smoking breather

[rajjes]

My 2 cyl Kubota z482 engine is producing a steady stream of what looks like exhaust from the breather nozzle on the valve cover.

I’m not sure of this is oil mist or exhaust.

Can someone advise on the likely cause of this? I have recently overhauled the engine with new rings etc so I hope it does not require major surgery!

I have seen engines with the breather routed to the air filter, but I am thinking of routing it overboard, is this advisable?

Finally, can someone provide the valve settings for these engines (same as Beta / Nanni?)

thanks for your help

 

[savageseadog]

Check how much pressure there is lower the better but you will probably always get some. Suggest you route the gases into the air inlet. The engine might already be equipped for this or you may have to provide a separator so oil can drain back into the sump.

 

[Jimmaccall]

Hello, the breather is letting the crankcase gases out. Inside the rocker cover there is usually an oil separator / gauze of some description and at a guess this has been cleaned out with degreaser as part of the engine work and in some cases (when it is foam) it is disgarded and not replaced. The gas is the result of piston and valve seal blowby and this is normally high in the first 250 hours following engine overhaul (before everything is nicely bedded in) and of course in the latter stages of an engines useful life due to ring and bore wear etc. You can route the gases into the intake but be wary, if there is a problem with the engine and the blow-by is severe, the oily gasey mixture can be enough for the engine to gain rev's without the input of fuel e.g. run away. Not good. Suggested next steps are:

1) Check that the oil separator / gauze is in place where the breather pipe exits the rocker cover (may be inside the cover)
2) Check what oil you have filled the engine with, ideally use CD grade engine oil for initial fill of a new / rebuilt engine as the latest oils (CF grade and above) are too good and don't allow bedding in. If CF or above replace with CD oil or similar.
3) Use engine throughout full rev range under load when possible ensure it is not allowed to idle for excessive periods. Bedding / running in isn't about taking it steady and being gentle unlike the old days.
4) Check the breather output in 250 hours, if not reduced or if it really is too bad to tolerate, get the crankcase pressure measured (pressure gauge / manometer in dipstick tube) and if over 2 inches H20 then the engine may have been overhauled with wrong rings for bore size or something. But lets hope its not that.

Gases wise, not sure of the normal marine procedure but in an unvented engine compartment it cannot be a good thing for the boats occupants, check other installations / compare with other boats if you can as they may vent gases out via venturi on the exhaust. Main thing is that the gases are allowed out of the engine without restriction as too high a crankcase pressure can cause leaks and push things like crankshaft seals out of position.

Not sure on valve settings but at a guess exhaust clearance will be greater than inlet once you get the figures.

Long reply but I love diesels, sorry.

Cheers, Jim

 

[rajjes]

thanks for the reply, will try out the oil change and hopefully is will get better!

 

[neil_s]

I started up my Bukh DV20 without the oil filler cap on. I was disconcerted to feel a substantial 'wind' from the open hole. Visions of worn bores and rings flashed through my mind, but when I put my hand over the hole, there was no pressure that I could feel. Could it be that this is due to the natural variation of crankcase volume as the pistons go up and down? You only feel the 'blow out' and not the 'suck in'?

Neil

 

[Shanty]

Valve clearances for the Kubota Z482 according to the manual are: 0.145 to 0.185mm. Doesn't indicate whether hot or cold - I suspect the settings should be with the engine cold, as the settings are given in the middle of a reassembly sequence.