How fast is fast???

[clive]

Further to my earlier post... I should perhaps add that my M18S engine has the inlet valve timing advanced by 18°. Easily achieved by using the 350cc engine timing 'dots' on the inlet cam gear. Rumour has it that the factory retarded the timing deliberately to make the engine more of a 'slogger' and better suited to hauling a sidecar.
I have also fitted a lightweight inlet pushrod rocker arm which is 1/8" shorter than the heavyweight equivalent arm. This changes the rocker assembly ratio, giving the inlet valve more lift. It's probably due to these mods, and the slightly raised gearing, that the bike runs happily at 70 mph.
John

From which year can you perform the above change - does it depend on whether it has hairpin or coil valve springs (mine is an iron head 49 500)?

Have you got it running again Samuel?

[Jdraper]

I fitted a cheap electronic rev counter which shows around 2800rpm at 60mph. I changed from a 16 tooth gearbox sprocket to 19 - quite a difference. May go down to 17 or 18 if I don't like it. 16 was way too low.

Not sure what a suitable redline would be, but it pulls strongly to 70, thereafter I will only go faster to overtake..

Jeremy
52/55 18S fresh(ish) engine

[Samuel]

Have you got it running again Samuel?

No touched it yet - it is garaged up in Rushden and I've been at work non stop for last few weeks.

[Pharisee]

I regularly run it along the A1 from my home in Lincolnshire to my old haunt in Hitchin and back.

Does that mean we'll see you at the Old George in Ickleford Wednesday evenings then John?

You'll need a good dynamo because it'll be dark by the time you get home!

Alan

I was having lunch at The Strathmore Arms in St Pauls Walden last Wednesday. Didn't know (or perhaps, didn't remember) about a meeting at the Old George. Maybe next time.
Dynamo and lights are ok, thanks

[Group Leader]

I was having lunch at The Strathmore Arms in St Pauls Walden last Wednesday. Didn't know (or perhaps, didn't remember) about a meeting at the Old George. Maybe next time.

http://www.jampot.com/forum/viewtopic.p ... 01#p224401

Alan

[Pharisee]

I fitted a cheap electronic rev counter which shows around 2800rpm at 60mph. I changed from a 16 tooth gearbox sprocket to 19 - quite a difference. May go down to 17 or 18 if I don't like it. 16 was way too low.

Not sure what a suitable redline would be, but it pulls strongly to 70, thereafter I will only go faster to overtake..

Jeremy
52/55 18S fresh(ish) engine

I've seen G80S power quoted as 28bhp @5,600 rpm (32bhp @5,750 for the CS)
With standard sprockets, (40/21 x 42/16), the overall top gear ratio is 5.0:1 for the G80S. That would equate to a top speed of somewhere around 85mph if you could hit peak power in top (with a 3.50 x 19 rear tyre)
The CS is significantly lower geared as standard (40/18 x 42/16) at 5.83:1 but has peak power at a higher rpm. It also has a larger 4.00x19 rear tyre with a proportionally larger circumference. Approximately 82mph at 5750rpm. Now... put a 19 tooth gearbox sprocket on the CS and the gear ratio drops to 4.91:1. That's much closer to the touring model ratio. That would give a theoretical top speed of just under 100mph.

As I said earlier, my M18S runs a 21 tooth engine sprocket and a 17 tooth gearbox sprocket. That's an overall top gear ratio of 4.7:1 and that's high enough for me. If you've got a 19 tooth gearbox sprocket with a 21 tooth engine sprocket, the top gear ratio will be 4.21:1. You would probably have to seriously slip the clutch and give it some beans to pull away from standstill.

John

[G12atlast_LAPSED]

In contrast to what has gone before: both my '55 18S and 50 rigid Model 18 are happiest at 40-50mph, even happier plodding down lanes.

Both will do 60 but, especially compared to a modern bike, are unpleasant to ride at that speed for anything other than brief bursts.

The 18S had noticeably more oomph than the 18 - I suspect this is connected with it being a 350 bottom end and perhaps the cam timing mentioned above.

It's quite possible that I may be a lightweight, effete biker but I would say the same of all the 500 singles I've owned across the range of Brit manufacturers (I've had about half a dozen). Enjoy them at the speed you feel comfortable with and buy a modern bike to go faster more comfortably.

[g80csp11]

my 1946 G80L has been known to do 70 mph on the odd occasion , but certainly not happy and seized an exhaust guide a week later .
generally happy at 50 -55 mph
Did mage to do westwood ho a few years ago 100 miles to Newbury for a midnight start and then 180 miles to Lynmouth overnight arriving early hours for breakfast
340mile back home on Sunday

I remember Bob Piper and Andy Davies pushing all the way home , 55 - 60 mph

now days stick to 50 -55 mph on it , not sure id want to ride it to a jampot or alternative after all its 74 years old and deserves some respect
ideal for club runs and riding don to the Talmag once a year

[Andy51]

Hi, my '54 18S runs HS cams, otherwise uses standard settings for the year, same as the CS version. It happily cruises at 70 mph with plenty in reserve. I have seen high 70s on the clock, and contemporary reviews in the day rated the 500 singles' top speed as low to mid 80s. The same sources put output of the road singles at around 25 bhp, very similar to its contemporaries. The Velo MSS (massively outsold its sportier brethren) and Vincent singles were slightly better at 27/28 bhp. None were designed for speed, but for all round 'plonking' and sidecar tugs. If you wanted to go fast on a single, you bought a Venom or Goldie (34/42 bhp) or, more likely, a twin. HS cams do give a noticeable performance boost, but make the bike 'uncomfortable' at under 35 in top, so no plonking through built up areas - you have to rev a bit through towns, unlike the 'cooking' version which is perfectly happy in top around town and is really in its element in top gear most of its time, as it was designed to be. The CS is also much noisier, both exhaust wise and mechanically (exhaust valve opens much earlier with higher pressure, and cams have no quietening ramps). There are also the brakes to consider when riding fast, AMC brakes were reckoned to be marginal even in the day, although most of its contemporaries also used 7 inch brakes, with the noticeable exceptions of BSA (8 in) and, of course, Vincent's dual set-up. Given the way I, and most club members, ride these days the value of HS cams is questionable, but when I fitted them some years ago I was less cautious about riding old bikes at speed. I have now got a modern bike and am now looking at reverting to H cams, as they are a better fit to my riding style on classics. Cheers, Andy

[SPRIDDLER]

En route to the Milan IJR (800 miles) 'Thrifty Peter' on his P11 and me on my '54 G3LS plus all camping gear met up by chance with a pal at a camp site in Switzerland in his posh motorhome.
We arranged to ride behind him next day provided that he kept to a max of 60 which he did wherever possible and for long periods at a time.
I found that at 55 to 60 my 350 runs into a sweet spot when vibration virtually disappeared and it seemed to spin quietly like a turbine but I did find it necessary to stuff a rag into the gap between the nose of the dualseat and petrol tank to quieten the annoying chatter from the carb.