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Balancing full size locomotive wheels

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Howard Lewis21/07/2018 20:56:14
1396 forum posts

Kenneth J Cook's book on his time at Swindon contains pictures of the Zeiss equipment used for optical alignment at Swindon. This gave such accuracy that parts such as connecting and coupling rods could be manufactured in the Works and merely lifted into place on a locomotive without any "fettling" to suit that particular locomotive.

With regard to balancing, on any reciprocating engine, because of the a portion of the weight of the reciprocating parts has to be taken into account, the wheels (in the case of a locomotive) or an internal combustion engine is unlikely to be in perfect primary balance. Once the machine begins to rotate, the balance weights produce a secondary force, acting at right angles to the primary. The dreaded Hammer Blow, so feared by Railway Civil Engineers. 4 cylinder engines with cranks at 90 degrees, and axles at 180 degrees were means of reducing this, improving overall Hammer Blow, and the riding, but likely to produce a modicum of "nosing". 

The best that can be achieved is to make the unit a 90 degree Vee, (As used on Brough Superior motorcycles.) Even this is not perfect, although the secondaries balance each other out, but not in exactly the same plane, so even a V Twin tends to "sqirm" in the horizontal plane. (And it gets worse as you progress through a V4 to a V8 or V16 because the couple increases because of the length of the engine)

V6 and V12 bring different problems, since the firing intervals are likely to be 120 degrees rather than 180, assuming a four stroke cycle, resulting in a 60 degree V in most cases.

In line 4 cylinder engines can be tamed using a Lanchester Harmonic Balancer. In this two shafts carrying weights, and timed to the crankshaft are driven at twice engine speed. Again, the balance weights have to be chosen to produce as great as possible balance. (Not always easy within the envelop of the engine)

A 3 cylinder, with crank pins at 120 degrees is naturally unbalanced, and requires really special efforts to reduce vibration. Balance weights will improve the situation, but not provide a complete cure.

Put two "unbalanced" 3 cylinders back to back to produce an in line 6 and the balance is good, but a couple will still exist causing the engine to "squirm".

By changing the position of the mounting points, a reduction on forces can be achieved (A E C did this with their 6 cylinder Diesel engines for vehicles, More recently, car engines did the same thing with 4 cylinder units ,by placing the placing the mounts on the torque axis, thus minimising the effects of the couple).

Probably perfect balance is obtainable; in Utopia!

Howard

Edited By Howard Lewis on 21/07/2018 21:01:16

Tim Stevens21/07/2018 21:21:20
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917 forum posts

Howard - Any (yes, any) piston engine can be balanced - at least as far as primary forces are concerned - by using two rotating spindles with appropriate masses attached. Both shafts need to rotate at crankshaft speed, in opposite directions, and how much mass, and where, depends on the layout. One of the cleverest versions of this idea was in the original Lanchester engine, which had two contra-rotating cranks geared together, each with a rod and piston moving together in parallel. By adding balance segments to both flywheels a layout which otherwise was guaranteed to shake was tamed completely.

To balance the secondaries, (left over when the primaries are cancelled) a similar pair of contra-rotating shafts are needed, but at twice engine speed.

Even then, you don't get a 'perfect cure' - you rarely do in life, never mind just engineering. But in practice, the tertiary and higher effects are usually so small that no-one bothers with them. But no doubt, in Utopia, it could be done.

Cheers, Tim

PS: I'm sorry I did not refer to 'hammer' by name, but I did cover the up and down shakes which are the same effect exactly.

Hopper22/07/2018 04:33:41
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2904 forum posts
48 photos
Posted by Samsaranda on 21/07/2018 16:34:26:

Hopper you mentioned “high performance Harley’s” what are they used in “lawn mower racing”? 🤔

Dave W

Now now. Harley-Davidson has held more speed records over the years than any British marque I know of. And won more flat-track championships and American national championships. And held more drag-race records.

And no Manx Norton back in the day ever went as fast as the 750cc sidevalve Harleys that were lapping Daytona at 149.9mph in 1968. (And those were a REAL lawn tractor with sidevalve engines!) Then when they went to overhead valve 750s, the Harleys continued to dominate flat-track racing well into the 21st century.

With a track record spanning from 1929 to the 21st century, the 750 Harley WR/KR/XR 750 would be the most successful production-made racing motorcycle of all time.

Yes, they are lawn tractors, but rather quick ones. smiley (And bloomin' 'eck they don't half vibrate with that 45 degree out-of-balance factor. The 149mph jobs at Daytona in '68 had shop rags wrapped around the footpeg rubbers just so the riders could keep their feet on them) at full chat.)

Edited By Hopper on 22/07/2018 04:40:06

Edited By Hopper on 22/07/2018 04:46:17

Mike Poole22/07/2018 10:29:47
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1495 forum posts
41 photos

Did the race winning Harley's actually have anything made by HD fitted to them? It seems that just about every bit of a Harley has a better after market part available. I think the race regulations for many of the Harley records were fixed to exclude any competition from other manufacturers who didn't make side valve v twins. It is true what you say though Hopper but it does need qualifying I feel. In a race where only Harley's are in the field I would put my money on a Harley winning.

Mike

Hopper22/07/2018 11:30:31
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2904 forum posts
48 photos

Oh, yes. The WR/KR/XR race bikes were made by HD. Of course they used magnetos and carbs by others as per normal. There were some aftermarket parts available but HD pretty much scooped up all the best tuners and got them working for the factory on contract, eg Tom Sifton, Jerry Branch. Very very few people ever bettered factory performance on the track. And if they did, they were on contract to the factory the next season.

No, the rules did not exclude all others. BSA Gold Stars and twins and Triumph twins raced against them for years. Rules were that bikes had to be based on a production model road bike (so no Manxes etc) and 750cc sidevalve raced against 500cc overhead valve up to 1969, which were pretty evenly matched. The Goldies and Brit 500 twins gave the lawn tractors a good run for their money. But the Harleys did not blow up as often so finished more races and got more points. From '69 onwards the rule was all 750cc OHV on the flat tracks and the legendary XR750 was dominant within a year or two of development for the next four decades or more. Now obsolete, they are still the machine to beat. There were a few years of brilliant road racing there when the Tridents and Rocket 3s were up against the early XRs, with a few Honda Fours and Suzi waterbuckets thrown in. Then along came the TZ350 two strokes and it was all over on the roadrace side of things.

However, as you say, many of the top fuel drag bikes have barely a Harley part in them. All aftermarket stuff twice the stock capacity, twice as strong etc etc, blown, running on nitro etc. Those are all HD Big Twin based, a whole different family of bikes from the 750 true race bikes, which are related to the road-going HD Sportster family.

There's a lot more to Harleys than big fat guys puttering around on big fat bikes. But most of it happened in isolation over the other side of the pond so we never heard about it much in the Empire. Bizarrely, the amount of development put into the sidevalves is on par with what went into the Manx or the Gold Star, but over a much longer period.

PS, how did we get on to this from balancing loco wheels? Sorry for the thread hijack. Lawn tractors and steam engines are kind of a commonality though I suppose.

Edited By Hopper on 22/07/2018 11:37:09

Edited By Hopper on 22/07/2018 11:38:42

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