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Hi all just toying with the idea of giving my cooper a bit more puff, what is a good useful upgrade to the 12a185 head or can the existing head be given a new lease of life .regards mark

Just to confirm here, your engine is a 997?

Yes my cooper is a 1962 997 cooper with a early head casting number.

OK, the head that you have is an early Cooper S Head, ie for a big bore engine. The CR would be pretty poor with that head. I'd suggest finding a 998 Cooper Head, casting number 12G295 but they are a little hard to come by. There is also a 12G206, which is the same casting, but has slightly smaller valves. The original head fitted to the 997 was a casting number 12G202, and I dare say lower in the RPMs, one of these would go much better then the head you have. Never know, you may even be able to do a swap with someone who may want your head.

Even when fitting the 12G295 or 12G206 heads, you'll need to up the CR as these have big combustion chambers. I'd suggest aiming for a CR of around the 10 to 10.5:1 mark. It will certain make it go a LOT better.

The 12A185 head referred is probably the small bore version and original to that engine. Spider, make a search om the forum for 12A185, you'll find a thread comparing the small bore and big bore versions with the same casting number.

ricardo wrote:The 12A185 head referred is probably the small bore version and original to that engine. Spider, make a search om the forum for 12A185, you'll find a thread comparing the small bore and big bore versions with the same casting number.

Cheers richardo, I actually looked in Vizards early book as it was close to hand. I am aware that there was an early 997 head and I think that one didn't have a temp sender hole, but can't recall for sure and I can't recall it's number off hand. I've just picked up Vizard's book to check again and it refer's to a 12G185 as an 'early yellow' head for MKI Cooper S.

I just now looked through some of my other notes and yes, the 12G185 is an early 997 Cooper Head, you are correct richardo and yeap, yet another error in Vizard's book.

If you can find a 12g206, as Spider said the valves are smaller than the 12g295 (actually the same size as the 202), and this will fit the small bores of the 997. It may require a skim to get the CR right.

Alternatively, if you have overbored the block a 295 will just fit without pocketing, but check the clearance first.

Thanks for your replies . I will now spend all evening trying to work out what they mean .how to raise cr and what that means anyway? Regards mark

Not really an error in Vizard's book. BMC used the same casting number, 12G185, on two entirely different heads. One a 1275 'S' head and one a 997 small bore head. It's a really odd thing for them to do and has caused confusion for decades.

Cheers,

Kelley

mascher wrote:Not really an error in Vizard's book. BMC used the same casting number, 12G185, on two entirely different heads. One a 1275 'S' head and one a 997 small bore head. It's a really odd thing for them to do and has caused confusion for decades.

Cheers,

Kelley

Oh OK, that's a little curious but not entirely surprising, a bit like all the varieties of 12G940 heads that they did, I think I've seen at least 8 different castings of them.

I've just had another look again - this time with my glasses on!!! I think the early 997 Cooper ones referred to here are 12G185 and the Early Cooper S ones are 12A185

Apologies if I've caused any confusion.

Just to confuse matters BMC also but the early 850 head casting number on the cooper s 185 as well

251 ENG wrote:Just to confuse matters BMC also but the early 850 head casting number on the cooper s 185 as well

Where's the smack head emonicon?

Here's my 1962 997 head. 12A185 for sure!