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balance factors #313879
05/17/10 9:32 pm
05/17/10 9:32 pm
Joined: May 2006
Posts: 309
Sanger, CA
jim schmidt Offline OP
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What do triumph twins use for balance factors?

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Re: balance factors [Re: jim schmidt] #313885
05/17/10 10:08 pm
05/17/10 10:08 pm
Joined: Jul 2009
Posts: 3,549
Vic. Australia
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Pete R - R.I.P. Offline
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Vic. Australia
There is a claim that T120 engines were balanced to 85%.However,if you measure one as it Triumph balanced it,you find its more like 80%.
For T140 engines the Triumph claimed 74%,which would be close to true.
In a Rickman frame,65% is recommended for Triumph twins.I hear that 85% is OK in a featherbed frame.

Pre-unit engines happily use 71% in Triumph frames.

Triumph balance-factors are quoted with a dry crank.When a unit crank is filled with oil,it effectively lowers the balance-factor about 2%.

Last edited by Pete R; 05/18/10 8:19 am. Reason: "Triumph balance - - 2%".
Re: balance factors [Re: Pete R - R.I.P.] #313893
05/17/10 10:37 pm
05/17/10 10:37 pm
Joined: Nov 2008
Posts: 2,799
Bishop, Calif.
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desco Online content

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Bishop, Calif.
I've always been curious, what does 85% & 71% really mean? And why not 100%?


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: balance factors [Re: desco] #313896
05/17/10 11:08 pm
05/17/10 11:08 pm
Joined: Aug 2001
Posts: 918
hampshire, england
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t120mike Offline
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hampshire, england
desco, apologies in advance if this sounds grandma and eggs but in a 360 parallel twin with no balancer shaft, you are trying to cancel out reciprocating forces (the two pistons rising and falling together) with a weighted flywheel which induces rotating forces. Clearly if the up-and-down forces caused by the pistons were completely cancelled out by the rotating forces, then the flywheel weight would have to be greater and you would still be left with strong front-to-back forces. The balance factor chosen is based on experimentation with a particular engine in a particular frame and the resultant is always a compromise leaving a bit of up-and-down combined with a bit of back to front which leaves a rotating vibration. This can be best demonstrated by placing the bike on the centre stand, starting it and (dismounted) rev the engine. The bike creeps backwards on the stand.
The percentages are a bit of a misnomer. If you weigh the pistons and rods and taking those weights, load up the crankpins to a percentage of that weight, the crank should be able to be rolled on knife edges without returning to the same spot. They drill bits out of the flywheel until this happens. Rocket science it ain't, but important, especially if they are to be raced! That's why most folk keep to stock!


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
Re: balance factors [Re: desco] #313903
05/18/10 12:08 am
05/18/10 12:08 am
Joined: Jul 2009
Posts: 3,549
Vic. Australia
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Pete R - R.I.P. Offline
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The mass of a conrod can be represented by 2 smaller masses;one at the big-end on the crankpin,and one at the small end on the gudgeon pin.
The big-end mass can be 100% counter-balanced,because it is always rotating and exerting centrifugal force.

The small-end and piston mass only exert force when the mass acellerates or decellerates.No inertia force is exerted when they are at maximum speed.
To balance this force at TDC,you would need a counterweight about 125% of the piston and small-end mass.To balance it at BDC you would need a counterweight about 75% of piston+small-end mass.To balance it at maximum piston speed (about 76 degrees before and after TDC),you don't need any counterweight.

So the best we can do on a single-cylinder or parallel-twin engine,with no separate counter-balance shafts,is to counterweight about 1/2 the maximum inertia force of the piston and small-end.There will be times when the piston exerts no force and the counterweight is causing imbalance force.

If the frame is more susceptible to vibration in the vertical direction,the balance-factor needs to increase slightly.If the frame is more susceptible in the horizontal direction,the balance-factor will decrease slightly for smoother running.

