On board 750

[Jerry Doe]

Forgot to mention I appreciate the view if the instruments during acceleration. I don't use a tach, so it was nice to see that old 750 Nortons can be wound up much further than 6K RPM.

You have what sounds like and performs like a quiet well-built motor.

Which electronic ignition is in that motor, or is it old school ignition?

It has got pazon ignition in it. Used to have tri spark.
It has bigger valves and head work, 312A webcam, radiused lifters/ followers.
Re balanced crank. ( was way off).
Premiers.
Brit euro exhausts.
Primary belt drive.
21 tooth gearbox sprocket.
19 inch rear wheel.
Definitely a fun bike!
I miss all those Essex roads too, but don’t miss the hay fever I used to get there. Maybe will be back one day.

 

[Schwany]

My 750 will carry on past 7500rpm if I let it
But it's all over way before then

My 6000RPM comment was supposed to be making a little Access Norton fun based on a member that said his bike wouldn't pull past 6000RPM. Timing was way off on that motor.

Seeing Jerry's tach getting up real close to 9K RPM was very satisfying to watch. Sure makes a big difference when things are done right.

 

[TomU]

My guess is the radiused lifters/followers and re-balanced crank had a lot to do with it. Jerry didn't mention it, but i'd guess at a reground cam as well and possibly stronger valve springs.

Not sure i'd be comfortable revving a stock motor up to 9k (or am i a worry wort)

 

[Jerry Doe]

My guess is the radiused lifters/followers and re-balanced crank had a lot to do with it. Jerry didn't mention it, but i'd guess at a reground cam as well and possibly stronger valve springs.

Not sure i'd be comfortable revving a stock motor up to 9k (or am i a worry wort)

Yes springs stronger.
It was a new cam (webcam 312A). I only have about 3K on this bike since ground up resto.

I don't usually ride it as hard as that. I normally ride 75-80 on a clear road. I had a rather strong coffee and that was the result. I don't think I revved it to 9K did I? I'm normally between 5-6K on tacho.

 

[EstuaryBoy]

My 6000RPM comment was supposed to be making a little Access Norton fun based on a member that said his bike wouldn't pull past 6000RPM. Timing was way off on that motor.

Seeing Jerry's tach getting up real close to 9K RPM was very satisfying to watch. Sure makes a big difference when things are done right.

I must've missed that bit (slipped out to the toilet, probably, it's an 'age' thing!) Seriously, though, still a healthy sounding and responsive motor.

 

[worntorn]

Yes springs stronger.
It was a new cam (webcam 312A). I only have about 3K on this bike since ground up resto.

I don't usually ride it as hard as that. I normally ride 75-80 on a clear road. I had a rather strong coffee and that was the result. I don't think I revved it to 9K did I? I'm normally between 5-6K on tacho.

You are correct.
The highest rpm shown on the tach was 6500 for a split second, the rest all below 6k.
Won't hurt a thing but sure sounds strong!

Glen

 

[Schwany]

Oh Farts!! My glasses must have been dirty. I was sanding paint before I watched the video the first time. I thought that 5 on the tachometer was an 8 and it was closer to 8500 RPM when shifting. Seriously that is what I thought I was looking at.

I just watched the video again with clean glasses and the numbers were clearer. 6500 max. Oh well, I was overly optimistic and hopeful. If I was familiar with a Norton tachometer I wouldn't have made the error. Last time I rode a Commando was 1986. I think it was all there, tach included. My P11 I've been riding off and on since the 70's has never had a tach on it.

Excuse the brief moment of excitement.

 

[TomU]

An engine with his specs should be able to go mid to hi 7s. Not sure i'd take it there though

A rotary Norton is a different matter

 

[Mart UK]

Jerry's bike sounds tight and smooth. Look forward to more clips.

But a confession: I doubt I'm alone in this, but I guess I'm not normal . I've had a few high revving 4s, but I just don't like the sound and feel of an engine at higher revs and always go back to twins. I'm really happy that an 850 pulls lovely 2,500 to 4,500rpm and sounds wonderful in that range. I can ride quite swiftly, overtake with room to spare and get a good lean on twisty roads within that rev range and still feel I'm giving the old boy due respect.

 

[worntorn]

An engine with his specs should be able to go mid to hi 7s. Not sure i'd take it there though

A rotary Norton is a different matter

They'll all go there for a bit. I guess the stock crank and cases are good reasons not to. That and the max bhp is at 5800 with stock cam, probably a bit higher (guessing 6500?) with something like a 312a.
So after 6500 rpm we are hanging on for less horsepower but maybe a big bang.

