diminished horespower in rebuilds

[M636C]

If we are talking diminished power in rebuilds, since GE engines are rarely rebuilt, they must have zero power after rebuild.

But to be serious, GM purchased Winton and EMC to get their foothold in the industry, and poured money into research through the 1930s until they got to the 567 and by the time they got to the 567C in the mid 1950s, they had a very reliable engine tailored to their application.

Alco purchased McIntosh and Seymour, and got the 539, which was a pretty good example of an engine but much heavier and older in design than the 567. They put money into research and built the 241 and the 244. The magazine "Diesel Railway Traction" indicated that in England, industry insiders felt that the 244 was so much in advance of other industry practice, particularly its power rating, that it could not be true. The 251 addressed the 244's problems but wasn't a great advance. One of the features introduced by the 244, a water jacket integral with the cylinder liner, was adopted by EMD in the 567C and solved many of the problems of the 567B and earlier engines. This feature wasn't used on the 251, because Alco were going back to basics, and the Alco engines didn't need the feature as much as the EMD engines did.

General Electric weren't sitting back to the extent that the view confined to the US Domestic market might suggest. They purchased the design of what became the FDL engine from Cooper Bessemer, just as the other companies had obtained the intellectual property required to build locomotive diesel engines - buying it. The little GE 70 ton units had a Cooper Bessemer engine, the model FWL, a six cylinder in line engine, but export units had been built in the late 1940s and very early 1950s using the FVL, a V-12 version of the same engine that already had all the basic features of the FDL as used in the Dash 9s. These locomotives went to Argentina and Australia, and in Argentina particularly were thought highly enough of that large numbers of the early export U series were also purchased, some of which are still in service. At least one of the old CB engined units, a shovel nose on the metre gauge, was still running in 2003 when I visited Buenos Aires, although it had been fitted with a locally built 6-251. This showed one of the problems of the CB engine - the twelve cylinder, with the same bore and stroke as the Alco 244 and 251, could only produce 1200 HP compared to 1600 HP from the 244 at the same time. In fact, GE built a further batch of metre gauge shovel nose units for Argentina fitted with the Alco 244, as being more suited to the local needs than the CB version.

GE spent their time and money improving the CB design until it could meet the Alco and EMD engines on roughly equal terms, and released it in the U25. It is now reliably running at a significantly higher power rating than Alco ever acheived, but GE have developed another engine, the GEVO, which appears to be an improved version of the HDL engine they jointly built with Deutz. GE have proven that they can improve an engine to meet the needs of the market. We will see if it will be as good as the 710 engine GM developed from their research in the 1930s and all their experience to date.

But GE didn't start new in 1960. In Townsville in Queensland now, there is a locomotive number 1150 with a builder's date of 1951 that shared all the basic features of the U series, particularly the engine. It has been restored to working order with its original Cooper Bessemer engine, and we can be sure that GE were always aware of how this unit and other around the world, were working while they were planning the U series.

Peter

[GMS-AU]

Hey , don't stop now gentlemen, this topic along with the Shells thread have really helped in my knowledge ( or lack there of ) of GM diesels as well as the other two. Here is years of collective knowledge briefly compiled into 3 pages. A humble thank you to all involved.

G M Simpson

[Anonymous]

Does anyone else snicker when they read the title of this thread? Is the government aware of this terrible tragedy? Should Mike Wallace do an expose?

OS

[Anonymous]

Gabe:

By the late 1950s, many of the problems that confronted Alco and EMD were moot, particularly metallurgy, and there was broad experience with light-weight, medium-speed diesel engines that did not exist in 1940. GE could purchase some of this experience, and a lot of it, such as metallurgy, they could get for free from the steel and alloy metal companies or by simply looking in the trade journals and inferring from one application into another similar application. Plus, GE had deep pockets to fund a detailed R&D project almost no matter how long it took. GE didn't need to build any locomotives to meet payroll, but Alco absolutely had to get product out the door or go broke, so Alco was really between a rock and a hard place.

