1275 Vs 1098

Post by **mu0u207b** » Sun Jan 15, 2006 10:51 pm

Hi there, you may have guessed from my previous posts that im looking at more power from the old moggie by looking at a 1275 midget head. I was wondering the pros and cons of machining my present head, 1098, to accomodate larger valves. Would this make the power more comparible with fitting the 1275 head.

Post by **Alec** » Mon Jan 16, 2006 5:35 am

Hello Mb,

I don't believe that it is worth modifying, as it is not just fitting larger valves, but reshaping the combustion chamber and opening out the ports.
A lot of work seeing as there are suitable heads available at a reasonable cost.

Alec

Post by **rayofleamington** » Mon Jan 16, 2006 11:00 am

The easiest option is to find a 12G295 head for the 1098 but you can use a 12G940 with a bit of work (either pocket the block to clear the valves or recess the valves into the seats a little to make sure they clear the block).
The 12G940 is a great head!

Post by **picky** » Mon Jan 16, 2006 5:00 pm

on the 1275 type heads the centres of the valves are further apart, which means you can fit larger valves without them touching. Unfortunately this also means that under certain conditions the valves may hit the engine block if you use a 1275 type head. I think that if the 1275 head is the only modification then the valves wont hit the block. But I agree with ray, probably better off at first to find a 12G295 head, (which was standard on the mini cooper) as the valves cannot hit the block with this head.

Post by **bmcecosse** » Mon Jan 16, 2006 7:46 pm

The 940 head is far superior to the 295 - and much less expensive too. Often only £10 on ebay, while 295 heads get stupid money. The 295 also needs skimming before it can be used - to get the CR up. Absolutely no point messing about with the 202 head - at a pinch you could put larger inlet vlaves in, but it's loads of work and just not worth it. The 940 head needs no skimming - and the easy solution is to sink the exhaust valves into the head by 40 thou. then 'unmask' the valve with a little grind stone in leccy drill and it will bolt straight on the 1098 engine, but do use a 1275 gasket, and 1275 rocker gear - OR, spend a few minutes re-aligning the original rocker gear to line up with the valves in the 940 head. Of course - no point changing the head unless you also fit a larger carb, and a decent inlet manifold!

Post by **iambiggles** » Fri Jan 20, 2006 9:32 am

bmcecosse wrote:The 940 head is far superior to the 295 - and much less expensive too. Often only £10 on ebay,

Quite a little collection of them here for sale too.......

http://cgi.ebay.co.uk/A-series-BMC-Mini ... dZViewItem

Post by **bmcecosse** » Fri Jan 20, 2006 2:15 pm

Crikey - he's got almost as many as me. The MG heads have slightly bigger inlet valves - probably a bit too big for a 1098 unless taking it to the limit - but ideal upgrade for a 1275.