chrishelen
N/A
When i take the oil filler cap off my volvo penta 10 hp when its running i get a lot of air comming out, is this ok or am i loosing compression past the rings, it starts ok and runs ok,
sump pressure
- Thread starter chrishelen
- Start date
oldharry
Well-Known Member
Unless the breather is blocked, then yes you have blowby caused by either worn or sticking rings. But make sure the breather system is working properly before you start pulling things to pieces.
Col
Well-Known Member
Did you do the compression test? There will always be a little "breathing" out of the filler cap. If the comp test came up OK, don't worry.
chrishelen
N/A
Thanks, no i didnt do the test, wish i had before i bought the think. rgrds chris.
hlb
RIP
Does it go round and round, making a chuf, chuf, sort of sound. Use any oil, or bang and clang a bit??
chrishelen
N/A
Har de flipping har
fisherman
Well-Known Member
FWIW my car started blowing oil out, I had to put a pipe and can on the dipstick tube to collect it. Unblocked the breather, problem gone. Volvo 740.
pheran
Well-Known Member
Why rings? Surely, if they are worn/sticking this would allow compression past them and DOWN the cylinders into the crank-case and thence, out of the c/c breather. On the other hand, worn valve guides would certainly account for chuffing from the oil filler cap.
chrishelen
N/A
If it was rings woulnt there be smoke coming out as well?no i think im worrying over nothing, when the piston comes down it would make pressure,yes?
oldharry
Well-Known Member
The oil filler cap is open to the crankcase - how else does fresh oil get to the crankcase! The breather system allows for minor variation in crankcase pressure such as the piston going up and down, thermal expansion etc. But if the rings are worn and allowing pressure to escape past them, then this pressurises the crankcase. Removing the oil filler cap relieves the pressure. Leaky exhaust valve stems never pass enough gas to pressurise the crankcase in the way the piston rings do.
And no, Chris, for some reason there is not a lot of smoke from a blowing engine. If the engine is running happily, and not actually pushing oil out of the breather, then it will continue to do so for quite a long time without harm. Eventually compression loss will start affecting startability. Yes the piston makes pressure as it comes down, but then sucks it back in when it goes back up again, so there is not a flow of fumes out of the breather just a chuffing which may be all you are seeing? Unlike a petrol engine the much higher compression of a diesel allows very little oil to get in to the combustion chamber. The real danger is the oil blows out throught the breather which is usually connected to the inlet manifold. If enough oil is blown into the manifold, the engine starts running on that - unstoppably! I have seen this happen on my old Sherpa van - the engine revved unstoppably to around 7000 revs with the ignition switched off - and survived! Didnt do much for my old ticker though!! /forums/images/graemlins/shocked.gif
To check for blowby, forget about compression tests. They will tell you very little on a single lung diesel. With the engine at working temprature, remove the filler cap, and hold a rag over it so no gas escapes. Rev the engine slightly for around 5 - 7 seconds then release the rag. If there is a 'whoosh' of gas then you have blowby. If not, you have nothing to worry about except a possibly blocked breather.
And no, Chris, for some reason there is not a lot of smoke from a blowing engine. If the engine is running happily, and not actually pushing oil out of the breather, then it will continue to do so for quite a long time without harm. Eventually compression loss will start affecting startability. Yes the piston makes pressure as it comes down, but then sucks it back in when it goes back up again, so there is not a flow of fumes out of the breather just a chuffing which may be all you are seeing? Unlike a petrol engine the much higher compression of a diesel allows very little oil to get in to the combustion chamber. The real danger is the oil blows out throught the breather which is usually connected to the inlet manifold. If enough oil is blown into the manifold, the engine starts running on that - unstoppably! I have seen this happen on my old Sherpa van - the engine revved unstoppably to around 7000 revs with the ignition switched off - and survived! Didnt do much for my old ticker though!! /forums/images/graemlins/shocked.gif
To check for blowby, forget about compression tests. They will tell you very little on a single lung diesel. With the engine at working temprature, remove the filler cap, and hold a rag over it so no gas escapes. Rev the engine slightly for around 5 - 7 seconds then release the rag. If there is a 'whoosh' of gas then you have blowby. If not, you have nothing to worry about except a possibly blocked breather.
chrishelen
N/A
Thanks harry,that all makes sense,put my mind at rest, made me chuckle about the sherpa and your old ticker though.
regards chris.
regards chris.
oldharry
Well-Known Member
Hmmm - you should have seen the smoke cloud. spectacular!
It was certainly one of the more exciting moments of Sherpa ownership..... /forums/images/graemlins/blush.gif
'More' exciting did I say? Should be - 'ONLY' !
It was certainly one of the more exciting moments of Sherpa ownership..... /forums/images/graemlins/blush.gif
'More' exciting did I say? Should be - 'ONLY' !
pheran
Well-Known Member
You're absolutely right Sir. I must have been having (yet another) senior moment /forums/images/graemlins/confused.gif
chrishelen
N/A
Harry, the engines finaly in the boat(nobody told me about the 7 degree angle on the gearbox shaft) after much chopping wood grinding steel and curseing, it lines up precislyish with the prop shaft,so if it is knackered its staying put,we did fix it with a big hammer, rgrds, chris.
