Crank case pressurisation?

[The Original Tom]

I've recently replaced my flame-traps and re-circ pipes with rocker cover filters. Yesterday I noticed that there was blue smoke blowing out of the filters (more so the near-side one, which is at the front of the engine)
I know that an amount is normal, but not how much. It's done 1700miles since I rebuilt it and honed the bores so it cant be glazed already can it? It runs mostly on LPG which doesn't "wash" the bores if it's a bit rich, as petrol does (I'm told) and I think the mixtures are pretty good.
Also I'm losing oil, but there are no leaks (no drips on the drive) and it doesn't blow smoke from the exhaust at all.

Hmmmm...

[Paul B]

I've recently replaced my flame-traps and re-circ pipes with rocker cover filters. Yesterday I noticed that there was blue smoke blowing out of the filters (more so the near-side one, which is at the front of the engine)
I know that an amount is normal, but not how much. It's done 1700miles since I rebuilt it and honed the bores so it cant be glazed already can it? It runs mostly on LPG which doesn't "wash" the bores if it's a bit rich, as petrol does (I'm told) and I think the mixtures are pretty good.
Also I'm losing oil, but there are no leaks (no drips on the drive) and it doesn't blow smoke from the exhaust at all.

Hmmmm...

You'll get some blow by gas, but it is hard to put a figure on how much 'too much' is over an e mail. I get a fair bit on my 80,000 mile motor, so i have rigged up a line from the carb base to one rocker cover, and the other rocker cover a pipe goes to the air filter, sucking anything in that does escape.

I did try it with just a K&N filter on the one rocker, but found drops of oil would congregate around the filter then jump onto the header or the firewall, making either a smell or a mess. Now I've plumbed it into the air filter I have no mess or smell.

[katanaman]

glazed bores can happen with in a couple of hundred miles from rebuild if the engine isnt run in properly. I am not saying this is what you have done just letting you know this can happen. You also didnt hone your bores you just scuffed them up with the tool you used so anything not square with the bores wouldnt have been fixed. Again this might have absalutely nothing to do with anything. Best way for you to tell what is going on is to do a compression test. This will let you know what is happening right away, if anything is happening at all.
K&N filters on their own isn't really a very good idea as your bound to always get a bit of mist. Either take the breathers back to the carbs so it gets burnt or put then to some kind of breather bottle/tank.

[Lewis]

-circ pipes with rocker cover filters

I found these rocker cover filters were nothing but irritating. What they do is cause the crankcase to have no 'suck' (i.e. vacuum) which can lead to oil leaks and so on.

Prime example - I fitted one to the LHS rocker on my V8 Dolly - next thing, it started leaking from the front of the engine.

Refitted the breather pipe into the intake, voila, oil leak gone.

Also stopped that mist being breathed in by ourselves in traffic jams.

The manufacturers had it there for a reason and in this case, it tends to be much more useful to have the manufacturers install in place Try putting your original one back on and see if the problem subsides

[The Original Tom]

I don't really find the smell a problem, as being a Land Rover there's so many of those already I don't notice it
I think I'll fit a box to condense out the vapour and trickle back down into the rockers again - hopefully to alleviate some of the oil loss.
I think a pressure test is also in order.
I think I ran the engine in fine - it was per the information given to me by RPI and people on the difflock.com forum.
The reason I fitted the filters was two-fold. One so that I wouldn't pollute the inlet air which is better for power, and two so that a problem like this would be immediately obvious!
Also worth noting is that it doesn't smell (to the best of my ability to smell given the throat-burning pain it inflicted ) like exhaust fumes.

[Paul B]

I don't really find the smell a problem, as being a Land Rover there's so many of those already I don't notice it
I think I'll fit a box to condense out the vapour and trickle back down into the rockers again - hopefully to alleviate some of the oil loss...

The thing is, the engine actually needs a slight vacuum inside to prevent the copious oil leaks that seem to spring forth once the stock rebreather system is removed.

With just the K&N filters you get a slight pressure inside the crankcase, which helps shove the dinosaur juice of out the various seals and gaskets.

My valley cover and crank front seal live a far less oily life with the positive crankcase breather system I made, essentially, a 12mm hose from one rocker cover, with a small dome nut rammed up inside, with a 2mm hole drilled in it to regulate flow. And then the hose goes on the large vacuum port on the Weber bottom.

[The Original Tom]

Right, well I'm running SU's. They have a port on each that is traditionally used for the rocker re-breathing, so a 12mm pipe from each side to each carb is the better idea is it? Rather than blanking the ports and sticking filters on the rockers?
The thing is although the ports mentioned are there for this purpose, I don't know whether they create enough of a vacuum that they would "suck" all the gasses out, or if they would just "accept" them.
If it's the latter then I'm not depressurising the crank case at all I'm just reducing the pure air in the cylinders.
Although I guess at 2500rpm (cruising speed) when the engine's breathing 4375L of air a minute, the relatively small amount of pollutant will have little effect on performance? And it's hardly a dragster either

So, what pipe have you used? I'd amagine it has to put up with a bit of a vacuum?
Oh, and anyone want a pair of 12mm rocker cover breather filters? Very little use...

