Air bubbles in the oil

[hydrolastic]

Hi guys. Old Mini here. Transmission in the oil pan. For years I have seen lots of air bubbles in the oil can't be good for the engine bearings. But hey I got a horizontal egg beater of a transmission slinging oil straight up. I noticed on pegasus a deaerating tank for a dry sump system. I am wondering how well this works and could I adapt it to work with a wet sump system. I also have thought about running oil through a oberg filter or some other way to get air bubbles out of the oil. I know someone will say just wait overnight .... I am hoping someone has dealt with this before.

[RDY4WAR]

What oil are you using? Some are more prone to aeration than others.

[V12MECH]

Had a few of these come through the shop, there's a couple of seals at gear box plate to engine block, one is an o-ring that if it failed could draw air, this was an early car mk1 or 2 ? . Anyhow ck out Hickey Race Engineering, guys got a great old mini site, covers tech problems, wish that was around back then, they are a topic unto themselves, just like the new BMW turd version we work on today.

[Walter R. Malik]

Hi guys. Old Mini here. Transmission in the oil pan. For years I have seen lots of air bubbles in the oil can't be good for the engine bearings. But hey I got a horizontal egg beater of a transmission slinging oil straight up. I noticed on pegasus a deaerating tank for a dry sump system. I am wondering how well this works and could I adapt it to work with a wet sump system. I also have thought about running oil through a oberg filter or some other way to get air bubbles out of the oil. I know someone will say just wait overnight .... I am hoping someone has dealt with this before.

A dry sump pump with a centrifuge stage works well for that.

[Sir Yun]

https://www.minimania.com/part/MIN500/T ... i-Cooper-S
7-ent has a version as well and when you dust of your cad skills and send the file to send cut send you well get something similar for less than $100.

[Walter R. Malik]

As I have said ... IF it is a dry sump, then an oil pump with a centrifuge section will help a lot.

[Kevin Johnson]

Hi guys. Old Mini here. Transmission in the oil pan. For years I have seen lots of air bubbles in the oil can't be good for the engine bearings. But hey I got a horizontal egg beater of a transmission slinging oil straight up. I noticed on pegasus a deaerating tank for a dry sump system. I am wondering how well this works and could I adapt it to work with a wet sump system. I also have thought about running oil through a oberg filter or some other way to get air bubbles out of the oil. I know someone will say just wait overnight .... I am hoping someone has dealt with this before.

Twelve years ago I made a test pattern for the Mini engine -- the transmission being combined with the crankcase (like many motorcycles) makes it undesirable to insert a layer between the block and case. I had been making patterns for the engine in varying capacities for many years prior to that. One is sitting next to me with a 1275CC pan. I can still remember being impressed that FedEx Ground managed to drop the block that I bought off of eBay and break off a projection on the pan rail.

Many of the air bubbles will be dissolved into the oil (the Bunsen coefficient is the term you will want to investigate: roughly nine percent by volume per bar pressure for paraffinic base stock). The free air bubbles that are entrained in the oil supply that DO NOT DISSOLVE are the danger to the bearings OR the bubbles that come out of solution whilst passing through the oil galleries (when the pressure drops below the saturation level for the fluid -- this is why the Porsche 944 and 928 have so many bearing failures). Main bearing damage from entrainment occurs roughly at 50% while rod bearings are in danger at 30%.*

I have not looked at the Mini oil pump but many patents exist that utilize a bleed passage that preferentially releases free air versus fluid. Porsche incorporated this technique in one version of their 928 pump. I try not to advertise on the forum. Attached below is a picture from 2010 showing possible modifications to a Mopar SL6 pump that may be helpful.

Just as an aside, the principle involved is the same as a hydrocyclone which is how many (most?) dry sump tanks operate: https://en.wikipedia.org/wiki/Hydrocyclone

*

J. K. Choi and his co-authors [9, 10] investigated
connecting rod and main bearing performance under
various aeration levels. They concluded that connecting
rod bearing performance was not significantly affected by
oil aeration when aeration is less than 30% at the main
oil gallery pressure, while the main bearing can tolerate
up to 50% aeration under their testing conditions.

[Sir Yun]

As I have said ... IF it is a dry sump, then an oil pump with a centrifuge section will help a lot.

it's not dry sump.
it's basically a large aluminum sump with the gears added instead of the normal sump in the inline version of the engine.

I don't know if it is a wide spread problem. Mini Migs run about 10 hours between rebuild/refreshes and are basically at 8500 for all of that. I have never heard anything about the inline version having much better bearing life The Choi paper suggest that you can have quite a lot or aeration so that is good I guess.

I would start, as always, with getting basics right. ie keeping the oil intake under the oil at all times (COP) , not having leaky seals, not having clogged strainers.
Enough carter ventilation, checking/cleaning the oil galleries, checking drilling position of all holes, general weirdness (it's BL, not Honda, half the people where hungover : so the oil galleries might barely connect ).

Change external oil fitting to decent sized ones, chase weird constrictions of gubbins before adding a band-aid. For instance if you have a oil filter attachment with bypass and it gets stuck open is will probably both aerate and not filter.

[hydrolastic]

Thanks guys I will take a good look at all of these things, I especially like the oil pump mod because its very similar to the mini oil pump. Hydro

[PackardV8]

Enjines is enjines. The Packard V8 had a systemic problem with air bubbles in the oil and always ate the three center mains before the rods.

[Kevin Johnson]

Enjines is enjines. The Packard V8 had a systemic problem with air bubbles in the oil and always ate the three center mains before the rods.

There is certainly a lot going on with the gallery feeds to the mains from the pump.

Packard_lubrication_a.jpg

Packard_lubrication_b.jpg

[Walter R. Malik]

As I have said ... IF it is a dry sump, then an oil pump with a centrifuge section will help a lot.

it's not dry sump.
it's basically a large aluminum sump with the gears added instead of the normal sump in the inline version of the engine.

I thought you were intending to make it one ... guess not.