Did your stock Commando crank blow at 8,000 RPM?
- Thread starter Rohan
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Rohan, the price is about right for mid 70's DAMHIK. The instructions that came with the Drouin recommended using a 24 tooth counter sprocket. The idea was gobs of torque and not revs. It delivered.
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Drouin advertised the early dyno curves to 8000, then later instructions said 6200 tops. If ya r clic on image it will open the whole view and tick the + mouse to see zoomed. I intend to dyno to Peel to 8000 someday before I die but she's been years acquiring what it takes to do that w/o much risk - I think. Almost know one races to max with cast iron last couple decade or more yet we hear very few failures in street bikes run to red line often. The think is even if it don't blow up on any of the 8000 events cracks may form that let go just idling later on. Centifugal blowers are not compressors so need to be loaded to make boost. Tom Drouin and Bruce McGregor both said they can spike their to 12 PSI yet a magazine editor whimpped out at 8 PSI.
Over the years of asking what breaks first the crank about always tops the long list and rods always the last thing to go. I have seen crank jump rope evidence galore = so not so sure its the pure spin sling force that cracks cast wheels but the internal leverage of angled journals taking the piston jerk down loads into the fragile wheel.
Over the years of asking what breaks first the crank about always tops the long list and rods always the last thing to go. I have seen crank jump rope evidence galore = so not so sure its the pure spin sling force that cracks cast wheels but the internal leverage of angled journals taking the piston jerk down loads into the fragile wheel.
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Rohan
'Back in the 1920s, about 50% was commonly used.
But then engine revs rose, and they found that anything creeping towards 80% or more could happily be used.
This is only a matter of a few extra, more or less, ounces...
'
Happily be used or NEEDED to be used ? I suggest the latter.
'Back in the 1920s, about 50% was commonly used.
But then engine revs rose, and they found that anything creeping towards 80% or more could happily be used.
This is only a matter of a few extra, more or less, ounces...
'
Happily be used or NEEDED to be used ? I suggest the latter.
You can nominate almost any balance factor you like for your engine, and the balance guy will do it for you - provided you are prepared to live with it.
Unless you have exceptionally heavy pistons or rods, its only a matter of + or - a few ounces.
Wonder what H*nda stepthroughs or Guzzi laydown singles balance factors are ??
Do they prefer the vibes more fore-and-aft, or up-and-down ?
Unless you have exceptionally heavy pistons or rods, its only a matter of + or - a few ounces.
Wonder what H*nda stepthroughs or Guzzi laydown singles balance factors are ??
Do they prefer the vibes more fore-and-aft, or up-and-down ?
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Rohan, I think you would find that those bikes are balanced to give min vibes at normal road speeds. The vibration is destructive to bottom end and it can make bits fall off the bike, and cause cracks to appear in brackets and frames. Prior to about 1930 the power benefit of running the motor using a lot of overlap on the cams was rarely realised. When racing led to that development, the revs used in motors naturally rose, and the balance factors were changed to stop the vibes at the top end of the rev range. It made the bikes more comfortable, however I suggest the primary reason was to stop breakages.
acotrel said:
If you have any evidence whatsoever that balance factors in engines can cause engine breakages, then I'm sure we would all be very interested to see.
Spinning cranks and reciprocating pistons/rods are inherently unbalanced, and can NEVER be prefectly balanced - so suggesting some setups can cause engine failure is rather a suspect claim, when the variation between factors is a mere few ounces different ??
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Some where mid way in the Crankshaft Porn thread I posted BSA research that show lowest average loads on crank/bearings was gotten in the low 50's BF. You can search up Triumph BF threads to read how they tend to dissolve various brackets from vibration fatigue no matter the BF but less so in 80's BF with solid mounted engine run towards redline.
The 2 factory Combats I've had both lit up like extra piston around 6800 and I'd hold on another 500 rpm to lower 7000's which alas happens so quick its hard not to just let 'er rip off another 500 into lower 8000's where cases can rip apart even if crank don't. Real Life on hot rod Commando engines to me begins around 6000, which is good to drag launch and not bog on clutch drops and about as low as I like rpm to drop on up shifts. To me 3rd gear is the weakess both for acceleration and strength of cog teeth to shed. Yoose guys do run em hard enough to run have that happen don't ya? I don't see engine as weakest link in kicking up heels.
