Engine Breathing

[Splat]

If you do either then you MUST baffle the pipe hole, or you'll just vacuum the oil out. I had a pipe welded to my inlet manifold and connected it to both the timing cover breather and the rocker cover. It draws through an MGB pressure limiting valve and works well with my Weber setup.

[Westfield 129]

If you are not running a mechanical fuel pump, put a hose fitting into the fuel pump boss if undrilled, or inatall an adapter that will allow a hose to be fitted (a standard race part for the A series).

Run this up to a catch tank/breather above the oil level, and you will have much better crank case ventilation.

Installing the front cover with the air oil separator/breather also helps. This can be fitted with a little conical filter (if your local emissions allow open breathers with filters). You can also plumb it to the air filter.

If you install a breather hose at the top of the engine, on the valve cover, make sure that it is baffled, or set very high on the cover. This may be problematic, as there is little bonnet clearance for a top rocker cover breather.

I have a baffled breather on the side of the rocker cover (as high as possible) with a baffle that I welded in place, a block breather at the old fuel pump boss (no need for a baffle on this one), and the front cover with the breather/oil separator. My catch/breather tank is always empty save for some condensation, and the oil stays in the sump. No smoke. And, no engine leaks.

You can also run a vacuum pump evacuation system, or one that uses a pulse air on the exhaust to provide vacuum. However, if that picks up any oil, you will have the equivalent of a Red Bull Air Racer... Smoke On! It is also necessary to eliminate any engine air leaks as the vaccum system requires the engine to be sealed completely to work properly. My own experience is that the three breathers work quite well, and that the complexity of the evacuation system is unnecessary.

One breather to the carburetor is never enough for a high reving 1275/1380. They need a couple of additional holes for proper crank case pressure relief.

[Westfield 129]

One more thing...

Have you done a cylinder leak down test? It sounds as though your extra boost is going out the rings, into the crank case, adding blow by pressure beyond the pumping pressure than would be normal for a high RPM operation. I had this once myself, and found that the top ring lands had broken, and the cylinder walls were scored. This is not unusual with stock type pistons. Also, this would explain all the oil going out of the breathers, and not being "burned".

I bet that you have quite a bit of smoke coming out of the crank case when you take the oil cap off.

Also, you might put a longer stand pipe on the distributor gear vent (I assume that you have taken the gear out) with a larger filter than the little one you had on the front cover. Or, cap the distributor drive hole, and move the vent to the fuel pump boss. -8 hose (1.2") should do it for a vent to the catch tank.

Also, you need a larger filter on the catch tank, which should be around 1 liter in capacity, with two inlets, and a drain back into the front cover as you are not using the air oil separator.

And... you might try one of those american hot rod type rocker vents, cast alloy, curved upwards, with a foam filter strip inslde. Don't forget to check all of the oil drain backs from the rocker box to the crank case, and make sure that the right restrictors are being used for the rocker arms so you are not putting too much oil into the top of the engine. Sometimes, it is necessary to add an external drain to the rocker cover back to the pan.

However, after reading the whole thread again, I think that your problem is the blower pressure,a weak set of pistons, rings and a poor bore finish that is causing your blow-by problem. The crank case pressure may be high enough to keep the oil from draining back into the pan...

I think that a leak down test is in order, along with a rebore and a new set of pistons and rings. Then, you should be able to reap the benefits of all that boost, torque and HP.

[jonclancy]

Jan, was that for Matt or me?

I've just started my freshly rebuilt engine and am running it in.

As I'm near to Merlin Motorsport (on the one day off a week I'll now have for the next couple of months), I can pick up what I need from there. What fittings do I need for the fuel pump boss, please? Do I drill and bolt onto the pump cover or is this a weld on job? I have a spare steel rocker cover I can get adjusted to suit. I can pick up a catch tank from Merlin.

Thanks - better dash!! Gatwick beckons with her siren call....

[Westfield 129]

I imagine that you can use a fuel pump cover, drilled and tapped for a barbed fitting for a -8 hose. You can weld if you want to, but I don't think that it is necessary if the material is thick enough to support an NPT or AN threaded fitting.

