Big valves or small valves

Time Warp

.......back to the 70's.
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This adds a whole new meaning to a 4 angle valve job, three on the valve seat and one on the steering head.
 
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I just heard from one of my customers that he has thinks the 1.5" valves will be too big for his 650SS and wants to return to 1.4" valves. So we're talking about remachining the 1.5" Kibblewhite valves to the smaller diameter (its been done before).
 
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That's my suspicion too.
I think Doug Hele, the designer of the 650ss head, was very clued in to valve size and port design for the rpm range used. That's why the 650s are such a hot little bike. It does have more valve per cc than an 850, but it also revs higher.
For the 750 Atlas, Hele increased intake size to 1.5" . This gives the Atlas and 750 Commando the same ratio of intake valve area to engine displacement as the 650SS.

I suspect the with the 850( 828), valve size isnt a big problem until you go for higher HP by moving the peak power level up. Stock 850 has max torque at 5000 and max HP at 5800.


Glen
 
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The old domni 500ss and 650ss offered the same size valves as Norton used in their 750s and 850s - 1-1/2 in and 1-5/16 ex. They just increased the bore and didn't bother enlarging the valves size to suit. See 500 and 850 pistons below.

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They should have upped the valve diameters - there's room for them and its what the bigger motors need.

Good evening Together,
As we all know the standard 850 Commando was NORTON‘s last effort to compete in the motorbike market, besides the Wankel or the Cosworth (both were underdeveloped or they didn'thave the cash to get the production started). But some reason that we all also know (no cash), unlike BMW they stuck to their oldish design of the well- known Commando.

While BMW developed a completely new engine around their old boxer- concept, Norton stuck to the outdated design with cast iron cylinder, the multi- piece crankshaft, which wasn’t only very flexible but also very expensive to produce, but also to the small valves of the 750- models.

All this doesn’t say that the BMWs had something new in their engines. Most of the development was also well outdated (the long push rods which made the valve gear rather flexible and so not very well suited to high revolutions/power output). And yet, they were good enough for some very interesting race successes.

Today the fastest BMW- boxer- engine I know is fitted with their traditional long- stroke crank, the short conrods of the R65/R45 engines and 48/42mm titanium valves. This engine was last ridden in a sidecar race at Spa/Belgium and was the fastest engine of the whole sidecar race. Oh yes, it has some very special porting, big 42mm BING carburettors (I think) and a special camshaft (Dr. Schrick???). It was built by the most famous BMW engine builder Dieter Busch. Ralf Engelhardt (the owner) told me that he can easily rev it to 10.000RPM (“but don’t tell Dieter”). And yes it has 1000cm².

I would have expected that NORTON’s would have done a similar thing to their engines, with bigger valves (maybe 41/36mm) a suitable and reliable aluminium barrel and a one- piece crankshaft, steel- conrods, maybe bigger big- end bearings and also plain main bearings. Yes, this development would have done them for another 20/25 years, as it did with BMW (from the first R50/5 well up to the last R 100 R Classic. No, we all know that they were in financial trouble (likewise BMW at the time, by the way) and so a complete re- design was out of reach for Norton. They went to Cosworth instead and went into real trouble. Who wanted the Cosworth or the Wankel??? I didn’t.

I myself did a lot of design- work on the NORTON cyl.- head and found that (just geometrically) in the 850cc engines 43/36mm valves can rather easily be fitted. The problem is the porting. You cannot easily raise the port- roof because you break through into the rocker- box (valve- spring seats), or on the right handside into the oil return- bore. So, all you can do is go sideways equal values to the right and left of the valve centre- line. One more thing one can do, is fit bigger valves (41/36mm) and align the ports to these bigger valves as precisely as you can.

You will find a problem with the rather big outer diameters of the valve guides of the 850- or the RH8 750- cylinder heads. These have outer diameters of 5/8” (approximately 16mm). As we all know you will have to alter the valve- angles with the Norton heads to clear the valves during overlap. So, the outer diameter would end up to be at least 18mm. But there are solutions. If somebody is interested, I could send you a drawing how I deal with this problem.

There is even a way to deal with the break through into the rocker- box, if you raise the roof of the inlet port. I haven't done this yet and I won't it's too much work for an old guy like me.

All in all, there is still a problem with fresh gasses getting lost during the valve overlap, finding their way directly into the exhaust- port. But, look at Paul Dunstall’s solution or again a raised inlet port roof.

I’m now 71years old and racing is far away for me, but I still have the aim to give other motorcyclists with much more modern bikes a ride for their money. I want at least the same performance as a BMW R 90 S. That’s why my Commando has 41/36mm valves and flowed ports (made by myself), a long rod- conversion (which is another story) etc.

I do know that I can never catch up with BMWs on German Autobahns because with these bikes you can ride full throttle the whole day without any trouble which I wouldn’t try with any classic British bike. These were simply not made for this kind of torture. But especially a Commando can still keep up with most motorcycles on twisty roads, because of their sheer torque.

That’s currently my way of thinking about NORTONs today.

