948 max bore size

[zabond]

G'day all from OZ I would like to fit 060" o/s 1098 pistons into a 948 block, the Vizard states on page 403 middle colum "this block can be bored up to 1/8" but in the next colum states "over boring the 948 to 2.6"[that's +060 on the 998 Cooper piston]"
as the 998 cooper is the same bore as the 1098, in one statement max bore .125" the other .132" so has anyone bored a 948 out .to 2.6" without having problems
ty Russ

[philthehill]

The chart Fig: 14.2 that you refer to is on page 386 of my edition of David Vizard's book Tuning BL's A series.
Personally for a 948cc I would go no higher than 998cc plus 0.0060" (1046cc) as you are getting very close to the block boring limit.
The problem with these oversize bores is that you are left with very little meat between the cylinders (especially between 2 & 3) for the cyl head gasket to seal against and that is why on the 1275cc engines when over boring the bore centres are moved.
What ever size you bore to - make sure that the piston land above the gudgen pin will not extend above the top of the block which means machining the piston or is so far below the top of the block that you have to machine the top of the block to get a reasonable compression.
The Vizard companion book 'How To Modify Your Mini' and gives additional details and suggestions on over boring the 'A' Series (Fig: 3 page 87).
Over the years various combinations of pistons have been used to give additional cc to the 'A' series i.e. A40 Devon and Hillman Imp.
Anyway the best of luck what ever you do.
Phil

[liammonty]

For what it's worth, my 948 is bored to 998 +0.0040", giving 1030cc, and this has given no trouble at all over 4 years or so.

[don58van]

Hi liammonty

What pistons are you using?

Regards
Don

[bmcecosse]

If using 1098 pistons you will need a 1098 crank, or face down the block to suit. Use a 1275 gasket ( and head for best power) if it looks tight, but it should be okay - 998 Minis are bored +60 andbeyond....

[liammonty]

Hi liammonty

What pistons are you using?

Regards
Don

Hi Don, the Pistons are Nural. They're flat topped which helps with the CR to go with the 295 head so I didn't need to skim it as much as if the pistons were dished. Could have used the original 948 rods, but I used a set of 998 Cooper ones, as the little ends are better on those.
Liam

[bmcecosse]

Why not use 998 pistons? 1098 are short,so the block will need skimming.

[zabond]

tks all for your reply
unfortunately pistons are in short supply down here, I can get hold of a 0060 over 1098 set as 998 are as rare as RHS, my ideal would be a + 0020 998 set, trying to get a price from Bullmotiff mini at the moment, if any one has a set for sale new or s/h please let me know.
liammonty ty that's what I wanted to know I don't realy want to go 0060 but it's good to know 0040 is ok
tks Russ

[philthehill]

I know you are looking for plus 0.020" but here is a bargain (at the moment).

http://www.ebay.co.uk/itm/WOLSELEY-HORN ... 4d3499a159