Irish Mini Owners Club

Gang
As part of my long term plan to upgrade power on my little 850 engine I have purchased a 12g295 998 cooper head. (RC 40, Freeflow manfiold, and twin 1.25 carbs also to fit)
I have to get head skimmed to get Chambers to correct cc so that I have correct Compresion to suit 850.
I do not want to bore out bigger size in block.(mini to stay at 850)
Have being reading a bit and seen some treads here and there about subject . But still unsure what next.

MAIN QUESTION IS .
Has anyone converted said head to suit a 850 and who or where best do I go for more info... price.. etc
Any help advise would be great as only going to do this once and Money as we all know is nowhere to be found.....

Thanks in Advance.

I don't have any chamber cc figures to hand but as far as I remember when this head was used on the cooper it was with flat top pistons which may not be available for 850's. This would mean you may have to skim the head alot and then you have to watch the main oil feed .I recently had 0.040" taken off a '89 unleaded head fitted to an 850 but the CR was still low.

The guy i sold my mk1 to got lloyd hutchinson to build him an 850 with a 12g295 head ,im pritty sure he had to cut pockets in the block to stop the valve's fowling the bore,the head was sent to med to be fully worked and so was the crank,it runs a piper cam ,he used the newer type 850 block as the old type only has one cam bearing,it got 50 odd BHP but cost alot to build!,il find out what pistons he used but i no it was bored and new bearings fitted

you do not need flat tops on a 850, as far as i know the 12g295 has 26cc and needs a 0.090" skim depending on your calculations, i'd say maybe a c/r of about 9.3:1

you may need to fit a smaller water pump to stop it fouling or if possible modify yours

Talk to Merlin

I have built a couple of these small bore units,

As has been said to get any kind of decent upgrade you need to to run flat top Piston some of the 850 had these if I remember it was the 1 cam bearing type,

You will have to skim a fair amount of the head to get a suitable compression 9:1 is about as much as you can safely go with out destroying the head.

As Albert has pointed out you will have to pocket the block to fit the head unless you want to over bore to 0.060" in that case you can use +0.020 998 pistons.

unfortunately none of this is cheep.

If you want a cheep 50hp build up a nice standard 998 with an SW5 cam and a 12G295 it will work and cost buttons. If you want the same power from a 850 with out over boring it, then prepare to spend a few quid
Regards,
Paul.

if you do a google search you will most likely get a much wider answer because its a popular upgrade, maybe 12g295 head on 850 or something, worth the look and you might even see what power output will be produced....

Cheers Lads
You have all said what I have read in books and some web sites.
Ever one mentions that head must be skimmed within a mm of its life.
Others have mentioned that a different head would be a better conversion.

Other option as ye have mentioned is a 998 block or if I had to is its possible to get my 1972 850 block up to 998.
I am looking at the best options to improve power and low end grunt.. But trying to keep car as standard as possible.
Do I get my existing 850 head worked to improve gases and put the 12g295 head idea to the side or
just fit uprated manifold , rc40 and the twins 1. 1/4 to head and block as is.
Thanks Again....