# diagnosing a rod knock on a diesel



## raymilosh (Jan 12, 2005)

hi all,
I am thinking I hear a rod knock on our 1970 Ford 3000 diesel tractor, but I'm kind of new to the noise of diesel engines so I am unsure, yet. It is a 3 cylinder engine. When I crank the engine over, I'm also suddenly thinking I am hearing low compression in one cylinder, too. A bad rod bearing shouldn't cause low compression though...unless the piston bent a valve, right? I am thinking I could diagnose if there is a rod knock by cracking open one injector line at a time when it is idling and seeing if one of them makes it quiet down (same as on a gasoline engine). That should work, no? 
I am also thinking I could get the pistons to top dead center one at a time and fill the cylinders with compressed air and listen for escaping air in the intake and exhaust to diagnose valve problems. Are there better ways to do it? I do own a diesel compression tester, but I haven't used it yet.


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## agmantoo (May 23, 2003)

Do not disturb the injectors! They damage easily and they will leak. As far as the knock. During cold weather you should not hear the knock on immediate startup unless the rod has already reached near failure and the crank is already damaged. If you are really concerned, cut the oil filter apart and look for minute metal particles. If there are particles present do not continue to run the engine. You can take the pan off and access each rod and use a product called plastigauge to ascertain the clearance. The pan removal takes the guesswork out and it not very mechanically demanding. If a valve is leaking the tractor will not make good power. Raw diesel fuel will be blown into the exhaust manifold and the inside of the exhaust pipe will be wet, often the manifold will weep diesel fuel down the side of the engine


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## moopups (May 12, 2002)

Another method of diagnostics is to place a wood stick against your folded over ear and move it to various parts of the running engine. The sounds are transfered via the stick and any that is loud indicating a part's looseness will be easy to recognize.


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## james dilley (Mar 21, 2004)

How is the Power when running?/ I had A detroit running ragged ,When the camshaft broke. it sounds like A rod when that happens!


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## raymilosh (Jan 12, 2005)

James,
It has had a rod knock type sound since we bought it a year ago. then the last time I started it it sounded like one cylinder was low on compression. It only ran for a few minutes before stalling again(it also seems to have a fuel supply problem) and I can't say I know how it was running.


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