Cylinder dimensions

[Anonymous]

This may be a question not many poeple could answer but is something currently on my mind.

In my experience with diesel engines, cylinder liners are conical when new. The dimensions at the top ring land area are smaller than the dimensions at the bottom. This causes a tighter fit at the top of the liner, compressing rings as the piston reaches top dead center. Because diesel engines are single acting, side thrust causes wear predominantly on one side of the liner, opposite the engine's direction of rotation. Over time, this will cause a bore to become out of round in the horizontal plane, and will give a barrel shape to one side of the bore in the vertical plane. General wear at the top of the bore will "open up" the liner's upper dimension.

Even though the days of measuring and replacing individual pieces in a power pack are long gone, it is still necessary to measure liner bores to determine how much life is left in the liner's service. Loss of taper can cause lower compression, causing loss of power. Barelling of the liner causes accelerated ring wear, and formation of a ring land at the top of the liner bore can cause broken rings.

All of this is well and good, but my question is how do these things affect the service life of a cylinder and rings in a steam engine's main and valve cylinders?

If a single acting diesel engine's cylinders are conical when new, what is "new Spec." for a double acting steam engine's cylinder. And, at what point would changes in cylinder dimension begine to affect ring life?

I know that the difference between "new" and "replace" in diesel engine liners is only a few thousandths of and inch. Are these measurements so critical in steam engines?

I'm sure these questions are specific and obscure to most poeple, but maybe they would at least make some interesting discussion, thats what's floating around in my head anyway.

[Overmod]

In most cases, the 'rings' in a conventional steam locomotive, as well as their fit, was sufficiently low-tech as to make differential boring somewhat superfluous. As you probably know, the Stumpf Uniflow cylinders had to be machined somewhat 'barrel-shaped' to be reasonably parallel when operating in steady-state due to the temp differential between the intake and exhaust-port ends; locomotive cylinders have a somewhat different profile BUT imho one of the theoretical uses for 'compression' (early cutoff of exhaust) is to keep heat relatively high just at the time intake will begin, avoiding early enthalpy drop.

Some interesting 'shoe' arrangements were used to support the piston in engines without tailrods. The ACE3000 was supposed to use 'diesel-style' multiple rings, which wouldn't work well at horizontal support, and therefore had tailrods specified -- this ensured reasonable concentricity under prospective expansion conditions, although I would be interested to see the wear patterns based upon actual steam flow through actual transfer porting under various over-the-road load and speed regimes.

[Anonymous]

QUOTE: Originally posted by M.W. Hemphill

I was under the impression that the cylinder bore of an internal combustion engine was tapered to be smaller at the top when cold to allow for differential expansion when hot, as the top of the cylinder runs hotter than the bottom. Wrong?

Mark, (can I call you mark?) you're probably right, but I do know that wear spec.s for liners include comparing measurements between different horizontal planes vertically to produce a number representing vertical bore taper.

That that slipped my mind is probably a sign of the time that has passed since I last worked as a mechanic.

[Anonymous]

QUOTE: Originally posted by Overmod

In most cases, the 'rings' in a conventional steam locomotive, as well as their fit, was sufficiently low-tech as to make differential boring somewhat superfluous. As you probably know, the Stumpf Uniflow cylinders had to be machined somewhat 'barrel-shaped' to be reasonably parallel when operating in steady-state due to the temp differential between the intake and exhaust-port ends; locomotive cylinders have a somewhat different profile BUT imho one of the theoretical uses for 'compression' (early cutoff of exhaust) is to keep heat relatively high just at the time intake will begin, avoiding early enthalpy drop.

Some interesting 'shoe' arrangements were used to support the piston in engines without tailrods. The ACE3000 was supposed to use 'diesel-style' multiple rings, which wouldn't work well at horizontal support, and therefore had tailrods specified -- this ensured reasonable concentricity under prospective expansion conditions, although I would be interested to see the wear patterns based upon actual steam flow through actual transfer porting under various over-the-road load and speed regimes.

I imagine side loading of a steam engine's piston is considerably less than an IC engine's, even without a tail shaft. It also seems steam engine rings are quite a bit "fatter" and do not use gas pressure for sealing but only spring expansion.

At any rate, steam cylinder bores then are parallel when new. Probably, that was the best that could be hoped for back in the day.

It's just that something I heard lately about ring life in steam engines being affected by choice of metal and temperature of steam got me to thinking of my own experience, where changes in bore dimention have a significant impact on ring life.

I guess to find a definative answer, I could compare bore/piston/ring spec.s between diesel and steam cylinders.

Just a thought, as crosshead guides bearing surface wears, this would probably add to piston side loading quite a bit.

[Anonymous]

QUOTE: Originally posted by M.W. Hemphill

John: Absolutely. You've been an asset to this forum, and I've learned a lot from you. The question about bore taper in IC engines I know I have seen as the practice for very small bores, but I don't know why one would bother in a medium-speed diesel engine such as an EMD, which has very loose tolerances -- for instance, the main bearings are not scraped to fit.

When you say scraping do you mean hand scraping? Hand scraping while highly accurate, is not done anymore, and is a lost art. My stepfather showed me how it basicaly is done, but it takes a long time to truly master. You can always tell a hand scraped surface by the pattern of the tool marks.

Main bearing bores in blocks too large to fit in a boring machine have to be align bored by a portable boring bar supported by spacer bushings between two bores separated by the bore to be cut. End bores are cut by supporting the bar from two inside bores.

What may be considered a large bearing oil clearance, may be absolutely necessary for a large journal, as a journal's diameter increases, so does the necessary oil clearance.

If loss of power cannot be attributed to anything simple like an air filter, or crankcase breather. Or, possibly fuel rack setting, or other mechanical reason, then loss of cylinder pressure must be checked.

Diesel engines are not compression tested like gasoline engines because while compression pressure may be somewhat higher, they can vary quite a bit under different conditions. The only way to check for loss of cylinder pressure from general wear is to inspect the liner, rings, piston, valves, liner/head sealing, and determine if replacement is necessary.

That stuff is old school nowadays though. With electronic engine management systems, a preprogramed diagnostic routine can be run, where the computer runs the engine at a set rpm, cuts cylinders out one at a time, comparing data, and determines performance of each cylinder.

[adrianspeeder]

One guy I know has an injector block out box he made himself in which he can tell the engine to shut off one injector at a time to learn all sorts of stuff. Fortunately, I have not yet needed to borrow it yet.

I have had the privilege to watch a master machinist do hand scraping.


Adrianspeeder

[Anonymous]

Cuting cylinders out on any diesel engine is simply what you do to find a dead cylinder.

On any high pressure system, crack a nut on an injector line.

On pre electronic Detroits, take a big flathead screwdriver, and while the engine is running, stick it between the rocker and the injector's tappet and crank down on it with your palm, holding the injector in a down position.

On other engines, there is a tool that looks like your hand making the victory sign and then curling your fingers, this fits over the rocker shaft, pushing it will then hold the injector in a down position.

My stepdad and my mom ran a machine tool rebuilding shop for about twenty years. They finally had to leave the business in the early nineties because there just wasn't any market anymore.

He did all hand scraping, but it is a very time consuming process.