[cphilip]

Running test

Ok so now the engine is running, I listen to it, getting past the noise of the combustion knock and try to determining if there is excessive knocking noise. If there is heavy knocking, red flag! Shut it off! This could be the equivalent of a fuel burning grenade. A knock inside of the engine means that heavy metal parts are making contact in a violent unlubricated manner and they can come apart. Do not stress test a knocking diesel, especially if you don’t own it.

So now I have a running engine that is not knocking, it is very important to get the engine hot at this point, I have experienced cold engines that were devoid of noises that had a pretty bad rapping sound when hot. This is commonly caused by a loose connecting rod bearing or main bearing that develops play as the parts expand. I have also experienced the opposite situation in which a cold engine is louder mechanically than when it heated up, because the internal parts heated up and fit better. There are too many noises and reasons for those noises, I’ll say that if I hear a lot of mechanical clatter, red flag and figure expensive repairs. A diesel may have a vibration at low idle that subsides at a working RPM, that is usually normal, however, a shaking diesel across the RPM range is a concern, red flag! Shaking could be caused by a dead or weak cylinder, meaning expensive repairs are in order. I like to load a diesel down at full throttle by dead heading the hydraulics against the relief valve, (for instance, holding a loader bucket tilted back until it cannot go any further). If the engine drops excessive RPM’s or stalls out it could be weak. When I am done running a diesel engine I will always restart it after I shut it off. It should restart instantly and it is one more check of the starter bendix and ring gear!

Blow-by

Blow-by is the pressure created inside of the engine by the compression gasses passing the piston rings. I check blow-by by removing the oil fill cap, feeling and seeing the pressure or smoke that blows out the oil fill hole at a low idle. Some blow-by is normal, I try not to freak out unless the blow-by seems puffy, very steamy or excessive. Most engines have a crankcase vent tube mounted to the valve cover or the side of the block. If I can find the vent tube I’ll just inspect blow-by exiting from the tube. Really worn out engines with a lot of blow-by might have a lot of smoke in the engine area that can exit through the radiator grill. If the radiator utilizes a pusher fan, it will look like there is smoke blowing out of the radiator grill. Frequently this oil vapor will accumulate on the radiator fins and collect dirt, clogging the radiator. Red Flag! When the vent tube allows the blow-by to exit under the engine I have seen what almost looked like another exhaust pipe exiting the bottom of the engine because of the excessive blow-by smoke. Diesel run on is a dangerous condition, in which the diesel engine will actually run on the excessive blow by gasses that have been routed back to the air intake of the engine. Diesel run on means that the engine can run full speed until it blows up, it can’t be shut off unless the air intake is blocked. Scary red flag! I also carefully remove the radiator cap and look in the radiator with the engine running to see if any engine compression gasses are entering the radiator forming bubbles, if I see bubbles in the radiator, red flag. At the same time if there is any oil floating on the antifreeze, then this baby needs further checking and a big red flag.

Turbochargers

The turbocharger is probably one of the most abused optional pieces on the diesel engine. The abuse takes place innocently because the operator never knows that the turbocharger (turbo) should receive special treatment. A turbocharger may achieve internal impeller speeds in excess of 100,000 RPM. Proper lubrication is vital. A minute or two of warm up before high RPM’s allows the bearings to get a good coating of oil. Letting the engine idle for a minute or two after a high speed run will allow the turbo to slow down and cool down. A turbo spinning after the oil supply has been shut down prematurely wears out the bearing surface and cooks the oil in the bearing chamber, a situation referred to as coaking. A bad turbo charger will allow oil to get past the seals and into the intake manifold or the exhaust manifold and show a lot of blue exhaust smoke and oil consumption. A turbo with a lot of bearing play will actually damage the impeller blades and produce no boost, thus the engine will not have normal power. A whistling exhaust sound is a common occurrence and can be a sign of trouble. However, I have experienced many whistling turbo’s that have no problems. I have heard that carbon and or dirt build up on the blades of the turbo can contribute to the whistling. Rattling noises from the turbocharger or oil leaking from the turbo are definite red flags.

Try to visually inspect the engine, if there are welds on the block where it had been patched then I red flag it. Leaks from gasket surfaces and seals are repairable but must be figured into the cost. Excessive oil or antifreeze leaking from gaskets and seals may be a sign of a lot of blow-by and or overheating.

There is really a lot to cover just trying to remember all the things that I look for when inspecting a diesel. Most of the time it is very easy, the engine is dry, clean, starts easily, has no exhaust smoke, and is quiet. Imagine designing and building the very first diesel engine, marketing and patents were a nightmare. It took years for Rudolph Diesel to get his engine to operate. It may have driven him mad, maybe it was suicide as has been written. I wish that Mr. Rudolph Diesel could have witnessed the vast use of his invention. We can all be grateful for his invention that was many years ahead of its time.

Ken Lebherz
Accurate Machinery LLC
9030 Hamburg Road
Frederick, MD 21702
Office 301-668-6013
Fax 301-668-6015
Mobile 301-471-0944
Accurate Machinery, LLC - Welcome to the Accurate Machinery Web Site
accumac@verizon.net