Turbo Main Bearings...
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found this on a site some may find this article intresting?

?TURBO MAIN BEARINGS?


"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

Edited by BENROSS on 17th Jun, 2005.

I had noticed that when I started building mine. So got the drill out and drilled right through the mains so oil hole on both sides.

This would explain why the engine I bought had only done about 6000 miles and the bigends were on there way out, and the mains seemed to be fine.

Very interesting that I am not the only one that has had this problem

I'd agree with Mike, Vegard.

Surely the mains would be well supplied by oil finding its way round the bearing from crank rotation, whereas for 50% of the time, the big ends would not be getting a good oil supply?

Yeah

Tom hit the nail on the head

Edited by mikemph on 17th Jun, 2005.

Just aswell really got a bargin. Engine fitted with new Omega pistons and slightly modded head cost me £250 so pretty good just need some ARP rod bolts and straight cuts and it will be ready to roll.

Aha...
I understand.
I'm fitting a 1275 A crank into an A+ block now. Is it OK just to drill with a regular hand held drill? Or, as the text suggests, regular A cranks does have a cross drilled main?

vegard, a hand held drill would do th job but a pillar drill would be better as you can give it a little more Omph!

i suggest using a cobalt drill with plent of cutting oil to do the job.

also place a "LITTLE" a wisker, taper on both sides of the hole.

an intresting topic info...

could save some pain in the back pocket for some of us

also worth concidering if i am righ ???
to confuse matters more?!!..............

say if we through drilled the crank and fitted this to a groved bearing block (ie) none turbo block wit fully croved bearings

would there? be more oil unavailable to the main bearings due to leak out ?

if this were so........

i think the oil pump would more than match the out strip!

your comments are welcome gents

Edited by BENROSS on 17th Jun, 2005.

I would think it would be about the same, basically the journal clearances is what will determine how much oil is leaked past the bearings.

If you consider the size of the oil drillings to the actually clearances think the area of the oilway cross section will be bigger than the overall clear area or at least I would hope so.

If not it would be starving the bearings of oil anyway.


Hope that makes sense

I've been out in the garage now, checking two cranks I've got. Both are A+, one of them of the Turbo 6581 variety

NONE have got cross drilled mains, and surely the turbo cranks did have the turbo bearings?

So.. Which are cross drilled from the factory?
Does this mean that one could use the non cross drilled crank and turbo bearings in a low revving engine?

Edited by Vegard on 27th Jun, 2005.

I know an ex-engine builder from somerset way who was very sucessful in the 70s and 80s who swore blind that the turbo bearings where the way to go on almost ANY engine build.

Alex

AlexF

Metro turbo weekend driver,Mini turbo in the making again!

Metro turbo weekend driver,Mini turbo in the making again!

http://www.minimania.com/msgthread.cfm?thr...=9999&subview=1

So, is it confirmed then? No A+ crank has got crossdrilled mains?

Any one want to confirm that the later A+ blocks all have the plain bottom bearing. I know that at least all 92 on engines have, though, suspect it may start as early as 87

Also is it not the fact that the cranks are not cross drilled but rather fed from two of the main bearings 180 opposing each other

Edited by Sprocket on 6th Apr, 2006.

I've had '87 blocks with the 'turbo' bearing arrangement - so take a guess on late 86 maybe???