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Best balance factor? Tonti framed 850 and 950

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c13pep View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 11:07
Lets just call it sludge to end the argument but whatever you call it then it wouldn`t have been there during manufacture, neither would any oil for that matter apart from brushed on assembly oil when the cranks were originally balanced. The word that seems to appear most in many of the articles written on balancing is `compromise` therefor it cannot be an exact science. For me if Dave Richardson quotes 50 or 52 then that would be good enough but I have never had any of my cranks balanced preferring, instead, to make sure that the rods and pistons are equal weights. If the engine does vibrate then I call it character and its the reason I enjoy riding the Guzzis so much.
CHRIS
you can`t have any fun in a straight line

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Phil View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 11:23
Exactley Chris, it is not a symetrical cyclindrical mass that can be balanced to spin vibration free. There is a reason why the twin contra-rotating balancer shafts were designed as a better compromise 🙂
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 11:29
FWIW, if memory serves (can't be asked to search for the book right now) my factory workshop manual describes the balancing as to put the c/shaft bearing faces on two knife edges, with a conrod + piston hung on the crank pin, and it should stay put in any position. (I.e. not roll.) That implies to me that the counterweight equals the rod + piston weight. Think that's right.


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IanB View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote IanB Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 13:31
Originally posted by Phil Phil wrote:

This is not an exact science as there are many variables and assumptions. Things like conrod length to stroke ratio have an effect. Assumptions are made regarding ring drag and the weight of the oil on the piston. For road engines the tolerance will be more than a few grams, I cant see why you would re-balance to account for the weight of the sludge removed from the trap.. did they take into account the mass of oil that would be in the trap cavity ?

All common sense, and presumably correct. At the same time, however, the difference between 50 and 52% does not seem like very much, but it's apparently an improvement. Perhaps the very factors you mention are the reasons for the difference between a "theoretically correct" 50% and a "practical best" 52%? I don't know enough about the process to tell.

As for the sludge trap - when I sent a crank in to be rebalanced about 20 years ago the company refused to do the job because I hadn't cleaned it out. I got the piss taken out of me, so I presume it was a novice error! (Only cost an extra set of P&P, fortunately!)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpc Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 14:46
"There are in fact so many considerations involved that it is impossible to quote one figure as being

ideal, since it varies with every type of engine, and even for the same engine in different or differently- 

equipped frames. The only source of reliable information is the parent factory who have certainly done a 

lot of experimentation."

...

"As an instance of re-balancing to suit different frames, the Speedway Vincent engine with the standard

66 per cent factor caused severe vibration in a very light dirt-track frame, until the factor was reduced

to 61 per cent, a matter of 1.3 oz at pin radius."

Phil Irving, Tuning For Speed.
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 15:55
If memory serves correctly, the chap at Basset Down when balancing my Triumph 6T crank told me that different factors can be used to move the point of maximum vibration or maximum smoothness to specific engine speeds.This was about thirty-five years ago so apologies if I've got that wrong.I'm sure someone knows if there is any truth in this.

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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 23:38
I have no doubt that is true. It's dynamic balancing in the end anyway.
Brian.

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