57 replies to this topic

[charliedurrant]

Hi,

I've just swapped out my 998 engine for a temporary 1275 engine. I have a 12g295 head and as I am very new to this I really don't know if it is any good for my pending engine rebuild. Photos attached.

1) The bypass hose connector is very corroded
2) Some valves are pitted

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So, how does the head look, is it scrap (bypass valve corrosion) or serviceable? How can I tell if it has been skimmed?

Charlie

[Cooperman]

You can have a machine shop blank opff the by-pass and use a water pump without the by-pass.
The head looks good to me, but just make sure you inspect it closely for cracks.
Don't worry about whether it's been skimmed as when you fit a 295 head to a 998 you MUST measure everything, do the compression ratio (CR) calculations and determine what size the combustion chambers need to be. Then have the head skimmed as necessary to give that combustion chamber volume. If you want a good result, guessing is not an option.
If you don't know how to do the CR measurements and calcs, come back on here for more advice.

[jaydee]

Its scrap, but if you want i can pay 10 quid for it and get it off you hands





Im joking, you have a good find there.
That head looks still unmolested, not skimmed for a 998, with original valves, and doesnt lock cracked.
Check also for valve seat recession.
Plug the by-pass hole, it just causes trouble, so plug it and drill three 1/8'' holes in the thermostat.

[bmcecosse]

Flog it on ebay - for a LOT more than that £10 cheekily offered above..... And then fit a much better 12G 940 head from a 1275 engine. It's much much better........

[Wright&Wright]

Don't be tempted to flog the head and then purchase a 12G940 head as bmcecosse suggests.

The 12G295 head was fitted to 998 Cooper engines and also 1100 midget/sprite engines. The head itself is quite hard to come by nowadays and is considered a substantial upgrade from the standard head. As said before, the head's chamber size must be measured to ensure that it has not been skimmed/molested. The 998 Cooper used D-Top pistons and therefore had a higher combustion ratio compared to dished or flat top pistons due to a larger combustion chamber. If it has not been modified then it is usual custom to skim the head to suit the flat top/dished pistons of a standard 998 engine to suit.

The 12G295 head outperforms the 12g940 head on slightly modified 998 engines because of valve sizes and port sizes. The 12G940 head should really only be fitted to 998 overbores or even 998's that are extremely modified, due to the fact that the valves and ports are far too big for a slightly modified engine.
Your best bet is to use the 12G295 head and smooth it out as much as possible and use rimflow valves (if the originals are too far gone), plus skimming the head to ensure the perfect combustion ratio.

Greg.

[twrminisport]

Looks fine. Get it skimmed to CR. ChEck first though.
Good clean
Take the bypass off altogether as above.
The 12g295 is better than the12g940 on mildly modded 998s anyway

Jesus

Edited by twrminisport, 16 October 2011 - 12:37 AM.

[charliedurrant]

All,

Thanks for the replies. I now know that:

1) The head looks okay so is worth investing in
2) The bypass can be blanked and I can use a metro water pump - http://www.minifinit...ic.php?p=870204

The head is from a 998 cooper engine. I have the 998 cooper engine but it is completely in bits - for someone who is new to this it's a bag of bits with no instructions and at each stage I don't know if each part is okay or not. I'd love to re-build the cooper engine but I have no idea what state it was in before it's dismantling and I could invest a lot of time and have a dud at the end.

I've bought the 'A series builder' DVD by Bob Sollis re rebuilding an engine and as he cleary states - always buy one that was working!

Therefore, I have a 998 A+ (leaking valves, through compression test, no 1 cylinder low pressure compare to the others), but it does work thus my thinking was to use the head on the A+ engine. The A+ engine does have a cracked casing around the sump plug. Someone has put in and wrenched up the wrong sump plug ( I had to use a breaker bar to get it out ) - is the 998 coooper engines gearbox casing compatible with an A+? So many questions and so many bits.....

Charlie

[bmcecosse]

Have you two guys above actually tried the 940 head on a 998 - or are you just following the 'party line'?? Believe me - the 940 is FAR FAR better than a 295 - itself a good head, but NOT nearly as good as a 940 on a 998.

[lapider]

if you have the original engine and the pistons are in good condition hold on to those as they are d top pistons only used with the 295 head thus making a brilliant base for the engine if used with the head as you would not have to skim it to get the correct compression ratio only to clean it up.

as far as fitting a 240 cylinder head bmcecossie is giving his opinion from his experience that he prefers 240 heads. the problem is that to get a 240 head to fit you need to pocket the block. this combined with the fact that most a series engine tuners including david vizard swear by the 295. generally people go for 240 heads because they can get one in good condition for a 3rd of the price of a similar condition 295. that and they dont mind pocketing the block.

i personally am using a 12g295 because i don't have to take the engine out to pocket the block to fit the head and if i ever want to put the car back to standard it is possible as once you have pocketed the block only 240 heads can be used.

[bmcecosse]

940 head - and no block pocketing involved!

[coopdog]

so whats the difference between the 295 and a standard 998 head?

[lapider]

not completely sure but i think its something to do with bigger valves and a smoother outer profile on the cylinder which aids the fuel and exhaust gas movement in and out of the chamber. if you look in the yellow bible vizard compares all the cylinder heads and shows the different pictures and profiles of the head

[twrminisport]

Bigger ports and valves and better flowing basically.

[Cooperman]

so whats the difference between the 295 and a standard 998 head?

The 295 is what is known as an 'open chamber head'. This means that the edges of the combustion chambers do not shroud the valve edges as they do in a standard 998 head ('closed chamber head').
The 295 is a very well-regarded head for a 998 so long as the compression ratio is checked and the head skimmed as necessary.

[jakejakejake1]

Im sorry if I have missed something but doesn't OP state that he has a 1275 engine, and that he has swapped out the 998. Because surely if this is the case than the 940 head would be the head to use.