2S Cam into an 850

I've put a new AN inlet valve into my 850 head and the measurement from the underside of the valve cap to the head's seating face is 1.351". The factory dimension for the fitted outer spring length for the Combat (2S Cam) is 1.321"
So 1.351 minus 1.321 = 0.030" - this gives me 0.030"for the spring seat and any shims ,The spring seat is 0.100 thick and so would over load the spring
I've machined the spring seat down to 0.065" thick as mentioned in the factory notes but that leaves me with the 0.030" - 0.065" = -0.035" ~ that's minus 0.035 inches. so to get the required fitted spring length do I machine the valve's collet shoulder up towards the valve tip so as to move the valve cap up 0.035"?
Lots of people have fitted this cam to their 850's but not read anywhere of this problem.
cheers

Are you caps steel , alloy or titanium ?

Yes, you can machine the valve stems to raise the collet, it is what Jim Schmitt does to fit his beehives. Is it the first thing you should do? Possibly not.

Why does the problem present itself? We should ask what is the history of the valve seat? Of course you may not know.

Has it been replaced at some point? Is the valve too far into the combustion chamber?

Remember that at some point you will be measuring the clearance between the valve at full lift and the piston, particularly if you are increasing compression as well, which you should be doing for the 2S cam.

Can the valve seat face be cut 0.035" to 0.040" deeper into the head without shrouding the valve?

The reason there isn't much talk abut this issue is probably related to the fact you are fitting a common high lift cam, but one that is happy using standard valve springs, seats and retainers.

So lots of people probably didn't check the installed height to fit this combination and haven't fussed too much with valve seating pressures. Indeed, I suspect that 0.035" extra spring compression isn't going to make that much difference.

Others will have felt that the critical issue rather than installed height is coil bind at full lift. 0.050" or more from coil bind at full lift is probably fine.

I been using a 2S cam grind in my 850 since 1982 and I am still using my original valves and springs without any mods to them, my ports have been done and my head has been shaved, my push rods haven't been mod, in all these years my head has only been off the motor a few times since, my motor runs very well and was my everyday rider till 2013 since my Thurxton has taken over everyday use but I am retired now, but the Norton still gets ridden regularly, when I first built the motor with the 2S cam I just made sure the valves didn't touch the piston tops, my motor still has a lot of compression even after all these years of running.
My stock motor use to only rev to 6500 RPM but the 2S cam will run freely past 8000 RPMs if you let it but not wise.

Ashley

wotcher Gotta DO , is - Have . 040 clearance . here & there .

.040 OFF coil bound , at full lift .

.040 clearance - piston to valve - wind in a extra one turn , is it , at the tappet adj. turn over judiciously , gingerly & cautiously If it STOPS , STOP .
alternately , fit the head without the .040 gasket , and turn the engine over . Same Cautions as before .

Your much better off with the W&S springs ( NORVIL ) if you can find em . Came with keepers caps & shims .



might want some carburation .


Rocker ratio ISNT 1 : 1 .

I bought a 2S cam a while back, and decided not to install it. Have you tried to get the best out of the normal cam ? In the 1950s, Australian riders such as the Hintons, Keith Campbell and Bob Brown raced Manx Nortons in Europe. Because we use methanol fuel in Australia, our guys were accustomed to the speeds in Europe. However they found the Brits could get their Manx Nortons going as fast as the Manxes in Australia, using petrol. It takes a lot of patience to get a motorcycle optimised. When I built my Seeley 850, I was not overly concerned what the cam profile and compression ratio might be. I simply adjusted everything to suit what is there.
Whatever the cam might be - within reason, it can be made to work.. All that probably happens when you change the cam, is you move and reshape the power band. You compensate for that with the bike's gearing, and the handling. The exhaust system might be more important than the cam profile ?

Like I said before AL you have never experienced a Norton with a 2S or a higher lift cam but my cam is not all that has been done to get my motor breathing as well open exhaust with only enough baffle to keep the cops off my back when in the suburbs.

Matt Spencer said:

wotcher Gotta DO , is - Have . 040 clearance . here & there .

