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

Was there enough flywheel left to say how/where the flywheel came apart ?
All the crankbolts survive and still done up, or nay ?

Duh this begs the $64,000 question, can a factory norton really rev to 8000, w/o floating the points or valves or over friction or just plain lack of carb feeding?
I assume Dances tweaked and lightened those areas. I ask because of the memorable event of just about to reach cab of a semi with on coming in my early days - suddenly Horrific misfires and back fires and clattering engine noises I quickly backed off of and snicked 3rd with less pull than planned saved us.
A few days later was deep red zone w/o issue on 1000 ft drag strip time trials till the the folded up for a spike of G force I'll never forget.

hobot said:

Duh this begs the $64,000 question, can a factory norton really rev to 8000, w/o floating the points or valves or over friction or just plain lack of carb feeding?

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850's almost certainly not, since the cam makes max power at quoted only 5800 rpm.
Big ask to go much beyond there.
And they do have a 7000 redline painted on.

The early 750s, when new, may be another matter.
Max power at 6800 or 7000, depending on where you read = different cam to later bikes.
And no redline on the tacho.
Roadtests back then mention more than once a good handful of revs.
We haven't finished quoting the mentions yet....

After 20K miles on SuVee 10.5 grand red line and Ninja 900 on track with 14,000 limiter I was rather depressed to say the least about wrong emotional decision on obsolete Norton Clunkermando. So I admit to deliberately trying to kill my 1st no name Combat after realizing how dangerous it was handling and leaking 13-14 areas and smoking, so wasted the last of my moving money on a dead end rolling soon basket case. 1999/2000 Y2K TEOTWAKI new years eve sort of mood > I ignored the tach and just went by pure best pull expecting the worst. I was already Hinge weary so waited to right place to let hair out > leaned and nice down slope LH turn then a steep rising RH, marked 20 mph, freaking thing lifted topping out 1st apex while leaned then touched down so snicked 2nd for some annoying tire spin hesitation then hooked up to finish the sharp RH in a snap and stayed on it to lift front again very soon after then too scared so slowed to compose myself of what I'd just got away with. I gave it angry hell another 20 miles but never had another good spot or adrenalin left to float front again. I was told this was that's bikes fate being a sales demo that stayed with the shop that eventually sold it to me. So some do some don't and some its just as well....

HIstoric racing started in 1973 in Australia, And at that time there were several 650 Triumphs racing , Most blew up very quickly. My mate never revved his over the prescribed 6,300 rpm. It is very fast and still together and it is set up to deliver max torque, not top end power. Triumph one piece crankshafts are pretty indestructible, so what are you to expect from a commando with standard balance factor at 8,000 RPM ? The mind boggles . Just before my friend died, I had a conversation with him about getting a commando going . His theory has never changed - short stroke, big ports, extreme overlap cams. That is all fine and dandy if you don't have to ride the thing around corners. There is an old saying 'torque wins races'. If you are getting into the cut and thrust around a twisty race circuit, a torquey motor with a light bike is superior to something which is committed to 'point and squirt'. Kenny Cummins using nitro is not all stupid. It increases torque without increasing the need for more revs.

Rohan,
'850's almost certainly not, since the cam makes max power at quoted only 5800 rpm.
Big ask to go much beyond there.
And they do have a 7000 redline painted on.'

Mine has the crank rebalanced to 72%, a close box, tapered ports , 34mm carbs on methanol On a race circuit, it spins to 7,000 in an instant, and I usually see the tacho hit 7,500 on every gear change, even though I try to stop it going there . I'm always expecting the big bang, however it hasn't happened yet. Gearing for the torque increase is very deceptive. I believe the 7000 RPM red line is probably 500 RPM too high for a standard motor, however I would have expected Norton to be conservative in setting that limt. My motor doesn't have lighter pistons fitted, and that is a worry with aluminium rods.

Yours is SOLID MOUNTED, and you have elsewhere told us about the cam timing fitted in it. !!!

Where are your engineering credentials to tell Nortons they have the redline wrong ???
40 years after the event.

My 850 I had in the late 1970s would pull strongly to 7000 in 3rd at a quick squirt.
How I used to tell if it needed a tuneup (points ignition !, twin amals to synch !! ).
It had S&W valve springs in it though, reputedly a long life version of what they were fitted with.

Rohan said:

Was there enough flywheel left to say how/where the flywheel came apart ?
All the crankbolts survive and still done up, or nay ?

Click to expand...

