Oil modifications
Turbo Mini Forums

first up i given the search function a good go.
please read and offer your thoughts i am thinking out loud trying to pick the good from bad in terms of mods

as you may know im building a turbo charged 1098cc motor intended for use on the street/track it will be a weekend car that i want to last a long time so im having a good go at getting things right after all its my second build but first solo

on my searching i found this thread http://www.turbominis.co.uk/forums/index.php?p=vt&tid=294002


My questions regarding this topic are in terms of getting more oil flow around the engine
so thats mains, big ends, thrusts, drop gears, timing chain, rockers, lifters and pistons..

lest start with my main concern the mains as seen in the link it seems well know that the big ends draw oil from the mains via centrifugal force so in my mind we need to ether restrict the big end flow or increase flow on the main two options said many times in the search function so how do we do such a thing?

i think i dont like the idea of restricting oil as that may lead to problems!
looking at the crank i see what looks like a restrictor in one of the holes on the big end this hole goes right throw to the main the other hole is only intersecting the other




i think you want to introduce oil to the big end at bdc just as it builds compression and also as it passes down on the first half of the power stroke or in other words just before/in front of the bearing is at max load
as for the mains im thinking i will use the grove all round ones to give a constant equal film also so long as there is oil the big ends will be feeding the big ends vs a plain bottom bearing that is mostly not feeding oil for half the cycle







to me it looks like its feeding oil behind the peak load? is this because it takes time to flow

Edited by Turbo This.. on 16th Aug, 2013.

After my center main bearing failure, I went mad reading up on plain journal bearing lubrication in an effort to better understand why it happened in the first instance (forgetting that Oring for a minute ).

I cam to a conclusion quite quickly that the average cross drilled crank might actually reduce the load carrying of the big ends. This was because as you have pointed out, the oil feed hole is now in a highly loaded region during the power stroke. once I understood this, I have not used a cross drilled crank. Is there any real need to? What you do have to consider is that the center main bearing supplies two big end journals while the other main bearings only supply the one. This means that the center main bearing has to flow twice what the others do. The cross sectional area of the center main oil feed is much the same as that of the others two. This is the main restriction to oil flow.

I have spoken with a couple of wise and wonderful people on this subject and they both said the same thing without being asked. Open up the center main oil feed.

Don't go mad with it, as you only need to increase the diameter of the feed a little to increase the cross sectional area a lot.

Plain bearings against grooved bearings. That has been discussed before. The conclusion I cam to is that the plain bottom bearing does exactly what it is supposed to, increase the load carrying ability, by nearly 75%. The fact that there appears to be an interrupted oil flow to the big ends is in fact nothing to be concerned with. The big end still receives enough oil flow to satisfy its demand (there is no point pushing more oil that is required up there)

one thing that is important is the bearing clearance. Figures quoted in a certain infamous yellow book are just wrong, and when I questioned the man in person, he got very irate lol. Bearing clearances need to be no bigger than 0.002" and better towards the 0.001" or less. This sorts of clearances on the lower end need to have bearing housings checked for size and alignment, and the crank needs to be straight, with accurate journal sizing (just doesn't happen on certain manufactures product) The finish of the journals is very important too.

When I get a chance, I upload the documents I found that explains how plain journal bearing lubrication works.

Colin, your problem, with the centre main issue was, the oil jets and high RPM above 7000 even for a split second, outstripped the flow of oil to the centre main for a second causing the damage.
With plain faced bearing,

If your crank had been through drilled on the mains the plain bearing would have received oil every 180degrees instead of ever 360 ........ my point in your case Colin is...... plain bearings and revs above 7000 without the crank been through drilled is asking for trouble! Especially with undercrown cooling jets fitted out stripping the flow........ hope this gives you some thoughts colin

The end bearing near the clutch end needs dremling out ill grab some pictures

Before anything I've decided to get a high capacity 'turbo' oil pump, that way I know I have plenty of scope for anything like this when the time comes.

grinded it out so it matches the bearing hole

they are way out on small bore engines, half the hole was coverd before I did this needs a little bit more but other than that should help

Also going to do Oil pump end aswell

Mini mag issue 184 april 2011 covered it with a how to guide on it

I'm in process of doing water pump end opening the water way up also tapped off first 2 holes on the block too so cylinder 4 gets cooler

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Edited by Chalkie on 16th Aug, 2013.

My mains cap and bearing holes were miles out. I eased the holes out so that the lined up with the bearings. At one end it was nearly 3/4 covered..