GE's timing was very good. They waited until EMD, Alco, F-M, and a host of other companies had done all the exploratory work in this unknown field, but not so long that the market was completely done. The best analogy I can think of is the man who lets the pioneers go out and do battle with the Indians and the grizzly bears, and then stakes his claim on the last of the good land. Poor Alco was pretty shot full of holes by that time, but it wasn't like they had much choice. Their window of opportunity was in the 1930-1939 time frame, but I'm not even sure that even if they had seen the light on January 1, 1930 -- a light which they did not see -- that they would have had the cash flow through the depression to bring it off. GE was using its cash flow from other mature divisions to fund an expensive and risky venture into locomotives, exactly as GM had done.

OS

[gabe]

QUOTE: Originally posted by O.S.

Jruppert: I greatly appreciate your expertise in engines -- I'm learning a lot from you and Peter that isn't really obvious in the engineering texts. But -- you knew that would have to lead to a "but" -- I don't think that War Production Board restrictions were really anything more than an excuse invented by railfans years later to explain away the failure of their beloved Alco. If one looks at the historical record when it's written by historians who don't have a pre-existing agenda to absolve Alco, it seems clear that Alco's most serious problem was that EMD had been developing a diesel engine since the early 1930s, and Alco hadn't. It was a very new and high-risk technology, and Alco waited far too late to get started. By the time they did, EMD had made all the mistakes that Alco was still destined to make, and EMD had solved them and Alco didn't even know what they'd be yet.

OS

OS,

Don't take this as a challenge to your position, for I am sure you are right and there is a rational explanation. But, I am curious as to the explanation.

Wouldn't GE have had an even larger technology gap to fill than ALCO since they got in the game even later and hadn't the rail background and connections that ALCO had? Yet, GE knocked off ALCO and eventually surpased EMD.

I am sure there is a rational explanation, it just isn't obvious to me.

A poster formerly known as "Gabe."

[Anonymous]

Jruppert: I greatly appreciate your expertise in engines -- I'm learning a lot from you and Peter that isn't really obvious in the engineering texts. But -- you knew that would have to lead to a "but" -- I don't think that War Production Board restrictions were really anything more than an excuse invented by railfans years later to explain away the failure of their beloved Alco. If one looks at the historical record when it's written by historians who don't have a pre-existing agenda to absolve Alco, it seems clear that Alco's most serious problem was that EMD had been developing a diesel engine since the early 1930s, and Alco hadn't. It was a very new and high-risk technology, and Alco waited far too late to get started. By the time they did, EMD had made all the mistakes that Alco was still destined to make, and EMD had solved them and Alco didn't even know what they'd be yet.

OS

[M636C]

An additional problem with the 244 was dilution of the lubricating oil, this particularly affecting the crankshaft as well as the alignment difficulties mentioned by jruppert. The best indication of this is the design of the 251 engine. While on the 244, the fuel injection pumps are located in the usual place, between the valve push rods driven directly by the camshaft. In the 251, the pumps are mounted further outboard and lower down, and driven by rocker arms off the lower side of the camshaft. This location greatly reduced the risk of fuel contamination of the lubricating oil.

Peter

[Anonymous]

QUOTE: Originally posted by Overmod

Weirdly enough, I would NOT have expected most of the crank breaks to be at the flywheel end. I'd have thought somewhere in between pairs of cylinders inducing the greatest mutual torsion... not working against flywheel inertia. I learn something every day from Randy...

Where were most of the breaks on the 16-cylinder 244s? (I've always wanted to know that!)

This isn't directly germane to *locomotive* crank breaks, but IIRC the breakage of GM truck diesel cranks is often somewhere other than at the rear main bearing. I read an account of one person with a 6.5TD who had a broken crank between the first and second pairs of cylinders. His complaint was that the engine ran a bit rough, and only seemed to make about 75% power... he was so right! Only the rear six cylinders were actually providing effective torque; the two in the front were mainly driving the auxiliaries; there was just enough interference between the two broken halves that they stayed in rough sync (think about how the injection pump wandered in and out of 'time' though, depending upon effective torsion... !)

Alco's 244 engine was rushed to market at the end of wwII because Alco was not allowed to produce a competitive road locomotive until restrictions of the war production board were lifted. It took them a while to establi***he criteria for a reliable crankshaft and also find a supplier that could consistently produce it. Other design problems in the 244 contributed to crankshaft failures, mainly the interface between the main bearing saddles and their respective caps were not designed properly, causing misalignment with wear, and thermal cycling of the block also causing misalignment problems from distortion of the block itself over time.

