Hints and Tips - Engine Balancing

On 16 Dec 98 Jim Runciman wrote...

Can anyone advise if there is a good reference book on crankshaft balancing. My particular interest is in the so called balance factor or the proportion of of the conrod which must be treated as reciprocating weight. I have seen huge variations in engine smoothness at high revs in 'balanced engines' and can only put the differences down to the balance factor.

Carl Cederstrand replied...

Dear Jim,

Hurrah, you understand! You are correct, the counterweights on the crankshaft indeed serve two purposes. They are sized to counterbalance the crank throws (crank pins) on the crankshaft and to also reduce the inertial forces generated by the connecting rod. Your understanding that the amount of counterweighting allocated to the connecting rod is usually calculated by dividing the mass of the connecting rod into two pieces is also correct. This two piece division makes the system easier to calculate. The best text I know of that discusses your question of the division of the mass of the connecting rod into two compoments (rotating and reciprocating) is:

Mechanics of Machinery, 4th Edition (My 1st Choice)
Ham, C.W., Crane, E.J., Rogers,W.L.
McGraw-Hill Book Company, Inc.
New york, Toronto, London
Copyright 1958
Library of Congress no. 57-6395

An additional text would be:
Mechanics of Machines, 2nd Edition
Ryder, G.H., Bennett, M.D.
Published in Great Britain, 1990
MacMillan Education Ltd.
London and Basingstoke
ISBN 0-8311-3030-X

There is also an out of print book that is listed at Amazon (http://www.amazon.com) that came up during a search at Amazon under 'automotive engine'. This book is: 'Automotive Engine Piston, Connecting Rod and Crank Dynamics' (Lab Manual) by Richard J Howell. The original published cost was $160.00 The title is aimed in the right direction and I have ordered a search for one. Other than its title I know nothing about this Howell book.

My very best wishes, Carl Cederstrand / Orange California

Maggie Shapland also replied....

I had a quick look at home and there is alot about crankshaft balancing (for all kinds of engines- not just 4 cyl) in:

Internal Combustion Engines: Heldt 1939
Internal Combustion Engine: Ricardo 1922
Automobile Engineers Reference Book: Molloy & Lanchester (the doyen of balancing) 1956
Theory of Machines: Toft & Kersey 1932- very mathematical

An alternative approach from John Hardy...

Here's what I do. Gather up all reciprocating parts that require balancing. ( crank, pistons, conrods, flywheel clutch etc) and take them to a balancing man. A racing engine builder would do. In exchange for coin of the realm he balanced the lot for me. He marked the relevent components so that I could reassemble them in the correct relationship to each other. Hey Presto.

Savings on book
Savings on balancing machinery (probably many many pounds)
Savings on headaches
Savings on cockups

Also, if it goes wrong I can blame someone else.


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