[sowen]

There's quite a suck on the breather ports on the SU's or any carb, so they should create a good vacuum inside your engine. Any oil resistant hose should be fine for the job. The original spec hoses look neater as they are moulded to the layout of the engine. How much oil are you losing?

I have all my breathers linked to one outlet open to atmosphere at the moment, and only get a little dribble of oil after long hot runs. At idle my breather seems to just 'breathe' on my finger. The plan is to eventually fit a catch tank so that I can re-use any lost oil.

I haven't experienced any oil loss though, and when I recently changed the oil, I filled the original 5 litre can that I tipped into it a year ago. I've probably done something like 1000 miles since I built the engine.

Simon

[Paul B]

..... At idle my breather seems to just 'breathe' on my finger....

I wonder what it is doing at 70mph/3000rpm hour though?

[sowen]

sowen wrote:
..... At idle my breather seems to just 'breathe' on my finger....


I wonder what it is doing at 70mph/3000rpm hour though?

I'm now tempted to extend the hose to the cabin and do the finger test on the motorway now

[The Original Tom]

I fitted some breathers to the the carb today, but I fitted it to the dizzy vac capsule hole.
This is only about 1 - 1.5mm diameter, so after running it up to temperature I looked underneath and there were some little oil puddles (never happened before!) I took off one of the pipes from the rocker cover and there wa a big 'Woosh' as the pressure escaped - fitting the breather there was clearly a bad idea as it created more pressure than vacuum!

Tomorrow I need to find a suitable fitting to screw into the inlet elbows, and put the pipe from each rocker into each carb elbow - this way each carb will get an equal amount of oil vapour.

Any ideas on the type of fitting I should use? I'm thinking of drilling out a pair of M12 bolts, and putting one in each elbow. Then the these can be bolted into the elbows. My only complication with this is that it would be hard to seal into a round tube section.
The reason I want to do this is that the original vacuum ports on the carbs are quite small-bore and won't give much vacuum especially as I'm using a cone filter.

[Paul B]

I fitted some breathers to the the carb today, but I fitted it to the dizzy vac capsule hole.
This is only about 1 - 1.5mm diameter, so after running it up to temperature I looked underneath and there were some little oil puddles (never happened before!) I took off one of the pipes from the rocker cover and there wa a big 'Woosh' as the pressure escaped - fitting the breather there was clearly a bad idea as it created more pressure than vacuum!

Tomorrow I need to find a suitable fitting to screw into the inlet elbows, and put the pipe from each rocker into each carb elbow - this way each carb will get an equal amount of oil vapour.

Any ideas on the type of fitting I should use? I'm thinking of drilling out a pair of M12 bolts, and putting one in each elbow. Then the these can be bolted into the elbows. My only complication with this is that it would be hard to seal into a round tube section.
The reason I want to do this is that the original vacuum ports on the carbs are quite small-bore and won't give much vacuum especially as I'm using a cone filter.

Don't put both your breather pipes to the carbs, as when your motor is under load you have very little manifold depression, and lots of blow by pressure, so you won't be sucking much from your breather system.

That is why I connected just one rocker pipe to the carb vacuum and the other goes into a hole in the base of the air filter, so I win no matter what happens.

You don't want too big a hole for your vacuum connection, else you'll not get your idle lower than about 1500rpm. Air will be sucked into the motor as if you had the throttle open a bit.

[CastleMGBV8]

The Rover V8 definitively requires positive crankcase ventilation, I tried it without on my rebuilt 3.5 and the internal pressure was blowing oil down the valve guides and it was smoking heavily.

You just need to replicate the original system. You need one small push on filter on the rocker cover with the small vent pipe and on the other rocker cover you need the flame trap and a length of tube with a PCV valve in it, which then connects to a Y piece which then go to the SU carbs original position.

If your missing any of the tubes or Y piece you can probably get them from Rimmer bros.

Kevin.

[tonydancer8]

just to confirm these coments, I was having smoke problems, see'lots of smoke thread' and it turned out to be a kinked breathewr pipe that someone had forced down by the inner wing. I,ve not run a rv8 before,
so after a £600 rebuild bill and still no better, it was only due to the guys on this forum that guided me to the answer!!!. 10 mins, a jubilee clip and smokes gone

[The Original Tom]

Right, I've plumbed in the vacuum hoses and topped her up with oil - I found where my missing oil was going - out the front valley gasket! There's a puddle in the top of my timing cover under the dizzy clamp! And its alldripping down the front of the sump. Hopefully this'll sort it - cheers folks!