max rev's?
- Thread starter john robert bould
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A Big little side note here >>
The Two Strongest Over Built Never Fail First items on a Commando of any model are The Z Plates and the Connecting Rods.
That is - something else must let go First=1st, before Norton Al Z plates or Al Connecting Rod break. In other words Rod are not the limiting factor in RPM wear and/or breakage so its foolish-wasteful to upgrade rods thinking its any kind of advantage or protection -UNLESS building a super duper expensive hi rpm special from the flywheel out. The factory rods are over built enough there is no known time/load fatigue limit to them by road or race users. All reports of rod damage follow something else letting go 1st=First.
I don't think anything would happen to the crank or rods of an 850 spun to 9000 but would expect the stock pistons to come apart after some fairly short time interval. A slo mo video would reveal the crank looking like a jump rope and the bearings looking like jello rings sending ripples into the drumming case walls but all still within elastic deformation spring back survival. I would expect the cast iron fly wheel to fly apart - after a bit longer interval - unless of course there was a lurking fracture line in its manufacture, which then can blow up well under 7000 out of the blue. This 9000 rpm assumes nothing attached to the crank ends of course as the alternator rotor will be bashing/melting inside of stator and the cam chain will be jerked on enough to damage tension-er to oil pump snout.
There are piston speed/accel. calculators online to plug in the stroke rpm and piston mass. Not snapping throttle shut at hi rpm is very good advice.
http://www.google.com/search?client=fir ... gle+Search
The Two Strongest Over Built Never Fail First items on a Commando of any model are The Z Plates and the Connecting Rods.
That is - something else must let go First=1st, before Norton Al Z plates or Al Connecting Rod break. In other words Rod are not the limiting factor in RPM wear and/or breakage so its foolish-wasteful to upgrade rods thinking its any kind of advantage or protection -UNLESS building a super duper expensive hi rpm special from the flywheel out. The factory rods are over built enough there is no known time/load fatigue limit to them by road or race users. All reports of rod damage follow something else letting go 1st=First.
I don't think anything would happen to the crank or rods of an 850 spun to 9000 but would expect the stock pistons to come apart after some fairly short time interval. A slo mo video would reveal the crank looking like a jump rope and the bearings looking like jello rings sending ripples into the drumming case walls but all still within elastic deformation spring back survival. I would expect the cast iron fly wheel to fly apart - after a bit longer interval - unless of course there was a lurking fracture line in its manufacture, which then can blow up well under 7000 out of the blue. This 9000 rpm assumes nothing attached to the crank ends of course as the alternator rotor will be bashing/melting inside of stator and the cam chain will be jerked on enough to damage tension-er to oil pump snout.
There are piston speed/accel. calculators online to plug in the stroke rpm and piston mass. Not snapping throttle shut at hi rpm is very good advice.
http://www.google.com/search?client=fir ... gle+Search
I've had a standard case/rods/crank motor at 9000 without it blowing when the throttle stuck open. It took about 15 secs to get off the track, stop the bike and disconnect the battery leads (no kill switch at the time) No ill effects, I used the motor for another 2 seasons, but repalced the rods as a matter of course..My current 750 with maney cases, crank and carillos is revved to almost 8000 all the time. power starts to drop off at 7800. Never had a problem with it.........but it's not a standard motor either 
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Seeley920, your excessive testing of 920 rpm is music to my ears as I'd only had Steve Maney lower 7000 rpm report to go by prior. Scary figures appear from power calculators after 7000 plugged in for Peel's set up. She's got hardened crank, Jim's light pistons/rods plus cyro tempered with friction and insulation coatings so temping to see what Big D's dyno shows at least once almost over doing it. I'm also planning on a plastic or Al witness bolt screwed in to touch flywheel rim then back off a bit to monitor the crank whip touching it to get idea of where to set rev limiter as never ever want another stuck throttle event in my life time. So what would be the acceptable crankshaft deflection limit?