Re: balance factors [Re: t120mike] #313904
05/18/10 12:14 am
05/18/10 12:14 am
Joined: Nov 2008
Posts: 2,799
Bishop, Calif.
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desco Online content

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Bishop, Calif.
My 72 does not creep backwards it leaps. Once it poked a hole in the garage wall and broke it's own tail light. Thanks, but now you will have to explain grandma and eggs.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: balance factors [Re: desco] #313956
05/18/10 11:35 am
05/18/10 11:35 am
Joined: May 2006
Posts: 509
melbourne, australia
7
76degree-triumph Offline
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melbourne, australia
Hi Jim, jumping the fence are ya? The grass is greener in triumph land!

In my norton cranked 820 dirt bike with a flywheel lightened as per your book I use 70%.

It runs slightly modified 850 norton rods and slightly lightened T140 pistons.

Its not a race engine but does run short gearing for the bush, so its quite revvy at most speeds but even on wide open back roads where you can reach maybe 60-65mph vibration has never been an issue.

It is mounted in a honda CR250frame, dunno if that makes it better or worse, but 70% works for me.


Cheers, Chris.


1950 Speed Twin outfit
1951 Thunderbird outfit (76 degree racebike, or is it 90 deg now?)
1955 BSA D3 minibike outfit
Triumph solo's
Re: balance factors [Re: 76degree-triumph] #314087
05/18/10 11:51 pm
05/18/10 11:51 pm
Joined: Sep 2006
Posts: 205
Rhode Island
cabletech Offline
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Rhode Island
76*T
Do you have a picture of that Trinda ?


1983 Husqvarna WR430
1973 T150
1974 T150
1975 T160
1975 T160
I'm now a triple Freak!
Re: balance factors [Re: cabletech] #314092
05/19/10 12:35 am
05/19/10 12:35 am
Joined: Aug 2001
Posts: 918
hampshire, england
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t120mike Offline
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Sorry desco, I guess I was alluding to an expression which didn't cross the pond. Try this: Teaching Grandma to suck eggs
FWIW


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
Re: balance factors [Re: cabletech] #314112
05/19/10 2:59 am
05/19/10 2:59 am
Joined: May 2006
Posts: 509
melbourne, australia
7
76degree-triumph Offline
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Originally Posted By: cabletech
76*T
Do you have a picture of that Trinda ?




1950 Speed Twin outfit
1951 Thunderbird outfit (76 degree racebike, or is it 90 deg now?)
1955 BSA D3 minibike outfit
Triumph solo's
Re: balance factors [Re: t120mike] #314118
05/19/10 3:22 am
05/19/10 3:22 am
Joined: Nov 2008
Posts: 2,799
Bishop, Calif.
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desco Online content

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Bishop, Calif.
Mike
Thanks for that. I am fortunate to have BBC in America on my TV and really enjoy some of the shows. Some I can not understand what they are talking about and others I can't even understand what they are saying. I looked up "Bob's your uncle" and penultimate. F-word and Top Gear.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: balance factors [Re: desco] #314152
05/19/10 10:49 am
05/19/10 10:49 am
Joined: Sep 2006
Posts: 205
Rhode Island
cabletech Offline
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Rhode Island
Looks like a CRF450 eater!


1983 Husqvarna WR430
1973 T150
1974 T150
1975 T160
1975 T160
I'm now a triple Freak!
Re: balance factors [Re: cabletech] #314199
05/19/10 3:13 pm
05/19/10 3:13 pm
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
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btour Offline
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Massachusetts, U.S.A.
Balance factor. Little did I know when I first heard of it and thought it was so necessary. laughing

One can get another crank, and gear two together.

Phil Irving pg 284.

