Are you using a 12G940 head?

[Peetee]

Is anybody out there using a 12G940 head on a 1098 engine without pocketing the block?
I know most people say it should be done but I'm sure somebody a little while ago said they were running one 'unpocketed' without a problem.
I've reached an impasse you see. No more available funds, a cracked 202 head (that I just spent hours gas flowing ) and a spare 12G240.
Alternatively does someone know what the max valve lift would be for this set up. I could check this against the space available just in case it has been skimmed in the past.

[ianselva]

Are you running a standard cam and rockers ?

[Peetee]

Yes, everything componant in the engine will be standard 1098cc with the exception of the cylinder head.

[ianselva]

I'll check tonight and let you know tomorrow

[rayofleamington]

I ran a 12G940 on a standard 1098 without pocketing the block. I ran it for 11 years (approx 60,000 miles) without problems.
The 12G940 is not really just one head as there are different variations of it but they should have the same valve size and valve position. To get away without pocketing the block you have to check the distance between the valve and the gasket face. On my head it was fine but on other 12G940 heads you could need to get the valves (or seats) cut back so that the valve can travel further before it reaches the block. Also if the head has been skimmed the valve is then closer to the block...
Therefore you just need to know your cam lift (someone will probably know, and the rocker ratio (which i think is 1:1 for standard rockers), then just check the distance between the valve and the gasket face. If the distance is less than the lift (cam lift x rocker ratio) then the valves will neeed to be recessed untill the distance is more than the lift.
The head gasket adds a bit of a safety factor to make sure there's a bit more clearance.

The 12G940 has good flow characteristics and valve sizes are the same as the much sought after 12G295
The 12G940 has a bigger chamber size, but if you're going to use unleaded fuel, then the lower compression is an advantage (high compression ratio and low octane fuel are not a good combination as this leads to pinking and therefore shortens the engine life).
Don't get me wrong - the standard compression ratio is not particularly bad regarding unleaded fuel but with it being a bit lower you won't be hurting anything.
If you use an fuel additive with octane booster then you don't even have to consider it but if you are like me and like to make savings, the additive without octane booster is cheaper.

[turbominor]

Hi Peetee

I have run a 1098 with a 12g940 with no problems (using a 1275 head gasket)

Best advice i can give it to bolt it down without a grasket, set the tappets tight and turn it over by hand very carefully. You can put a layer of bluetak on the block directly below where the valves would be.

Iain

[Peetee]

Thanks for that lot folks. Basically I'm trying something in order to get the car back on the road asap. Weeks ago I was looking forward to this week to do the work necessary. Then the weather and cracked head came along to spoil the party

[Cam]

(which i think is 1:1 for standard rockers),

I think standard rockers are about 1.25:1

[ianselva]

Standard valve lift is 0.250in at the cam , this is multiplied by 1.245 which is the rocker ratio.Don't forget to add in the thickness of the gasket in your calculations.

[Matt]

peetee I have a 12G202 kicking around and I am in southampton this weekend if you would like to use it for a while.... I might need a bit of a clean tho....

[Cam]

I might need a bit of a clean tho....

What about the head??

[Kevin]

As it blew a gasket last week

[bmcecosse]

The 12g940 head has bigger valves than the 12g295 - even the normal 940 is bigger, and the ones fitted to Cooper S ang early MG Metros had even bigger inlets. The combustion chamber is SMALLER than a 202 head - 21.4 cc against 26.4 for the 202, and the 295 is 28.6 if I remember correctly. So the 940 will give a very useful increase in compression ratio. If you think it's too much then spend a little time grinding away at the edges of the combustion chambers to unmask the valves - particularly the inlets. You really should grind pockets - you may get away with out doing so if the cam is standard. Check with some blue-tack and see how much clearance there is - not much I am sure ! the pockets can easily be ground in with ana electric drill and mounted points - tales longer to seal it all up to prevent swarf getting in the engine, and to clean it all up afterwards than it does to make the pockets. Well worthwhile fitting this head - I have done it several time s before on Minis - you also need the 1275 rocker gear because the valves are on different centres and the old 1098 rockers will not line up correctly. However - you can take it all apart and re-align the rockers, it just takes time and patience. You must do it though - don't just ignore this !! Or you might end up with a broken rocker/smashed valve/ruined engine !! Note - you also must check the head can seat down onto the block without fouling the water pump - often the flange on the pump needs filing down to make sure the front edge of the head has clearance - and lastly - you must use a 1275 head gasket !! Good luck.

[rayofleamington]

The combustion chamber is SMALLER than a 202 head - 21.4 cc against 26.4 for the 202, and the 295 is 28.6 if I remember correctly. So the 940 will give a very useful increase in compression ratio.

Yes sorry - I completely mixed up the combustion chamber size of the 12g295 which is bigger with the 12G940. Thanks for putting up the right info

[Matt]

Kevin, Different head! Cam, our drain is blocked so we are trying not to put too much water down it! (but I did mean the head needed a clean!)