Heckler
Active member
Stu, many thanks for that photo and cracking open your spare valve! Very useful. Do you happen to have a photo of the underside of the diaphragm too?
As for intake vacuum, yes there is one, or suction at least. The pistons down-motion generates suction on the intake manifold (which moves air into the cylinder), and the open hose does get some of that suction applied to it through the air intake mushroom. Bit like a hoover sucking up dust despite not having a vacuum-tight connection to the floor. You can check this yourself by holding your hand around the underside of the mushroom as the engine runs - definite quite a bit of air being sucked in.
When taking off the hose from the breather valve while the engine runs, I can hold it partially shut with my thumb and also feel air moving through, so that's how the crankcase fumes are sucked through and into the air intake manifold for burning up (so they don't get vented out the car, or in case of a boat, all over the engine room).
It only needs a small vacuum to have a light airflow through the crankcase, you don't want too much - which is where that valve comes into play. The way I understand its workings is that the diaphragm gets sucked down a bit in case of too high suction from the air intake and restricts the airflow, thus reducing the flow through the crankcase to the desired amount. If it's stuck and doesn't do that job, too much air goes through there and you end up sucking oil out of the crankcase and into the air intake manifold, which in extreme cases could lead to a runaway engine, although in my case I just noticed the clear hose had oil in it and it was dripping from the bottom of the mushroom. Also, oil consumption went up to something like 200 ml after a day or two of motoring (bit fuzzy on the exact numbers here). That fits the picture too, as the engine was slurping its own oil into the air intake, instead of just whatever blow-by fumes end up in the crankcase.
Having nothing to loose, I've meanwhile sprayed a bunch of degreaser into mine (after removing it from the engine), shaking some now liquefied black crud out, then poked it with a screwdriver to get the diaphragm moving again and finally applied repeat suction/pressure on the tiny breather hole at the top of the cap, which eventually dislodged something and it now shuts again with a click as per the test in the Haynes manual. Having seen your disassembled photos now tells me that if the tiny breather hole at the top can hold pressure, the diaphragm must be intact, so there's hope it'll work again. Hard to tell without motoring for a few hours, but we'll find out eventually.
As for the replacement part hunt, I've found a few cross-reference numbers, which I'll leave here for future reference:
1W8361 CATERPILLAR INC. DBA CATERPILLAR
8N7680 MITSUBISHI CATERPILLAR FORKLIFT AMERICA INC
Seems some distant relative of our engine was also used in forklifts. With the help of that, I've found one in the US for $38 with a photo that looks pretty promising: https://www.ebay.com/itm/CT1W8361-NEW-VALVE-PCV/262924757590
Will see if I can find someone in the US to forward one to me.
Have just put it back together! Its easy to peel back like i did with side cutters, the other side was dry as a bone so no leaks there. Bobc idea looks good, Id just do as he did. Your oil consumption? I think you are overthinking it. I am still convinced the valve does nowt in our application.
. Did anyone try the Caterpillar part, and did it fit?
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