The 650 Norton thread

[Fast Eddie]

annajeannette... you are replying to comments posted in 2012... by a member not seen on the forum since 2015...

 

[t ingermanson]

I'm going to risk some ire, and breathe a bit of air into this one.

While researching the difference between a 650ss and Mercury, I'm not getting very consistent performance info. Seeing a variation in bhp, from a claimed 47 to 52 (most claiming 49 for the 650ss). With the single carb on the Mercury, I would expect lower performance values, but not sure how much.

Does anyone know if the Mercury was detuned more than just the subtraction of a carb? Still running the SS cam? Same 9:1 pistons? I read that it may have been "tuned for unleaded fuel", but what does that really mean? Given the reputed state of Norton at that time, I can't imagine there was much done engine-wise for the inventory-clearing exercise that the Mercury seems to have been.

Somewhere THE INTERNET claims the Mercury was more of a "touring" bike, and I understand the lower compression Atlas was marketed as such, but can't find any actual information that points to a touring intention of the Mercury other than a single carb. Is that all it took to make a "touring bike" out of what was marketed as the top road scorcher the year before?

I understand the 650ss changed over to larger concentric carbs late in its run, and therefore the Mercury too? Is there a measured power loss? Many say their Dommie "runs better/stronger/faster/louder with monoblocs", but what's the data, if any?

Does anyone have any Norton literature or period magazine testing that differentiates the two models more? I'm mostly concerned with motor differences, not the tinware.

Thanks.

 

[norton bob]

Most likely that the Mercury was a stopgap to use up the remaining feartherbed stocks. Why touring Trim?, a likely explanation is that they did not have/could not afford the Expensive deep valenced chrome guards so reverted to the cheap light painted guards and painted case ,a single carb fits well with that image. Can't imagine that they would have commissioned a batch of LC pistons just for that. Even if there is somewhere an "Official" explanation I would take it with a pinch of salt as they were past masters in propaganda.

 

[t ingermanson]

Most likely that the Mercury was a stopgap to use up the remaining feartherbed stocks. Why touring Trim?, a likely explanation is that they did not have/could not afford the Expensive deep valenced chrome guards so reverted to the cheap light painted guards and painted case ,a single carb fits well with that image. Can't imagine that they would have commissioned a batch of LC pistons just for that. Even if there is somewhere an "Official" explanation I would take it with a pinch of salt as they were past masters in propaganda.

Yes. Exactly, and why I would like to figure out what was actually inside one of these motors from the factory and what I should expect to see when opening one up.

The info on the 650ss seems pretty exhaustive, but not much is out there when it comes to the Mercury.

 

[dynodave]

I'm pretty much in agreement with NB.
The 650 components readily available to assemble this slimline should be fairly straight forward.
There are several examples of 06-0380 head cores originally intended for commando, as being finish machined as small bolt pattern, small combustion chamber, no spigot counterbore, and featherbed top of head oiler, regular 1.4" intake valves instead of 750/1.5" .
SS cam like ALL NHT of that period(61-70). crank, rods, cases (finished for small bolt pattern barrels) only difference is the flywheel.
All you need to do is reintroduce the 1x2 intake manifold from the early atlas.
Turn it over to the marketing department and bingo, one carb touring bike.....LOL

 

[t ingermanson]

I'm pretty much in agreement with NB.
The 650 components readily available to assemble this slimline should be fairly straight forward.
There are several examples of 06-0380 head cores originally intended for commando, as being finish machined as small bolt pattern, small combustion chamber, no spigot counterbore, and featherbed top of head oiler, regular 1.4" intake valves instead of 750/1.5" .
SS cam like ALL NHT of that period(61-70). crank, rods, cases (finished for small bolt pattern barrels) only difference is the flywheel.
All you need to do is reintroduce the 1x2 intake manifold from the early atlas.
Turn it over to the marketing department and bingo, touring bike.....LOL

That sounds great, what was expected, and what I was hoping for. Just picked up a late Mercury motor, so it'll be interesting to see what's inside as opposed to the 67 650ss motor I've got. I realize they were all built at once according to lore, but the number is late in the run, so it may have something interesting going on. Or perhaps not any more interesting than any late 650ss.

 

[norton bob]

John Hudson ,Norton factory guru and the most practical Norton owner ever ,ran a Mercury to the end and thought very highly of it.

 

[elefantrider]

"I understand the 650ss changed over to larger concentric carbs late in its run, and therefore the Mercury too? Is there a measured power loss? Many say their Dommie "runs better/stronger/faster/louder with monoblocs", but what's the data, if any?"

I'm currently looking for the same info. What are the induction differences between years of 650SS. Some of the 650 inlet tracts I've seen have had tube reducers. What was the hot induction setup for period race 650SS-based Domi bikes?