Hi John,
I think the safe revs have as much to do with the skill or lack of, of the Fu!*wit that last had the engine apart and hammered it back together again. I had a 750 back in the 70's that hadn't long been rebuilt before I got it, besides the chaincase the left hand carb and a few other bits falling off in the first few days of owning it I managed to snap the crank on the D/S main bearing adjacent the crank cheek within about a month of ownership. I wouldn't have minded so much if i was wailing it around at valve bounce trying to outdrag Z1's but i was in top poodling up the A1 at about 4,500 revs 70 MPH. Felt it go straight away and pulled the clutch in and beside the broken crank the only damage was some light scuffing on the inside of the crankcases where the flywheel had rubbed and a secondhand replacement complete with rods from Duggie Clarks had it sorted. I guess the crank was probably damaged by the incorrect grade of hammer being selected by the DPO getting the inner race of the main bearing of the crank. Other than ham fisted eediots I guess the only other danger lurking is the notorious D rods fitted to MK3's which can let go at any rpm and any age as my mate found out to his cost which virtualy totaled the whole engine of his MK3. My current 750 I normally rev to a max of 6000 and sometimes 6500 if I am feeling reckless. :twisted:
Best
I think the safe revs have as much to do with the skill or lack of, of the Fu!*wit that last had the engine apart and hammered it back together again. I had a 750 back in the 70's that hadn't long been rebuilt before I got it, besides the chaincase the left hand carb and a few other bits falling off in the first few days of owning it I managed to snap the crank on the D/S main bearing adjacent the crank cheek within about a month of ownership. I wouldn't have minded so much if i was wailing it around at valve bounce trying to outdrag Z1's but i was in top poodling up the A1 at about 4,500 revs 70 MPH. Felt it go straight away and pulled the clutch in and beside the broken crank the only damage was some light scuffing on the inside of the crankcases where the flywheel had rubbed and a secondhand replacement complete with rods from Duggie Clarks had it sorted. I guess the crank was probably damaged by the incorrect grade of hammer being selected by the DPO getting the inner race of the main bearing of the crank. Other than ham fisted eediots I guess the only other danger lurking is the notorious D rods fitted to MK3's which can let go at any rpm and any age as my mate found out to his cost which virtualy totaled the whole engine of his MK3. My current 750 I normally rev to a max of 6000 and sometimes 6500 if I am feeling reckless. :twisted:
Best
Ah Duggie .....now there's a name from a while back......
Hobot, the 9000rpm was with the clutch in, and I wouldn't recommend it.....I was expecting a piston to come through the tank, but I got away with it that time.
I think most of the cranks available now will have uncertain provenance anyway.....I have broken 2 Mk3 cranks in a season before splashing out for the Maney one
The motor I use now sees 8000 pretty regularly though, but it has all the right bits!
Hobot, the 9000rpm was with the clutch in, and I wouldn't recommend it.....I was expecting a piston to come through the tank, but I got away with it that time.
I think most of the cranks available now will have uncertain provenance anyway.....I have broken 2 Mk3 cranks in a season before splashing out for the Maney one
The motor I use now sees 8000 pretty regularly though, but it has all the right bits!
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Ugh guys I too have lost engines a few times no fault of my own but d/t bad parts before me or stuck throttle out of the blue after 3 seasons w/o a hint of that on a cold start.
Seeley, Ms Peel has the best stuff money and famous builders can provide so 8000 rpm under load - according to conservative use of engine calculators implies its more than enough to do what I seek or just tear up drive train and tire first. I am very relieved to know you can get away with it, then so should Peel, now and then.
Ms Peel is built to take the Drouin which has non linear boost increase as rev's build and even more so if throttle snapped to spike loads. I don't think I'll have to rev to 8000 to spank what I'm after, just to do a dyno, drag strip or top speed attempt. I think Peel's crank can take the extra hi torque loads better than the jump rope of rpms. I do think that the isolastics with tri-links can out handle any solid chassis of course- having tested that in spades against myself on my boney ole race shod SV and with very angry then even more upset sports riders with worn down knee pads. If you ain't able to calmly enjoy testing tire spinning and sliding traction *before* entering turns then ya don't know what you are missing out on. Someone remarked an oz of handling is worth a pound of hp, boy howdy does that ring truth to me. About 3 seassons and $7000 more to go.
