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A And A+ Block Interchangeably?


Best Answer DeadSquare , 13 September 2019 - 05:44 AM

I gather that "Least cost path" is important, but do examine the bores of the replacement block for wear, feeling for a lip where the top ring comes to at the top of the stroke, and the hard shine, called glaze, that drops the efficiency of the rings.

 

So that nobody says afterwards "Why didn't anyone say that":-........Proper advice in this case really ought to be that you rebore the replacement block and use the old clutch / flywheel, crank, rods and new pistons.

 

If nothing else,  makes sure that you have had a look at the condition of the bearings in the eventual engine, marking the bearing caps before you start so that you know what goes which way round and where.

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#1 Andrew850

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Posted 12 September 2019 - 03:30 PM

A friend has an unmodified ‘84 Mayfair 998 with a badly damaged block. I am trying to help them get it back on the road cheaply. I found them a nice replacement 998 block at a good price but it is a ‘78. Can I simply use this A block with the A+ head, box, and ancillaries without major issues? I read that the piston tops are A/dished and A+/flat, does that mean that we would have to plane the head to keep a reasonable CR? My own Mini is a ‘61 850, so this is outside my knowledge zone. We are in Canada where A+ Minis were never sold so used parts are very rare. Any practical help would be appreciated.

#2 DeadSquare

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Posted 12 September 2019 - 06:41 PM

Have you found an A block with crank, rods and pistons, or just the block ?



#3 johnv

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Posted 12 September 2019 - 06:59 PM

Over here a+998s are 2 a penny, a blocks are much more sought after. That doesn't help does it

#4 nicklouse

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Posted 12 September 2019 - 07:56 PM

The only non interchangeable parts are the alternator mounts and the dizzy, dizzy drive and the dizzy clamp. As to the compression it all depends on what you actually have and find.

#5 Andrew850

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Posted 12 September 2019 - 09:44 PM

Thanks for the replies. To answer DeadSquare’s question, the block comes complete with pistons crank and bearings, all looking very clean and original. It was a good working engine removed to make way for a VTech, and it has just been separated from its box, clutch and head. As to Nicklouse’s point, Assuming that nothing has been modified, would swapping an A+ head onto an A block with original dished pistons result in a drop of CR without skimming?

#6 DeadSquare

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Posted 12 September 2019 - 10:11 PM

Yes, the CR will be lower, but on the whole, the octane rating of fuels seems to be dropping world wide, so I'd just accept that it is a 25 year old example of a 75 year old engine and enjoy it as it is.

 

If you want performance, the low compression will be an advantage if it is supercharged.



#7 Andrew850

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Posted 12 September 2019 - 10:23 PM

Thanks. It might make sense to resurface the head anyway. I think it might have been a blown head gasket that led to the wrecked block in the first place. The goal is “least cost path” to a reliable engine.

#8 DeadSquare

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Posted 13 September 2019 - 05:44 AM   Best Answer

I gather that "Least cost path" is important, but do examine the bores of the replacement block for wear, feeling for a lip where the top ring comes to at the top of the stroke, and the hard shine, called glaze, that drops the efficiency of the rings.

 

So that nobody says afterwards "Why didn't anyone say that":-........Proper advice in this case really ought to be that you rebore the replacement block and use the old clutch / flywheel, crank, rods and new pistons.

 

If nothing else,  makes sure that you have had a look at the condition of the bearings in the eventual engine, marking the bearing caps before you start so that you know what goes which way round and where.






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