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Required balancers


fretman

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Can any body help with the following information, came across it in model engineering
I believe the 4's and 6's required balancers, as there was always pistons in opposing phases, causing torsional vibration. the 5's did not require it as with a crank in 5 phases, no two pistons were in opposite phases. Not sure about the 3LW's but they probably needed no balancer either. Some of our Gardner experts can probably explain this better. Regards, Combustor.

 

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Old Iron In The Outback, Kimberley, West Australia.
Toys include Ruston 3VQ, Lister CS 8/1, VA SOM plant.
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It's to do with the firing order on an internal combustion engine and the vibrations caused by different cylinder combinations. 4 cylinders are worse for vibration than 6. The more cylinders have the potential to be better due to the angular separation of the torque pulses - some cylinder arrangements and firing sequences work better than others. Then you've got the beaming of the complete transmission and the harmonics in that to add into it along with the interaction with the mountings and thehull structure... It's not a simple issue - we have whole departments at work that deal with this.

 

Richard (RLWP) was a powertrain designer in a former life. He'll know more.

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Always thought the boxer twin and three cylinder engine with 120o crank was the minimum cylinder configuration to provide even firing order. Put two of the latter together and you have a straight six engine with both primary and secondary engine balance.

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2 & 3 LW's have bolted on balance weights on each crankshaft web

4 LW's don't have any additional balance weights

5 LW's have bolted on balance weights at each end of the crankshaft

6 LW's don't have any additional balance weights but do have a torsional vibration damper at the front end of the crankshaft.

 

In very simple terms rotational balance and torsional vibration can be considered as two separate things

 

Torsional vibration is caused by the power stroke of each piston twisting the crankshaft.

 

This becomes additive unless damped out to stop it reaching a critical point

 

Rotational balance needs to be achieved to prevent overload of the crankshaft bearings.

 

The text books that I have take 14 pages to explain all the different parts of this conundrum

 

Steve

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I understand the larger LWs (my spares manual suggests only the 6LW) had a damper assembly, I assume between the flywheel and the crank. I have never seen one of these, perhaps one the experts can explain....?

 

The damper is fitted at the front end of the crankshaft, According to my spares manual the 6LW had 4 different versions over its production life.

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