Best Regards

Klaus Monning
 
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.. I can never catch up with BMWs on German Autobahns because with these bikes you can ride full throttle the whole day without any trouble ..
or "Autobahnfest" , like they say in Germany.
Something a Norton will never be. Not even the new ones.
If, for sake of the argument, an 850 Commando had 100 HP from the factory out, we would still have the same discussion: " I like what I have, but would be happier if I had more.." ( power)
A different approach would be to accept what you have and try to use it more efficiently.
I believe it is a typical American way of thinking:
If in need, don't use less, but produce more..
 
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@Klaus Monning
Hallo Klaus, why don't you get the area in the rockerbox welded up in order to raise the port perhaps 1-3 needed millimeters?
I'd also assume (from my experience prepping various heads) that if you swing the valve outwards for bigger valve one achieves a way better SSR that will be less turbulence prone, with less need to raise the port roof.
I would have to look through my port molds but i remember that the commando head was not even that bad, but that the bend in the carb manifolds gave me shivers and stomachache just looking at it.
For the increase in guide outer dia. one could theoretically weld the guide hole shut and redrill it on the mill, but it's somewhat a torture chamber job with very little margin to err.

Herzliche Neujahrsgrüße

Christian

Ps: regarding the bush kneelers I think I remember that at least on the ones i saw that they were using huge Dell'orto SSI's.
But to be honest the 70's Beemer heads are even worse than Commandos with a 100degree faucet elbow turn right in the intake port.
 
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Hello Christian and All,
Yes, that exacly is my idea. Press- fit and weld a flanged bush that has a hole for a smaller diameter valve guide and weld it in place. One probably needs a longer valve or at least a valve where the grooves for the keapers are higher up in the shaft to compensate for the thickness of the flange. This solution is not finally designed or tested but I'm thinking to do so. After all, I'm a retired design (and sales)-engineer.
There is something I wanted to add to my above article:
The reader might get the impression that I am a BMW enthusiast. No, I'm not. The biggest and nicest difference of the NORTON is:
The NORTON has punch and the BMW what ever the volume is, has not. That's why I stick to the NORTON untill I can't kick it to life because of senility.
Good Night and keep healthy.
 
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Welding an alum tube into the valve guide bore for a smaller guide is no problem. Re-angling the new guide and machining through one side of the welded in alum tube is also not a problem. I have see ports with aluminum 1/2 tubes bolted to the port floor through the bottom (towards the valve seat end) to raise and re-shape the port floor. You can also weld it at the manifold side as shown (beginning of project).

93006209_10217572083153545_848280981835087872_n.jpg


92695210_10217572409961715_8193069344582795264_n.jpg
 
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During the 1960s a change happened in the motorcycle customer base. Many people rode motor scooters which kept their clothing cleaner. Others bought Mini Minors or Japanese motorcycles. Nortons had a problem - the riders' mindsets had changed and the old style 1950s' bikes became out-moded. No sane person really needa real motorcycle any more. Triumph's bathtub Thunderbird was an attempt to compete with motorscooters. As were Ariel Leaders. A complete rethink was needed. Norton made AN ATTEMPT with the Commando. But the Japanese won all the way to the bank. My methanol-fuelled T250 Suzuki racer would make my Seeley 850 look stupid on most race tracks. I chose to sell a very good Yamaha TZ350G to buy the six speed close ratio gear box for my Seeley 850.
- I must be stupid ? I road-race a motorcycle for enjoyment. If I owned a road going Commando, it would be for the same reason.
Harley Davidsons are good mile-eating road bikes. I once owned a 500cc Indian which did similar.
 
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So far valve size seems to being discussed relative to capacity , what about inlet choke diameter, that surely is important .
 
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@oldmikew
Did you say Jehova?
Just kidding that's what I ment with various parameters as correct inlet choke diameter is also depending on valve timing in particular Ivc.

Kind regards Christian
 

Fast Eddie

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So far valve size seems to being discussed relative to capacity , what about inlet choke diameter, that surely is important .
Depends what you mean…

Yes, valve size, along with everything else in ‘the system’ needs to be designed to work together.

But, big valves DO NOT necessarily mean big ports. This is where loads of folk go wrong, big ports = lower charge flow but lower velocity = more top end power at the expanse of reduce low and mid range power.

Folk often assume the same is true of bigger valves, but it is not.

My 850 RH10 head is an example, Comnoz flowed the head but most of the work was in the areas around the valves throat, the ports were NOT enlarged, the valves WERE.

The difference, before and after, on the same Dyno, + 9rwhp peak and more power and torque in the mid range too.
 
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@oldmikew
Did you say Jehova?
Just kidding that's what I ment with various parameters as correct inlet choke diameter is also depending on valve timing in particular Ivc.