I tested my factory rebuilt Trixie to the max only once, playing like i was on Peel after sports squadrons left w/o me while still putting on helmet and kick off and would catch up with em going full tilt boogey but so pathetic in the turns here its was like shooting ducks in a bucket - but Trixie ain't no Ms Peel and holding WOT on her about constantly for 20 miles is disappointing experience power-time-speed-handling wise its not worth it so just gave up on that like I have balloon tire moderns only good in bee lines. Other time I pressed Trixie to almost max was tagging along with a squad of hot to trot riders on every version of the most expensive high end elite sports bikes sold in 2012, they'd commented how nice an antique I had then stiffened up annoyingly when I mentioned I'd tag along for a while. Trixie could accelerate about as well as they would let theirs out and as I was hanging back not to worry them I had to out accelerate them as last in long line to pass a car with less distance left to do so. They'd run up to 125ish max, which I could match with Trixie but I held to only 115 so not to over strain Trixie for no good reason. This made me lose a few 100 yd on them in the opens but being corner cripples they'd wisely slow up for real turns so I could catch up to em and almost hang turns as fast as they, working to keep Trixie innate isolastic hinging in range I could use body to dampen out w/o lossing control. This requires WOT with least let offs but not holding WOT beyond 6500 ish for long. If I was in Iowa or Kansas or Oklahoma or Texas then the long opens would be senseless to try to keep up with good modern bee line wonders- until next Peel 8000 rpm tolerant comes on line. Constant pressure fed into chambers acts like higher balance factor and takes the peak loads off piston reversals down somewhat but sure ain't really a Norton inside doing it.
The 2 factory Combats I've had both lit up like extra piston around 6800 and I'd hold on another 500 rpm to lower 7000's which alas happens so quick its hard not to just let 'er rip off another 500 into lower 8000's where cases can rip apart even if crank don't. Real Life on hot rod Commando engines to me begins around 6000, which is good to drag launch and not bog on clutch drops and about as low as I like rpm to drop on up shifts. To me 3rd gear is the weakess both for acceleration and strength of cog teeth to shed. Yoose guys do run em hard enough to run have that happen don't ya? I don't see engine as weakest link in kicking up heels.
I tested my factory rebuilt Trixie to the max only once, playing like i was on Peel after sports squadrons left w/o me while still putting on helmet and kick off and would catch up with em going full tilt boogey but so pathetic in the turns here its was like shooting ducks in a bucket - but Trixie ain't no Ms Peel and holding WOT on her about constantly for 20 miles is disappointing experience power-time-speed-handling wise its not worth it so just gave up on that like I have balloon tire moderns only good in bee lines. Other time I pressed Trixie to almost max was tagging along with a squad of hot to trot riders on every version of the most expensive high end elite sports bikes sold in 2012, they'd commented how nice an antique I had then stiffened up annoyingly when I mentioned I'd tag along for a while. Trixie could accelerate about as well as they would let theirs out and as I was hanging back not to worry them I had to out accelerate them as last in long line to pass a car with less distance left to do so. They'd run up to 125ish max, which I could match with Trixie but I held to only 115 so not to over strain Trixie for no good reason. This made me lose a few 100 yd on them in the opens but being corner cripples they'd wisely slow up for real turns so I could catch up to em and almost hang turns as fast as they, working to keep Trixie innate isolastic hinging in range I could use body to dampen out w/o lossing control. This requires WOT with least let offs but not holding WOT beyond 6500 ish for long. If I was in Iowa or Kansas or Oklahoma or Texas then the long opens would be senseless to try to keep up with good modern bee line wonders- until next Peel 8000 rpm tolerant comes on line. Constant pressure fed into chambers acts like higher balance factor and takes the peak loads off piston reversals down somewhat but sure ain't really a Norton inside doing it.
]
In a 20+ pound flywheel, it must be added.
Unless you opt for a o% BF or 100% BF, its going to be a good few ounces or some piston-generated vibes anyway.. ??!
Thats why you fit strong enough main bearings....
And Sir Eddy's engine, almost same flywheel, same main bearings, is 12,000 rpm stuff ??
And Atlas engines are reportedly balanced to 82 %.
Thats the few extra ounces already - and its not the Atlas engines that have bottom end problems... !
Rohan said:
grandpaul said:
In a 20+ pound flywheel, it must be added.
Unless you opt for a o% BF or 100% BF, its going to be a good few ounces or some piston-generated vibes anyway.. ??!
Thats why you fit strong enough main bearings....
And Sir Eddy's engine, almost same flywheel, same main bearings, is 12,000 rpm stuff ??
And Atlas engines are reportedly balanced to 82 %.
Thats the few extra ounces already - and its not the Atlas engines that have bottom end problems... !
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