"Many years ago Dr. Lanchester propounded the theory that a reciprocating weight could be balance by two weights rotating in opposite directions, and this system was used for some time in the "Valveless" car, which had two crankshafts geared together and operating pistons which moved in unison."
The idea was resuscitated by Velocettes, 20 years ago, in a pair of experimental machines. The crankshafts of these paraellel twins lay fore-and-aft and were coupled by gears of approximately 5 in. pitch diameter.
With the shafts rotating in opposite directions, it becomes possible to counterweight each shaft by 100 per cent. of the reciprocating weight, because at the mid-points the unwanted horizontal force which makes this amount of counter-weighting impracticable with a single is exactly balanced by a similar force from the other shaft."


He also shows the Brough Superior "Golden Dream" with four pistons and two cranks geared together as an example of an extremely smooth design.

He says basically what Pete R. has explained. And recommends a balance factor of 66 percent. But it all depends upon the frame and engine mounting. Unfortuneately it is matter of trial and error to find the best. And one can chase vibrations up and down the rpm. range, so one should settle for where the bike is mostly used. He also warns not set up a destructive internal vibration.

So like Pete says, the rotating mass of the crank can be balanced, but if one tries to then balance the up down motion of the pistons, one would over balance the crank so the movement in the fore aft was out of whack. So you have to compromise and that is called "balance factor". Then of course one also has to consider the "rocking" effect.

And,

"Irrespective of whether two pisotns move in unison or alternately, the secondary harmonic of the primary inertia force acts upwards at tdc and bdc, but downwards at the mid[positions. As each secondary force is one-quarter of the primary, and both act together, the net result is a secondary out-of-balnace force equal to one-half the primary from one cylinder only, but occuring with a frequency of twice engine speed."

So, its a wee bit complicated, in practice. Balance factor that is.

I gotta say, John did a great job, without getting complicated. My bike feels nice and smooth, especially between 4,000 and 5,000 rpm, and since the real feel of power starts dramatically at 4,000 rpm, this is just fine. And I have to say, the more time and miles roll by, the feel of this power kicking in at 4,000 seems to be increasing (subjective of course). So much so, that I hardly want to run it below 4,000 rpm. The engine seems to want to be there, else it is like running with lead sneakers on, like I was depriving it of something, and making it work harder than need be. And the hills around here are endless, so sometimes I am really exceeding the speed limit laughing Varoom. Up and around.....

I have no idea why this effect would increase over time. I could chaulk it up to the weather or gas right now, or where the valve lash is set, but I do not think so...

Now, how did you do that John?

Last edited by btour; 05/19/10 3:28 pm.

Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: balance factors [Re: btour] #314214
05/19/10 4:28 pm
05/19/10 4:28 pm
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
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btour Offline
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So, you get two. Triumph engines. Face them front to front. Cut the fronts off the cases, and weld them together in the form of a V which can be balanced anyway. Then gear the cranks together. See above. Couldn't the intermediate gear be used to drive, and of course you would have to have an electric start.

What a beast! Boy would people would take note. I wonder what the frame would look like. I guess one could skip the V part to save space. Should be smooth and powerful though.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: balance factors [Re: btour] #314321
05/20/10 12:33 am
05/20/10 12:33 am
Joined: Aug 2001
Posts: 918
hampshire, england
T
t120mike Offline
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hampshire, england
Been done, twice to my knowledge, (once recently got best in show at Stafford and once years ago but changed hands at auction last year in the States) But both these had chain between cranks, not gears.
There was a bloke on this forum who was building a V4 engine out of two twins, on a single crankshaft. Whatever happened to him?


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
Re: balance factors [Re: t120mike] #314371
05/20/10 10:57 am
05/20/10 10:57 am
Joined: Sep 2006
Posts: 205
Rhode Island
cabletech Offline
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Rhode Island
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=196342

Isnít this you t120mike? Got any pictures of this project?

Last edited by cabletech; 05/20/10 10:59 am.

