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Heavy vs. Light Cranks #104751
11/04/06 5:55 pm
11/04/06 5:55 pm
Joined: Aug 2002
Posts: 690
Carmel, CA
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Doc_dup1 Offline OP
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Carmel, CA
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


Doc

Mostly Triumphs with a few BSA's a Norton, and two BMW's

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Re: Heavy vs. Light Cranks #104752
11/05/06 4:04 am
11/05/06 4:04 am
Joined: Oct 2006
Posts: 19
Austin, Texas
shagitrotten Offline
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shagitrotten  Offline
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Posts: 19
Austin, Texas
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
11/05/06 4:38 am
11/05/06 4:38 am
Joined: Aug 2005
Posts: 1,211
Tulsa, Oklahoma, USA
S
Steve in Tulsa Offline
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Posts: 1,211
Tulsa, Oklahoma, USA
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
11/05/06 2:27 pm
11/05/06 2:27 pm
Joined: Mar 2005
Posts: 10,219
Boston, Massachusetts
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John Healy Offline

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“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
11/05/06 2:49 pm
11/05/06 2:49 pm
Joined: Oct 2006
Posts: 208
Nova Scotia
R
relicduke Offline
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Posts: 208
Nova Scotia
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
11/05/06 7:15 pm
11/05/06 7:15 pm
Joined: Aug 2006
Posts: 730
Dordogne, SW France
johnnyrvf Offline
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Dordogne, SW France
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. bigt


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
11/05/06 8:17 pm
11/05/06 8:17 pm
Joined: Aug 2001
Posts: 7,204
Vermont
Jon W. Whitley Online content

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Jon W. Whitley  Online Content

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Doc,

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!

beerchug


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project

Re: Heavy vs. Light Cranks #104758
11/07/06 12:24 am
11/07/06 12:24 am
Joined: Aug 2002
Posts: 690
Carmel, CA
D
Doc_dup1 Offline OP
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Carmel, CA
Thanks, I think I will search for a 69 or later crank. Does anyone know how late I can go? Are all of the 650 cranks the same?


Doc

Mostly Triumphs with a few BSA's a Norton, and two BMW's

Re: Heavy vs. Light Cranks #104759
11/07/06 12:58 am
11/07/06 12:58 am
Joined: Aug 2001
Posts: 3,913
Houston Texas
Britbodger R.I.P. Offline
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Houston Texas
Of interest maybe is that Stan Shenton of Boyer racing fame in the early 70's in his book
"Triumph Tuning" advocates use of the heavier crankshaft for road racing.

He doesn't say why, but my guess is that its because the heavier crankshaft is better able to absorb shock loads and provides for smoother power delivery.

Just my 2c

Re: Heavy vs. Light Cranks #104760
11/07/06 2:51 am
11/07/06 2:51 am
Joined: Feb 2006
Posts: 221
Greenock, Scotland
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gearhead1951 Offline
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Greenock, Scotland
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
11/07/06 1:57 pm
11/07/06 1:57 pm
Joined: Feb 2006
Posts: 221
Greenock, Scotland
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gearhead1951 Offline
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Greenock, Scotland
Simple physics!! A rotating mass stores kinetic energy, the greater the mass the greater the energy!!

That energy is added to the power impulses when you are pulling out or dropping a gear to accellerate (more bottom end torque!!

Re: Heavy vs. Light Cranks #104762
11/07/06 2:40 pm
11/07/06 2:40 pm
Joined: Nov 2005
Posts: 1,346
spfld vt
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phantom309 Offline
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spfld vt
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
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Re: Heavy vs. Light Cranks #104763
11/07/06 10:16 pm
11/07/06 10:16 pm
Joined: Feb 2006
Posts: 221
Greenock, Scotland
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gearhead1951 Offline
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Greenock, Scotland
Panic, I think you are confusing "horsepower" with "torque".

A lighter crank will allow an engine to achieve a higher rpm and spin up faster, thereby making more "horsepower"

A heavy crank will always (all else being equal) pull better off the line and runn smoother than a light crank

Re: Heavy vs. Light Cranks #104764
11/08/06 12:52 am
11/08/06 12:52 am
Joined: Aug 2001
Posts: 3,913
Houston Texas
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Houston Texas
Warning! You are stepping on dangerous ground here gearhead eek .

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.

Just my 2c

Re: Heavy vs. Light Cranks #104765
11/08/06 1:07 am
11/08/06 1:07 am
Joined: Aug 2005
Posts: 1,211
Tulsa, Oklahoma, USA
S
Steve in Tulsa Offline
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Joined: Aug 2005
Posts: 1,211
Tulsa, Oklahoma, USA
Panic
Quote:
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?


Quote:
what Panic doesn't know about HP and torque and related topics isn't worth knowing.
Yep. I believe that.

Quote:
Just read some of his papers.
I have. And I learn.


Steve in Tulsa
Re: Heavy vs. Light Cranks #104766
11/08/06 1:20 am
11/08/06 1:20 am
Joined: Feb 2006
Posts: 221
Greenock, Scotland
G
gearhead1951 Offline
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Posts: 221
Greenock, Scotland
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
11/08/06 3:22 am
11/08/06 3:22 am
Joined: Aug 2001
Posts: 7,204
Vermont
Jon W. Whitley Online content

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Hate to hear about dangerous ground being stepped on here eek That's amazing stuff there clap

All Doc wants to know is if he can go with a heavier crank from a different year engine confused

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.


:rolleyes:


Posted by Britbodger:
Quote:
Warning! You are stepping on dangerous ground


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project

Re: Heavy vs. Light Cranks #104768
11/08/06 2:12 pm
11/08/06 2:12 pm
Joined: Mar 2005
Posts: 10,219
Boston, Massachusetts
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John Healy Offline

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Posts: 10,219
Boston, Massachusetts
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
11/09/06 9:24 pm
11/09/06 9:24 pm
Joined: Aug 2001
Posts: 4,382
Santa Barbara, California
KC in S.B. Offline

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So after all the Hi jackers have cleared..... :rolleyes:
Has anyone actually done that job?? It looks like that flywheel is a REALLY close fit!. KC


Down to 1 BSA, 2 Triumphs, 1 '56 Chevy
Oops,.. add 1 Sporty
Re: Heavy vs. Light Cranks #104770
11/10/06 12:09 am
11/10/06 12:09 am
Joined: Aug 2001
Posts: 3,913
Houston Texas
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Houston Texas
Jon,

Think that you may have misunderstood/misread my post.

No big deal tho'

beerchug

Re: Heavy vs. Light Cranks #104771
11/10/06 2:12 am
11/10/06 2:12 am
Joined: Aug 2001
Posts: 7,204
Vermont
Jon W. Whitley Online content

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Posts: 7,204
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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 bigt
Anyhow,no harm no foul.

beerchug


Originally posted by Britbodger:
Quote:
Jon,

Think that you may have misunderstood/misread my post.

No big deal tho'



Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project


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