Kind regards Christian

Christian
I am only trying to reference my own experience..The rm1 head was specified asbeing 28.5 mm choke and equiped with30mmmk1 concentrics.. I found a substantial performance increase by going upto 32mm mk1s... Sometime backin the 1980s when Jehova was still spelt Paul Dunstall and reading esewhere that the fastest 750s where post combat but with 32 mm ports., I followed suit.Possibly with a sight top end gain but the reults were disappointing. Perhaps as Fast Eddie suggested I should have fitted bigger valves and might yet try this
But mycurrent thinkingis to attempt to sleeve downto the original 28.5.
I am inthe slow process of building a Maney engine ,with Steves crank ,cam,head and cases so all out performance is not the objective fromy original 750engine .
 
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Depends what you mean…

Yes, valve size, along with everything else in ‘the system’ needs to be designed to work together.

But, big valves DO NOT necessarily mean big ports. This is where loads of folk go wrong, big ports = lower charge flow but lower velocity = more top end power at the expanse of reduce low and mid range power.

Folk often assume the same is true of bigger valves, but it is not.

My 850 RH10 head is an example, Comnoz flowed the head but most of the work was in the areas around the valves throat, the ports were NOT enlarged, the valves WERE.

The difference, before and after, on the same Dyno, + 9rwhp peak and more power and torque in the mid range too.

I started out with a bog standard 750 purchased new and assumed that evrything had been designed to work together, and onthis bog standard engine I found that 32mm carbs instead of 30mm gave a substantiall performance increase.... Contrary to expectation .theengine didnot respond as well to having32mm ports tomatch 32mm carbs . It has always puzzled me. It is hard to believe that at 32mm the 750 commando head is overported.
 

Fast Eddie

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I started out with a bog standard 750 purchased new and assumed that evrything had been designed to work together, and onthis bog standard engine I found that 32mm carbs instead of 30mm gave a substantiall performance increase.... Contrary to expectation .theengine didnot respond as well to having32mm ports tomatch 32mm carbs . It has always puzzled me. It is hard to believe that at 32mm the 750 commando head is overported.
According to Comnoz’ head flow testing 32mm is even too big for an 850, unless peak hp is the goal.

OEMs are juggling many things, performance is a compromise aimed at pleasing many different customers; commuters, tourers, third wheelers, racers, etc. Plus, of course, they’re made down to a price. Therefore, achievable improvements for individual needs are quite understandable.
 
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I started out with a bog standard 750 purchased new and assumed that evrything had been designed to work together, and onthis bog standard engine I found that 32mm carbs instead of 30mm gave a substantiall performance increase.... Contrary to expectation .theengine didnot respond as well to having32mm ports tomatch 32mm carbs . It has always puzzled me. It is hard to believe that at 32mm the 750 commando head is overported.
A step down from Carb to intake can work wonders.
I don't think the science has been explained. It's one of those things that just seems to work, although perhaps not on every engine type.
This gain with an oversized carb and step was discovered by the BSA Goldstar experimental tester Roland Pike, quite by accident. An assistant brought the wrong carb for a Goldstar, I believe it was a 350 and he fitted a 500 carb. The bike made extra power on the dyno. The mistake was discovered so they tried blending the manifold to the oversized carb ( step removed)
The extra power disappeared.
Put the step back in and the power came back.

Glen
 
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I started out with a bog standard 750 purchased new and assumed that evrything had been designed to work together, and onthis bog standard engine I found that 32mm carbs instead of 30mm gave a substantiall performance increase.... Contrary to expectation .theengine didnot respond as well to having32mm ports tomatch 32mm carbs . It has always puzzled me. It is hard to believe that at 32mm the 750 commando head is overported.
My 850 has 34mm Mk2 Amals on 30mm ports with the first inch of the ports tapered 2mm per side. The cam is nothing special but it is advanced 12 degrees and I have a 2 into 1 non-restrictive exhaust system.. But I use methanol fuel run very lean right down the needles with slightly over-rich main jets. In races, it is very difficult to stop from over-revving the motor. And the overall gearing I run is extremely high for the short circuit on which I usually ride. If you improve the midrange power of your motor, you don't usually detect an improvement until you raise the gearing. I run very close gearbox ratios with high gearing.
'Because I can' is never a good reason for doing anything. It is easy to make the ports in a Commando head bigger. Any idiot can do it.
When I ride my bike, I usually keep the revs between 5,500 and 7000 - even in the slowest corners. I never rely on throttle response. If you lose revs with a Commando engine, you will wait forever to get them back. So how you ride the bike is important. I try to never ride behind other guys in corners. If you go out on the ripple strips with them, you are playing their game. If your steering geometry is right, you can ride under them and much faster. Then the next straight is not so much of a problem. You can enter each straight going at least 10 MPH faster then everybody else, and it takes a lot of horsepower to make up for that.
 
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I think what happens in both exhaust and inlet ports is sonic. If you can hear it, it is sonic. When you use a flow bench, the gas speeds are not sonic, so you make an assumption.. If you have huge ports, the gas speeds drop unless the revs are very high. The cam and exhaust system you use , determines the revs where the power band occurs. The limiting factors with the Commando motor are the crankcases and the crank balance factor. My crank is balanced to 72 %. At 7000 RPM, the rigidly-mounted motor runs dead smooth. Isolastics make the motor FEEL smooth - they do not protect your crankcases. from being damaged by the crank.
 
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