RPM a cautionary tale

Somewhere, in the bottom of a drawer, I've some photos of what happened to my first ever Commando over 30 years ago. I keep them in the dark as it's an event best forgotten. I'd bought it from a guy who, in hindsight, may not have been as mechanically adept as he thought, but that was another story. Anyway, to the subject of RPM. I was out for a ride on the Commando, and had stopped and was chatting with a guy on a Triumph. On setting off, I gave the Commando some beans up the quiet country road we were on. I used to be careful with the revs, but on this occasion, wishing to show the Trumpet a clean set of heels, I was perhaps not so careful, and remember having the throttle on the stops with the engine under a lot of load. Somewhere, between 2nd and 3rd, I either missed the gear, or it jumped out, but I do remember the Tacho well into the redline.
There was a loud bang, a shudder through the frame, then silence. The bike was then just coasting, so I brought it to a halt, slithering the last few yards on an oily tyre. The Triumph rider caught up, and incoherently , using language such as "unbelievable", "disastrous", "lucky to get away with that" etc proceeded to point back up the road at the debris strewing the carriageway. Looking down at the engine, I could see a small hole in the top of the casings, through which I could clearly see the road. The Flywheel had exited the bottom of the casings, and was lying a few hundred yards back up the road, amongst the alloy shrapnel bits. Unfortunately, on exit, it had more or less flattened the frame cross brace under the engine, pulling the downtubes inwards, and cracking the frame in two places(my memory can't recall exactly where). The frame was a write off, the cases and most of the engine was trashed, I think the barrels/head were recoverable, but the bottom end was gone, camshaft bent, primary case damaged etc etc etc.
Ugh, still makes me sad today, and it's hard to talk about :cry: , as I was kinda hard up back then, being just an apprentice, the bike was my sole form of transport and I'd saved since starting work to buy it. I sold the lot for spares and bought a scrappy trail bike for commuting. Maybe I should dig out the photographs and scan them, may be therapeutic.
I should have learned my lesson, but here I am 30+ years on still trying to finish the design Norton started...........

Oh my greasy heart goes out to you w/o a rev limiter. At least ya made your point against the Triumph so share the results of your successful disaster please.

Back in 71, my mate deceided to show the "lads" looking from the rear transit van ,[seddens]they where egging him on, So he give the commado the berrie's!
A down change into warp gear and followed by a big hand full . Crank shaft and rod flew into bits! not sure if he got past the van? But Norton replaced the engine at a small cost. Painful lesson's ,he never did it again ...stripped the bike later and sold it for £100 in bits.

I take my mk3to the redline quite often and have always done so, never worried about it Didn't think they were that fragile? Maybe I am on the cusp of total destruction. Norton did beef up the crank a bit along the way and added Superblends, not without reason. And then there was the Combat, known for bottom end failures. Were these exploding bikes Combats?

Glen

Combats definitely represent the larger share of exploding Commandos, yes.

Taking a Commando to the red line is one thing, taking it BEYOND the red line is another thing altogether.

Recently I have stopped taking it quite so high. Max torque with the 850 is at 5800, so there is little point in going beyond that really, although it was fun.
Also, one good reason for owning a modern high powered bike is that, for me at least, it has taken away all desire to beat on the old bikes. I just enjoy the old ones for what they are.

Glen

Well put Glenn
YING

worntorn said:

...one good reason for owning a modern high powered bike is that, for me at least, it has taken away all desire to beat on the old bikes. I just enjoy the old ones for what they are.

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Quite so.

I guess I will add my story of Commando-woe to the pile:

I was 19 years old, my first CDO (1973 850). Leaving work one day I "let the wick out" lofting the front wheel a bit which seemed to delight the folks getting off work so after turning the corner I really let it out!! I lofted the wheel in first, shifted the 2nd and as the wheel left the ground the gearbox made a sound I can only describe as mechanical mayhem.

After my buddy with the truck showed up and the bike cooled down we found that the Mainshaft had twisted in 2 pieces!, this started the gearbox troubles that plagued me for years as I (I figured this out later) had pulled the case out of square so it ate shafts and bearings forever more.

Vince

Hehe, total success and total failures mark the highlights of my memories too.
The Combats only blew up d/t bad manufacturing of a number of items that are easy corrected so Combats last as long or longer than the more lugging performance or operated Cdo's. You can serach forum for Combat article that tell the long line of sad details that eventually put Norton under.

