I am about to rebuild my 67 T120 and I want to convert it to a heavy crank. Can I just change the flywheel or do I need to change the whole crank shaft? Anyone know of a good heavy crank or flywheel for sale?
Mostly Triumphs with a few BSA's a Norton, and two BMW's
Whats all this 'ere now? (in my corniest British accent) What's with the heavier crank? I did read Kevin Cameron's article on harmonics but isn't he famous for tuning 2 stroke GP bikes w/ultra lightwieght parts and crazy rpms? What does a heavier crank do for the twins? Torque? Smoothness? Longevity?
Re: Heavy vs. Light Cranks#104753 11/05/064:38 am11/05/064:38 am
Do a search on the competition board. Type 'crank shaft' as your search word. You'll find some excellent info on the subject. These guys know their stuff. They build and race. All I can tell you is with a lightened crank your acceleration rate will increase. But, AIUI, once at speed ( higher RPM )it will be harder to maintain since you have lost the inertia of the heavier flywheels. It's a "balancing act" so to speak. Are you racing or on the street? Heavy should give you a smoother street engine through out the range. How heavy is the question. The competition board guys will know. HTH
Steve in Tulsa
Re: Heavy vs. Light Cranks#104754 11/05/062:27 pm11/05/062:27 pm
“Cameron's article on harmonics but isn't he famous for tuning 2 stroke GP bikes w/ultra lightweight parts and crazy rpm's?”
Sort of, but he was the brains behind Todd Henning's 4 stroke 350 and 450 Hondas where they used stock weight flywheels. This, after a lot of work on the dyno with different flywheel weights. The technology is being used by people drag racing Harley's and few think they are using crazy rpm's and lightweight parts by today's standards.
This is an area where the technology is only just filtering down to the smaller engine manufacturers and well-funded private race teams. I suspect it will be 5 years, or longer, before the technology will be available to the high-end enthusiast market.
Re: Heavy vs. Light Cranks#104755 11/05/062:49 pm11/05/062:49 pm
First thing, I went to the comp. board and tried every combo of crankshaft andflywheel and got no results . I ran a de-tuned 66tt engine in a hardtail frame for a few years and found little difference from the "R" engine except for the acceleration. By de-tuned I simply mean I put in 7.5 pistons in place of the 11's that were in it.
poverty is the mother of invention
Re: Heavy vs. Light Cranks#104756 11/05/067:15 pm11/05/067:15 pm
Me again, when honda went for more with their V4 superbike engined RC45, they ended up putting 30% more weight into the crank as the horsepower went up : it did at least two things, 1 Made the bike more rideable 2 Made the engine more reliable , and this motor reved to 15k, it's worth checking out the spintron site for the more technical details. Johnny.
What d'ya mean it won't rev to 10? 1965 BSA A65D Lightning Rocket 1976 K*w*s*ki Z900. 1978 Triumph Bonn3ville (930 T160 Powered T140) 1988 H*nd* RC30 1990 Moto Guzzi California 3 1993 Y*m*h* TDM 850
Re: Heavy vs. Light Cranks#104757 11/05/068:17 pm11/05/068:17 pm
Before Einstein's theories, mathematical computations and other scientific data are presented, I will apply the laws of KISS. As we know, Triumph changed cranks throughout the run using lighter and heavier flywheels. As you know, and the reason you are thinking heavier flywheels is to reduce vibration. So, can you change the flywheel or should you change the whole crankshaft?
Looking through my vast library of parts books and other books outlining the changes, what years, how heavy, balance factor, etc. It appears that by part number, the crankshaft from 1967 stayed the same through early 1969 and then the heavier flywheel was introduced. The rest of the parts stay the same by part number. Me, I would look for one of the heavier cranks if this was what I was after and keep my other crank stored. If your goal is just to have your daily rider help keep the vibes down, then go for it. Hope this helps!
A greater rotating mass will smooth out the vibes due to power impulses and higher compression ratios better than a lesser mass and will also improve lower rpm torque, I agree that a crankshaft designed for the greater mass would likly be more reliable than one you cobble up in your garage
Re: Heavy vs. Light Cranks#104761 11/07/061:57 pm11/07/061:57 pm
The only stock cranks I have seen that seem to live in road racing are Andrew Cowells very light crank that EV has done for him.Maybe ED can let us now what he has learned.I could go through about two stock cranks a year.