I do not know what that would mean as far as any trend towards the most common location of failures in a 244 crank, but can say that a failure caused by stress from misalignment would most definately be accompanied by unusual wear in adjacent journal bearings.

[Anonymous]

I have noticed a trend in European diesel manufacturers switching from single large turbochargers of the past to multiple smaller turbo chargers operating in stages. This is supposed to make turbocharging more responsive to part load conditions.

The newest trend is smaller turbochargers that are simply replacing a larger turbocharger because design advances have given the smaller unit the same capacity as the larger unit.

There have been many marine diesels built in history that are reversible and or capable of running on different numbers of cylinders. The most common mechanism for this is having the valve rockers pivot on a shaft of eccentrics that when rotated either raises or lowers the rockers onto their respective camshaft. For reversing, there may be either two separate camshafts - one for forward running, one for reverse; or a single camshaft with two sets of lobes.

[M636C]

With all this discussion of "blanking cylinders" I feel I should mention the main propulsion engines of the Royal Australian Navy's "Anzac" class Frigates, which are an MTU 12-1163 TB93, a German built four stroke with a similar bore and stroke to the EMD 710, 230mm x 280mm. They have an extremely complex system of turbocharging, made more complex by the fact that the engine can be run using one bank of six cylinders only, so the ducting has valves to ensure that the exhaust and inlet passages only supply (and receive from) the six working cylinders. I believe the inlet and exhaust valves on the shut down bank are held open to reduce pumping losses, but I can't remember how. I was shown one of these engines at the factory, and the turbochargers and ducting pretty much doubled the height of the engine.

The reason for wanting one quarter or less power is that the resistance of a ship through the water varies as the CUBE of the speed, so to go twice as fast requires EIGHT times the power. When you are just cruising around waiting for something, the additional fuel saving is worthwhile.

This engine has a maximum power of 6000 HP compared with the similar sized EMD 710 which would be rated about 3000 HP under the same conditions. The ship can make about 23 knots with both MTU diesels at full power, but can run at more than 27 knots by turning off both diesels and using a GE LM2500 gas turbine rated at about 25000 HP. The single turbine drives both propellers. The fuel consumption of the turbine at part load is so high, that it is worth having the diesels just for cruise power.

Peter

[GMS-AU]

Down-rating engines happens in the truck industry as well for the same reasons. The Cummins M11 engine can come in various ratings down to about 240 hp. At this hp the engine will " live " longer as it is under stress. Remember the old Cummins 300 was about a 13 litre's engine where as the M11 at 11 litres is of course 320 hp. More hp for less capacity, and I guess a shorter engine life. Look at the car industry and the sort of power that is available out of say a 2 litre 4 cylinder engine these days with EFI.

True on a diesel loco load on the engine may be the same but if the engine is derated then it simply can't supply as much power to the alternator and that will help the traction motors last a little longer as well. I am presuming the engine is stripped as it needs it anyway so when it is rebuilt then it is downrated then. As discussed here and elsewhere the 2 stroke is at its peak economy per fuel consumed at about notch 7, up in the rev range where the turbo is free wheeling. ( Please correct me if I am wrong here )

On WC's SD45's were they downrated to 3200 hp to prolong engine life and increase economy? ( If at all ) I would presume that would only be done via the injector pump and not a total rebuild.

G M Simpson

[Anonymous]

I find no possible justfication for nueturing engines. I would want the engine to be big and strong because the more horses availible to do the work... the less "work" the engine has to do to move the load. Makes sense?

I have driven a Cummins M11 under steel loads (slightly more than 320 horses) and burned basically all the fuel per hour I could get into the engine while crossing mountains. A more expensive Detroit or Caterpiller at a higher horsepower rating will get the same load up the hill without burning so much fuel or stressing the componets.

For railroads, I am thinking why isnt the load on the engines constant, they are basically turning a generator to create electricity for the motors down below? If you only can create so much Wattage and Amps to a certain limit to feed your motors.

