Main bearing performance. Grooved or non grooved?
Turbo Mini Forums

http://vandervell.co.uk/images/slideshow/h...ngPerforman.pdf

That pretty much explains it, plain bottom is better, and not likely to cause any real issue with big end oil supply as previously thought. But, the A seies may be a little funky in this respect. Unless some one wants to fund the research, we will never know for certain

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I read this a few weeks ago when we were last debating this point.

It's interesting reading.

Now what material bearing should we use?

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

Interesting article but the one thing they completely miss out (unless I have missed it from a quick read) is which main(s) are No2 and No3 big end fed from ???

All their graphs show the middle (of five) behaves very differently to the others.

Being a five main bearing engine they tested, there are two possibilities, only one of which could be compared to the A series.

Schrödinger's cat - so which one am I ???

Which is why I said the A series was a little funky

Colin, I agree entirely...

On 5th May, 2011 Sprocket said:
Which is why I said the A series was a little funky

Schrödinger's cat - so which one am I ???

The first graph might suggest that the main bearing 3 is supplying big end 2 and 3 with main bearing 1 and 5 supplying big ends 1 and 4 respectively. In which case, the situation is not so different. There are comments in the text that the center bearing is the most important, but did not say why, since a five bearing crank is less likely to load up the center bearing in the way that a three bearing crank does.

It certainly opens up some discussion.

I have not read the article but I did make up my mind the other day that plain/groove is the combination I'm sticking with.

My mate has a 1380 a-series with powermax pistons, standard rods, and standard crank featuring the groove/groove bearing shells. This engine was not new, but had been rebuilt by a very reputable engine builder so parts were within tolerence. It covered 3 15 minute sessions at combe,and about 10 1/4 mile runs maximum rpm was somwhere near 8500 for the drag racing before big end knock sounded coasting down from one of the 1/4 mile runs.

I will try to get some pictures of the damage, but the main bearing is totally shot and the big end has been hammered out like plastercene around the big end. I wonder whether the main bearing failed first due to insufficient support from the grooved bottom shell, starving the big end of oil. suprisingly the journals are not scored to shit for some reason, but a new crank will be being fitted.

One more 1/4 mile run though and the engine would have been spread all over the track mind. The driver has no mechanical sympathy which probably doesn't help though.

Edited by minimole23 on 7th May, 2011.

I doubt there is anyone who could attribute an engine bearing problem due to having flat bottom shells.

As crappy as Leyland etc were...obviously they and other engine makers have done the research and seen there are no negative side effects.

I regularly ran mine hard to 7500rpm and never once did the big ends show any problems due to lack of oil.
When I had a 286 cam in for a few days ( what a piece of shit in a turbo engine ), it was happily revving to around 8200rpm. Mind you, there was nothing at all below 5000rpm which is why I removed it.
Never did the big ends any harm


If your main bearings have failed, either the build wasnt right or the oil supply or oil was poor.

There is no way it's down to the design of bearing.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will