Do you spin your stock Commando over 8,000 RPM?

There is no guarantee how accurate the SSM tachos are. Would it be reaonable to assume that they may read up to 10% high, much like the speedos ?

My tacho is built out of a T160 unit and for some odd reason they don't have a red line on them and I rode around for years thinking that it was at 7500.

On my standard Mk3, I regularly saw 7500 in third before changing up but I don't think that it ever ran that high in top with a 21t sprocket on.

I've done Autobahn days up from southern Germany with the clock close to 6000 most of the way but any faster than that would be 'thrashing' rather than 'cruising' in my opinion.

Good point about tacho accuracy.
I have seen something that speedos were required to show more than true speed for legal reasons,
and that maybe tachos were more accurate.
But this could be total BS.

Exhibit 1.
These from published roadtests of early Commandos.

Note the graph of speeds and gears - and the graph drawn to 8000 rpm top speed !
This commando appears to be quite low geared (small gearbox sprocket), so to get that top speed would need a few revs on in top.
Note too the indicated gearchange points at redline...



And from another test - no redline on the tacho.



Next exhibit will be a quote about revs and 1/4 mile speed testing....

Rohan said:

Click to expand...

Note the dashed lines beyond 7,000 RPM indicating theoretical/unknown/assumed/whatever.

Also note, it was a 1/4 mile test, so the main curve was also theoretical.

Extrapolation is an art.

Amazing how the RPMs never dropped at the gearchanges!

I want one of those engines...

110 mph/8000 rpm in 4th is very low geared. Smiths gages in good order are as accurate as any ever made, after a very short interval .5 sec to stablize. As long as there is not much crank flex going on then everything is oil layer protected. I want a witness bolt run up against the flywheel to see when the crank is flexing enough to back off from.

Phil Irving's book says to check tach with a single flourescent shop light. It strobes 3600 per minute, in US with 60hz power. Turn other lights off, rev motor till strobe and crank harmonize, have friend read tach.

My tach and speedo have always been dead nuts on. I checked the tach last year with a fancy digital strobe tach looking at the crankshaft and it was right on the money. If your readings are off by 10% that is a lot. If it is off that much then there is something wrong.

I've wondered if, after the Combat and Pre-Superblend issues, whether the factory might have specified an optimistic tach to hold the revs down.

batrider said:

My tach and speedo have always been dead nuts on. I checked the tach last year with a fancy digital strobe tach looking at the crankshaft and it was right on the money. If your readings are off by 10% that is a lot. If it is off that much then there is something wrong.

Click to expand...

I think that my instruments are pretty good actually. I was just pondering the possibility that an indicated 8000 rpm might not really be quite that high.

batrider » Tue May 14, 2013 8:57 am
My tach and speedo have always been dead nuts on. I checked the tach last year with a fancy digital strobe tach looking at the crankshaft and it was right on the money. If your readings are off by 10% that is a lot. If it is off that much then there is something wrong.

Click to expand...

I've researched this for 14 yrs now and found claibration tests of our era Smith's that showed them dead on in mph and rpms with only a partilar second delay to stablize follow fast changes - otherwise follows about exactly speed and rpm you can depend on. They are more accurate that a lot of digital speedo and tachs, just so company can deny their clock made you speed or over rev as both set to read couple mph faster though the tach may be dead on. I watched in horror on Peel throttle stick as KS shot out from under leg faster than gravity so I stumbled back a step while letting go of throttle too but still had eyes on the tach to see it get near top of red zone hesitating an instant by which time I got forward enough to snap throttle shut but the fuel puddles somewhere must of got suddenly sucked up as a second more HORRIFIC rev up ROAR lifted the engine up front iso so hard it slapped my panic strength grip right back at me, which SHOCKED my to my core and also added to my second stumble back, eye's still locked on the tach but the needle had hit the peg and then flat dissapeared from sight as I dragged my myself back engine had stablized by time I snapped the fatal error closed for sucking on top piston inertia to take the spunk out of Peel. I rate the peg backside at 11,000, bouncing back in a visiable blur to 4-5000 off back of tach ~12-13,000 and vanishing completely from sight > who the hell knows but did not get back into blur state on throttle chop till over a second later then took ~3 more seconds to stop. Took another second for the shed sheet metal to stop ringing echos but I'm not over it yet.

All's I can say is if ya spend enough on a crank and welded racer cases that can take this there are other things that fail first and worst. For one thing Peel not longer sports a mag rotor on the end and might beef up the oil pump snout too and the TS cover boss the crank end whips bust out.

