Big valves or small valves

acotrel said:

'I discussed head choices extensively with JC at the time (top marks for patience Jim) and the summary was that a FA head gives increased performance, a ported RH10 with a milder big valve job gives more, and a ported big valve FA would give more still.'
- You used the word 'would', perhaps you meant to say 'might' ? - You do not know what you are going to get until you have done the deed. If you are wrong, you have probably stuffed the cylinder head.

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No Al, I meant ‘would’ because Jim has done it, so knows.

@jseng1

Call goodson if it's the one I use they carry it.
Originally I think from down under but costs a premium.
White gooey stuff, i use it for race valve guides.
But check the loctite page there are also some high temperature compounds by them but they might need some tempering.

Kind regards Christian

If you race a Commando and followc the other riders on the wide line in corners, you will need a lot of horsepower. But if your bike turns early as you gas it immediately after braking for a corner, you can stay hard on the gas all the way around the corner while the other guys are struggling in their power game. When you are at full lean on the wide line, you become more depended on your tyres and the power of your motor. If your bike stays more upright in corners, you can ride under the other guys and come out of the corner much faster. Then when they have their bikes upright and accelerate hard, they have to make up what they have lost in the corner. Bike handling is about oversteer and understeer. If your bike does not handle, you cannot get the power onto the ground. When your bike is difficult to tip into a corner, that is understeer. When you run wide when you accelerate, that is also understeer. Your bike needs to oversteer when you gas it when you are on a lean, and also tip into corners easily. Then engine power becomes less of a consideration.
I was racing in the 1960s when the two-strokes began beating the Manx Nortons. The biggest difference in the bikes was the angle of lean. It was almost impossible to get as much lean on an original Manx Norton, but bikes with 18 inch wheels usually had better rubber. The steering geometry of the two strokes was very different, they had more understeer than a Manx. The game changed. It became more about higher power and better tyres, than better handling. Commandos are lighter than many other bikes. Play with your strengths, not your weaknesses.
In the straights on a race track, my bike is barely fast enough to keep up. But it is still fast enough to win.

@acotrel
Al with all respect, this thread is still bout valve sizes, cam lift, Port diameter etc. and not riding techniques.
Please don't hijack it with off topic stuff.

Kind regards
Christian

Here's another pic Klause asked me to post. Also note that my roadracing friend Mick Ofield who worked at the Norton race div also told me about threading in valve guides.

jseng1 said:

Here's another pic Klause asked me to post. Also note that my roadracing friend Mick Ofield who worked at the Norton race div also told me about threading in valve guides.

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Thank you very much Jim,
you are a genius. Only thing is, that I don't thread in the guides but the inserts. The guides could be standard 750 guides with a press- fit of 0,03mm. These are angled, not the inserts. That is only necessary if previously the big guides from the 850 were used.
Once again Jim. Please ask me for a favour.
Best Regards
Klaus

Fast Eddie said:

No Al, I meant ‘would’ because Jim has done it, so knows.

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Was the valve modification discussed with the new makers of the FA cylinder head ? It sometimes makes sense to stay ahead of the game.

As I understand it, the makers of the FA head are targeting the market for those wishing to buy a replacement head for their mostly stock motorcycle. Whilst some improvements are included, it’s designed to fit a standard bike and take standard components and not require careful set up for valve clash etc.

Although John has said he may look to cater for the hot rodders later on. But this won’t be in the form of off the shelf ready to go heads IMHO as the possible permutations are endless … and the market tiny.

Glen - I also discussed with JC my head options pretty extensively when I rebuild a while ago.

My motor has, 9.5:1 +40 pistons, Webcam 312a, 4" radius lifters, Dynamically balanced to 63%, Camshaft dialled in at 104.5 L/C inlet, 12 pins between idler and cam sprockets, Idler gear now 5 teeth counter clockwise from original marks.