The flywheel split right through the bolt pattern and most if not all the bolts were in place and in decent "looking" shape. I did not reuse them. The bob weight struck the bottom of the frame tube beneath the front of the seat and landed on the trans. I remember seeing one fist sized bit of flywheel flying out at 2 o'clock and about 30 degrees off horizontal. It felt like a slap in the pants and then silence while I coasted down the straight. Makes me cringe at a fool who would race a Commando engine in a twin loop frame with a cast iron flywheel. If it were not for the main frame tube stopping the bob weight it would have passed staright through an alloy fueld tank and nailed me in the chest or sternum.

So to the point, the flywheel was less than stock. Yes it was the OEM flywheel but the outter radius was trimmed down for lightness and rebalanced.

I would venture to say it would have lasted longer if the perimeter was not trimmed.

hobot said:

Duh this begs the $64,000 question, can a factory norton really rev to 8000, w/o floating the points or valves or over friction or just plain lack of carb feeding?
I assume Dances tweaked and lightened those areas. I ask because of the memorable event of just about to reach cab of a semi with on coming in my early days - suddenly Horrific misfires and back fires and clattering engine noises I quickly backed off of and snicked 3rd with less pull than planned saved us.
A few days later was deep red zone w/o issue on 1000 ft drag strip time trials till the the folded up for a spike of G force I'll never forget.

Click to expand...

Good guess there hobot. The bike was fitted with a Norris RX cam, RD race springs and all titanium valves. That is how I got away with it for so long. The point is that taking the crank/flywheel assembly a little past 8,000 rpm is not a gauranteed bottom end failure BUT I don't want everybody going out there and trying. It is still a crap shoot, especially with a cast iron flywheel.

It would be interesting to know how much variance there was in the valve spring rates and and seat pressures of the Nortons of a given model. that would be a big factor in whether the engine would rev up without valve float.

I didn't know squat in '99 like even where the ignition was coming from ok, ugh.
I assume my no name Combat had over worked springs so floated to soon and lucked out it didn't blow and seize up and eliminate a novice. We all, that's left, lucked to make it past the young wild stupid phase and mostly the bikes too.

Could have been the same valve spring rate and seat pressure but response was due to a more aggressive cam.

Anyone have knowledge of whether the Combats came with different valve spring rates or seat pressures?

Hm, in 1st no-name Combat I later found it'd inhaled thumb nail size throttle slide and had beaten up the valve lips and peckered the chamber surfaces so may have bent stem some to hang up sooner than expected in good shape stock kit. I ordered parts to replace using same pn as standard 750's. On that first week semi pass panic attack the tach was not working so just going by seat of pants novice learning curves i lucked out to survive. Personally I like the more brutal torque hit thrust of Commando than the lower but longer lasting pull of hi rpm many gear moderns. I was pleasantly surprise like acetrel that the higher I geared the better I liked the pull in all gears, but 3rd > I'd sometime just skip to snick 4th for the efficient pull sense instead of just more rev noise than acceleration. Still do commonly on Trixie who I don't wring out as only a mere factory Combat not worth damaging for such little extra thrill.

I love the Commando sense of power delivery so much i've spent about 1/6 my life working up one to scare the shit out of me w/o over reving damage risk. May have to sell Trixie to get a shot of taking Peel places to have show downs. Them balloon moderns have many race starts in tight clusters at about every real turn, not so on Peel the turns are where she lays down more power and acceleration than in bee lines as the side force vectors add to the forward force vectors. 90% of money needed is already spent so on final wrap up spending this year.

Dances with Shrapnel said:

Could have been the same valve spring rate and seat pressure but response was due to a more aggressive cam.

Anyone have knowledge of whether the Combats came with different valve spring rates or seat pressures?

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Norton used the same valve springs, inner and outer, for all the big twins, from '63 to '75. Nothing special for Combat or PR. Some variations in seat pressure, depending on whether insulating washers are fitted, but I don't know of any differences other than that.

Ken

My short stroke 500 Triumph would rev to 10,500 without ever tangling or floating valves . However the cams had over 360 degrees duration, and very small lift in comparison with the race cams usually used in 650s, and a slow lift rate. If you go silly and use radical cams to get more top end, you can have problems when you get there. It would be possible to use a milder cam in a commando and still rev to 8,000, how would you get the bottom end to stay together ? To my mind, there is a rev limit to the design, and I always work within it. When you go outside it, the law of diminishing returns often applies. You can make the crank better, and the cases thicker, the improvements are linear, but as the revs go up the loads increase as the square of the velocities involved.