To me stripping engines in a shop takes man hours that costs money. I think any kind of savings will be wiped out by this work and also any future problems that will come up down the road.

[2c]

[Anonymous]

I know on Detroits, the air box covers have pockets cast into them. Because Detroits recieve their air from the V, broken rings, metal shavings, whatever is loose in the cylinder flies right into those pockets. Is this the case with EMD's?

What Randy says about where cranks break makes sense, when a crank "winds up", the greatest stress should be at the flywheel end. Usually what causes a crank to fail is fatigue from tortional vibration. Tiny cracks form in the filets around the oil holes and the filets between the journals and crank lobes. If two cracks meet, the failure begines a greatly accelerated pace.

If the crank fails elswhere it is probably due to some extreme shock like a siezed piston, hydraulic lock, or an imperfection - an Inclusion - in the metal. These types of failure are immediately recognizable by the crystaline structure of the fracture.

A failure by fatigue over a long period of time will show a very small definate starting point with circles of increasing radius growing from that point - "beach marks", the fracture as a whole will have a smooth appearence, usually the last part of a fatigue fracture will be crystaline as the remaining material is no longer strong enough for a typical load.

Oh, I just have to add, RANDY IS THE MAN!!!!! - most of what we say is speculation, leave it to Randy to say say something that puts it all to rest !![8D]

[Randy Stahl]

I've seen a similar situation on an EMD. A broken crank at the accessory end caused by faulty air compressor grommets, the air compressor siezed up and snapped the crank between #1 and #2 mains. The locomotive ran... sort of, with only the rear 14 cylinders. Not much for oil pressure though. I recall the bosses running the engine up until it siezed.
Randy

[Overmod]

Weirdly enough, I would NOT have expected most of the crank breaks to be at the flywheel end. I'd have thought somewhere in between pairs of cylinders inducing the greatest mutual torsion... not working against flywheel inertia. I learn something every day from Randy...

Where were most of the breaks on the 16-cylinder 244s? (I've always wanted to know that!)

This isn't directly germane to *locomotive* crank breaks, but IIRC the breakage of GM truck diesel cranks is often somewhere other than at the rear main bearing. I read an account of one person with a 6.5TD who had a broken crank between the first and second pairs of cylinders. His complaint was that the engine ran a bit rough, and only seemed to make about 75% power... he was so right! Only the rear six cylinders were actually providing effective torque; the two in the front were mainly driving the auxiliaries; there was just enough interference between the two broken halves that they stayed in rough sync (think about how the injection pump wandered in and out of 'time' though, depending upon effective torsion... !)

[Randy Stahl]

QUOTE: Originally posted by Overmod

I suspect that the 'long term' effects while substantial may be easy to document. My understanding is that EMD engines with bad power packs are fairly common in service, and often the engine isn't pulled for service until a certain number of them are dead. (Whether or not the engine is pulled immediately for something that isn't an individual-cylinder failure is another matter).

Randy, is there any 'preferential' location for powerpacks to go bad? If not, there can't be any good prediction of what the torsional stress in the crank would be, or what the long-term implications of peak stress might entail. It's been my suspicion for some time that dead cylinders were a major contributing factor to some of the crank breakage on the 20-cylinder engines.

Other reasons why two-strokes don't make 'twice the power' of a four-stroke: a scavenged engine doesn't have the charge density of a four-stroke with intake valves in the conventional position, given equivalent levels of boost. I can't find the reference to 'bmep', but the effective cylinder pressure on a two-stroke might as well be no higher than boost pressure by the time in the stroke that the scavenge ports begin to be exposed, or you'll start to get gas cutting on the rings, one of the places you'd least want it.

Oh, by the way, there are a couple of 24V71s on sale if you want 'em. TA's, too!

http://mdeltd.com/product.php?product=Marine%20Engines

(Scroll down the page a ways to find them)

Nifty looking things; they don't look to me as if they use a pair of 12V71 cranks bolted together, either... There are apparently quite a few yachts that have these things. One wonders, though, how many hours you'd get if you got 1800hp @ 2300 rpm out of them for any length of time <8-O

Usually a dead power pack means that the cylinder has lost compression, hole in a piston , dropped valve , broken rings , broken test ****. All of which would cause excessive crankcase pressure tripping the engine protector OR causing a crankcase explosion. Every 6 months a compression test / airbox inspection is done and the weak ones are changed. 99% of the broken crankshafts Iv'e seen are right where you expect them... at the flywheel end.
Randy

[Anonymous]

How does exhaust timing differ between turbo and non-turbo engines? you could probably compare exhaust timing at the camshaft between two engines of the same model, but this wouldn't tell you how that difference was determined. That's a question for engineers in a laboratory.

