Thumping sounds in 567 powered locos......

Hi there

take a look at this video.

http://www.youtube.com/watch?v=bNR8dYzeCkc

Sorry it's a bit long, and the start of the engine is in the second half of the video.
It's a roots blown 567

when the engine is starting there is a slow deep banging sound, which seems to follow the engine even as it goes into idle speed but it gets softer.
You can hear it after the guy yells "hot start".
It is a very deep bass pounding.

Anyone have any idea what this sound is?

Also, one thing I never understood is why these engines sound so "chopped" and rythmic, even though they have so many cylinders.
Why is it that EMD engines follow that wam wam wam wam rythm when
their cylinders are actually fyring 12/16 times more frequent than this
sound

Sounds like the air compressor. They thump and pump with a "hollow" thumping sound, at a steady rate, seperate from the clatter of the 567 valvetrain and rod noises. the sound actually reverberates from the air filter canisters, on top of the compressor, as it's more like an intake sound the compressor makes.

but why is the compressor on when the engine is starting? Wouldn't it make sense to turn it off so the engine starts easier?

No easy way to shut the compressor off, since it is directly coupled to the crankshaft.

Rich C

Are you suggesting that the compressor is always pumping air?
Even when the compressor sound stops? (I mean in normal operation, not starting)

It could be a Vapor-Clarkson Steam Generator if the loco is equiped with one? Older F Units and GEEP's fit for passenger service had these and had a Tic-Toc sound like a clock. Such a sound can be heard in one of the Pentrex Films on there Video on "Union Pacifics Feather River Rotory" Snowblower.

I don't think so. The same sound is heard on turbocharged 645 EMD's too. (and roots 645)

dieselsmoke wrote:Are you suggesting that the compressor is always pumping air?
Even when the compressor sound stops? (I mean in normal operation, not starting)

When the locomotive air is up to operating pressure, depending on the compressor used, the intake check valves are either held open or closed, so that no additional pressure is generated. IIRC most are held open, using the air pressure in the tanks to push a diaphragm against the backside of the valves. This is why when the engine is idling and up to pressure you can sometimes hear a huffing sound coming from the compressor intakes, as air is drawn in and pushed back out the intake filters.

Rich C

So are you saying the deep sound at the start is indeed the compressor?

dieselsmoke wrote:So are you saying the deep sound at the start is indeed the compressor?

I would say so.

dieselsmoke wrote:So are you saying the deep sound at the start is indeed the compressor?

No, the compressor is that pissy sound, keep in mind the compressor is next to the camera (about 1 foot to the left). The deep pulsing rumble to me, based on my experience with a 8 cylinder 567C, sounds like the normal sound of the diesel popping in the cylinder. That sound can really only be heard when your head is under the hood or next to the exhaust, any further away it just blends into the song. If you watch any of the (technically good) old WW2 American Diesel Sub Movies when they are in the engine room, you can hear the same sound.

The sound that would worry me is the deep hollow drumming sound you hear as the camera person walks along the engine. Not sure what that sound would be. Then again my head has yet to be that low on a running engine.

Rich C

The deep sound I'm talking about corresponds to rpm (one bang per one revolution it seems).

In one revolution, there are 12 ignitions in this engine, and they should all sound at least remotely equal in volume.

So the deep banging seems to be 12 times slower than ignition sounds, so it can't be that.

Ahhh, Just tried the video with headsets and I think I heard what you were asking about. If you are talking about the deep low bruuumm sound till the engine catches then are just quick brums (1/2 second or less long) till she gets up to speed, that is most likely the intake stroke of the compressor. You can also hear 3-4 of them when they were priming the engine (spinning over with the compression reliefs, he calls them flash cocks, open).

IIRC that sound is actually the check valve stem vibrating against the seat caused by the air passing through it because of the piston retracting down the bore. The stem is spring loaded to keep 1-10 lbs of pressure against the seat. It is rarely heard when the engine is up to speed because of the quantity of air passing through it snaps it full open.

Sorry for the confusion,

Rich C

thanks, that sounds like it might be it

I also have one question. Do you have any idea why do (this is most noticable on tubocharged EMD's) these engines seem to pulsate?
For example, when you listen to the turbocharger on turbocharged 645's and 710's it seems to go we we we we we instead of a continuous turbine tone in idle (some sound smoother than others but all seem to have this pulsation).
Of course all engines have torque pulsation, but the frequency is rpm times number of cylinders (for two-strokes), yet the turbo seems to pulsate
at rpm frequency.
I would assume it is wear (causing some cylinders to be stronger), if it weren't for the fact that even latest SD70ACE's seem to have that we we we or wah wah wah in the idle.

The compressor isn't necessarily that "pissy" sound, it's the rythmic thumping sound, you hear. The compressor runs continuously, and it "loads or unloads" according to the pressure regulator setting, on the high side, of the compressor. There are sound baffles in the intake, to minimize the sounds, but they are still evident. You certainly don't have to be under the hood, or in the engine room to hear one running. They are loudest at idle, when the diesel isn't too loud to overpower the sound. the loco starts pumping air, as soon as the loco is started, and the electrical system closes the relays in the secondary panel, located at the rear of the loco. The "pissy" sound can be the air venting from the low water shut down button, cylinder compression and a small amount might escape from the unloader, before it charges. Been starting one every day, this past week. The sound is the compressor, in this GP-9 I'm stuck on.