6400 rpm in top

21 tooth sprocket and a bog standard original bore MK3 850, other than ancient Boyer ignition, a skinny head gasket and open peashooters. This figures to just under 110 MPH according to the big white book.
Actually, it still was creeping up there a bit, might have pulled a couple of hundred more revs, but 6400 felt like enough to ask of it with my big old body on there. With a small slender rider and maybe some narrow bars, 120 MPH should be attainable.
Anyway, with me on there, it pulls quite swiftly to 6400. Who says MK3s are slow?

Glen

Hi Glenn

In my younger days (17 years old) and with a new stock standard 74 850 Commando under me, skinny as all shit (9 stone nothing) with standard gearing (19 tooth sprocket) my bike at flat out got to 116 mph and 6,500 rpms and just couldn't get any more out of it, after 1980 when I built it to the Featherbed frame and lots of work done to the motor and a lot of weight taken off the bike and the same 19 tooth sprocket on I was clocked doing 125 mph two up coming down a hill (police radar trap) and the rpms where well over 7,000 and the motor still pulling (shit I am in trouble now) luck was with me that day, the old copper on the radar trap was a old British bike owner and rider we sat on the side of the road for about a hour or so just talking bikes, he was very impressed with what I have done to my Norton (21 years old at the time) and what work was done to the motor, he was more impressed when I told him I built the bike by my own hands without having any experance at all building bikes or motors, just a manual with a high performance section in the back (still have that manual but it has seen better days) after talking I was expecting a big fine, he just said on your way son and slow down.

Now that I am older and more wiser, well maybe, with the same 850 Featherbed (now 56 years old) I am happy to just take it over the ton evey so often (shit I love ridding this Norton) with a lot more improvements over the last 40 years of ownership (more so in the last 5 years) given the chance it would still pull well over 120 mph, but I am happy to just criuse along the highway sitting between 70 and 90 mph and it happerly sits on that all day long, but the law is making it so much harder these days with their hidden speed cameras (wish I was still in the 70s and early 80s) such is life.

Ashley

ashman said:

850 Commando
with standard gearing (19 tooth sprocket) my bike at flat out got to 116 mph and 6,500 rpms

Click to expand...

There is a (fair) bit of speedo or tacho error there. ?
The workshop manual quotes a stock 850 with 19t as ~100mph @ ~6500 rpm.
You'd have needed 7500+ rpms to do 116 - or a 22 t .

Some of the older magazine tests quotes the shown and actual speedo mph,
and that would be at the upper end of speedo errors allowable ?
Cheers.

Incidentally, redline with a 19t is 107 mph.

Worth getting a GPS speedo app on your mobile phone and taping it onto your handlebars if you really want to know how fast you're going. Deadly accurate and free. then finally just chuck the old speedo away 8)

Anytime I've been at redline, peering at speedos or mobile phones to see if its xx4 or xx5 or xx6 mph or rpm down to the last digit wasn't on my mind...

But we take your point, gps speeds are extremely accurate - once you get much above walking pace.
Good suggestion.

I worry about it when i go over 5500. Many years ago didnt worry about anything, but now since i read access norton stories, 5500 is enough, i start thinking about gearbox failures or some crazy thing even though its all new +3000 miles and probably not gonna fail. Its fast enough for me too. Also i know i take a lot longer to recover from broken limbs now i am in my 50s lol

I agree Jerry, staying below 5500 is a wise thing with these old treasures. I haven't tried the top end on this bike for several years and after reading here of bikes topping out at pretty low speeds, I had to see if my memory of 110 MPH or so was correct. I think this is pretty decent top speed for any stock Commando, especially with a large rider spread out like a flying squirrel on those super wide Western bars.

The tach on this bike is dead smooth, still doesn't mean it is correct, I realize. I could just clip the TOMTOM rider on there to know for sure, but probably won't.
The scenery had a nice blur to it, I know it was well over the ton, good enough for me.
The engine sounded terrific, but then it's been said that they always sound great just before they blow!

Glen

When your 17 years old and have a brand new 850 Commando and everything is new, the speedo and taco were pretty well right on and the speedo did match the speeding tickets that I got at the time (young and silly), as for failures you didn't even think about them when young, as for gearbox bearing failures there was nothing about it when the 850s where new, I was lucky mine blew at 12,000 miles outside my house when I put it in gear in 1979, I had owned it for 3 years from new when it blew.
As for now I don't rely on speedos or tacos even since they have been full rebuilt, after 40 years of ridding my Norton I know what speed and revs I am doing just by the sound of my motor and I haven't had a speeding ticket on it for over 25 year now on it, as for my Triumph Thruxton, well thats another story.

Ashley

My problem was the brakes. Hit the back of a ford capri that was reversing out of a driveway and I was doing approx 60 mph (about 19 yrs old on 750). Had a bad back ever since. I know my brakes are good now, thanks Matt

Rohan said:

ashman said:

850 Commando
with standard gearing (19 tooth sprocket) my bike at flat out got to 116 mph and 6,500 rpms

Click to expand...

There is a (fair) bit of speedo or tacho error there. ?
The workshop manual quotes a stock 850 with 19t as ~100mph @ ~6500 rpm.
You'd have needed 7500+ rpms to do 116 - or a 22 t .

Some of the older magazine tests quotes the shown and actual speedo mph,
and that would be at the upper end of speedo errors allowable ?
Cheers.