Cutting short the power stroke is a compromise, but poor skavenging also cuts power.

[Anonymous]

The Detroit 71 series manual has a section with an illustration showing a vacuum test of the piston pin bore to ensure air tightness. In my experience as a technician, this is archaic, because nobody assembles power packs anymore, only preassembled power packs are installed, but it does show that it is important to stop communication between the skavenging ports and the crankcase.

As a technician, I have never heard of backpressure having to be measured, but it is probably of concern to an engineer. I imagine backpressure after the turbo is more important for everyday consideration. For an engineer, it would be usefull to compare exhaust backpressure before the turbo to boost pressure on the cold side to determine a turbo's efficiency. Backpressure may be higher because of a turbo, but so is intake pressure and combustion pressure, so really the question is, "Does the relative differences in pressures change?", and this is probably a reflection of a turbo's efficiency.

[Overmod]

About the scavenge ports/exhaust ports: granted, but my point concerned the effective limit of the piston excursion under power. There can't be any 'blowback' from the piston through the transfer ports to the crankcase under any circumstances. If the exhaust valves open 'early' (as you rightly note they do) it still further reduces the effective duration of the power pulse.

How much earlier do the valves have to be set to give the 'momentum' you mention on an EMD turbo engine over a range of engine speeds? Seems to me you'd have to do this as a compromise, because the back pressure would range substantially depending on the degree of actual boost once the turbocharger turbine took up its proportion of the load (from the mechanical drive) -- which leads to another tech question: what IS the measured back pressure at different loads/speeds on a turbo 645 or 710?

[Anonymous]

Overmod, very cool. It looks like three eights put together. the exhaust manifold looks homade! 1800 hp from three eights would be 600 hp from each eight, which sounds about right for a marine application 8V71. The only problem I see is the crank is very long. They run to 2300 rpm, but I remember some owners saying they're much happier at 2100 (detroits).

Oh, as far as cylinder pressure being above boost pressure when the scavenging ports are uncovered, doesn't sound right, because the exhaust ports should already be open when the ports are uncovered. Two stroke engines open their exhaust valves slightly early while there is still pressure in the cylinder, the resaulting "pop" gives momentum to exhausting gasses as the ports are uncovered.

[Randy Stahl]

18 psi is about right... you can see and hear when the covers are on loose , especiallt in throttle 8
Randy

[oltmannd]

The 3-5 psi for a roots blower engine sounds right, but for a turbo it sounds low. Looking at some test data from 1986 turbocharger/fuel efficiency tests on an SD40-2 at Conrail's test lab in Juniata, we measured about 18 psi.

[Overmod]

I suspect that the 'long term' effects while substantial may be easy to document. My understanding is that EMD engines with bad power packs are fairly common in service, and often the engine isn't pulled for service until a certain number of them are dead. (Whether or not the engine is pulled immediately for something that isn't an individual-cylinder failure is another matter).

Randy, is there any 'preferential' location for powerpacks to go bad? If not, there can't be any good prediction of what the torsional stress in the crank would be, or what the long-term implications of peak stress might entail. It's been my suspicion for some time that dead cylinders were a major contributing factor to some of the crank breakage on the 20-cylinder engines.

Other reasons why two-strokes don't make 'twice the power' of a four-stroke: a scavenged engine doesn't have the charge density of a four-stroke with intake valves in the conventional position, given equivalent levels of boost. I can't find the reference to 'bmep', but the effective cylinder pressure on a two-stroke might as well be no higher than boost pressure by the time in the stroke that the scavenge ports begin to be exposed, or you'll start to get gas cutting on the rings, one of the places you'd least want it.

