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why were the Metro-Vik Class 28s concentrated upon Barrow?


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I think the two stroke engine vs. four stroke engine debate is one of those debates that is a bit over blown. Originally two stroke engines were seen as offering higher energy density than four stroke engines but that isn't necessarily true and some of the modern very highly blown four stroke engines are ahead of most two stroke engines on that score. A two stroke engine can dispense with inlet and exhaust valves, but the payoff if you take advantage of that potential is far less potential to optimise engine performance using variable inlet and exhaust timing. The cylinder head and timing arrangements of a two stroke engine can be a lot simpler but again, you lose a lot of potential engine controllability and performance optimisation. I've never found that the added simplicity of two stroke engines (noting that it is incorrect to assume that all two stroke engines are simpler than four stroke designs) never really translated into better reliability for medium and high speed engines although the conventional wisdom of four stroke designs offering superior efficiency generally was true. In fact the worst engines I ever had to work with were Detroit high speed two stroke engines, ghastly pieces of garbage. The really big engines are all two stroke but they're a completely different ball game from small high and medium speed engines.

Aargh! Memories of Destroyed - oops, sorry, Detroit - Diesels...

 

*goes off to look for a darkened room to lie down in...*

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People who say that the GM 2 strokes are simple engines are wrong. The GM engines have valves in the cylinder head just like a 4 stroke, and these are worked by a camshaft, just like a 4 stroke, but only admit inlet air. The exhaust is through ports in the sides of the cylinder liners. The engines in the CoBos were conventional 2 strokes, with the inlet and exhaust through the cylinder liner ports with no valves in the head. Although why they were fitted with reed valves as these had been proven to be unreliable in automotive use years earlier is a different question.

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Aargh! Memories of Destroyed - oops, sorry, Detroit - Diesels...

 

*goes off to look for a darkened room to lie down in...*

I was on an offshore ship with two Detroit V16 harbour generator sets. Twin turbo plus roots blower, 1800rpm and 500kw. Possibly the worst engines I ever saw. They were certainly the noisiest. We only used them in port thankfully as reliability wasn't their strong point, they were pigs to work on and oil changes every 250 hours. It was more effort keeping them in good order than the 4 Wartsila W32V12 main generators each of which pumped out over 5MW. And I wasn't the biggest fan of Wartsila engines. Quite how Detroit managed to make engines that bad is a mystery.

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Don't mean to be unduly pedantic, but the FL9 is a B-A1A, the centre axle on the six wheel bogie is unpowered.

 

Nice locos though

 

Yes, correct. I'd forgotten that small detail!  As you say, fine looking machines.

 

David

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Don't mean to be unduly pedantic, but the FL9 is a B-A1A, the centre axle on the six wheel bogie is unpowered.

 

Nice locos though

 

Are you sure it is not a Bo-A1A?

 

And come to think of it why are 31's A1A-A1A, rather than Ao1Ao-Ao1Ao?

Edited by Titan
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Are you sure it is not a Bo-A1A?

 

And come to think of it why are 31's A1A-A1A, rather than Ao1Ao-Ao1Ao?

I'm going to regret this I suspect, but I'm not sure I can think of anything with unpowered carrying wheels between a pair of rod coupled drivers (or why you'd attempt such a thing).

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I was on an offshore ship with two Detroit V16 harbour generator sets. Twin turbo plus roots blower, 1800rpm and 500kw. Possibly the worst engines I ever saw. They were certainly the noisiest. We only used them in port thankfully as reliability wasn't their strong point, they were pigs to work on and oil changes every 250 hours. It was more effort keeping them in good order than the 4 Wartsila W32V12 main generators each of which pumped out over 5MW. And I wasn't the biggest fan of Wartsila engines. Quite how Detroit managed to make engines that bad is a mystery.

 

Um?  12V71NA makes 1800 RPM/500 kw.  (So, in real terms, 12 cylinders, 71 Cubic Inch/cylinder, NA= Roots Blower only).  Someone somewhere was way off if they were tubo 16's, thats a 1mw set not a 500 kw set.  (the Tribals had those, we had the 12V71NA's).  Ask our crews what they think of the 850kw MWM's on the CPF- what a dog they are.  They are known as the "Make Work Monster"...  Best genset engine I have had to live with are the little Yanmar 3 cylinder 10 kw sets.  Add fuel and go, and go, and go.  As regards Detriot Leakers, that's key to their proper function- if it isn't leaking oil, then it doesn't have any in it, or something else will go wrong with them soon.   We didn't mind them, they had been put in to replace Deutz engines in 1984-6, which apparently were complete dogs.  Also note, a 12 will run quite happy as a 9, but only puts out about 300 kw while doing so.