Incidentally, redline with a 19t is 107 mph.

Click to expand...

Well Rohan what workshop manual quotes and what happens in real life is two diffrent stories and as for redline at 107 mph is crap as stock they never made it to redline (7,000) 6,500 at the most, you can dispute me if you wish and I don't care, all I know is what I say is pretty close and my speeding tickets match my speedo within 1 or 2 miles diffrents and I was caught a few times over the ton and lost of licence 2 times for it.

Ashley

Yeah, I had a car like that, if you gave it a big rev standing still the speedo would say 100 mph. !

If your story doesn't match the workshop manual, and your speedo doesn't match the tacho,
are you saying the workshop manual is wrong ??

If the numbers don't match up, you have to ask why ?

My 850 I had some years back seemed about right at ~80 mph with the tacho at about 4500.
About where the workshop manual say with a 22 tooth - which I had fitted.

Did 850 models really come with a 19t sprocket as standard ??
Thought that Nortons learned that lesson with the 750...

Gidday fellas and shielas of course. Hope u r all well.

We do all to be showing our age here hey what?.

Bloody hell. 6400 RPM is over 100 revs a second. the piston speed has to be close to 60MPH ??.
Since we telling war stories, a quick one.

I am very close to 60, and have a degenerative type muscle condition.
A sane person probably would have bought a honda by now.

Starting can sometimes be a big problem. but there ways around this. (mates).

But on the days I can start it, I start it on its wheels now..
hanging on at 70 MPH especially with cross winds, I cannot go more than about 3 hrs at a time.

at 70 MPh my speedo is just a touch over 4000, more like 4200. I dont know how that goes to the calculated speed.

I have not lost my licence now for many years, but it was a common occurrence once upon a time.
These days I dont go much above 65MPH at around 3600 rpm.
U have to keep up with the semis on the highway, I dont like B-doubles passing me, very dangerous.

but I have had my bike since 1976. a real dog then but only cost $800 Aussie. it cruised easily at anything over 5000 RPM. Done a few years in Western Queensland. very hot in summer. Only ran straight 50 weight oil back then.
Did no damage but rattled a lot.

A couple of photos of my fastback. About to slip some premiums Amals on. My old Mk1's lasted forever, horrible idle and all, but there comes a time!!.re the photos, I only own the Norton.

Beautiful Fastback.

Cheers.

ashman said:

Well Rohan what workshop manual quotes and what happens in real life is two diffrent stories and as for redline at 107 mph is crap as stock they never made it to redline (7,000) 6,500 at the most, you can dispute me if you wish and I don't care, all I know is what I say is pretty close and my speeding tickets match my speedo within 1 or 2 miles diffrents and I was caught a few times over the ton and lost of licence 2 times for it.

Ashley

Click to expand...

My '73 850 would always pull redline. I was tired of getting beat by my mates Combat so one day I put a Dunstall (Blair) 2-1-2 exhaust on it and at the same time changed to a 19 tooth sprocket. With the speedo reading a hair over 111 mph I had to roll off the throttle to avoid overreving the engine and boy did she get there quickly. The only time it wouldn't pull redline was when I installed a belt drive primary and miscalculated the ratio and ended up with too tall a gearing.
I had a Bonnie that read 130 mph when flat out but I knew that couldn't be right so I took the speedo into our local Smith's agent and had the speedo tested. It read spot on at 100 mph and 1 mph over at 130 mph. It was suggested that vibration might be causing the error so next time I flogged it to 130 mph I whipped in the clutch and the speedo instantly dropped to 115 mph.

So are you suggesting that 116 @ 7500 is possible in an 850 with 19t ?
Or its a vibrating speedo ...

Surely your top speed depends on what ratios are inside the gearbox ? If you are running very high overall gearing with a close box, after the bike has lurched up to a fairly fast speed the close ratios get the bike up to top speed faster, and that top speed is a bit quicker. It's a matter of keeping the engine on the boil and riding the top of the torque curve.

acotrel said:

Surely your top speed depends on what ratios are inside the gearbox ? If you are running very high overall gearing with a close box, after the bike has lurched up to a fairly fast speed the close ratios get the bike up to top speed faster, and that top speed is a bit quicker. It's a matter of keeping the engine on the boil and riding the top of the torque curve.

Click to expand...

Ultimate top speed doesn't really depend on the lower ratios.
A Commando box has a 1:1 top gear ratio, effectively it bypasses the gearbox by locking the output top gear to the back of the clutch. So long as you change into top at reasonably high rpm, only the top gear determines the top speed.

Rohan said:

So are you suggesting that 116 @ 7500 is possible in an 850 with 19t ?
Or its a vibrating speedo ...

Click to expand...

I suspect vibration is a factor. Ive always stuck to the 7,000 rpm redline. One year on the last ride of the season I saw 7300 in second gear and later when I had the head off there was evidence of a slight kiss from a valve in the carbon on top of one piston!
My speedo reading of 111 mph seems to be in line with your theoretical top speed of 107 mph.

Thats not 'my' theoretical top speed.
Thats one of the numbers listed in the Factory Workshop Manual.
(And 7000 rpm is redline, although it mentions elsewhere that max cruising speed rpm is less)

19t @ 7000 rpm = 107 mph
etc etc
23t @ 7000 rpm = 130 mph