1983 Husqvarna WR430
1973 T150
1974 T150
1975 T160
1975 T160
I'm now a triple Freak!
Re: balance factors [Re: cabletech] #314395
05/20/10 1:53 pm
05/20/10 1:53 pm
Joined: Nov 2005
Posts: 7,411
Back on the mainland!
JubeePrince Offline

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Back on the mainland!
Chris -

Wow! I would suspect with that rear sprocket and light frame you have a hard time keeping that front end on the ground, altho it looks to be well balanced...

Is that rear disc on the same side as the sprocket? Nice work!

Trinda....or Tronda....or Nornda....or Trinonda....or.... laugh

Cheers,

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
Re: balance factors [Re: JubeePrince] #314506
05/21/10 10:44 am
05/21/10 10:44 am
Joined: May 2006
Posts: 509
melbourne, australia
7
76degree-triumph Offline
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I usually call it a Tronda. If the coppers catch me then its a 1976 T140!
JB have a look at the distance between the rear axle and the crank centre line. Much to far and it spins the tyre rather than lift the front end.
Thats a pain in the freckle when you want to clear a log or go thru a creek.
I'm rebuilding the engine at the moment and it will go better than ever, leading to more wheel spin.
So its going into a OIF. But it will use the existing front and rear ends, inc brakes but I may shorten the swinging arm slightly.
I plan on moving as much weight as possible to the rear of the machine.
Maybe then it will look like a 1976 T140??
Lots of work, but I dont mind.
Cheers, Chris.

P.S. Jim you started this post, are you still out there?


1950 Speed Twin outfit
1951 Thunderbird outfit (76 degree racebike, or is it 90 deg now?)
1955 BSA D3 minibike outfit
Triumph solo's
Re: balance factors [Re: 76degree-triumph] #314545
05/21/10 4:11 pm
05/21/10 4:11 pm
Joined: May 2006
Posts: 309
Sanger, CA
jim schmidt Offline OP
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jim schmidt  Offline OP
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Sanger, CA
I am forever collecting balance info and have tried all the factors. After all that I have settled to 70% for all around smoothness.

Note that many singles from Manxes to speedway bikes run around 68% for vertical engines and down to between 50 to 60% for inclined motors.

The reciprocation weight is the bottom line for smoothness. Now I can frequently rev my street Nort to 7000+ and smile instead of griting my teeth.

Re: balance factors [Re: jim schmidt] #314680
05/22/10 11:31 am
05/22/10 11:31 am
Joined: Jan 2005
Posts: 1,662
East Bethany New York
Dick Harris Online content
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Morn'n Jim, I also have tried factors between 47-87,mostly road bikes,and my thinking is that the side to side balance is more important than the actual factor number. As an example,one web could be an ounce light and the other web an ounce heavy and the crank would still balance on streight edges,nowever, you can imagine roscking motion that would create.My '57 TR-6 is balanced at 70% and it is a joy to ride. Most of the unit 650's I do are at 85% and this seems to work out well. I asked the late great Jack Wilson about this one time and his reply; "for the 500's 74% and for the 650's 85% seems to work the best" I wouldn't argue with "the man" Dick

Re: balance factors [Re: Dick Harris] #314687
05/22/10 12:12 pm
05/22/10 12:12 pm
Joined: Nov 2005
Posts: 1,346
spfld vt
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phantom309 Offline
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spfld vt
my thinking is that the side to side balance is more important than the actual factor number.

I agree with you on this Dick. I think the side to side is it.I have run 68 to a bit over 85.


Tim Joyce
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Re: balance factors [Re: phantom309] #314698
05/22/10 1:28 pm
05/22/10 1:28 pm
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Posts: 1,114
Noblesville, IN
Jack Adams Offline
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The only real X-factor is the sludge trap. Dave Nourish did mine at 85%(no sludge trap) and I have no complaints. It is certainly smoother than the stock motor. Jack

Re: balance factors [Re: Jack Adams] #314709
05/22/10 2:55 pm
05/22/10 2:55 pm
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spfld vt
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phantom309 Offline
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spfld vt
You still have a good size hole there for oil if its like mine. Just no trap


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