Oh, by the way, there are a couple of 24V71s on sale if you want 'em. TA's, too!

http://mdeltd.com/product.php?product=Marine%20Engines

(Scroll down the page a ways to find them)

Nifty looking things; they don't look to me as if they use a pair of 12V71 cranks bolted together, either... There are apparently quite a few yachts that have these things. One wonders, though, how many hours you'd get if you got 1800hp @ 2300 rpm out of them for any length of time <8-O

[Anonymous]

Actually blanking a cylinder in a four stroke engine should have a very different effect than in a two stroke engine.

For one, power strokes in a four stroke engine are divided into 720 degrees, while a two stroke's are divided only into 360 degrees.

comparing pistons, con rods, cranks between two and four strokes of comparable output, the four stroke's are always far heavier. In a two stroke engine, mean effective pressures are lower, and the piston is always subject to positive cylinder pressure; this allows two stroke engine components to be much lighter. This is probably why I see so many comments on how EMD's load so much quicker.

The part about mean effective pressure is also one reason two strokes don't make twice the power of a four stroke, another could be pumping losses, because two strokes move about twice as much air.

Anyway, all of these things probably point to blanking cylinders of a two stroke having LESS effect than in a four stroke engine. If a two stroke engine lost a cylinder for any reason, it would probably run smoother than a comparable four stroke losing a cylinder.

The thing is that would be an emergency situation and not the expected running condition of the engine. What would be the long term effect of running an engine with an imbalanced firing order?

[Anonymous]

Assuming the v6 and the v8 have the same v angle, stroke and journal dimensions, the block would have to be shortened anyway because the crank needs to drive accessories, oil pump, cams, etc.. Which was my point: if you are going to correct the firing order (build a shorter crank), then you also have to cut the block.

[Anonymous]

I would think that a real world example (that we non-locomotive-owning folks could do) of cylinder blocking would be to take a V8, choose two cylinders opposite in firing order and remove the spark plugs. Now start it.
While the V8 is a four-cycle and the engines discussed in the thread are two-cycle, I would imagine the effect would be similar. Also, if one were to install a crank from a V6 (never mind the mechanics- it's been machined to fit) one could run the engine with two cylinders unused with degraded performance but not shaking itself to pieces.

I would think you would almost be required to change the crank.

[Anonymous]

Supercharger is not the right term for the blower on a Detroit Diesel, blower is the correct word, because the blower is geared to turn about one and a half times crnkshaft speed to provide a small amount of pressure for exhaust scavenging.

Supercharging weather by turbo or blower is when at the end of intake stroke, the cylinder air pressure is higher than atmospheric. A blower used in the capacity of supercharging can then be called a supercharger. I did not know that Detroits could use a larger blower as an option for supercharging.

In my own experience, I have seen 12v71's are in fact two 6v71's bolted together. 71 blocks and all Detroit blocks are machined with flush ends to which an adapter plate is bolted for accessories, etc.. This allowes an engine to be built in many diferent configurations, the "front" could be on either end of the block, regardless of direction of rotation, fuel pump, heat exchanger, and any other accessories can be mounted in a variety of places. Detroit is not the only manufacturer to do this. EMD blocks have a similar appearence, but the end plates are welded, and the block is a complete block for however many cylinders the engine has.

That said, there is no reason that I can see why a 20 cylinder block cannot be cut to any number of cylinders, because of its construction is of separate peices welded together, instead of a solid casting. Oil and coolant passages are also less of a problem, the block is "dry" with coolant jackets integral to the cylinder liners, and flowing directly to each cylinder head bolted directly to each liner. Coolant flowes from cylinder to cylinder via jumpers. If a block were to be cut, I imagine great care must be taken to maintain proper alignments.

The reason I know that EMD crankshafts and camshafts are modular, is because I used to have an EMD manual for 645 marine engines, it was quite a while ago though, about ten years ago, before my kidneys failed. I was borrowing it from a freind, but it got stolen from my truck because I was living in a bad neighborhood. If I remember, there was a chart showing the bolt pattern of the crank's and cam's ends and the correct holes to align when assembling a crankshaft or camshaft. If for some reason a journal was damaged beyond repair, the whole crank or cam does not need to be replaced, also, if an engine was to be decommissioned and the parts were still usable, they could be assembled in a different engine, but I don't remember any direct reference to modifying the number of cylinders in an engine.

