Bigger Valves for the RH 10 Head?

Dan1950 said:
My bike does great when I roll the throttle on to pass a car. Problem is it runs out of steam as

Well if I do get 7,000 RPM it will be more power because right now I can't get anywhere near it in 3rd or 4th gear.

Granted I know it's running rich but since I need to pull the head and most likely the cylinders anyway I'm not going to go halfway on this thing.

I've always been able to extract extraordinary power without sacrificing reliability or driveability. I have a knack for putting a package together.
Click to expand...
Where you get to in the rev range depends on where you start. On public roads you don't usually keep your revs between 5000 and 7000. With a wide ratio gearbox, you are really battling.
Commando cranks are probably balanced to be smooth at 4000 RPM. If you are riding along at 4000 RPM on a normal Commando, and whack the throttle open, you would probably wait forever tp reach 7000 RPM
 
acotrel said:
Where you get to in the rev range depends on where you start. On public roads you don't usually keep your revs between 5000 and 7000. With a wide ratio gearbox, you are really battling.
Commando cranks are probably balanced to be smooth at 4000 RPM. If you are riding along at 4000 RPM on a normal Commando, and whack the throttle open, you would probably wait forever tp reach 7000 RPM
Click to expand...
My last motorcycle would make my asshole pucker when I opened it up. I think I can make my Norton do i the same although I don't think it will ever match my 86 in Panhead on top end.
 
Dan1950 said:
I loved the modified Flathead 80 flywheels I had in my Panhead.

Everyone told me I was building it wrong, that I needed light flywheels so I could get my revs up.

My reply was that I only had to get them up once.

I had a 2.60 Andrews low gear that would wind out to about 55 mph. When I shifted the second it would jump to 70 mph and then it was time to shift to the close ratio third. I could hit 4th in the 8th mile.
Click to expand...
My short stroke Triumph motor had the lot done to it - revved to 10,500. I rode a 500cc Manx - it was slower but faster around a race track. I was once told ' with a torquey motor you don't need a close ratio gearbox' - I think that was supposition - like what a lot of teachers do ?

It is very nice to find someone who has had similar experiences to my own..
 
Dan1950 said:
My last motorcycle would make my asshole pucker when I opened it up. I think I can make my Norton do i the same although I don't think it will ever match my 86 in Panhead on top end.
Click to expand...
The last time I raced, I used a 4 speed close ratio box with very high overall gearing. The clutch start was difficult, but everywhere else, the bike was perfect. I was silly. I have bought a 6 speed TTI box, when all I really needed to do was fit a standard Commando first gear to get me off the line.
 
My 500cc Triumph did not make my asshole pucker, it just scared me shitless. The slightest wrong move and it would try to kill me. With the Seeley 850, there is none of that. It is quick and smooth. The heavy crank is a joy.
 
acotrel said:
I love the heavy crank in the Commando. Once it is spinning high, nothing stops it. Race-changing up through a close ratio box with that crank is really great. You can play it like a piano.
Click to expand...
Not arguing at all, but I'm exactly the opposite. I'm really fond of engine brake. With a lightened crank and other bits of rotating mass, I get fast spin up and a lot of engine brake when I let off the gas. Much easier for me personally to go fast trough corners without as much hand and foot brake. Well, when I had 16" biceps and was fit as a fiddle anyway. Now days I don't push very hard at all. Racing around on the street can be painful when things go wrong trying to predict how safe the next blind turn might be. Yeah I know it's not the same yadda yadda.
 
This thing funky old thing would scare most people. It was just another one of my boring street bikes. I didn't pay much attention to the tach when I rode it.

Bigger Valves for the RH 10 Head?


It was fun to ride. Didn't scare me or make my butt cheeks tighten up. They were already tight as a tiger. Does that make me a bad person? lol
 
Dan1950 said:
Nope. If I could ring out 5,500 RPM on a 4.520 inch stroke, in a Panhead hog, I see no reason why I can't get 7000 out of a 3.5 inch stroke.

That is if I can get the top end to breathe. The Panhead had oversized intake valves and Port work behind a 1 7/8" manifold.
Click to expand...
Better get some Molnar cases then. And a stronger crank.
The stock items arent made for high rpm.

Glen
 
Last edited:
"I've always been able to extract extraordinary power without sacrificing reliability or driveability. I have a knack for putting a package together."

It'll be interesting to see what you come up with
Just wondering why you'd ask about tuning on here?
Keep us posted
Cheers
 
Dan1950 said:
I'm running Tri Spark ignition.

