Bigger Valves for the RH 10 Head?

Dan1950

Dan1950

1974 MK II Roadster
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Trixie needs to be woken up, nothing drastic, just a combination that will give me more midrange and top end power. An 850 Combat so to speak.

10:1 static CR with a cam grind that will yield a dynamic CR similar to the stock 850 Commando.

Static Vs Dynamic Compression Ratio | Piston Ratio

Static vs Dynamic compression ratio and how Camshaft duration and lift effects overall engine motor compression in the combustion cycle and tuning
www.enginebasics.com

Slightly larger intake valves with some bowl and seat work.

I just want to wake it up in the 6000-7000 RPM range while still having a user friendly motorcycle.

What sort of pitfalls as far as IN/EX valve head interference do I need to watch for with various cam grinds.

I do not want to alter the valve guide angle in the head so please refrain from going down that route.

I've been down this road before with Panhead Hogs and SB Chevy V-8s. Both were running 10.5:1 static CR but utilized cam grinds to reduce low RPM cylinder pressure with great results. Both engines ran well on unleaded 91 octane fuel and were well mannered for daily use. Docile under 3000 RPM but came on like a freight train above that.
 
Dan1950 said:
Trixie needs to be woken up, nothing drastic, just a combination that will give me more midrange and top end power. An 850 Combat so to speak.

10:1 static CR with a cam grind that will yield a dynamic CR similar to the stock 850 Commando.

Static Vs Dynamic Compression Ratio | Piston Ratio

Static vs Dynamic compression ratio and how Camshaft duration and lift effects overall engine motor compression in the combustion cycle and tuning
www.enginebasics.com

Slightly larger intake valves with some bowl and seat work.

I just want to wake it up in the 6000-7000 RPM range while still having a user friendly motorcycle.

What sort of pitfalls as far as IN/EX valve head interference do I need to watch for with various cam grinds.

I do not want to alter the valve guide angle in the head so please refrain from going down that route.

I've been down this road before with Panhead Hogs and SB Chevy V-8s. Both were running 10.5:1 static CR but utilized cam grinds to reduce low RPM cylinder pressure with great results. Both engines ran well on unleaded 91 octane fuel and were well mannered for daily use. Docile under 3000 RPM but came on like a freight train above that.
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Dan, How much money do you have? :p
 
concours said:
Dan, How much money do you have? :p
Click to expand...
That's another criteria. Nothing exotic or overly expensive.

I am interested in coated pistons to reduce cylinder wall clearance.

Emphasis on reliability and longevity over absolute maximum power.

I have found that a well thought out "package" that has everything working in harmony will often out perform more radical builds in everyday street use.
 
Not absolutely familiar with this about an 850, but 750's respond well to a simple camshaft swap.

That said, my late uncle told me he had to change a soft cam in an 850 once, and he could not get a standard cam from his supplier in a timely manner. So he substituted a 2S cam he had on the shelf. He said they should have done that from the factory...

I personally like the 3S better than the 2S - more performance across the entire range.

FWIW
 
Derek beat me too it. I was overthinking it.

You could wake it up with more cam without too much else, but once the cases are apart you might as well do what you want to do with it and see how it goes. It would depend a little on how much torque you think you need as to what cam to use is concerned. No need to get real radical.

I'm not an 850 owner, but I don't believe that makes much difference as to how to make more power is concerned.

The guys doing head work are really pricey, so warm up that credit card.

The JS2SS cam, JS valve kit, and radiused stock lifters would probably work well if you really want more beans up top. That cam also makes good street torque as long as you don't over gear the bike. I think Nigel (Fast Freddie) put a JS1 cam with radiused stock lifters in an 850 with more head work, and liked it, but I am not speaking for anyone other than myself. Maybe he'll tell you what he thinks about it, or you could search through some of his older threads.
 
Some good info here, especially the Comnoz posts in the first 2 pages

commando camshafts

Now a Megacycle 560-D+ and JSMotorsports Norris D, .405" 296° 105° flat Norris fuel/drag competition cam. Racing springs, Megacycle spec sheet @0.040" lift. They want $356 to ship one to me. Norris fuel/drag competition cam. Racing springs and pistons required. Lift 405", Duration 296*, Lobe...
www.accessnorton.com www.accessnorton.com
 
You need to get comfortable, get a pen and notebook, and read through this thread:

Head flow testing.

I would like to build up a database of flowtests on modified Norton heads. The tests would be done on one intake port and be from 0 to .450 lift and would include a single velocity measurement measured central in the port 3/4 inch in front of the guide. If anyone has a modified head setting...
www.accessnorton.com www.accessnorton.com

What I can tell you is this: After Comnoz did my RH10 head it gained 9rwhp on the dyno. That’s a direct before and after comparison.
 
Fast Eddie said:
You need to get comfortable, get a pen and notebook, and read through this thread:

Head flow testing.