As described the drive train is weaker link than the engine survival. Ms Peel in her hey day took out the 3rd gear teeth taking off after a Ducati Monster I'd slowed up behind a car so they could catch up but then freaked out on what they saw and nailed in so took me a bit to catch up on their tail lens, Just heard some tinkling sounds but didn't give shift trouble till after a stop and we took off again, then had to limp home in 4th.

I figure life is so short might as well use up everything around us before we go go.
Even if un admitted to self ya got to be a bit crazy to ride and even more so to take known fast flight risks, but its so fun while it lasts.

If max torque for a commando occurs at 5,800 RPM, doesn't it make more sense to use a 6 speed CR box and keep it there while you pedal your way up to high speed ? It is overall acceleration which counts, waiting for the motor to overcome its lag after a gear change, doesn't help the forward motion. I use very high overall gearing, but close ratio gears in the box. With a 4 speed CR box, take off is slow but once mobile the bike is very quick. If you want to go drag racing .....? I think that when I bought my 4 speed CR cluster it cost about $600, I wasn't smart enough to use a standard commando first gear with it.

acotrel said:

If max torque for a commando occurs at 5,800 RPM, doesn't it make more sense to use a 6 speed CR box and keep it there while you pedal your way up to high speed ? It is overall acceleration which counts, waiting for the motor to overcome its lag after a gear change, doesn't help the forward motion. I use very high overall gearing, but close ratio gears in the box. With a 4 speed CR box, take off is slow but once mobile the bike is very quick. If you want to go drag racing .....? I think that when I bought my 4 speed CR cluster it cost about $600, I wasn't smart enough to use a standard commando first gear with it.

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Have you actually ridden a stock 850 ?
Makes good torque from quite low in the rev range - just put it in top and twist the go button.
Must be one of the strongest engines low down in british motorcycling ?

Vincents are reputed to be not that different.
And, on paper, cannot match Commando acceleration - unless you have a Black Lightning ?!

grandpaul said:

Combats definitely represent the larger share of exploding Commandos, yes.

Taking a Commando to the red line is one thing, taking it BEYOND the red line is another thing altogether.

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All early Commandos had no red line marked on the tacho.

And the 750 I rode for a quick squirt around the block, not a Combat, didn't stop revving at 7000....

worntorn said:

I take my mk3to the redline quite often and have always done so, never worried about it Didn't think they were that fragile? Maybe I am on the cusp of total destruction. Norton did beef up the crank a bit along the way and added Superblends, not without reason. And then there was the Combat, known for bottom end failures. Were these exploding bikes Combats?

Glen

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My 850 I had back in the late 1970s I used to test if it needed a tuneup by giving it a quick squirt in 3rd gear - if it didn't just touch the ton @ 7000, it was out of tune. That was about the end of the revs though, those later cams weren't as revvy as the early 750s had. Make sure you have enough teeth on the sprockets though !! It had S&W valve springs too, supposedly stock springs didn't have a long shelf life - for racing it was recommended they be changed every 2 races ?!

Rohan said:

All early Commandos had no red line marked on the tacho.

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Only the earliest Commando tachos had no red line (RSM3003/10).
The RSM3003/12 tacho with red line was fitted from around early-mid '69.

Not in pictures of road test bikes it wasn't ?

worntorn said:

Also, one good reason for owning a modern high powered bike is that, for me at least, it has taken away all desire to beat on the old bikes. I just enjoy the old ones for what they are.

Glen

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New 'Combat owners probably said the same thing in 1972.

Rohan said:

Not in pictures of road test bikes it wasn't ?

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Which road test pictures?

The 750SS, Cycle Guide Sept 71, for one.
Will get a pic.
b&w pic, so red may not show too well ?

Reading a bit deeper, this bike may have been a prototype, or earlier bike with SS bits fitted. ?

Rohan said:

The 750SS, Cycle Guide Sept 71, for one.
Will get a pic.

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No need, I've got it, and the red line is there, you just aren't looking closely enough.

The tacho by that time was the RSM 3003/15

Rohan said:

b&w pic, so red may not show too well ?

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Yes, funny how red doesn't show up well in black and white photos, I've noticed that too.