 

James

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I'm going to regret this I suspect, but I'm not sure I can think of anything with unpowered carrying wheels between a pair of rod coupled drivers (or why you'd attempt such a thing).

 

Indeed, the original warship diesel hydraulics were A1A-A1A with both driven axles on each bogie coupled via carden shafts rather than rods.

Edited by Titan
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Um?  12V71NA makes 1800 RPM/500 kw.  (So, in real terms, 12 cylinders, 71 Cubic Inch/cylinder, NA= Roots Blower only).  Someone somewhere was way off if they were tubo 16's, thats a 1mw set not a 500 kw set.  (the Tribals had those, we had the 12V71NA's).  Ask our crews what they think of the 850kw MWM's on the CPF- what a dog they are.  They are known as the "Make Work Monster"...  Best genset engine I have had to live with are the little Yanmar 3 cylinder 10 kw sets.  Add fuel and go, and go, and go.  As regards Detriot Leakers, that's key to their proper function- if it isn't leaking oil, then it doesn't have any in it, or something else will go wrong with them soon.   We didn't mind them, they had been put in to replace Deutz engines in 1984-6, which apparently were complete dogs.  Also note, a 12 will run quite happy as a 9, but only puts out about 300 kw while doing so.

 

James

 

I did say they were the worst engines I ever saw.... They were hideous things, quite what Detroit were doing when they designed the things I've no idea. They were very small bore, more like a pumped up truck engine than a marine engine. I can't remember the engine model, I tried not to think about them too much. The company tried pushing the oil change intervals up but reverted to 250 hours when they started suffering catastrophic failure. Pumping the oil out after 250 hours it was like HFO, it was worse than oil that had done 10'000's of hours in the Wartsila's.

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Indeed, the original warship diesel hydraulics were A1A-A1A with both driven axles on each bogie coupled via carden shafts rather than rods.

What interests me is why 31's were A1A-A1A, why not 1Bo-Bo1. Why put the carrying axle in the middle? Weight distribution?

 

And as for coupled axles, apart from the hydraulic transmission diesels, most French electrc locos are either B-B or C-C, with monomotor bogies, a single motor driving all axles through a gearbox & final drive. I can't think of any diesels with monomotor bogies-can anyone enlighten me please?

 

cheers N

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Good question, and weight distribution might well be part of the answer, but another possibility is that there was not enough room to place the gubbins associated with the traction motors on axles next to each other while still needing 3 axles per bogie for route availability.  113 tons is a bit of a lump for 4 axles.

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And why exactly are 31's so heavy? For a similar power, classes 24-27 & 33 managed with 25 or so tons less? Is it the design of the bodyshell, or the fact that they used a 12cyl engine? You'd think re-engining with the Sulzer 8-cyl machine used in 33's would have made more sense, that would have made a lighter engine.

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What interests me is why 31's were A1A-A1A, why not 1Bo-Bo1. Why put the carrying axle in the middle? Weight distribution?

 

And as for coupled axles, apart from the hydraulic transmission diesels, most French electrc locos are either B-B or C-C, with monomotor bogies, a single motor driving all axles through a gearbox & final drive. I can't think of any diesels with monomotor bogies-can anyone enlighten me please?

 

cheers N

The 31s were built as A1A-A1A essentially because they were too heavy to be Bo-Bos and the engines were too gutless to drive six traction motors.

 

Nine tons heavier than a Deltic with less than half the power illustrates perfectly how far off "state-of-the-art" they were. Essentially, they were old-fashioned when they were new but because nothing on them has ever had to do much, they have proved very durable.

 

A1A bogies were an established design derived from American practice dating back to when they were building over-weight 1500hp diesels. A 1Bo bogie would have been breaking new ground and that's the last thing the Brush 2s were about.

