Tag: Diesel engine

I just finished another pre-purchase mechanical survey, and doing a blow-by test on the engines is part of our investigation. Each time, people always ask ‘What is blow-by?’

Basically ‘blow-by’ is the air and combustion gases from the cylinder, on top of the piston that escape past the piston rings into the crankcase. No engine will have perfect sealing rings, though as the rings, and cylinder wear the blow-by will increase giving an indication to the engine health.

Blow-by not only is a tell-tail on the engine health, but there are several negative effects. Blow-by not only pressurizes the crankcase but also introduces combustion gases that contain unburned fuel, particulate matter, and oxides of nitrogen emissions. They also create condensation due to the temperature differential of combustion gases and the crankcase.

Blow-by tears the oil from the piston and rings. At first it vaporizes and then it becomes an aerosol, which you see as a film or fumes around the crankcase vent tube. When mixed with engine oil, blow-by produces sludge and acids that attack all engine parts. The unburned fuel dilutes the lubricity and viscosity of the engine oil, attacking engine bearings, the valve train, and cylinder walls.

When the blow-by becomes more than the crankcase ventilation can handle, other problems start to happen, from blown out crankshaft main seals, to an engine ‘run away’, where the oil vapor becomes a fuel for the diesel engine and it then starts running on it’s own engine ‘oil fuel’, with no ‘standard way’ to shut it down – a run away engine is rare, but extremely dangerous.

Power Point presentation from the Mining Diesel Emissions Conference October 7-9th, 2014 – Retrofit Crankcase Ventilation for Diesel Engines: https://mdec.ca/2014/S6P2-Stekar.pdf

Controlling Blowby in Diesel Engines by Ray Bohacz, 3/20/2019 Successful Farming: https://www.agriculture.com/machinery/repair-maintenance/controlling-blowby-in-diesel-engines

Causes of Diesel Engine Oil Blow By by Tony Oldhand – It Still Runs https://itstillruns.com/causes-diesel-engine-oil-blow-6930901.html

Twin Cummins 6BTA5.9’s getting ready to be lifted out for rebuilding after the interior, galley, and seating was removed to gain access.

The Cummins 6BTA5.9 engines do not have replaceable liners like their bigger cousins, so a proper engine rebuild requires services from a professional engine machine shop where the engines are dissembled, measured, and then machined to specifications ensuring a reliable and bullet-proof rebuild.

Once the engines are rebuilt, they will be run up on a dyno for the break-in, as well as to ensure the engines are running at 100% before going back into the ‘hole’. The other benefit to running the engines on the dyno – the team will tweak the engines for maximum fuel efficiency!

Next will be the removal of the engines – stay tuned!!

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