I want to increase midrange torque and raise the power curve from 3000-7000 RPM.

A mild static CR boost and appropriate cam grind will also be employed.
Click to expand...
In the mid '70s I ran a motor based on cam, head and pistons from a factory race 77x80.4 short stroke, but with an 89mm crank. JPN ran similar 850 engines for Dave Croxford in '74.

Max rpm was 6800, pulled like a train from 4 up to that, but didn't want to rev higher. I forced the issue a couple of seasons later running too low final gearing, it was pulling 7200 in top when it went bang, still have the pistons, one with the big valve buried in it!

Of course, today you can buy pistons, rods and cam train that will be happier up there, and I rev my current 750 short stroke over 7000....it has Maney cases and light flywheel crank, JSM Pistons and Rods, about 10.5 compression a PW3 profile cam and lighter valve train, and a standard Fullauto.

But this doesn't fit the brief you set. And personally, I think it misses the point of what an 828 road bike is about. Work for more mid-range and enjoy that.
 
Last edited:
Dan1950 said:
Nope. If I could ring out 5,500 RPM on a 4.520 inch stroke, in a Panhead hog, I see no reason why I can't get 7000 out of a 3.5 inch stroke.

That is if I can get the top end to breathe. The Panhead had oversized intake valves and Port work behind a 1 7/8" manifold.
Click to expand...
I have given my view on why you shouldn't, which might be more important than if you can or can't.

But I will have to ask the secondary question, to delivering the arse puckering performance you speak of, what are you going to use as a gearbox?

What primary ratio are you planning?, and will you be making your own outrigger bearing set up or going whole hog with a TTi?

Ignore these points, and the arse pucker may be more to do with trying to come to rest with a locked gearbox!
 
baz said:
"I've always been able to extract extraordinary power without sacrificing reliability or driveability. I have a knack for putting a package together."

It'll be interesting to see what you come up with
Just wondering why you'd ask about tuning on here?
Keep us posted
Cheers
Click to expand...
I'm asking about tuning because to put together a well balance "package" I need as much relevant information as I can find to make choices. Although I have a good basic knowledge about how cam grinds, static CR, port size/shape, valve size combined with rotating assembly geometry contribute to power curves as well as the affect of gearing, I have little 1st hand knowledge of the idiosyncrasies that pertain to the 850 Norton.

I'm not looking to extract maximum HP, I just want everything to work together efficiently for solid performance with good rideability and reliability.

I do not plan to abuse the gearbox with hard shifts or hole shots. I also have a knack for operating machinery to get good performance without breaking things.
 
Last edited:
lcrken said:
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
Click to expand...
 
I prefer the feeling of exhilaration over pucker.

I'd ride it as is for the remainder of the good weather. Tear it down this winter and see what condition everything is in. Then you can freshen it up a little and perform your tuner magic in time for next riding season.

I can tune well enough but achieving extraordinary power from an old classic Norton twin is really optimistic. Me, I know when to quit trying at 71 years of age. Don't expect floating the front tire 6 inches off the ground for 30 yards rolling on the power in 3rd. I hope you get there though.
 
Schwany said:
I prefer the feeling of exhilaration over pucker.

I'd ride it as is for the remainder of the good weather. Tear it down this winter and see what condition everything is in. Then you can freshen it up a little and perform your tuner magic in time for next riding season.

I can tune well enough but achieving extraordinary power from an old classic Norton twin is really optimistic. Me, I know when to quit trying at 71 years of age. Don't expect floating the front tire 6 inches off the ground for 30 yards rolling on the power in 3rd. I hope you get there though.
Click to expand...
"Extraordinary power" is a relative term. Maybe better than what would normally be expected is a better way to describe it.

When all components (cam, heads, CR, rotating assembly geometry, induction, exhaust, gearing, etc.) compliment each other, you are leaving nothing on the table.

And yes, this is research for my winter project. I know that the right intake is sucking oil through the guide, cylinder pressure is a bit on the low side and the jetting is too fat. throttle response is good so the needles seem to be the correct taper/notch.

I could re-jet it and get better top end performance, but for right now it starts well, fuel economy is acceptable, it pulls well up to about 5000 RPM as long as it isn't at WOT and it is very reliable. I see no point changing jets until the engine has been rebuilt to new specs.
 
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.
Click to expand...
Does anyone have a CNC 5 axis porting program, for your head ? others may know .?
 
You must log in or register to reply here.
Back
Top