which main bearings to use?
Turbo Mini Forums

Hello,

I'm rebuilding mine engine and bought some new bearings for the crankshaft.
In the engine was one shell grooved and the other smooth, what i believe (after reading this site) is the stronger type.
Now i got a set off glacier with both shells grooved
And i also noticed that the "tab" on the smooth shell is in the middle and the grooved one got it on the side.

So i think this will not fitt:(
Has anyone the right artikel number for me so i can order the correct bearing so i can start building mine engine?

thanx in advance

there is nothing wrong with a A-series that a turbo can't fix.

www.turbomini.nl

You need a set of A+ main bearings to fit from 1985 onwards, this is when the smooth lower bearing shell became standard across the board, before this they were only fitted to A+ turbo motors, and the lesser engines had all grooved shells. You must have been supplied a set of earlier A+ or A series shell bearings.
I sourced the shells for my engine from Avonbar, they will sort you out if you ring and speak to Ian.

It's no problem to file a groove in the centre and fit the later bearings.
Did this last friday and the crank can spin easily with just two fingers and a drop of 20-50
Regards
dave

I will go for some new bearings. 1985 and onwards.
thanx for the advice you both

there is nothing wrong with a A-series that a turbo can't fix.

www.turbomini.nl

There was an excellent discussion on the Minimania website concerning non grooved shells and cross drilled mains, but i cannot find it. It's said that to use the plain lower shells, you'll need cross drilled mains. This is obviously not true as no A+ crankshafts are cross drilled. It is however said that for out and out racing, the plain bearings are NOT the ones to use.

I thought i red something in that line on minispares. But one grooved and one smooth is what came out off the block so i thinking off putting the same back in.

What are you running at the moment?

there is nothing wrong with a A-series that a turbo can't fix.

www.turbomini.nl

Yes, use whatever that came out. It looks as for road engines the plain bottom ones work perfectly. I use both, but I'd go for the grooved ones in anything revving more than 6500rpms continuously.

Vegards, Did anyone give a reason why the non grooved lower shell was not suitable for race use?
Did they say it would be OK for use with a cross drilled crank?
Regards
dave

Because the big end bearing would be starved for oil 180 degrees of crank rotation.
If you cross drill the mains, this bould be eliminated.

Actually you are more likely to maintain a good oil film on a plain shell than a grooved one. If you think about it what your hoping to do is maintain an even film thickness over the width of the shell under load. With a plain shell you'll have a pressure gradient, high in the centre - decreasing towards the edges. The groved shell will actually have a greater drop in pressure as it crosses the edge of the grove. Sharp edges are not good for smooth fluid transfer.

So long as the oil is introduced to the loaded portion of the bearing at the relevant time to give the best lubrication at the point of highest loading the plain shell is more than sufficiant. However if the lubrication arrives at the wrong time relative to the increase in loading the bearing will fail.

My choice? Plain lower bearing with a cross drilled crank. Gives the best oil film support and the best support of the lubrication system by oil supplied at the write time to support the bearing and again at a time of lower load to help maintain the bearing, including it's thermal properties.

Every day is a school day ...........

How fast and how expensive ...... the same question...

So How come BL engineers & D Vizard claimed it was much better in load bearing terms and yet above 6,500 rpm it's no good and likely to fail.
Can't quite understand.
Regards Dave

It starves the big ends!!!! Good for mains, rubbish for big ends.

Vergard, Penny has dropped, (english saying)
I have read what you said and not what I was expecting to read.
Good job I have a x drilled crank to use with my late block/bearings.
Regards
dave
does it not piss you off being right all the time!!

As Vegard says ....... the topic is regarding the mains and the loading between mains and big ends are different. Once you consider the interactions between all the areas it can look different again.

It's one of those things where there are compromises to be made and when that happens there is no choice but to break out the calculator!


As a serious question how many people are taking their turbo'd motors above 6500 regularly? I know that mine used to produce peak power (Avonbar original phase2 cam) peaked at 6100 and was noticably falling away at 6500.

Every day is a school day ...........

How fast and how expensive ...... the same question...

Ok, fairy snuff but the Don uses a very specialist 4 valve engine.

I should have been clearer ..... how many people with a turbo 5 port A series who's car wears a tax disc with pride rev their motors past 6500 routinely?

Every day is a school day ...........

How fast and how expensive ...... the same question...

Why does it make a difference, it still uses the same crank rods and bearings.

Tom are you reving to 9k with standard A+ rods and a basically standard, i.e. no major work, crank? Very brave if you are.

Every day is a school day ...........

How fast and how expensive ...... the same question...

They have had work, but the basic configuration is the same.

When I get home i'll post the loadings and peak piston speeds for that Tom!

Edited by Joe C on 26th Sep, 2007.

mini7 engine's used to get rev'd to 10,000rpm with standard rods, pistons and cranks (stress releived rods and crank). now they use omega pistons.

with the turbo engine my rev limiter is at 7,000 but i normaly change at 6 to 6,500 due to the drop off in power, otherwise i would rev it to 8,000. cant see a problem and not had a problem with N/a's reving to 8,000

my old MG metro used to rev off the gauge and would normaly point at the digital clock

Another lesson learned...good topic

indeed, i have been educated.

need to start ordering bits for my new engine....need to find a metro engine/1275 a+ engine first though.