Seeley, Ms Peel has the best stuff money and famous builders can provide so 8000 rpm under load - according to conservative use of engine calculators implies its more than enough to do what I seek or just tear up drive train and tire first. I am very relieved to know you can get away with it, then so should Peel, now and then.
Ms Peel is built to take the Drouin which has non linear boost increase as rev's build and even more so if throttle snapped to spike loads. I don't think I'll have to rev to 8000 to spank what I'm after, just to do a dyno, drag strip or top speed attempt. I think Peel's crank can take the extra hi torque loads better than the jump rope of rpms. I do think that the isolastics with tri-links can out handle any solid chassis of course- having tested that in spades against myself on my boney ole race shod SV and with very angry then even more upset sports riders with worn down knee pads. If you ain't able to calmly enjoy testing tire spinning and sliding traction *before* entering turns then ya don't know what you are missing out on. Someone remarked an oz of handling is worth a pound of hp, boy howdy does that ring truth to me. About 3 seassons and $7000 more to go.
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snakehips said:
Hi Snakey.
Would that type of break be caused by flexture? Hobit always use's the term "jump Rope" when relateing to crank flex ...and as my MK 3 will have the D rods..am i on death row :!:
I have no idea if all MK3's were fitted with D rods and I am sure with your in depth knowledge of part numbers and engine numbers you would know better than me but if I had a Mk3 I would lift the barrels off for peace of mind. As for nothing wrong with D rods I know of two Mk3's that have spat their rods out the cases but I have never heard of an earlier type rod failing also I believe Les Emery will not carry out any further work on a customers bike if he identifies D rods being fitted unless the owner agrees for them to be changed. Yes I am sure they are as good as any other rod until they break. :roll:L.A.B said:
Best
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snakehips said:
The subject of D rods has been raised a few times, and I also understood that D rods were supposed to be dodgy-however Joe (ZFD) appears to dispute that, and-up until now, no forum member seemed to have any first-hand experience of any D rod failures.
http://www.norvilmotorcycle.co.uk/techtalk35.htm
There was never any diffence in the part number-however as we know D rods are easily recognisable.
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I've seen years of post both swearing at two piece D rods and those swearing by them, sheeze.
Its no analogy to say the crank shaft turns into a jump rope shape at hi rpms, the drag inertia of the pistons resisting direction change at TDC pulls the crank center upward at same time the ends past the bearing are pointed the opposite direction. Its really too obvious after an unloaded stuck throttle for over 3 seconds that makes tach needle bounce so hard/fast off peg it completely disappears, then takes a few seconds of finally shut throttle before it slows up enough to even see again as a bouncing blur, ugh. If this ever happens again I hope to have presence of mind to hold WOT and just use kill switch but in such excitement/noise in closed tin shed to see seams flapping open like waves breaking on a beach and bolts stretched - slammed back like a real cartoon engine, I was not up to it. Best I can describe the sound [which did not misfire a beat] was a full orchestra on amphifers tuning up while being dropped through the roof tin and rafters.... Took 30 sec for smoke to clear enough I could see the head was still on and then almost that much to see details like fins. Peel had her
hollow 2-1 Dunstall long dong exhaust on at that point. INSANE/BERSERK.
Amazingly she started again and I got another 2000 miles out of her but she topped out in power at 5000 rpm, and so began her new engine project...
I think the cryogenic tempering saved crank fracture and even helped self correct the 1/8" DS and 1/16" TS run out I measured at first to find only 1/2 that on each side after the 2000 miles limping around depressed riding.
