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While dyno testing my 1275 a block in my mk1, I had some oil leak out of the valve cover breather at 4500 rpm. I’m told this is caused by blow by in the crankcase building pressure and slowing oil down from returning down the pushrod tubes. Rockers then just flinging the excess oil around? Is my only option here an engine rebuild as the rings aren’t sealing? Any one have experience with this? Thank you

To further clarify - motor is a A block 1275 out of an Austin America

What kind of rocker cover breather is it? Does it have a baffle to stop oil going straight up through the breather tube?

There's a saying about A-series motors, "If you think you have enough breathers, add one more."

timmy201 wrote: ↑Sat Jun 04, 2022 9:51 am What kind of rocker cover breather is it? Does it have a baffle to stop oil going straight up through the breather tube?

It’s an original mini fin rocker cover with the breather on the back by the carbs. Currently no baffle, but reading about closed chest blocks like the America needing more venting. Open to suggestions on baffle systems/setups.

Attached is the last photo I have before sending off to the rolling road.

You have a Breather of some type on the top of your clutch housing .. check its not blocked or give it a run without that in position as this is a crankcase vent .. warning with that area then open do not drop anything into the then open hole.

You need to create some positive crankcase ventilation. A oil separator canister on the drop gear housing feeding crankcase gasses to the draft tubes on the later twin carbs you have linked together,is the best solution.

I have two breather canisters, one on the drop gear housing & the mechanical fuel pump opening.
Each one is linked to a draft tube on the carbs.

Terence wrote: ↑Sat Jun 04, 2022 6:53 pm I have two breather canisters, one on the drop gear housing & the mechanical fuel pump opening.
Each one is linked to a draft tube on the carbs.

Could you send some more pics of your setup? Would like to see close ups of your canisters, fittings etc, especially the clutch housing side and draft tube side. Ty!

Those little breathers on the Minifin rocker covers usually do what you describe. That's why they were deleted in later ones.

As has been said by many people already. Fit lots of breathers. My favourite is one that goes up the back from the mechanical fuel pump hole, if you have one.

SF_Mini wrote: ↑Sun Jun 05, 2022 11:03 pm

Terence wrote: ↑Sat Jun 04, 2022 6:53 pm I have two breather canisters, one on the drop gear housing & the mechanical fuel pump opening.
Each one is linked to a draft tube on the carbs.

Could you send some more pics of your setup? Would like to see close ups of your canisters, fittings etc, especially the clutch housing side and draft tube side. Ty!

Sorry for the late reply, I was reworking my breather system. I added an oil/air separator to remove the condensation.

I have a rocker cover like yours and the breather pipe is too small. The original tin rocker cover has a 1/2" breather pipe attached to it which is less restrictive than yours.
Think I'd add another breather tube on the heater valve end similar to what the race engines have,

whistler wrote: ↑Sat Jul 02, 2022 5:13 pm I have a rocker cover like yours and the breather pipe is too small. The original tin rocker cover has a 1/2" breather pipe attached to it which is less restrictive than yours.
Think I'd add another breather tube on the heater valve end similar to what the race engines have,

I have a second oil separator on the mechanical fuel pump aperture that is tee’d to the drop gear housing separator with 1/2” ID hose.
The smaller 5/16” hose that feeds to the carb draft tubes increases the air velocity.
Slow in/fast out.

I based this breather install on the way it was done on the later Metro system where the timing cover breather & the drop gear housing breather are connected together and then fed to the carb with a reducer Y fitting.

You will need to source a 5/16” /8mm Y fitting to split the feed into the twin carbs.

I should update that I’ve gotten a breather canister and fed them back into the twin carbs. Successful thanks to the advice here.

How many miles / km has the engine done ?