That said, to me, it makes no sense to blank cylinders without changing the firing order, and assembling a shorter crank and cam means the block has to be cut.

I have read that EMD thought long and hard before deciding to build a 20 cylinder engine, because they knew it would break crankshafts. What promted them to explore was IIRC, a Japanese company had succesfully built a 20 cyl. marine engine, that proved to be reliable. About ten years ago Detroit built two 20 cyl. 71 engines as an experiment for an offshore cigarette boat, which was successfull. A twenty cylinder engine has an awfully long crankshaft, and the windup must be terrible, allowing tortional vibration to amplify. If it was hard enough to build one in the first place, why mess with it?

I know enough to know what I don't know, and developing a mathematical model of all the forces and vibrations in a crankshaft is WAY beyond my knowledge or experience. I once copied the equations describing a piston's motion relative to a crank's radius, and a given rod length - "rod ratio", it's three pages of trigonometry and calculus! And that's just figuring the motion let alone the forces or the vibrations. I know enough that I can look at it and point out the major parts and the general meanings, I suppose if I had to, I could take the time to learn more, but if you have ever took the first step of trying to design something, even if you know the equations, that doesn't tell you where to start !!! When all you have is variables and no constants, maybe you understand the relationship between the variables, but that doesn't help you !!!

Anyway, if you can see from the getgo that blanking cylinders is asking for trouble, a complicated mathamatical study is probably not a good idea either !!

[broncoman]

in notch 8, how much manifold pressure is being produced a turbo on a 16-645. Does a supercharger, produce as much as a turbo or is it just there for the scavange effect. On the smaller detroit motors that have both turbo and superchargers there is an option to go with a bigger supercharger in-lieu-of having a turbo, so horsepower loss isn't as much as it could be by removing the turbo. The five year turbo life seems to be a constant even on the smaller ones also.

[Overmod]

Ditto with oltmannd. This started getting really interesting a bit earlier, when jruppert originally discussed the dynamic-balancing characteristics of 20cyl vs 16-cyl 2-strokes.

I never had firsthand knowledge of 20-to-16 conversion methods; have only seen anecdotal and Web discussions (including that material for ship-engine conversions; there are oil-field engines that are 'converted V-8s' (Ford 460 being a common block) in which four cylinders are powered and four are converted to air compressors or pumps. Discussion of design and balance of these things would be fascinating... but it would be a stretch to consider that to be 'on-topic' for a railroad thread ;-D

I did understand 'blocking off' cylinders to consist of removing power packs for the 'holes' involved, and plating off the crankcase to maintain scavenge pressure, capping or bridging lube lines, etc. etc. etc. It would be my suspicion that 'derating' a 20-cylinder engine would be least cost-intensive if the original crankcase, crank, etc. could be preserved intact, and this would to me imply that the four cylinders taken out of 'service' would NOT be four in a group at one end of the engine if the thing were to be (1) kept in dynamic balance (static balance being done with ringweights on the disconnected crank throws), (2) done to minimize torsion peaks in the crank due to firing order vs. peak compression effort, and (3) built so that its 'new' critical-speed or resonant-vibration characteristics were either known or equivalent/better to existing 645 practice.

Be interesting to see jruppert's detailed analysis of the forces involved in a 20 vs. derated-16 engine with different cylinders out but using the same crank. (Might also be interesting to see whether one or more of the 'removed' cylinders could be changed over to air compression and perhaps improve the dynamic characteristics, without decreasing fuel efficiency (etc.).

My own suspicion btw. is that converting 'extraneous' engine cylinders to air compression, on a locomotive which by law has to have a certain enablement for brake air, is in the same category as 'thermodynamic' enhancements to traditional steam locomotives -- they might work in theory, perhaps even promise Big Money Savings, but by the time you plumb them up, provide redundant safety valves, relief lines, dryers, traps, etc. the overall cost might not be worth it. I can just see some fresh-out-of-college engineers saying 'we can draw the compressor intake air from the filtered intake manifold!' without wondering what this might imply on an EMD 2-stroke...