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

lets put our handbags away and see what others have to say.

Do many people drill to the other side?

"Cars are a lifetime of pain"

What way dose the oil flow down the crank?

When Nick Swift first built my engine he told me cross drilling is a waste of time, that crank did thousands of miles over 7000 rpm and up to 9000 very often

I seriously doubt it!

And yes, I tend to be having lots of bad days in the last few months. "you need to relax colin"

points taken.

anyway, with plain bearings the bearing only sees oil ever 360 degrees so ... if the mains oil gallery was drilled straight through it would see a lick of oil every 180 degrees helping the situation, because there is more loading on the "centre main" its possible that's why the bearing Wears more and or..... fails,

have a look at this write up I found Many years ago

"Turbo" main bearings were designed by Leyland’s engineers to meet a perceived need. It was decided probably by both theoretical calculation and practical test that the turbo Metro engine with its increased bearing loads needed a better bearing, so what they did was remove the oil groove from the bottom bearing shell giving roughly 30% more bearing area. It is claimed that this gives about 80% more load carrying capacity, exactly how 30% more area gives an 80% increase in capacity I’m not sure but this figure is widely claimed in both Minis and other engines and is not disputed.

O.K if it is possible to remove this groove one must wonder why it was there in the first place? To explain that you need to know a little of how the engines lubrication system works; Oil is pumped through galleries in the block to the main bearings, it passes through a hole in the bearing into the aforementioned groove, from here it flows sideways across the bearing, some of it leaking out the sides, the rest is forced into holes in the crank, travels through the crank and exits through a hole in the big end journal where it lubricates the big end / conrod bearing before leaking out the sides.

Now the next step is to think about what happens if we remove one of these grooves, remembering that turbo bearings still have a grooved top bearing. As the hole in the crank passes the grooved top bearing oil flows through the crank to the big end, no worries here but as the hole passes across the non- grooved shell there is only a gap of 0.002" for the oil to flow through therefore very little if any oil is fed to the big ends during half of every revolution, whether there is sufficient residual oil is debatable I think there isn’t. O.K. so why don’t all the turbo Metro engines suffer bearing failure?

The reason is the main bearing journals are "through drilled" that is to say that they have two oil holes 180 degrees apart so while one hole is in the non-grooved bearing the other hole lines up with the grooved bearing. Why am I telling you all this ? Not all Mini cranks have "Through Drilled" main journals! Fortunately most of them are but I have seen nitrided cross drilled "S" cranks that are not. So if you are building an engine or having one built and the subject of "turbo" bearings comes up have a good look at your crank before proceeding.

This matter is not something that I thought about until an engine I built had a big end failure, and after talking to a number of other engine builders they had not thought about it either. The cause of my big end failure has not been determined but I am almost certain that "turbo" bearings played no part in it. There aren’t a huge number of engines around using these bearings probably due to the price and the hassle to modify the block to fit them,but I haven’t heard of any failures. In fact I have used successfully myself, but only with through drilled cranks. I am not suggesting that there is anything wrong with "turbo" bearings at all, just saying look before you leap. You have been warned.

I see no one is listening to me again lol, no surprise then

the input is grate guys please dont get nasty tho..

that is a good read sprocket make me think a lot more..

as Chalkie said the holes on small bores do not line up! just needs some attention with a grinder an easy fix really but some thing to keep in mind

in terms of bearing material what are/have people used and had good or bad experience with?

at this point i agree with drilling the center main feed hole a touch larger and fitting plain/grove bearings with out cross drilling as i will red line at 6500-6750 thats what the cam is and its a long stroke @ 83.72 mm

can we shed some light on the two holes on the big end? one looks like it has a restrictor in it? its a 998 crank in the picks..

OK so here is a question.

Has anyone suffered a big end failure on cylinder 2 or 3?

Edit..... Has anyone suffered a big end failure?

Edited by Sprocket on 16th Aug, 2013.

Only once but was my own silly fault

I seriously doubt it!

Yes i moved to the darkside

Instagram @jdm_brett

has anyone done a mod to get extra oil to the timing chain?

Theres tons of oil in the timing chain - it unnecessary

I seriously doubt it!

only the oil getting pressed out from the end cam and crank bearings ive not seen how much or litle actulay flows there but surely a bit more cant hert things?
im looking to reduce wear and quieten it down

More oil will just cause drag, if fitted correctly there will be no wear and will be quiet

I seriously doubt it!