Re-Boring MPI sleeves ?

[buckman63]

I have a high mileage mpi engine I'm rebuilding to standard. There is a noticable ridge in the bores where the ring travel ends and the ring gaps are big. The pistons are standard size ( 70.3 ? ), so this will be the first working of the engine. Can the block be relined, at what cost ?, or is a re-bore to 73 the normal option ??

cheers

[Cooperman]

If it is standard, you can go up in several increments before you need go to the expense of sleeving. The over-bore sizes are

+0.020" - Will give 1293 cc
+0.040" - Will give 1310 cc
+0.060" - Will give 1330 cc
There were pistons at +0.080" available some time ago, but I think they are NLA, so the next size is to bore to 73 mm which will give 1380 cc. so long as the block is offset-bored at 1380, it is possible to go to 73.5 mm and, maybe, 74 mm, although at those last 2 bore sizes you do risk going through the block wall, so after 1380 with offset, it is probably best to liner the block. To liner a block and bore back to 1275 will cost between around £200 and £300, so best to just bore it out to max. first.
For pistons for up to 0.060" over bore the best value seem to be the Hepolite 21253. At +0.020" the part number is 21253-20.

I hope this helps,

Peter

[buckman63]

Thanks Peter. I'm looking for just the minimum to keep it close to standard, so that info is perfect.


Cheers Bob

Edited by buckman63 on Sunday 30th August 19:04

[Dino42]

I would have though that for a standard mpi 21251 pistons would have been more suitable?

[Cooperman]

No, the 21253 is a much better and stronger design as it has oil holes below the bottom ring whilst the 21250 & 21251 have long-ish slots.
Also the comp ratio is more correct with the 21253. The other 2 pistons will drop the comp ratio.
If you are doing a complete rebuild, you should always check the comp ratio and have the block deck and head machined to give the right figure. the tolerances on Rover parts are not exactly what you might call 'precision engineering'.
Should you need more detail on how to do the comp ratio calcs, just come back on here or PM me.

Peter