.040 OFF coil bound , at full lift .

.040 clearance - piston to valve - wind in a extra one turn , is it , at the tappet adj. turn over judiciously , gingerly & cautiously If it STOPS , STOP .
alternately , fit the head without the .040 gasket , and turn the engine over . Same Cautions as before .

Your much better off with the W&S springs ( NORVIL ) if you can find em . Came with keepers caps & shims .

Performance Mods

PERFORMANCE MODS

commando.yolasite.com

The Story of the Fastest Norton

Here's the story and it's not a bad read and even if there's only a grain of truth it is still a bloody quick old cycle. Cash

www.accessnorton.com

might want some carburation .

https://www.motos-anglaises.com/catalogues/Dunstall/manuel_dunstall_1970_preparation.pdf

Rocker ratio ISNT 1 : 1 .

Click to expand...

I suspect there are some big porkies in that fastest Norton story. The cam they describe is " like that used in the 650ss". That would be the stock profile that was in every non Combat Commando, nothing special there. It makes less power at 6250 than it does at 5800. It doesn't make 68 bhp at crank or anywhere else.
They had that bike doing 100 mph sideways wheelies with just the 68 claimed bhp.
Low 11s in the quarter ? You need about 100 bhp minimum for that.

A fun read tho, even if it's fiction!
Glen

worntorn said:

I suspect there are some big porkies in that fastest Norton story. The cam they describe is " like that used in the 650ss". That would be the stock profile that was in every non Combat Commando, nothing special there. It makes less power at 6250 than it does at 5800. It doesn't make 68 bhp at crank or anywhere else.
They had that bike doing 100 mph sideways wheelies with just the 68 claimed bhp.
Low 11s in the quarter ? You need about 100 bhp minimum for that.

A fun read tho, even if it's fiction!
Glen

Click to expand...

In late '75 I saw the engine from that bike!

I knew Dave Rawlins from club racing a production Fastback in '75, and I was starting a build for open class racing using a new Rickman chassis.

Dave sent me to see his colleague, well ex-colleague, Mike Sadler. Mike had been made redundant and was selling the motor he was building for his own Rickman racer. I bought it and went to collect. In the corner of his shed was his own bike, and he told me that the motor in that held 4 world records on the drag strips, yep, that was the Baker engine from the bike in the article.

Both Dave and Mike have now passed on, but coincidentally after more than 40 years I had made contact with both of them on Facebook before they did.

In chats, the same comments made at the time were repeated.

The motor I did buy came in unbuilt form, all new pieces and a few lightly used special pieces. So several parts were MkIII parts from the experimental shop where Mike worked, and others were shorts stroke parts from Thruxton.

I never met John Baker, but I did own the short stroke head he had reworked for Mike Sadler for several years.

The motor was an 850 and did not rev over 6800, except when it went bang at 7200! And it's difficult to compare gearing because following Mike's advice I used a 33t engine sprocket with the Commando clutch and subsequently a small gearbox sprocket.

That 11 second stuff is just a bit tough to believe, unless they were using nitromethane?
A friend of mine modified his Thruxton R then went drag racing with it.
He also ran it at Bonneville several times and managed to get a two way 151 mph from it, after a few years of modifying. Initially in stock form his Bonneville speed was 133 mph.
On the dragstrip he did very well in 75 or so runs. His technique is very good and he managed to beat a great number of newish litre sport bikes and 600cc Supersport as well.
I think he only lost in a couple of races, one was with a zx1400.
His very best 1/4 mile time was 11.2 seconds, corrected for elevation.
I have watched his videos and know that these are real results.
The bike is making about 115 bhp at crankshaft, according to dyno runs.

Just for fun, he races a modified and much lightened Rocket 3 here.
This is an 11.83 second run at a fairly high altitude.





