Mini Engine

[panky]

Sorry it's not a Minor but it is an A series - well A+ and looking for a little advise.
My '91 Cooper has been sulking in the back of the garage for too long, nearly five years because of a mayor oil leak, we're talking oil slick proportions, so I decided to have the engine out. I suspect the leak is from the gearbox so I have a replacement to fit - but while it was out I stripped the engine. It was running very well with just a little smoke on start up so new valve stem seals and rings I thought.
The bores look excellent and the pistons are stamped as in the pic[frame][/frame]

I assumed the + 0.508 is the over bore size in mm and after a quick calculation that comes out as .020" so just making sure that I'm not barking up the wrong tree before I order new 20 thou rings.
I think I need new mains and big end shells too, the crank looks fine ( no scoring, discolourtion or chatter) but the shells look a little worn. The mains are actually a lot better but while it's apart it seems daft not to do them. These are stamped +.020 so no issue there.
Any advice welcome.


I've had the car since it was three years old and it had not long had a re-con engine fitted, it had 26K on the clock then and it's just about to go round the clock so it looks pretty good for all the work it's done - twice yearly oil changes didn't do it any harm [frame][/frame]

[IslipMinor]

How bizarre! Why on earth make it complicated - 0.020" is just that, why convert it into a meaningless metric value?

Many years ago we had a contract to make a series of specialised machines, to the customer's design in imperial dimensions, and had completed the first batch of 6. We were about to start the second batch of a further 3, when the customer contacted us to say they were 'metricating' and going to redesign them in 'metric' for the last 3.

A number of months later we received a large parcel of drawings, and set about identifying what had changed and where we would need to make new jigs and fixtures. After working on it for 2-3 days, we found that actually nothing at all had changed, except all the drawing were now 'metric'. What this meant was that every single imperial dimension had been converted into the metric equivalent, and the original imperial dimension removed - so 1" = 25.4mm etc. We had to convert them all back to imperial just to find out that no actual changes had been made - incredible!

Getting back to your point - yes I would believe that the pistons are +0.020" and if the other journals are as good as the 2 big-end ones shown, new big-end and mains shells and thrust washers should sort it out well.

[panky]

Just what I wanted to hear Metrication gone mad, but maybe these pistons were made abroad, who knows.
I'm a bit mystified at he discolouration on the shells almost as if the crank was flexing. I think I'll fit a centre main strap, it does get driven erm ...'spiritedly' - it's a Mini after all.

[oliver90owner]

The big end bearings look as though copper backing is evident. New shells may keep it going for a long time, but it would be prudent to check the journals for wear, particularly ovality.

The centre main may well be shot (typical, particularly if over-revved) and that is causing the apparent uneven wear. Better to check and get it right as it should then go another 100k. Crank bearings will be -20 thous (so undersize), but beware that if it is marked +20, then that may mean the engine has been line bored and larger OD shells fitted (crank may be a standard size!). Only seen it on a couple of occasions - one was my ford car and the other was a Fordson tractor, but it may be more common on performance engines.

RAB

[les]

What is the engine capacity, 998cc ?

[panky]

It's a 1275, 1293 with the extra 0.020"

[panky]

The big end bearings look as though copper backing is evident. New shells may keep it going for a long time, but it would be prudent to check the journals for wear, particularly ovality.

The centre main may well be shot (typical, particularly if over-revved) and that is causing the apparent uneven wear. Better to check and get it right as it should then go another 100k. Crank bearings will be -20 thous (so undersize), but beware that if it is marked +20, then that may mean the engine has been line bored and larger OD shells fitted (crank may be a standard size!). Only seen it on a couple of occasions - one was my ford car and the other was a Fordson tractor, but it may be more common on performance engines.

RAB

Thanks for that, I'll mic them up in the morning and see what's what. The shells were marked 0.020 not + 0.020 as I said earlier, my mistake

[les]

It's a 1275, 1293 with the extra 0.020"

Oh ok, I,was going to offer you a crankshaft, with standard ( I think) journals but it's a 998

[panky]

Thank you very much for the thought it was most kind of you

[oliver90owner]

+ 0.020 as I said earlier, 

I thought that might be the case. Normal practice, I believe, is for blocks to be bored out to non-ID shell size. Both my engine and the tractor were line bored at +15 thous.

RAB

[oliver90owner]

Bump!

What did you find with the centre main bearing? Just interested to know whether your 'spiritedly' driving has caused some typical wear (such as I found on my Ford engine of many years ago).

[panky]

Sorry I did measure them and all journals are within .001" over circumference and width. No scoring or discolouration either so I'm a happy puppy The bores are very good, I pushed an old top ring down with a piston and found no difference in the gap when compared to that with the ring at the very top so conclude minimal wear. The ring gap, however, was way out of tolerance at over .025" so they are well worn and will be replaced along with new bottom end bearings.
The marks on the old shells makes me think the crank was flexing under high load so I'll be getting the main bearing centre cap machined flat to take a strap. Over all I'm delighted with the condition and the re-build should be easy enough, Even picked up a recently reconditioned gearbox at a bargain price to complete the build
Edit
.001" not .0001"

[oliver90owner]

Ahh, right...

A hardened crankshaft, not a regular one. Pretty well perfect at less than a tenth of a thou.

[panky]

Wrong again .001"