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Smoke from Oil Filler/Rocker Box Cover Part2
Monty2556 - 13/10/14 at 05:24 PM

OK, so having listened to all the excellent advice this is what I've done so far:
Compression test, hot with throttle open, 160 psi on three cylinders and 155psi on the other. Blown through crankcase breather so that's clear. Drained oil and refilled it with correct amount. Still got lots of smoke coming from oil filler and very lumpy tickover which eventually stalls. Any ideas?

Nickp - 13/10/14 at 06:33 PM

Your compressions sound decent enough, so I'm guessing your lumpy running isn't related to your smoking issue.

mookaloid - 13/10/14 at 08:00 PM

reading some of your other posts, you are using a down draught carb yes? if so there should be breather tubes running from the rocker cover and one from the flame trap or pcv valve on the side of the engine block. these should be tee'd into a boss in the inlet manifold which will (if working correctly) suck the fumes through the inlet system and the engine and out of the exhaust.

If this is not what you have then perhaps something is disconnected which would account for the smoke coming out of the rocker cover and could also cause an air leak and lead to the rough running?

Monty2556 - 13/10/14 at 09:20 PM

Yes you're correct, I've got a 32/36 Weber which I bought secondhand, serviced and fitted. There is a pipe running from the pcv valve up to a tee piece in the inlet manifold but the other side of the tee piece is just blanked off. Should I have a pipe running from the rocker box to the blanked off side of tee piece. There is quite a lot of smoke coming from the oil filler though.

Monty2556 - 13/10/14 at 09:32 PM

Just had a look on ebay and Burton Engineering and although I can find rocker covers they don't seem to have any breather pipes. The only one that does is for a dry sumped engine. Are you saying that the breather pipe is required because I've fitted a twin choke Weber? Many thanks.

cliftyhanger - 14/10/14 at 07:28 AM

Trouble I have had in the past where a car is breathing heavily is that if the breathers are fed into the manifolds (usually via a valve on "my" cars) they screw up the mixture by pushing extra air in.
It seems to work better if the hoses are fed into the air filter as there is still suction but it doesn't affect the mixture. However, the filters seem to clog fast...
Maybe try blanking off the manifold and venting the engine to atmosphere, see if you can retune the carb to get better running.
If so, I would run the breathers into a catch tank with a stainless scourer inside (helps condense the vapours) placed somewhere where it will hopefully keep cool. Then run a hose up to the air intake from the catch tank.

Daddylonglegs - 14/10/14 at 08:42 AM

I had a similar thing with our Discovery earlier this year. It was chuffing white smoke out of the oil cap in the rocker box cover and ran a little down on power. Turns out it was the head gasket blown between #4 pot and the oilway (common fault by all accounts). Replaced the head gasket and all was fine. I obviously couldn't check for compression as it is a diesel and I don't have the specialist gear to do that, but it still ran reasonably OK but just the unburnt diesel smoke fro the gasket.

HTH

mookaloid - 14/10/14 at 02:12 PM

quote:
Originally posted by Monty2556
Yes you're correct, I've got a 32/36 Weber which I bought secondhand, serviced and fitted. There is a pipe running from the pcv valve up to a tee piece in the inlet manifold but the other side of the tee piece is just blanked off. Should I have a pipe running from the rocker box to the blanked off side of tee piece. There is quite a lot of smoke coming from the oil filler though.


You need to think about how crank case pressure and the breather system works.

If you assume that pressure will build up in the crank case due to a bit of leakage past the rings, rise in temperature, things moving about etc. and that oil mist and a bit of smoke will inevitably form, You need to ask your self 'where will it go?'

The original system was designed to change the crank case pressure into a vacuum situation where the air (or fumes, oil mist, smoke etc,) are sucked through the breather system and the fumes are expelled through the inlet manifold, burnt in the engine and expelled through the exhaust.

In its simplest form there is only one tube from the engine block to the manifold (or air filter box) Via a spring loaded valve (PCV) so that it isn't permanently open. This tube sucks the fumes out. In order to suck the fumes out, air must be allowed in to the crank case. This is often done by means of a vented oil filler cap. The vented cap is therefore there to allow air in not to allow fumes out.

Sometimes there is a pipe connected to the rocker cover via the T piece which might compensate for an engine that doesn't have a very easy air passage to the crank case void from the rocker cover.

So if you take the filler cap off there shouldn't be pressure forcing smoke and fumes out of the filler cap if the breather system is working correctly. If you have satisfied yourself that the breather system is working correctly then it must be being overwhelmed by excessive crank case pressure which is usually caused by worn piston rings/bores.

To work out if the rings/bores are worn, do the compression test again with a bit of oil injected in the bores. if the readings go up significantly then this could be the problem.

Monty2556 - 14/10/14 at 06:36 PM

I've heard about doing a compression test with oil in the bores but I understood that it didn't work very well with the bowl in piston arrangement of the 1600 xflow. I presume because the oil will sit in the bowl.