650SS speed issues, vibration and everything else

The gearing you quote is good enough for over 110 mph. So either the speedo and/or the rev counter are dodgy or the clutch is slipping. Probably all of these!!!

My own 650 is a jack hammer special above 70 mph, whereas my previous Atlas 750 was turbine smooth.

The difference........the Atlas had super-light pistons matched with a balanced crankshaft. The 650 had the opposite because I was trying to beat a build deadline and did not stick to my original plan.

To stop the 650 clutch from slipping I had to wind the adjuster nut nearly fully home. You then need a Gorilla sized hand to operate the lever. Plus the cable keeps breaking. A belt-drive conversion is one cure for these problems.

No need for CNC rods as better forged rods still availiable. Hemmings can advise on forks. If existing pistons in good order get them lightened and the crank balanced. 80 mph is only a cruise for any good SS ,the std 88/99 clutch is good for a ton .

Some good points here Dave. Out of balance carbs will cause bad vibes and rob the bike of power. Are the carbs correct for the engine? I put two big concentrics on my 650 bike and it actually went slower!!!

I only found a 5 speed gearbox useful on a track day run. An AMC 2 gearbox is fine for the normal power range of the 650 engine.

Previously Tom Mudge wrote:

Hello, first time forum poster, long time stalker. Probably met quite a few of you at the rallys.

On to the serious stuff, bought a 650ss in bits. kinda threw it together. It rode OK, but needed to come apart again so istripped it back down after a rally and made a list of stuff that i thought was all sorts wrong.

Mainly the speed of the thing was all off, got onto a nice stretch of road and opened it up. i got 80ish mph, in top gear, at red line (WHAT!? the book said 115!).

Another problem with the bike was that i lost feeling in my right side after 10 mins, the left side took only another 5 mins. It shakes like crazy!

ive attached a photo of my sprockets n' clutch. engine sprocket is 21T, clutch 42T, Gearbox 19T and rear is 42T.

Im going through the whole thing changing & lightening all sorts, from drums to disc brakes. 4 speed gear box (why? why was this a thing!?) to 5 speed. and suspension ("road holder forks"!? you mean "bottom out Stalks"!!).

Can anyone suggest whats going on? any help would be greatly appreciated. Thanks in advance!

Hello Tom, it does sound as though the clutch is slipping, but don't believe all the speed claims made for the 650ss - I had a brand new machine 1967, which was well run in and would manage just over 100mph(indicated ) in 3rd but on the straight would never go any faster in top! It also threw oil out of the engine breather after driving for about 30/40 miles, didn't burn any oil though and when returned to the dealers was taken by the late John Hudson who altered the return pipe in the oil tank, checked the engine settings and track tested it at Elvington, and confirmed that it was correctly set up and would only hint at the fact that the speedometer was very accurate-hence a disappointed buyer as I went proddie racing with it - eventually getting somewhere near the claimed output after spending a lot of money(oversized carbs, inlet sleeves removed, curley cams, h/c pistons special v/springs, etc)

Regarding the vibration, did you check the primary chain tension afterwards, I had a similar happening at a track day with my current 650ss,the bike slowed and vibrated badly, I was thinking all sorts but the gearbox had moved under braking and downwards gear changes and pulled the primary chain tight.

As for it shaking, that's a headache, could be tyres/tyre pressures, rear/front suspension, head bearings, sw/arm bushes, wheel alignment - AAARGH!!

good luck with it, hope that its nothing major!!

Regards Terry

Hi Terry, After 1963 you did not buy a new Norton. It was a lash up by AMC . I'm not surprised you were dissapointed. Even in the good old Bracebridge St days the bikes were not totally consistent .If you got a good one they were brilliant but everything had to come together just so.

I've got the answer.........its not the clutch slipping. Its the Rev counter drive box. These came with a choice of 1:1. 2:1 or 4:1 ratios. It is quite obvious that you've got the wrong one and your engine was only actually peaking at 4000rpm. You need to open the throttle a bit more.

Looking back at some of my old Magazine road tests. I note that the 750 Commando, with a 19 tooth gearbox sprocket was only good for 105mph two way average. This rose to 115 when the g/box sprocket was changed toa 21 tooth item.

The Motorcycle, in a 1962, got their 650 to a two way average of 111 mph. They quote a final gear ratio of 4.53:1 which suggests an AMC2 gearbox using 21T engine, 19T gearbox & 43T rear sprockets. Assuming little tyre and clutch slippage this equates to an engine speed of around 6500 rpm. To achieve 120 mph, on this gearing, would require over 7000rpm.

This is useful gearing chart, just add your own ratios and sprocket sizes and bobs your uncle!

http://www.gearingcommander.com/

dan

Hi Tom,

Totally agree withPhil,on your gearing 100mph should be around 5750 revs. At 8000 rpm I think your engine would have been strewn along the hard shoulder. Unless your miss a gear, it's unlikely you will over-rev the engine in top so give it what you can with the right conditions and see how it is then. Regards, Richard.

Terry makes a very good point. 115mph may have been possible with a factory prepared road test bike but pretty unlikely from one off the showroom floor - despite what some people claim.

Before going wild with major expenditure, some time spent on the simple things may well make a substantial difference. Ignition timing and carb tuning being the first items, though if you are a student of that excellent tome Tuning for Speed, tyres, chassis and brakes arewhere you start. Then transmission and finally engine. For vibration, the head steady is the most obvious culprit. When mine was loose, the vibration shook the plates off the battery.

Purist, me? Nah, anything that makes a bike more usable has got to be a good thing. Looking forward to seeing how this one turns out.