Hi
I have got a 1275gt engine that is going to need a rebore, i need some help on what is the maximum size i can rebore it to without having to change anything like the crank, just need some help really!
Any help would be greatly appreciated,
thanks
1293 (+0.20") , 1310 (+0.40"), 1330 (+0.60") these are all quite reliable sizes
at maximum 1380 (+73.5) but the block will be scrap after as it wont be able to be rebored, and the bores will ne to be offset which will cost quite a bit more!
mines a 1310, hilift cam, modded head and produces 85 bhp and the benefit is that it can still be rebored again.
if i were you id go to 1330 maximum, youll have reliability and if you need it reboring again, you wont need to search for another block, these are getting scarce now, because people over bore them.
Hi,
You could quite easily go yo 73.5mm (1380), however if you are going to all this trouble then you will really need to build the whole bottom end
Regards Martin
MRA Minis
07789 872368
There is a growing attitude amongst Mini owners I speak with that says you should keep the re-bore sizes to a minimum. If everyone goes to 1380, then in a few years there won’t be any blocks to re-bore. it is difficult (some say impossible and I think that’s correct) to sleeve back a block which has been bored to the absolute maximum. Thus a max-overbored block is then scrap. Eventually we’ll run out of blocks or they will become mega-expensive.
My favourite bore size is 1330 (i.e. +0.060"). You can still sleeve from this size when it’s worn and 1330 gives a few bhp more than a 1275. Pistons are relatively inexpensive (Hep 21253 is good) and the re-bore costs are acceptable. No gasket issues with this size either and less tendancy to overheat due to block wall thickness reduction.
my engine builder advised a 1330 when i asked about him building me a 1380
It does seeem a waste to bore straight out to 1380, I have quite a few blocks at various bores, so I can simply bore out the nearest to suit the requirement
However if we start out with an offset bored block then you have the option of going all the way from 1293, 1310, 1330, 1360, 1380, 1399 and if you can find some old triumph pistons 1425. I personally don’t go over the 1380cc self imposed limit, however sometimes needs must.
Still, casting a new block will be fun … especially when I add a few tweaks to enable a slightly larger bore etc … and of course they wouldn’t be as cheap as the current available blocks
Regards Martin
You could use a little reverse logic - sets of pistons crop up on fleabay quite often a decent set inc rings retail at about £180 so its your biggest parts outlay in a rebuild / bore - raid ebay get some suitable pistons then (when they’re confirmed A-OK) get you block rebored to suit.
I’ve got a 1301 - i.e 1275 +0.030" - not a popular size now - don’t know why…?