 

John

Edited by Dunsignalling
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People who say that the GM 2 strokes are simple engines are wrong. The GM engines have valves in the cylinder head just like a 4 stroke, and these are worked by a camshaft, just like a 4 stroke, but only admit inlet air. The exhaust is through ports in the sides of the cylinder liners. The engines in the CoBos were conventional 2 strokes, with the inlet and exhaust through the cylinder liner ports with no valves in the head. Although why they were fitted with reed valves as these had been proven to be unreliable in automotive use years earlier is a different question.

They wheren't normally aspirated engines they where pulse wave pressure charged hence the reed valves.

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The 31s were built as A1A-A1A essentially because they were too heavy to be Bo-Bos and the engines were too gutless to drive six traction motors.

 

Nine tons heavier than a Deltic with less than half the power illustrates perfectly how far off "state-of-the-art" they were. Essentially, they were old-fashioned when they were new but because nothing on them has ever had to do much, they have proved very durable.

 

A1A bogies were an established design derived from American practice dating back to when they were building over-weight 1500hp diesels. A 1Bo bogie would have been breaking new ground and that's the last thing the Brush 2s were about.

 

John

And yet, in terms of power to weight ratio, a class 20 is virtually the same as a 31, at about 9.5kW/t.

 

For comparison, Deltic=24.6kW/t, 24-27 ~ 11.5kW/t, 37 = 11.8kW/t, 40= 11.5kW/t, Peak ~13.5kW/t, 47~17kW/t, 50 = 19.5kW/t.

Edited by rodent279
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And yet, in terms of power to weight ratio, a class 20 is virtually the same as a 31, at about 9.5kW/T.

 

For comparison, Deltic=24.6kW/T, 24-27 ~ 11.5kW/T, 37 = 11.8kW/T, 40= 11.5kW/T, Peak ~13.5kW/T, 47~17kW/T, 50 = 19.5kW/T.

Surprised that the Peaks came out so well, relatively speaking. Without looking at the figures I would always have assumed they were amongst the very worst.

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Surprised that the Peaks came out so well, relatively speaking. Without looking at the figures I would always have assumed they were amongst the very worst.

Well, for less than 25% more weight than a 31, they have over 75% more installed kW (135t against 110t, 1865kW against 1096kW).

 

I reckon in practical terms, that makes a Peak worth about 4 coaches over a 31.

Edited by rodent279
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Putting aside the point that the 31 was very much a first generation diesel that was less 'efficient' and much more reliable than a Deltic (or a Western, which was even lighter), they were in my experience a sluggish lump of a thing with probably the most luxurious and spacious cab I ever encountered.  They were, I thought, a poor replacement for our Hymeks at Canton, twice the size and nothing like the pocket rocket performance of a D70xx, but they were capable of easily being fitted with air brakes and eth (impossible on a Hymek), which, along with bombproof reliability, and a very smooth power delivery as with all Brush products making them favourites for Royal Train service, has ensured their longevity.  They were at least more comfortable to work on than the awful Class 25s.  On the face of it, an underpowered, overweight, oversized locomotive doesn't have a lot going for it, but service use often proves otherwise.

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Well, for less than 25% more weight than a 31, they have over 75% more installed kW (135t against 110t, 1865kW against 1096kW).

 

I reckon in practical terms, that makes a Peak worth about 4 coaches over a 31.

 

And a 'Western' nearly 2 coaches better than a Peak, but in practice there wasn't much in it!  But the argument is pertinent in economic terms; 4 coaches is potentially 284 paying bums on seats!

Edited by The Johnster
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The issue of concentrating certain types of locos to sheds for both spares and expertise has a long history. Burton shed had all the Reidinger valve geared Crabs and the Caprotti Standard Cl5s were concentrated at Patricroft and St Rollox. Late in steam days when works were closing Eastleigh works were suddenly faced with some of Patricrofts Caprotti, the language of the valve setters is not recorded!

 

David

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And yet, in terms of power to weight ratio, a class 20 is virtually the same as a 31, at about 9.5kW/T.

 

For comparison, Deltic=24.6kW/T, 24-27 ~ 11.5kW/T, 37 = 11.8kW/T, 40= 11.5kW/T, Peak ~13.5kW/T, 47~17kW/T, 50 = 19.5kW/T.

 

I reckon a Warship trumps all of those power outputs - except a Deltic! 2200hp in 80 tons....that's 20.2kW/T by my reckoning

 

Phil

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