Wiped center main bearing
Turbo Mini Forums

mg metro water to oil cooler?

http://www.youtube.com/watch?v=GUhWrGgOEjI

Still watching that oil gauge

Of on holiday soon in the Mini, so 1200miles all in. That might settle my nerves if it survuves, but then there is that bloody head gasket!!

may be should you take a five port head in your boot (in case of...)

I have been trying to understand what caused this failure as there has yet been no real reason found, and Im not use that the missing O ring was the route cause. I have still found fluctuation in oil pressures in varying conditions after the rebuild, and its always been playing on the back of my mind.

After speaking to a couple people, my engine builder and the other from the company I work for in the US about a machine failure at work, I asked them about this failure on a personal level.

It has been speculated that the larger bearing clearances suggested by certain engine builders, might actualy cause more harm. The reasoning behind this could perhaps be explained by an article I found, its the closest I have found to what was explained to me. It was suggested that this situation might not be pressent at all engine conditions.

http://www.machinerylubrication.com/articl...p?articleid=754

Basicaly the larger the clearance, the more movement, the greater chance of 'Dry whip'.

It has also been said that although the crank may flex, it will only flex as much as it is un suported. Increasing bearing clearance alows more flex and movement in the bearing which could result in this 'Dry whip' phenomenon.

So, wher am I going with this. The engine is due a rebuild, and during this time i will be changine to the groove/ groove bearings and closing up the bearing clearance and then see what happens. I am putting the oil pressure fluctuations doen to a combination of oil feed to the main, cam bearings, and the location of the oil pressure regulator on the MPI block at the end of No3 main bearing gallery. I suspect the oil jets are pulsing also at their lift point due to this fluctuation in pressure, which is adding to the problem.

Time will tell

When you say the Groove/Groove bearings do you mean the old A type ones,

I can only advise on my own expereience here but I would never fit these over the Later A+ type as the only Time I have ever had Main bearing failure has been with this type of bearing, Since I moved the the Later A+ type bearing in ACL duraglide I have never had any Main bearing problems on any of my Race engines

Paul, did you use cross drilled mains with these plain bearings?

Yes vegard MED full worked cranks,IMO i think that the non grooved main bearing offers a better filament surface with a reduced presure area

The failed bearings do look like oil stavation. I don't think the missing 'O' ring had much to do with it.

I see that you say you've put some BMW Oil Jets in. Could you provide a bit more info as to what these are and where in the oil circuit they are?

Also, I'm sure that you do know what you are doing, however what type of engine lube did you use on assembly and did you crank it over to get oil presure before starting it after your rebuild?

For this HP output I would recommend 2.5 to 3 thou main bearing clearances (which is I think what you said you have. This will not cause any undue crank whip, especially with the oil presures you have.

Considering that the centre main copped it the worst, I'd guess (at this stage) that the oid centrufuged from the main by over-feeding 2 and 3 Big ends at higher RPM

I cannot understand why a bigger bearing clearance can reduce crank flex. There isn't supposed to be any contact between the two, and there WILL be oil between the surfaces as long there is sufficient oil flow/pressure.

If you search for BMW jets, you should find what you're looking for.

Edited by mowog on 11th Dec, 2009.

Edited by mowog on 11th Dec, 2009.

Edited by Sprocket on 12th Dec, 2009.

How much 'whip' is considered satisfactory.

The crank flexes, I had the pistons touch the head when the bearing failed. I am not convinced the crank does not flex with a propper bearing clearance, et alone with a slightly larger clearance.

I am not clever enough to prove otherwise, and I will just have to take your word and experience that its not an issue and look for an answer else where.

How many other center main failures have gone un solved? I think Paul Wiginton suffed this without reason.

Yes I did, last year. New shells before Avon and they were knackered by MITP with no road miles. It had very good oil pressure etc, I only knew something was up as it wouldnt rev past 8,000 as quickly as previous.
I showed them to Steve at MED who I bought them from and he said if it was anyone other than me he'd think it was debris damage but he knows what a fussy engine builder I am so it must be a bad bearing.

Paul

I seriously doubt it!

If something is worth doing, it's worth doing half of.

Sprox: Is this crank crossdrilled?

yes