Morris Minor Owners Club

BACK TO THE DRAWING BOARD ,HAD REMOVED DEFUNKED ENGINE 1098 BECAUSE OF FAILED REAR OIL SEAL GARAGE UNABLE TO FIX ADVISED TO PURCHACE SECOND HAND ENGINE CHEAPER IN THE LONG RUN , ANYWAY THIS ENGINE HAS BEEN NOTHING BUT A NIGHTMARE ESPECIALLY BUYING FROM A DEALER, BUT GETTING TO THE BIG QUESTION REMOVED THE PISTONS AND BIG END BEARINGS AND THEY WERE WELL PAST IT ! SCORED AND SCRAPED BUT AS LUCK MAY HAVE IT THE CRANKSHAFT APPEARS TO BE FINE ALL SMOOTH ALSO THE CYLINDER BORES CLEAN AND SMOOTH THE THING IS THE OTHER ENGINE STRIPED DOWN PISTONS ALL LOOK OK SO CAN I FIT THE PISTONS FROM THE DEFUNKED ENGINE INTO THE ENGINE IM TRYING TO REBUILD IV,E ONLY JUST ORDERD A FULL SET OF STANDARD PISTON RINGS AND BIG END BEARINGS THE ONLY THING IS THE FAULTY PISTONS ARE MARKED WITH A NUMBER 4 ON THE FACE OF THE PISTON ALSO STAMPED WITH A 4 ON THE ENGINE BODY AND THE GOOD PISTONS I INTENDED TO USE HAVE A NUMBER 3 ON THE FACE OF EACH PISTON WILL IT BE OK TO USE THESE I WAS TOLD THEY WERE A QUALITY CONTROL ITEM NUMBER I HAVENT GOT A MICROMETER SO ANY WAY TO MEASURE THE DIAMETER OF THE PISTON HOPE THEY ARE OK TO USE OTHERWISE SCRACHY HEAD TIME AGAIN THANKS FOR HELP PS THE BOUGHT ENGINE IS OVER THREE YEARS OLD NOW SO CANT TAKE IT BACK HARDLY USED THE CAR DUE TO THE PROBLEMS,THANKS

There is no seal at the rear of the 'A' Series (803cc/948cc & the inline 1275cc) fitted to the Minor - only a return scroll on the rear end of the crankshaft.
If your main bearings are good there should be no reason that the rear of the crankshaft leaks - but if you have substantial piston blow past and poor crankcase breathing any problem with the rear main will be exaggerated.
You are correct that the number 4 and 3 are the grading numbers for the bore and pistons. Not all pistons and bores are what they should be size wise. See BMC wksp man Section AAA. 5. and Fig AAA.1 for further details.
Pistons and bores should be matched i.e. No: 4 grade piston should be fitted into a No: 4 grade bore.
You may find that the No: 3 grade pistons are a bit sloppy in the No: 4 grade bores but so long as the rings and piston ring grooves are good it may be worth a try. The difference between a No: 3 grade bore and No: 4 grade bore is only a couple of thou so it may work - but there is no guarantee that it will.
It is considered poor engineering practice to fit used pistons from one engine into the old/used bores of another engine.
But if needs must.
I would fit new rings to the pistons and glaze bust the bores.
If you are prepared to accept that it might result in an engine that may not be absolutly perfect - I would give it a try.
Best of luck.
Phil

Hi Phil do you think that if I buy a new set of standard pistons these would be ok in the engine block I removed the damaged pistons from and would I have to ask for pistons with the number 4 stamped on the top or is this not the practice now,theres so many if,s and but,s about renewing pistons and rings etc ,like will the bore,s be perfectly round or slightly oval and I have no way to check this, so if there,s no number on the piston face of the new pistons i buy it could be the same size as a number 3 that I already have! can you give me some idea what I should be aiming for I know the best way will be to remove the engine and have the block checked out and maybe bored with pistons to fit but never having striped down an engine before im in uncharted sea,s looking forward to your comments thanks Norma and co

As regards the bore/piston grading - the current practice is to bore to the pistons - therefore you will not find the grading numbers on new pistons.
Only when engines are being built on a mass production scale as undertaken by BMC would you need to grade pistons and bores otherwise there would be a lot of reject pistons and cylinder bores. The grading got around any size variations in the production process.
I would advise that you get the block re-bored - the engine reconditioning company that undertakes the re-bore can normally supply suitable pistons and re-bore to suit those new pistons.
Only use a reputable re-conditioning company for the re-bore.
No doubt someone on here will give details of a suitable company for your location.
Note: You will need to post your location.
Phil

CRANKSHAFT APPEARS TO BE FINE ALL SMOOTH 

Not necessarily a good indication, but at least a start.

Crankshaft dimensional deviation is far more important and should be measured carefully. If any crank shaft bearing is scored it will almost certainly need a regrind .

The shell bearings have a miniscule coating of bearing metal over a much more wearing backing material. If any areas of copper or steel are showing, it means they have been out of spec and 'past it' for some time, provided lubrication has prevailed.

Because the shells are precision items and require close fitting tolerances, any ovality of the big end journals of the crankshaft will likely exceed running tolerances at installation. The centre (particularly) main bearing surface will be worn near the webbing than in the centre. The wear tolerance is very tight if bearings are to survive intact for many thousands of miles.

Piston ring grooves are also often worn oversize. They can be repaired, but not without cost, or machining equipment (I can enlarge the grooves and make wider rings for engines, for which spares are not available, but I would not contemplate doing this with an A series engine).

Bores should generally be serviceable if not noticeably worn in diameter (check ring gap at worn and unworn areas), but can be worn oval or tapered leading to poor bedding in of new rings (or never fitting properly). A distinct wear ridge at the top ring limit of travel often indicates a likely out of spec bore, although many replace rings, after removing the lip (or by fitting stepped top ring sets to avoid ring breakage or further ring groove deterioration), as a stop gap repair.

Piston fit to bores can be checked with feeler guages, but somehow I think I would agree with PTH and advise you getting the engine reconditioned professionally. There may be other issues, not even considered so far, that require addressing in order to have a reliable unit for many thousands of miles. I reckon the crank needs regrinding and the cost of a rebore and new pistons is likely far more economic than fitting new pistons in a worn bores.

Thanks to Phil and Oliver, I,ll ring a local auto machine co tomorrow and try to get an estimate on the cost of crank regrind and bored block with pistons and rings supplied I,ve already called at the premises which was recommended and they seemed busy with loads of work so I hope its a good indication of how good they are plus the,ve been in businessfor about 50 years,i,ll keep in touch and let you know how I get on,as requested I live in Newcastle on tyne so any local help would be appreciated regarding engine repairs thanks Norma and co