The FA CNC head has 1.5mm oversize intake and a little work in the valve guide and bowl area, lightened rockers and JC's conical spring kit.

Edit: these are before/after on the same FA head.

Flow



Velocity


I like how this motor works. It does rev slightly high, but as I ride mostly around home and it is twisty and hilly and not mountainous, it is great. But, based on riding in the Cascades, and then riding this bike all over NZ, and given what you say you want, I would think that with the stock cam and a ported head similar to this, you would get what you would like.

So 1.5 mm over must be the 1.560" size that Ken mentioned?
According to the calculators 1.56" is the right size for a 6000 rpm 920.

The stock cam hits max torque at 5000 and max bhp at 5800 so that should be a good combo.
I have a second RH10 head here to play with.
I might ask Herb Becker to do the shaping, if he is accepting work. He reshaped my 650ss intake ports without changing the size at the manifold. His report was that "the clutch held before port shaping and slipped after shaping."

Glen

Yup - 39.6 = 1.559

Thanks for the valve info
For those who wonder what all the fuss over midrange is about-

Here is a map of our area. We live in the flat area by the Ocean. The bumpy red line is the TransCanada highway, one of a few ways out of here, all through the mountains.
The mountains shown are the Coast Mountain range, the Canadian name for the Cascade range mentioned by Gortnipper. It is the first of many ranges encountered on a Tour of BC.
This is a small portion of the Challenger Map, a relief map of the Province of BC, made by a Mr. Challenger in the 1950s.

60 minutes drive out of Seattle (which is sea level) is a lower elevation Snoqualmie Pass - 2,726 ft (831 m)

There is also Stevens Pass - elevation 4,061 ft (1,238 m) about 1.5 hrs out of Seattle and a bit further North.

Around the corner from that is Blewett Pass, which connects those two highways, at an elevation of 4,124 feet (1,257 m).

So, some reasonable climbing around in the Cascades - but maybe not to Ludwig's standard. ;-)

Then there is Washington Pass at about 5500 ft . Over in Montana there are also some very big climbs. Beartooth Pass is about 11,000 ft.

Glen

Yeah, I was just illustrating what you can get to on a day trip drive out of town and back. Forgot Chinook Pass elevation 5430 ft./1656 m.

Fast Eddie said:

As I understand it, the makers of the FA head are targeting the market for those wishing to buy a replacement head for their mostly stock motorcycle. Whilst some improvements are included, it’s designed to fit a standard bike and take standard components and not require careful set up for valve clash etc.

Although John has said he may look to cater for the hot rodders later on. But this won’t be in the form of off the shelf ready to go heads IMHO as the possible permutations are endless … and the market tiny.

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I have a standard Australian made Fullauto on my 750 Short Stroke race bike and don't see it in any way to be a limitation. It has been skimmed to raise compression. Bigger valves might help, but it won't be adding more than a few % at the back wheel. Similar for more port work.

If John does as he suggests and produces basically a big valve ready version later, it would be an improvement for a race bike. But really, most people just don't need that, even if they want that.

Hello,
I don't think there is much one can do to prepare a Fullauto- head for a later Big Valve Conversion as long as you stick to the 1/2" (outer diameter) valve guides. A conversion to 41/33mm valves is rather straight forward and wouln't cost you too much, because you just drill the guide- bores with that new angle with the new diameter. What ever the angle may be, the diameter will never be bigger that the standard 5/8" of a 850 head. So, for any conversion like this standard 850- guides can be used (allthough, they'll have to be turned to suit).
Maybe a cylinder- head for a 850 could benefit from "standard" valve sizes 41/33 or 41/36 (mm). In any case it must be well reviewed if this conversion would result in quantities which make it economically worthwhile for the manufacturer.
A conversion like the one on my drawing is only necessary, if standard sizes with outer diameters of 5/8" were previously used (a pity for all old 850 and RH6S/RH7- heads). I must say that the RH6S/RH7- heads are pretty rare,
Best Regards
Klaus