Tim Joyce sponsors D@D cycles Works shocks Glass from the past
Re: Heavy vs. Light Cranks#104763 11/07/0610:16 pm11/07/0610:16 pm
Warning! You are stepping on dangerous ground here gearhead .
With all due respect and while acknowleging some of the valid points that you have made, my opinion, and I feel sure other's opinions as well, is that what Panic doesn't know about HP and torque and related topics isn't worth knowing. Just read some of his papers.
Re: Heavy vs. Light Cranks#104765 11/08/061:07 am11/08/061:07 am
T.C. Christenson's engine builder, John Gregory, road raced a 500 Norton twin in the sixties. He made a crank with no flywheel, just three porkchop wieghts and it had buick connecting rods. The bike was great on short tracks, but on long tracks he had to add an outside flywheel so the bike would hold speed in top gear against wind and hills.
(featherbred 7-18-06 ) This is what I meant by harder to hold at high speed. Yes, there's no flywheel. But wouldn't a "too light" flywheel have the same, or similar, effect?
what Panic doesn't know about HP and torque and related topics isn't worth knowing.
Yep. I believe that.
Just read some of his papers.
I have. And I learn.
Steve in Tulsa
Re: Heavy vs. Light Cranks#104766 11/08/061:20 am11/08/061:20 am
I am retired member of the US Navy, Engineman 1st class and I freely admit I don't know everything there is to know about engines.
But I do know a considerable bit, A 6-71 GMC diesel (426 CID) has a 400lb flywheel and this is because the compression is at 23 to 1 and this engine is not to be revved beyond 5000 rpm
By contrast, a 426 chrysler hemi has a flywheel that is about 65 to 70 lbs and can rev to 7000 rpm
You cannot compare a diesel's torque and horsepower curve to a gasoline engines, but if you reduce the fly wheel mass of any existing engine by a significant amount you will need to rev it much higher in order to launch without killing it and you will feel much more vibration than when you had the "stock" flywheel, yes you will improve "horsepower" at a higher rpm but you do lose bottom end "torque"
Re: Heavy vs. Light Cranks#104767 11/08/063:22 am11/08/063:22 am
Hate to hear about dangerous ground being stepped on here That's amazing stuff there
All Doc wants to know is if he can go with a heavier crank from a different year engine
Maybe if Doc had said he wanted to build a 1200cc engine from his 650 and run it at the Salt Flats I could see the run down of what it would take and then that thread could be re-directed to the Competition Board where mathematical equations and the theory of relativity and any other theories that may apply can be discussed.
With all due respect for both gentlemen, I suggest that we take Jon Whitley's advice:
If one or the other wishes to discuss this further I would suggest they re-start the discussion on the Competition site.
Also on Jon's suggestion we can answer Doc's question:
"I am about to rebuild my 67 T120 and I want to convert it to a heavy crank. Can I just change the flywheel or do I need to change the whole crank shaft? Anyone know of a good heavy crank or flywheel for sale? Thanks, Doc "
The simple answer is Yes. You can change to a heavier flywheel, but you would have to rebalance the flywheel. Neither are a difficult job, although finding a heavier flywheel might take some time. The flea markets are full of Triumph crankshafts where the "mechanic" beat it out of the timing side crankcase. The end of the crank that feeds the oil is mushroomed over. Pick up one of these and swap the flywheel.
You can also use any flywheel up to the point where Triumph switched to the metric timing side bearing (bring your calipers 1 1/8" timing side bearing journal is what you are looking for). Again it will need to be rebalanced to your rods and pistons.
Now I loved my 1967 Bonneville, with its light flywheel. But I liked my '68, '69, '70.... I am sorry, just got to admit it, I was happy just to be on any Triumph.
Re: Heavy vs. Light Cranks#104769 11/09/069:24 pm11/09/069:24 pm
I guess the intent was that you were trying to tell gearhead1951 that he was up against serious competition in the engine building department and that he should tread lightly.I guess it was the word dangerous that threw me off Anyhow,no harm no foul.
Originally posted by Britbodger:
Think that you may have misunderstood/misread my post.