P11 gets the JSM treatment

baz said:
The kids holding their ears is a recent thing
Years ago I would run with just the downpipes or a set of drag pipes and I never saw kids holding their ears
Nowadays I see it a lot and that's with stock peashooters and balanced downpipes
It must be the way they are taught to hate fossil burners I guess?
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Yeah, I was gonna say something much worse about the current political climate where I live, but didn't. Might offend some of the grown up people in the audience.

The kids also make the your a low life and I'm a superior being face. If adults are with the kids they do the same ear covering superior being face thing. I laugh at 'em in my helmet, and give 'em a thumbs up or wave.
 
You've changed the rod ratio but the stroke is still the same as before, that is set with the crankpin offset.
Honestly after heaps of reading, I don't think a minor change in rod ratio makes much difference at all. There are as many experts in favour of the lower ratio as in favour of the higher ratios. The really high RPM screamers tend to use a higher ratio, there could be something to that.
Supposedly lower revving engines like the Norton get more midrange grunt with a lower ratio.
But I'll wager it's not much!
In one article a hotrod shop changed the rod ratios quite dramatically while keeping everything else the same. They dynoed before and after
It made a very small difference, something like 5 HP on 450, more or less margin of error.
For the pistons to be light they need to be short and that moves the wrist pin up a bit. Gotta have a longer rod then to make it all work in the same old engine.

Glen
 
Schwany said:
.................."and performed a professional session of blank staring"
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You crack me up there with some of the things you say Schwany! Keep on keepin' on! Seems like you're getting it dialed in though, Cj
 
worntorn said:
You've changed the rod ratio but the stroke is still the same as before, that is set with the crankpin offset.
Honestly after heaps of reading, I don't think a minor change in rod ratio makes much difference at all. There are as many experts in favour of the lower ratio as in favour of the higher ratios. The really high RPM screamers tend to use a higher ratio, there could be something to that.
Supposedly lower revving engines like the Norton get more midrange grunt with a lower ratio.
But I'll wager it's not much!
In one article a hotrod shop changed the rod ratios quite dramatically while keeping everything else the same. They dynoed before and after
It made a very small difference, something like 5 HP on 450, more or less margin of error.
For the pistons to be light they need to be short and that moves the wrist pin up a bit. Gotta have a longer rod then to make it all work in the same old engine.

Glen
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Thanks Glen

I have made it to moron. Took long enough.

I've watched the rod length rod ratio video before, but like I said my brain won't hold that info long. I knew what I was thinking didn't make a lot of sense without the crank changing shortly after I replied, but got the dinner is ready call and never got back to delete my confusion. ;)

Thanks to members that sent the explanation content.
 
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Schwany said:
I have difficult time being too serious. Plus, I figured I could not be the only one that stares at their bike trying to work up the motivation to dig in.
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You are definitely not alone - I have caught myself staring in silence for what seemed like hours, just drinking in the nuances of my bike sitting on the bench…. It is part of the therapy….
 
It's when it becomes a burden you need to take time out or break something!!
 
Schwany said:
I have difficult time being too serious. Plus, I figured I could not be the only one that stares at their bike trying to work up the motivation to dig in.
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I once saw a fridge magnet for sale which said " Don't take life too seriously, there is only one outcome" It fitted my philosophy pretty well, wish I'd bought it.
 
I'm really liking the JS2 cam with my Barlow ported small valve head, my 2 into 1 exhaust, and the 35mm FCRs. Anyone with some motorcycle riding experience could ride a Norton with this cam in it. Very linear power band, and the motor goes to a steady idle almost right away after cold started in 57 degree weather. I do have to blip the throttle some and hold it for maybe 40 seconds before it sounds right to me. No chokes on the big FCRs. I am using a TriSpark ignition that might be running around 30 degrees all in. Not sure. Strobing my bike is a pain so I put it off. Anywho if I retard it any significant amount it doesn't idle as nice.

Moving the needle clip to the 3rd position from the top on the FCRs seems to be a good starting point for this motor configuration. The FCRs are from a Sudco 750-850 Commando kit. I keep forgetting to write down the needle number, but it and all the rest of the jetting is whatever Sudco uses as default for 750-850 Commando motors. My intake manifolds are modified 32mm Commando Mk2 spigot manifolds. I don't think that means a lot, but you can't buy a set done the same.

Only noise my motor makes now is the rattle of the FCR slides at idle. Otherwise it's kind of quiet for a Norton if you don't count the exhaust.

I did change my gearing a little. The previous incarnation was a 22-42 in the primary and a 19-42 gearbox to the rear wheel. I took the 22 tooth engine sprocket out and replaced it with 21 tooth and replaced the 19 tooth gearbox sprocket with a 20 tooth gearbox sprocket. Much nicer but it could just be the fact that the motor works better with the parts that are in it now.

Motor is definitely running smoother at street speeds with the lighter pistons. Rebalancing the crank is not going to be necessary for me. It could be for someone else that is more sensitive to whatever it is they are sensitive to. It's no sewing machine far eastern manufactured motorcycle. Feels like a nice running old Norton twin to me. Much nicer ride than it was previously.

Still getting accustomed to giving the big 4LS front brake the respect it requires. That thing can easily put you on the tarmac riding a relatively light bike if you grab a handful.

No regrets with the results of the project so far. It was a bit of work, and there were some user errors along the way, but I overcame all that eventually.

The JSM treatment gave the old turd a new lease on life.
 
worntorn said:
What sizes are the valves in your small valve head?

Glen
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I was thinking stock 750 valves is small around here, but maybe I made it sound like the valves were smaller than stock. Wasn't trying to do that.

They are standard size valves for a 750 sold by Jim Schmidt and come with his beehive spring kit.
 
back tracking a bit...on the grub screws locating and securing the bronze lifter blocks...since it is essential to secure the lifter blocks...and the hole drilled into the block is very short, I used two set screws in both holes with locktite. They won't budge after that.
 
seattle##gs said:
back tracking a bit...on the grub screws locating and securing the bronze lifter blocks...since it is essential to secure the lifter blocks...and the hole drilled into the block is very short, I used two set screws in both holes with locktite. They won't budge after that.
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That is a good safety measure. I brushed some paint on the threads and the heads of the screws after getting it all assembled. Paint usually works on screws on bikes that don't vibrate too hard. It is a Norton motor in a solid mount though. Thanks for reminding me. I should check on those and do the same since I've been on a couple of rides.
 
This motor runs on the hot side at traffic stops after the build, not seize up hot, but hot in town. I'm not looking for tips on things to check or guesses on why it is so. I'm a competent guesser and somebody already mentioned it could be the higher compression. It's not retarded timing.

I carburate the motor with 35mm Keihin FCRs and found the as delivered jetting from Sudco works well with this JS2 cam and the higher compression pistons. The same jetting also worked well with the previous build that included the 2S cam. Only difference was I could run leaner idle mixture and slow jet adjustments with the flat top Commando pistons and 2S cam. That tune was not good with the JS2 cam and higher compression pistons.

For the most part I richened it up everywhere using the screw adjustments without changing any jets. I could list the tune, but it wouldn't do anyone else any good. You already have your long-standing tuner heroes for that kind of thing. ;)

Off to roast a whole hog. When I get back from that party, I'll install that NEB clutch and see what else I can screw up.
 
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