Mini Mania here in the US has a purpose built breather/cover for the fuel pump opening, drilled and ready for installation, but I bet that same part is available through Peter May, MED or other BMC A specialist.

BTW, I use "socketless" hose (push on type Aeroquip or Goodridge) and appropriate fittings for my oil systems, and for some secondary coolant hoses. The fittings and hose are good for 150 psi, are easy to assemble (boiling water and some lubricant, then push the hose over the fitting), requiring no clips. Also, the price is quite good, and you get to avoid all those puncture wounds from stainless steel strands.

Use a liter catch/breather tank with two or three entries. If you are really sharp, you can plumb the drain tap at the bottom of tank to your front cover to drain any oil that has separated out back into the engine. This only requires a small diameter hose, say -3 or -4. Make sure that it has a large enough breather.

If you have the front cover breather, use a small conical breather at that location, unless you have enough entries in your breather tank.

[jonclancy]

Thanks Jan.

I'm looking at getting a pair of 90 deg fittings to 5/8 spigots, and cutting/welding them to the rocker cover and fuel cover. Plumbing this lot into a catch tank and see how I go with that.

My distributor popped out when I put the restrictor in the line to the carb. Clearly a bit of pressure in there that needs relieving!

[jonclancy]

Thanks Jan.

I'm looking at getting a pair of 90 deg fittings to 5/8 spigots, and cutting/welding them to the rocker cover and fuel cover. Plumbing this lot into a catch tank and see how I go with that.

My distributor popped out when I put the restrictor in the line to the carb. Clearly a bit of pressure in there that needs relieving!

Fittings something like this:

http://www.ebay.co.uk/itm/151635055699? ... Track=true

Catch tank something like this:

http://www.ebay.co.uk/itm/ALLOY-RECTANG ... 53e89e67e1

[jonclancy]

Anyone got any opinions on the items I linked to above before I get them ordered, please?

[Westfield 129]

It looks like a lot of work...

A standard American style catch tank with a pair of inlets and a vent on top does the trick. These are simple to install, include the breather filter, and have mounting tabs.

Then you can use standard NPT fittings at the tank in -6 or -8. I found my Allstar Performance tank on Amazon. http://www.amazon.com/Allstar-Performan ... ather+tank

You can plumb the drain back into the front cover (-3 hose and a small nipple, brazed to the top of the cover), if you want to eliminate the drain cock. Moroso and Jazz also have useful tanks. The Jazz tanks are plastic, and some very small ones, should space be a problem. I have one of these little breather tanks on my car and it works quite well.

For the rocker cover, Weld (or just braze) a simple brass nipple to the side of the cover, as high on the side of the cover as you can. Weld a sheet metal baffle over the hole on the inside, with the opening(s) so that oil can flow through and down. I brazed a brass barb to the side of my cover and welded a bit of bent sheet metal inside the cover with about 1/16" (or a little less) clearance over the opening.You do need to weld in a baffle or the thing will pump oil overboard.

But you don't have to bother with the rocker cover if you have both the front cover breather and the -6,-8 fuel pump cavity breather. That should be enough. Try your fuel pump cover plate with a -8 hose barb welded or threaded into place for your crank case vent.

And... There are the cast alloy chimney type breathers that bolt to the side of the rocker cover with a foam filter strip inside. Edelbrock, Moroso and Moon Equipment have them. Try an American style speed shop like Summit or Jeg's. Amazon also has breather tanks from the hard core racer supplies, such as HRP World, Racer Parts Wholesale and Pegasus Racing.

If you actually blew the distributor out of the engine, you might have a very serious blow-by problem, too much oil in the crank case, or a very loose distributor... I have never seen that, even on an A series that had no breather at all. A cylinder leak down test may be in order if the extra holes don't work.

[jonclancy]

Thanks Jan,

I've ordered a catch tank. I assume that the fuel pump boss work would need to be done during a rebuild. So, I'll be going with timing and rocker cover vents to my catch tank.

Cheers

Jon