin (2016) are good examples of engines which excels with high torque at low revs. The latter engine produces 80 Nm torque @ 3230 rpm! Peak power output is 55 PS / 54 BHP (40.5kW) @ 5900rpm. CR is 10.55:1 . Compare these figures with the 828cc Commando motor: 76 Nm torque @ 5000 rpm and peak power of 51 PS / 53 BHP (38 kW) @ 5800 rpm. CR is 8.5:1 .

It's all about how your design envelope is set. Conventional tuning measures would allow us to exceed the Street Twin's performance figures by increasing the CR, install bigger inlet valves, improve fuel/air mixing and upgrade to digital ignition and fuel management including detonation sensors. However, to increase torque _and_ lower the rpm @ peak torque, considerable improvements in the engine's breathing is required. For a 4 valve design, you will need a big bore/short stroke engine layout.

While these developments are challenging enough, the real challenge isn't the top end but rather the bottom end and the transmission. If you want a reliable bike, the entire driveline needs to be upped. With the altered bore/stroke parameters, a completely new engine would be required.

-Knut

I could see 8 valves being an upgrade, but DOHC cannot be fully exploited without a lot more RPM than a Norton engine can tolerate. So without going to a very short stroke to reduce piston speed and some major strengthening of the crankcase, a DOHC Norton is fantasy.

Danno said:

I could see 8 valves being an upgrade, but DOHC cannot be fully exploited without a lot more RPM than a Norton engine can tolerate. So without going to a very short stroke to reduce piston speed and some major strengthening of the crankcase, a DOHC Norton is fantasy.

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And then it's not a Norton, is it?

While I was at Norton, we tested a DOHC 750 engine, based on the Atlas/Commando engine, on one of the dynos in the Villiers test lab.

To minimise the amount of redesign effort, they kept the original camshaft drive sprocket and ran a chain through the former pushrod tubes up to the head. To get it to fit, they used a narrow chain, maybe 3/16". Since it was close to 36" long, It was too stretchy to maintain the valve timing accuracy and the engine never ran very well. The project was canned without the engine ever getting into a bike.

Was that the motor planned for the P11 back in 1965?

frankdamp said:

While I was at Norton, we tested a DOHC 750 engine, based on the Atlas/Commando engine, on one of the dynos in the Villiers test lab.

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This would have been the P10 project conceived by AMC's chief of design Charles Uddal. I am sursprised you say the engine was never fitted into a frame. At the National Motorcycle Museum near Birmingham (UK) a complete bike is on display. Apparently the bike was tested on the road as well but there were overheating problems. This is not surprising for a prototype.

https://www.flickr.com/photos/jorvikiwi/5162310475

Some more history on this project:
http://www.captain.norton.clara.net/cnn1sec8.html
http://www.ntnoa.org/History.htm

To say it's based on the Atlas is true as far as the chassis is concerned. Being a unit construction engine, the design bears little resemblance with the Commando apart from the slanted cylinder and head. Internals may be derived from the Atlas though. Camboxes remind of the Porcupine E95 engine.
I think the camshaft chain and overheating problems could have been sorted if development had progressed quicker, maybe with some outside help.

-Knut

NMM picture is not the motor described by Frankdamp.

What I was on about has more to do with the way our creativity is being stifled these days by the rules we impose on ourselves. To my mind, it would be possible to build a very good DOHC Commando, however what would we use it for ? It could be the 750cc equivalent of the 500cc Paton. Perhaps if we changed away from historic racing and more towards retro and improved historics, there would be more opportunity for creativity ?