I would like to build up a database of flowtests on modified Norton heads. The tests would be done on one intake port and be from 0 to .450 lift and would include a single velocity measurement measured central in the port 3/4 inch in front of the guide. If anyone has a modified head setting...
www.accessnorton.com www.accessnorton.com

What I can tell you is this: After Comnoz did my RH10 head it gained 9rwhp on the dyno. That’s a direct before and after comparison.
Click to expand...
Is that bolt-on with no changes to carburetion other than minor tuning and same exhaust before and after? Big increase of HP on a Norton. :cool:
 
Schwany said:
Is that bolt-on with no changes to carburetion other than minor tuning and same exhaust before and after? Big increase of HP on a Norton. :cool:
Click to expand...
No other changes.

But, the rest wasn’t stock!

The bike was built with 10.5:1 JS pistons, JS#1 cam, FCR35s.

Thats how it was on the before and after runs.

Stock unbalanced pipes and peashooters.
 
It shows how important the head design is.
Doug Hele added nearly 20 bhp to the Dominator99 when he made it into the 650ss.
Most of that gain came from the new head design.

Glen
 
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Just get yourself a Fullauto, with standard valves, it'll do what you need, and it's just a straight swap over with no waiting.....

And as a bonus you have yourself a spare head on the shelf! or an item to sell on at a good chunk of what you just paid out.

Before you scream about money, you have new metal, well machined and not porous, with much better inlet and exhaust porting, new valve guides, new seats, new exhaust threads.

Go price that handful with labour, shipping, waiting and 'risk' on your old head.

...risks...

The person you choose to do the work takes years or fails to complete it to your satisfaction, or at all. Or they find way more wrong with your head than you ever imagined...or the shipper (2 ways) loses it!

All of these things have happened to people who, as their bonus, had a bike they weren't riding whilst waiting for the head to come home.
 
All good advice above.
Worth noting though, Nigel's modded rh10 made more power than a Full auto. A lot more and I suspect
the cost would be about half.
You would have to wait for Jim to get to it.
I believe Madnorton has posted dyno results from an 850 with a Full auto head.
 
worntorn said:
All good advice above.
Worth noting though, Nigel's modded rh10 made more power than a Full auto. A lot more and I suspect
the cost would be about half.
You would have to wait for Jim to get to it.
I believe Madnorton has posted dyno results from an 850 with a Full auto head.
Click to expand...
Who did the head work?
 
Bigger valves might mean heavier valves. The valves if my head are standard and mu valve gear has not been lightened. I only have a very mild cam grind. I usually change up at 7000 revs, but often see 7500. With my motor, I believe the things which make it quick are the 2 into 1 exhaust system and the jetting. However it is too loud. If you improve your motor's torque, you usually do not know it until you raise the gearing. And a close ratio gearbox will help any bike accelerate faster, especially when it has a heavy crank.
 
Well, it would be hard to argue with Steve A's post. But, getting back to the original question, you can normally fit larger intake valves, out to the limit of the seat insert, without any guide mods, but you do have to check for valve-to-valve interference for anything other than the stock cam. The valve can go at least .060" larger on the stock seat, and maybe slightly more. My memory says I used 1/16" larger intakes back in the day. That's what Axtell used on his 750 race ported heads back in the '70s and '80s. Worked ok with his cams, but might have valve-to-valve interference with some of the high lift, wide overlap cams. Kibblewhite sells a .060" oversize Commando valve that I've used to convert heads a couple of times with no problems. But if you want the full benefit of the larger valve, you need some port work to blend the new seat into the port and combustion chamber. That used to take a lot of hand work with a porting tool. It's a little better now with contoured carbide cutters and such, but it still takes some hand work to finish. Still, you'd probably pick up some performance improvement from just the larger valves and a decent multi-angle valve job.

Ken
 
FYI - this is the result of Jim's work on my Fullauto head vs. the stock FA.

comnoz said:
So now that I identified a problem with my prior velocity readings and corrected them -here is the flow tests with the 1.5mm oversize intake and a little work in the valve guide and bowl area.

Nice improvement for a steetbike running a .400 lift cam.

Flow
Muttster: A long, slow '74 resto-mod


Velocity
Muttster: A long, slow '74 resto-mod
Click to expand...
 
Contact Norman White and have him fit a PW3 cam , I did with my 850 with a rh10 and the result is great, Norman says 20% increase across the range , mind you as he said the 750 reacts better to tuning than a 850, It did take me almost 20 months of persuasion to have him take it on though but its great .
 
colin davie said:
mind you as he said the 750 reacts better to tuning than a 850,
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As I understand it, that’s coz the valves (unchanged from the 650 I believe) aren’t really big enough in an 850 to allow it to properly benefit from other flow work.

Edit: that should have been ‘unchanged from the 750‘. Thanks Glen.
 
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