Seems to me that the strength of the commando lies in it's midrange, and I always try to work with that. The main problem I've had was when using the 4 speed CR box. The motor has plenty of grunt, however getting the bike mobile during a clutch start meant cooking the clutch. Otherwise I lost too much ground in the first few seconds of a race. Lowering the overall gearing to get decent starts meant the bike wasn't fast enough at the ends of the straights, and trying to change gear below 7000 RPM was hazardous. I've found the bike very deceiving as far as gearing is concerned. I've drastically increased the overall gearing to knock its backside in, and it just went faster. Riding it you wouldn't expect that, it spins up extremely quickly, however you would believe it is giving its best. I havent tried the 6 speed TTI box yet because I've had a bit of grief lately, and lost motivation. I'm OK now and starting to move on, and I'm a bit more enthusiastic and feel good when I think of my bike. I cannot afford to race it at present and I find it difficult to get my head around now that my mate has gone who used to help me at race meetings. I've also very recently lost my partner in crime at Winton Motor Raceway who was the CEO and our club president, and held the money bag.
I would say one thing though, my Seeley 850 is exciting and safe to ride fast. I never owned anything else which was so outlandish. I will be there again.

I would love to hear what Herb Becker, Doug Macrae , Kenny Cummins, and Jim Schmidt have to say about using a commando engine at the top end of the rev range. To me it seems a pointless and expensive exercise with little potential benefit. Perhaps I'm just a silly old fart and my Seeley just feels fast to me ? I've only had one good look at the really fast guys in our period 4 historics however I know what my own bike can do. With the 4 speed box, it had the potential to win against the 1000cc CB750s, however the loss at the starts meant it would be difficult. The 6 speed box might make a difference ? That stagger off the start is a real problem, and I don't like dropping the clutch on a heap of revs.

Herb Becker, Doug Macrae , Kenny Cummins, and Jim Schmidt are all most famous for removing the factory stockness of Norton items out of their race bikes so does not fit in this subject. TC did not he just used nitormethane. Fact remains there's a lot more reports of getting away with 8000 for a time than blowing right up - so man up on throttle holding and see where it gets ya - as it may be a times you'll never forget - which is priceless.

hobot said:

Fact remains there's a lot more reports of getting away with 8000 for a time than blowing right up...

Click to expand...

I have yet to see a report (on this forum) of a basically stock Commando surviving 8,000 RPM for more than a few seconds (including TC), even on several other re-worded threads that have yet to produce a single one. And that most especially includes the original story that was related in specific wording, then back-pedal argued in totally different wording.

Besides the fact that it hasn't been done (for more than a few seconds), there have been plenty of replies by several relatively credible members, all pointing to the same fact: there is no point in going beyond 7,000 RPM (much less 8K)

Still, some of the discussion has been informational...

Grandpaul, are you arguing with hobot? :lol:

I'm just saying that in their era there is evidence enough by personal reports here and other places and even advertising and tests chart going to 8 grand w/o breaking right then and then. So plenty of em were wrung TF out to 8000 often enough to know they could take it for time just how much time who knows. The Desert reacers in early days ran over 8000 grand occasionally on cast iron. I'm not going to do it and don't reccomend doing it but Norton gave a bit of resevere in the 7000 limit for 750's. With the key word stock in the equation its a silly question to me any way you look at it - nowadays when no one expects a Commando to get there first.
.

Btw running a Command in its red zone might be more impressive that the best illicit sex you know you can't get away with for long but OH LA LA while it lasts!
It ya want to ride thoughtless in safe zone disconnect the tach as it will sound more strained than it is to back off with reserves.

We wouldn't argue that its not wise to spin your Commando that hard - its over the listed redline, after all.
Little suggestion that your crank will immediately explode if you did though, back then anyway...

The opening/introductory words from a CycleWorld roadtest of a Command production racer, circa Dec 1969
"Rare is the road rider who has not, regardless of what he is riding, twisted the throttle just a little harder than is necessary to get from Point A to Point B. In every rider, there is a little bit of a racer. The road, fraught with perils real and imaginary , public and private, becomes a temptress at every curve".

And later, in a Cycle test Jan 71 of a similar bike "Starting off the performance phase of the test was the quarter mile. This is where the tall gearing proved to be a drawback. Getting off the line was hardly inspirational and winding the engine past 7000 rpm and feeding in the clutch didn't help either".
They quote max power as 68 @ 7000 rpm. And don't sound to have treated that 7000 rpm as redline ?. Tacho photo shows no redline marked...

I have a Commando road racer in which I went through two crankshafts. One was a crank failure and one was a spectacular flywheel failure. I regularly punished the bike with shifts at 8,000 to 8,300 rpm. So I see where hobot is coming from and I concur. I recommend not revving beyond red line and for even the mildly tuned Commandos (with a proper 53% Balance Factor) there is no need to rev higher than 6,500 - 7,000 rpm.