Crank Case Breather

[hkp57]

After I had fitted a Webber carb to my 1.8 b series in place of the SU's we had a miss fire issue which was traced back to the spark plugs.

Two of the plugs (Brand New) were bad so she ran quite cleanly once changed.

As the new manifold did not have a port for the crank case breather to hook into I thought I would just run it into a catch tank.

To me when the engine was running with the breather open to atmosphere it seemed to be putting out a lot of vapor, i put it down to being cold.

Took it for a spin round the block and after 10 minutes it burped a glug of oil out the breather with the resulting smoke as it hit the exhaust got the heart going.

So I nursed it home and waited for the catch tank to arrive, when it did I piped it up and it had a K&N style breather on the catch tank.

With the engine running is still seemed to breathe very heavy with vapor coming out the catch tank breather?

Whats the forums thoughts on this? I recently refurbished the head and did a leak down test which showed no real issues, compression is good!

[stevejgreen]

Re: Crank Case Breather

Hidden behind the exhaust manifold are two cover plates giving access to the followers and push rods.
The front cover plate is a wire wool filter trap, usually with a connection to the inlet manifold as a crankcase breather, the rear one is just a blanking plate. Take care as the gaskets for each are different, some parts books say they are the same!

Parts lists etc are available here and many MGB specialists will have stock.

[hkp57]

Re: Crank Case Breather

Not sure I understand your post Steve.

I dont need the parts as they are already installed and i have piped it to a catch tank as there is no connection at the carb or manifold for it.

My question is about what amount of vapor is expected out of the vent? Also even if it did go into the inlet manifold I am not sure I would want that glug of oil going in there!

[HairyDave]

Re: Crank Case Breather

Maybe the engine design requires negative crankcase pressure and the glug of oil was a build up rather than the steady dispersal. Should your engine be blowing vapour from the crankcase. My B engine doesn't. Occasional cloud of exhaust smoke yes crankcase no.
BTW what do you think of the weber carb?
Dave

[stevejgreen]

Re: Crank Case Breather

Glug of oil could be related to a blocked crankcase breather filter.
is your oil filler cap a vented one too? The rocker compartment also gets pressurised via the push rod holes.

[hkp57]

Re: Crank Case Breather

Maybe the engine design requires negative crankcase pressure and the glug of oil was a build up rather than the steady dispersal. Should your engine be blowing vapour from the crankcase. My B engine doesn't. Occasional cloud of exhaust smoke yes crankcase no.
BTW what do you think of the weber carb?
Dave

If it does it again i might drill and tap the manifold and tie the vent in there, it has a boss on the casting so should be thick enough.

As for the Carb it is great, much more consistent to set up than the SU's but that might have been due to them being worn.

Auto choke works great.

[hkp57]

Re: Crank Case Breather

Glue of oil could be related to a blocked crankcase breather filter.
is your oil filler cap a vented one too? The rocker compartment also gets pressurised via the push rod holes.

Yeah the rocker cover cap is vented and clear

[dbazdavies]

Re: Crank Case Breather

Usually lots of smoke out off the cranlcasr breather means there is a problem with the sealing of the piston/rings with the pressure building up on the crankcase and out of the breather !! Do a compression check especially as you fouled up 2 plugs !!!

[hkp57]

Re: Crank Case Breather

I will when I get back from Angola next.

[cameronfurnival]

Re: Crank Case Breather

just my twopennorth I believe on this engine that there needs to be negative pressure to the crankcase. No pressure (or allowing the positive pressure from the crankcase to build up) can allow various seals to leak (as indicated by baz). The tappet chest filter often gets bunged up with hard carbon deposits and it is worth cleaning/ renewing this as Steve indicates. The breather tube needs connecting to the air filter to maintain the (low) pressure rather than the manifold which would provide too much suction.

[HairyDave]

Re: Crank Case Breather

In my Haynes manual and on my 1800TC engine the pipe comes up from the tappet chest to a Y piece thence(Nice word) to a pipe on each carb on the engine side of the dashpot. This means that ay crud bye-passes the dashpots. There should be a reducer or small hole in the outlet of the tappet chest to reduce the flow.

[hkp57]

Re: Crank Case Breather

From everything I have been able to read here and other forums the common theme is a catch tank on its own is not the answer as it is best to have a very small vacuum on the front chest cover.

Now I dont have the SU carbs to govern that vacuum, and i dont want to put oil vapor or worse through my nice new carb I plan to do the following when I get Home.

1. Remove the chest cover and make sure it is clean and clear.

2. Do a compression test to check for issues with rings, pretty confident they are fine as the fouling was purely fuel and no oil which was fixed with the new plugs

3. Remove the blanking plug from my new inlet manifold

4. Install a new PCV assembly to the manifold

5. pipe the inlet of the PCV to the front chest cover vent.



Some interesting information links

http://www.mossmotoring.com/crankcase-ventilation/

http://www.mgb-stuff.org.uk/cb.htm

http://mgaguru.com/mgtech/engine/cv103.htm

[cameronfurnival]

Re: Crank Case Breather

a pcv valve would work well - just don't bung the vent pipe directly into the manifold

[dbazdavies]

Re: Crank Case Breather

the idea is to stop the engine fumes from getting into the atmosphere - if it is fumeing badly then it gets sucked into the engine and plays havoc with the fuel mixture and also the mixture settings for an MOT !!!