Bearing Clearance

[engineguyBill]

Engineers say that is enough but we keep having failures.

What are the exact failures that you are encountering with this engine?

[engineguyBill]

At 950 RPM, I don't think the harmonic dampener is an issue with this engine . . . . .

[ptuomov]

What are the exact failures that you are encountering with this engine?

An excellent question.

[ptuomov]

At 950 RPM, I don't think the harmonic dampener is an issue with this engine . . . . .

I think (but do not know) that this depends on crankshaft length, cylinder pressures, etc. I wouldn't rule that out if the failure is the crankshaft breaking.

[Kevin Johnson]

At 950 RPM, I don't think the harmonic dampener is an issue with this engine . . . . .

Okay, but if it IS equipped with a torsional damper and IS being operated to factory specs in an application it was designed for then you can see the faulty logic being employed. Right?

[engineguyBill]

An engine of this sort probably has a price tag with seven digits or so, therefore we can probably assume that the machine is being operated within design parameters and factory specifications.

[Kevin Johnson]

An engine of this sort probably has a price tag with seven digits or so, therefore we can probably assume that the machine is being operated within design parameters and factory specifications.

Ergo, if it has a damper then it should be checked.

[dannobee]

See what similar engines in that class are running. There's only a few players in small ship/locomotive/generator/ag water pump engines in that area. MAN, Cat, EMD, etc. See what they're running for bearing clearances in their tried and true engines. If yours are way out of whack, look there. If they're in the same ballpark, look somewhere else as Kevin stated.

The heavy rail that I currently work in uses electric motors, so no help there, but the Cat 3612 is in the same class and same hp range as yours. Their manuals are available online (I had access in the past but no longer). Maybe reach out to those people working on them. If your engineers are dead set against listening, ask them what their competitors are doing, then whip out a copy of the service manual page. Maybe then they'll listen.

[hoodeng]

Would be handy if the o/p could tell us how the failure in manifesting itself, what running hours are involved and is it happening within a running time band as Bill has said. I don't think its breakage as he is asking clearance advice,which suggests to me bearing related failures.
Is there spectroscopic irregularities in services?

These type of engine manufacturers as has been pointed out have pretty strict specifications, service schedules and TBO schedules.

Cheers.

[Kevin Johnson]

I can understand why he is restricted from commenting by his employer.

Here is a completely made-up story to illustrate:

Hi,

I work in an atomic energy plant and the coolant pumps keep on failing. The engineers say that everything is okay but I think there is something wrong because the pumps keep failing.

And so on.

Just insert a controversial activity of your choice.

[harleyboy2003]

i work daily with large natural gas industrial engines. As an example a Waukesha 275 16 cylinder displaces 17000 cu.in. Power output is 5000 hp and 26000 ft.lbs @ 1000 rpm. The main bearing journal measures 8.850 and has a specified bearing clearance of .0065 to .0105 . The oil pump moves 266 gal of oil per minute @ 60 psi . Obviously 0.003 bearing clearance just isn't going to work ! The other concern I have is , on large engines like these web deflection MUST be checked when installing the engine to a skid or bed plate. The sheer mass of the engine when torqued down Will distort the crank center line and proper shimming of crankcase mounting points along with web deflection measurements is mandatory! Failure to do so will result in smoked bearings

[Kevin Johnson]

i work daily with large natural gas industrial engines. As an example a Waukesha 275 16 cylinder displaces 17000 cu.in. Power output is 5000 hp and 26000 ft.lbs @ 1000 rpm. The main bearing journal measures 8.850 and has a specified bearing clearance of .0065 to .0105 . The oil pump moves 266 gal of oil per minute @ 60 psi . Obviously 0.003 bearing clearance just isn't going to work ! The other concern I have is , on large engines like these web deflection MUST be checked when installing the engine to a skid or bed plate. The sheer mass of the engine when torqued down Will distort the crank center line and proper shimming of crankcase mounting points along with web deflection measurements is mandatory! Failure to do so will result in smoked bearings

First response to his query:

Going by the Tribology Handbook, Section A9, Fig. 9.5. Recommended minimum (diametral) clearance for steadily loaded bearings, your stated minimum clearance is borderline. His is clearly out-of-range but we do not know whether this is a fresh engine design or an engine that has been in steady service and suddenly exhibits repeated failures.

Obviously the engineers felt they could play with a minimal recommended clearance in both cases.

The point about the bedplate is important -- that is a standard admonition even when changing fasteners much less adding a [girdle].

Perhaps during an overhaul the assembly was mistakenly dropped and distorted said plate. We just do not know.

[Vintagewrench]

The original specifications of many of the early vintage passenger car and racing engines that we rebuild do not exist anymore including bearing, and piston clearances. Research in the past has turned up the rule of thumb clearances used by those in the field in the past, in engine repair manuals, engine bearing manufacturers service manuals, and the "Machinists Handbook."

We found that most sources recommended .001" clearance for every inch of shaft or cylinder bore size. Using these clearances over the years has worked very well and we have not had any problems with pistons, or main, rod, and cam bearings seizing or scoring over the years.

The Federal-Mogul Engine Bearing Service Manual's we have from the 1940s to '60s spells out the same .001" clearance for every inch of shaft size and on the plus side specifies to add at the most, another .001". In house experience has proven that a liitle loose always works better than a little tight.