 

[worntorn]

The bike was pretty good out of the box, according to my friend Murray Neibel.
Murray raced at the Westwood circuit with a Norton Manx and later a Suzuki x6. He generally won the 250 championship there.
He told me that the 650ss bikes surprised everyone when they showed up sometime around 1963.
The 650ss that held the track record thru the early sixties used a Manx frame for the weight savings.

Some 650ss owners fitted 99 pistons into their 650ss engines. I've forgotten if it was the dome of the 99 piston or the wrist pin location that gave the 650ss substantially higher compression with the 99 pistons. Iirc it moved cr from 8.9 to about 11 to 1.

Glen

 

[acotrel]

I was under the impression that the only twin carb 650 was the Manxman. Was that a 650SS ? My mate had one - it had ape-hanger bars as standard. It was pretty quick. Norton twins seemed to be fast even with only one carb. I think they were just built better than Triumphs. The Norton factory had a different mindset. Turner was not interested in racing, but that was what Norton were really about, at least early on. Peter Williams did not seem to get much support.

 

[acotrel]

I'm currently looking for the same info. What are the induction differences between years of 650SS. Some of the 650 inlet tracts I've seen have had tube reducers. What was the hot induction setup for period race 650SS-based Domi bikes?

I would love to own that bike. It would be a real buzz. Most people probably do not see in it what I see. A 650 can be better than an 850/

 

[acotrel]

I think a lot depends who was working in the factory. It is probably almost impossible to improve on the head design of the Manx and still stay two valve. The guys who build race bikes probably do not usually adjust their thinking to cater for road bikes. That is the reason Peter Williams suffed-up the steering geometry on the first Commandos. It would be interesting to get one and fit a steering damper.
In the old days, it was thought that steering dampers were used to fix bad handling. That race steering is very different to road steering.

 

[worntorn]

All years 650ss were twin carb.
The Manxman came first. It was essentially just a peanut tank 650ss in gaudy colours that Norton thought would sell well in the US.
They were wrong!

 

[worntorn]

Manxman and 650ss

 

[Schwany]

Most people probably do not see in it what I see.

Of that I am certain.

 

[acotrel]

I often wonder about the difference between twin carbs and single carbs. A single carb requires less work to get tuned, so it might more often be tuned with less error. When I was a kid, we tried to copy racers. But I think we often fooled ourselves. The main thing with four-stroke motors seems to be, to avoid over-porting them, and getting the needle and needle jet, and ignition advance right. A hot cam makes a difference, but it changes the power band, and the wrong exhaust can stop it from working.
There were not many bikes which were faster than a 500cc Manx in Allpowers races prior to about 1963, but a 650ss was. The Super Rocket BSA was fast - twin carb, not that it means much. When you see these things, you never know how the bikes are geared. They are faster and slower in different places. THe most memorable 650ss I watched, was at Bathurst in the hands of Jack Forrest. But he was an international rider, so the bike would have been really right for the circuit.

 

[elefantrider]

For best performance, I think the standard rule still applies: single carbs for single cylinders.

Dual carbs for dual cylinders.

Still looking for any information on 650ss different induction set ups.
Here is a 650ss racing head with inlet reducers.

 

[Seeley920]

I think a lot depends who was working in the factory. It is probably almost impossible to improve on the head design of the Manx and still stay two valve. The guys who build race bikes probably do not usually adjust their thinking to cater for road bikes. That is the reason Peter Williams suffed-up the steering geometry on the first Commandos. It would be interesting to get one and fit a steering damper.
In the old days, it was thought that steering dampers were used to fix bad handling. That race steering is very different to road steering.

STOP, Stop with the BS.

Peter Williams did not "stuff up the geometry on the first Commandos" He wasn't even working for Norton at the time. The first Commando Peter saw was at the Earls Court Show, just like the rest of the public (he told me so himself)

What was wrong with the Commando steering geometry.... factually, not in your inexperience and meanderings.

Do tell us! You have been corrected on this (and everything else) on multiole occasions.

Commandos were not designed as race bikes, nor were many other bikes .... the world doesn't revolve around racing. Most people wanted a bike to go to work on, not to race

 

[worntorn]

and BSA SuperRockets were never twin carb....or fast.
There is an optional a10 twin carb head that BSA offered in the parts catalogue. These are very rare and expensive today.
According to those that have fitted it, it adds no power. I guess it isnt a good design.

Glen

 

[dynodave]

and BSA SuperRockets were never twin carb....or fast.
There is an optional a10 twin carb head that BSA offered in the parts catalogue. These are very rare and expensive today.
According to those that have fitted it, it adds no power. I guess it isnt a good design.

Glen

BSA A-10 cylinder head profiles

BSA cylinder head profiles

Drive Train- featherbed

featherbed/Wide line engines and codes 500cc code 12-2 and 600cc code 14 Code is on LH side of case under barrel. Later ones are adjacent to patent badge on...

nneno.org

Drive Train- featherbed

featherbed/Wide line engines and codes 500cc code 12-2 and 600cc code 14 Code is on LH side of case under barrel. Later ones are adjacent to patent badge on...

nneno.org