Its no analogy to say the crank shaft turns into a jump rope shape at hi rpms, the drag inertia of the pistons resisting direction change at TDC pulls the crank center upward at same time the ends past the bearing are pointed the opposite direction. Its really too obvious after an unloaded stuck throttle for over 3 seconds that makes tach needle bounce so hard/fast off peg it completely disappears, then takes a few seconds of finally shut throttle before it slows up enough to even see again as a bouncing blur, ugh. If this ever happens again I hope to have presence of mind to hold WOT and just use kill switch but in such excitement/noise in closed tin shed to see seams flapping open like waves breaking on a beach and bolts stretched - slammed back like a real cartoon engine, I was not up to it. Best I can describe the sound [which did not misfire a beat] was a full orchestra on amphifers tuning up while being dropped through the roof tin and rafters.... Took 30 sec for smoke to clear enough I could see the head was still on and then almost that much to see details like fins. Peel had her
hollow 2-1 Dunstall long dong exhaust on at that point. INSANE/BERSERK.
Amazingly she started again and I got another 2000 miles out of her but she topped out in power at 5000 rpm, and so began her new engine project...
I think the cryogenic tempering saved crank fracture and even helped self correct the 1/8" DS and 1/16" TS run out I measured at first to find only 1/2 that on each side after the 2000 miles limping around depressed riding.
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In the late 70's thru early 80's I raced speedway sidecars on a 1/4 mile dirt track, my compatition- 900 kwakas 900 yamaha twins over bored 8 valve rickman Triumph's
810 Dunstall nortons, I ran a 850 Norton with a shurock supercharger 1 3/4 SU carb with twin float bowls running methanol, my Norton opponents were reving past 8500 and threw rods on a number of times where i tried 6800-7500 and never threw a rod though at the end of the season the big end area of the rod was egg shapped, so yes i think the alloy conrod is a limiting factor.
810 Dunstall nortons, I ran a 850 Norton with a shurock supercharger 1 3/4 SU carb with twin float bowls running methanol, my Norton opponents were reving past 8500 and threw rods on a number of times where i tried 6800-7500 and never threw a rod though at the end of the season the big end area of the rod was egg shapped, so yes i think the alloy conrod is a limiting factor.
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I can't say if D rods are more prone to break or not. I do know that when I assembled my MK3 thirty years ago it had one D rod and one non-D rod as original. I had not heard of any problems with D rods at that time. During the next 10 years, first as an 850 until it swallowed an Amal slide and then as a 920 until I got tired of blowing head gaskets and burning oil and then back to an 880, I run the dew out of that motor and rode it several times 450 miles across Nebraska at 6200 to 6500 RPM on I-80. I never had any rod problems until one time I dropped my weight on the starter and there was gas in the cylinders. One of them got .020 shorter and the other got .100 shorter with a little compound curve in the middle. After being told there were no new stock rods available I built a new motor with Carrillos and a steel flywheel. Jim
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The race bikes had steel one piece cranks.............revving a road bike with 3 piece bolt up crank much above 7.5k for any extended period of time, may well result in a very large repair bill.
Carbonfibre said:
It took them a while to figure that out. ?
I'm sure if you read the race accounts, someones factory race bikes' iron flywheel punctured their rear wheel at Daytona.
Which begs the question of what they did with the earlier 500 race bikes ?
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Al rods can be made to hold up to the toughest dragster power, so it ain't the alloy that's the problem, if there is one in Norton rods. Of course Norton may of skimped on rod engineering but I don't think so - so far. Crank jump rope shape distorts and binds the journal alignment which would tend to tear off the end cap, then the rest is history. Al caps have to be made bigger than steel ones of course so would of needed bigger crank case bottom for those.
Over the last 36 years, the success of the Bill Miller Engineering Forged Aluminum Connecting Rod in drag racing is unparalleled. The BME Rod is unquestionably the number one choice of professional drag racers.
http://bmeltd.com/rods.htm
Over the last 36 years, the success of the Bill Miller Engineering Forged Aluminum Connecting Rod in drag racing is unparalleled. The BME Rod is unquestionably the number one choice of professional drag racers.
http://bmeltd.com/rods.htm
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