Glen

One of my friends is a big millionaire - he owns Motec. He has worked on tuning cars and motorcycles for several decades. His engine management systems are used in Porsches and Ferraris. Many years ago, I had a conversation with him about ignition systems. He does not sell an ignition system on it's own - only ever complete engine management systems. In the 1970s, he was in the UK, and fitted an EMS onto a Honda. They simply fitted injectors into the bellmouths of the carbs, and turned the fuel off to the carbs. They immediately picked up a second per lap. It does not sound like much, but it is a lot. I think the bike was the one Barry Ditchburn rode at Mallory Park when Hailwood won on a Ducati.
The upshot of my conversation, was - to use a better system, we would need a throttle position sensor.
When you use petrol as fuel, you are really behind the 8-ball. It has twice the calorific value of methanol, but when you use methanol, you use twice as much. The difference is in the level of mixture control you can achieve. With petrol, your tuning errors are twice as big.
When you fit a different cam, you still have the same problem.
I have fitted race cams into old motorcycles for many years - I always got a stronger power-band - but I did not re-tune the motors and exhaust system to adjust to the different cam. So there was probably always untapped potential.
A standard Commando cam has similar timings to a Triumph E3134 race cam. It should be good enough, if everything else is tuned to suit it.
Have a look at the start line in this race, and you will see the Motec Honda.

When I had road bikes, they always had hot cams. But I was too stupid to tune the motors and exhaust systems properly. If they ran well, I thought they were OK. With the hot cam, they were always quicker. Some of my mates had similar bikes, but new - they always seemed to be better. Back in those days, I believed I knew what I was doing. - Then I went racing and found out different.

worntorn said:

I suspect there are some big porkies in that fastest Norton story. The cam they describe is " like that used in the 650ss". That would be the stock profile that was in every non Combat Commando, nothing special there. It makes less power at 6250 than it does at 5800. It doesn't make 68 bhp at crank or anywhere else.
They had that bike doing 100 mph sideways wheelies with just the 68 claimed bhp.
Low 11s in the quarter ? You need about 100 bhp minimum for that.

A fun read tho, even if it's fiction!
Glen

Click to expand...

'Then I went for it, Blasting down the smooth bitumen with my chin on the tank, boots on the rear pegs and left hand holding the fork leg to keep it out of the wind.
Clutchless gear changes were made with my left hand so I didn't have to move my feet from the rear pegs.'

If the motor makes less power at 6250 RPM than it does at 5800 RPM, I would modify the exhaust system. When data is multivariate, cause and effect become patterns. We usually only change one factor at a time, but when tuning a motor we need to consider the variables in combination with each other. Changing a cam but retaining a restrictive exhaust system, does not do much. The exhaust system, inlet tract, cam, jetting and gearing all work with each other. When we start changing things, we need to notice trends, and try to optimise to suit the way the bike is to be used. In many situations, peaky power delivery can be worse than smooth power delivery.

Yes and after the Combat fiasco Norton was quite happy with a bigger, beefier engine that made max power at a bit lower rpm. More power thru the meat of the rpm range, about the same at top, but uses less revs to do it.
Not a bad solution to a serious problem.

Glen

worntorn said:

Yes and after the Combat fiasco Norton was quite happy with a bigger, beefier engine that made max power at a bit lower rpm. More power thru the meat of the rpm range, about the same at top, but uses less revs to do it.
Not a bad solution to a serious problem.

Glen

Click to expand...

Trouble with that is it puts more torque into the already on-the-limit gearbox

That is true. A motorcycle mechanic friend of mine worked at repairing Commandos beginning in the mid 70s right up until he passed away last year.
He told me that he saw many more gearbox problems from 850s. Part of that might be due to the greater number of 850s, but it also makes sense that the extra torque adds strain and that means more wear.
They do seem to hold up fairly well to a stock 850 if used for normal road use.
Another clubmate has a stock 73 850 which has owned since 77 when it had less than 10,000 miles. It was his only transport for many years so he racked up the miles, 128,000 to date.
He rebuilt the engine top end at about 70,000 and totally rebuilt the engine just recently. The gearbox got new bearings just because it was apart for this major redo of the bike.
All else went back in, still original shafts and gears.


Glen

A belt drive primary is greatly appreciated by the transmission.