Glen

 

[ashman]

A hot cam, head work, balanced crank and all tuned right these motors well rev freely and go well over 7K RPMs and keep going till something goes bang and some hot cams don't kick in till over 4k RPMs so its up to the owner how far they want to take them to, I know my stock motor could never rev past 6.5K RPMs with valve bounce but the Hot motor just revs freely, but the cam works better from 4K up to 7k, but I love my motor and won't go past that but its a lot of fun on a light weight bike, that's built for it.

 

[worntorn]

My stock 850 will rev way past 6500 in the first 3 gears, but there's no point in doing so when max bhp is at 5800.
I don't recall seeing a dyno printout showing power levels against Rpm above 6500 with any of the various hot cams. I have a hunch those cams are mostly made to produce max power at 7 k or below as the (stock case+crank) engines tend to blow to pieces if held much above that.

 

[worntorn]

Here's a chart showing a stock cam hitting max around 5700 in a somewhat tired engine and then the same engine rebuilt with PW3 cam and other mods. That version makes max bhp at 6000 rpm , loses a bit to 6300 then really tails off.

Dyno runs before and after engine mods

I wanted to share my recent experience. I rebuilt my 850 MkII engine last year. Before I took the engine apart I did a test on the dyno to have a base line. After the rebuild I did another run last week. The engine has around 8000km on it now. See below comparison of power and torque. Same Dyno...

www.accessnorton.com

 

[TomU]

Need bigger valves and more fuel

 

[Schwany]

I have JS's copy of the PW3 with smooth ramps (PW3 is his definition) BSA lifters, his springs and pushrods, yadda yadda. It's a JS2SS, or commonly referred to as a stage 2 cam. Slighty lighter balanced crank, light clutch, mild port work, Carrillo long rods, short skirt Wiseco high CR pistons, 35mm FCR carburetion with my tune. I should put it on a dyno and get a nice disappointing reality check. It might make a couple more HP than a stock 750, and hold slightly higher RPM without flying apart. The motor could do 90 all day long, but I couldn't with a solid mounted motor. I'd need image stabilization for my eyeballs.

The 2 into 1 exhaust with the 4-inch megaphone and buttload of SuperTrapp plates set up I have makes the motor sound like it's wound up to 11K RPM. Might be half that in reality based on what has been said in this thread. I actually thought a built Norton engine had the potential to wind up tighter.

Really have to apologize again for the 9000K RPM comment. That is inexcusable and grounds for termination.

 

[Fast Eddie]

It’s very easy sometimes to get carried away and think more revs equals more go. I had a mate once who used to remorselessly thrash his car, as a passenger you could clearly feel that the acceleration had fallen off a cliff, but you couldn’t tell him !

However, sometimes max acceleration is achieved by revving passed peak power, it all depends what the torque and power is doing AFTER you’ve changed up, especially if you’ve got a wide-ish box and a narrow-ish power band.

 

[gortnipper]

It has got pazon ignition in it. Used to have tri spark.
It has bigger valves and head work, 312 webcam, radiused lifters/ followers.
Re balanced crank. ( was way off).
Premiers.
Brit euro exhausts.
Primary belt drive.
21 tooth gearbox sprocket.
19 inch rear wheel.
Definitely a fun bike!
I miss all those Essex roads too, but don’t miss the hay fever I used to get there. Maybe will be back one day.

Almost identical spec to my 850. JC did my head (as I am guessing he did yours too) and supplied the 312a and radiused lifters.

Mine has 9.5:1 pistons, did you increase the CR on yours?

Mine spins up VERY fast and likes it 5-6k as well. I have to watch it, as I have spun up to redline without noticing quite a few times.

 

[acadian]

Ditto experience here, my 750 is spec'd exactly as Jerry's and similarly revs happily up past 7k, though on local expressways here in the metro Toronto area, getting there is likely to land you in the hospital or a jail cell

 

[gortnipper]

Ditto experience here, my 750 is spec'd exactly as Jerry's and similarly revs happily up past 7k, though on local expressways here in the metro Toronto area, getting there is likely to land you in the hospital or a jail cell

 

[baz]

The last time I got my 750 to 7500 rpm I was dialing in my new tm40 carburettor
(This is with a completely stock engine)
It had a flat spot at just under 7000 rpm
Once tuned out the motor just kept on revving,it was still revving above 7500 but there was no more power there
At least I know it'll do it without blowing up if I miss a gearchange
Wouldn't want to sustain those revs too long!!!