13 replies to this topic

[Matt Zane]

I'm interested in fitting a 1275cc A+ head to my 1000 I know that the head needs to be skimmed by 90-100 thou to bring up the compression, but the thing is what about the bypass hose?

If i buy a head from an a+ engine is there a simple job of getting it modified and dropped on, or will the a+ head simply not fit a standard a-series?

Plus will a 11 stud head fit on a normal 9 stud engine, without putting extra studs in?

[minimanclive]

To fit a 1275 head on a 1000 engine you'll need to pocket the block to stop the valves hitting it.
You can make up an alternative to the bypass hose. I've got a take off under the thermostat housing (like a Metro one) and that feeds back to the bottom hose to give the bypass.

The A+ head will fit OK. I don't think any of the A+ heads were 11 stud. Certainly the MG Metro wasn't. But an 11 stud head will fit a 9 stud block OK.

[clubman katie B.F]

have done this a couple of times. i just drilled the heater take off hose on the left hand side of the block. the two threaded holes are there for the heater thingy anyway. otherwise, am sure it is no different

[royallingham]

You do NOT skim the 12g940 head when fitting on a 998 - the CR will be high as it is ! You can either make pockets in the block - OR get someone to sink the exhaust valves into the head by 4 mm. Sure - this loses a tiny bit of power - but the gain from the 940 head will far outshine this slight loss. It's just an easier way to use the head without modifying the block. Be GLAD there is no bypass hose - either get a Metro water pump with no hose connection (only about £10) or - find a way to block off the hole in the existing pump. The bypass hose was/is a constant source of misery for A series owners for years and years - at long last Rover realised it is a waste of space and got rid of it ! Either keep your heater tap open all the time - or drill a couple of 3 mm holes in the rim of the thermostat to allow ater to circulate. And of course - you must use a 1275 head gasket - and the 1275 rocker gear because the valves are set on diffrent pitches. You CAN re-align/shim your 998 rockers to suit - it just takes a while !

[dklawson]

I'm curious about the bypass hose statement above. I have a 12G940 and it has a bypass connection. Was this dropped on later castings?

[Dan]

Make that 6, 6mm holes in the thermostat. You need to have roughly the same area of hole as the cross section of a 1/2" pipe. Or you can fit one of the later sandwich plates under the thermostat which has a hose outlet and plumb that into something. It is quite important to use the heater outlet at the traditional end of the head as well though. There is a plug made to cover the water pump bypass inlet available from most of the specialists.

[Matt Zane]

what about the 12g295 cylinder head?

that needs skimming right?

I assumed that was a 1275 head, is it better or worse than the 940?

what exactly is pocketing the block? can i do it myself or do i need to get the block out?

and I have experience of bypass hose hell a friend of mines midget was blowing bypass hoses on average of three a week before he got the problem sorted

[dklawson]

The bypass hose doesn't have to be an awful thing. If you have either the head or water pump off you can use a piece of high-quality 1/2" ID heater hose to replace the stock item. It's cheap and you can even buy hose reinforced with Kevlar to make the bypass hose last a lot longer. The flimsy repair hoses made with the accordion pleats have a terrible reputation for short lives.

EDIT:
Sorry Matt... didn't mean to ignore your question. The 12G940 is a 1275 head. Pocketing the block is making a little spotface/flat-bottom counterbore on the top surface of the block to clear the valves when the larger bore cylinder head is installed. It's best done by a machine shop (isn't your word for that "engineering works"?). The depth of the pockets must clear the heads of the valves taking into account whether or not you're running a high-lift cam or something other than standard ratio rocker arms.

Edited by dklawson, 19 July 2005 - 02:24 PM.

[Matt Zane]

Thanks DK

I'm thinking that I just want some extra power from my 1000 but i'm not really keen on removing the engine, as my plan is to get my car on the road and run it a bit while building up somthing that'll blow your pants off, so I don't want to have to whip the block out and get it machined just to gain a bit more power as thewhole unit will be out in 6 months.

so with that in mind do people think the 9 stud 12g295 will be the more viable head for my pimpmobile?

or is there no way around this with out a load of machining?

[Leonard]

the 12g295 is from a 998 cooper, and fits any 998 engine, but something has to be done about the compression ratio, although i cant remember what

[bluebottle]

the 12g295 needs skimming when used with a standard 998 engine , to get the compression up. on the original 998 cooper they has flat top pistons with a 'd' shaped raised section to get the compression up.

[royallingham]

12G295 head - if you can find a good one - will need about 80 thou skimmed off. It's not as good as the 940 - but better than standard. As I said earl;ier - just get the ex valves sunk into the 940 head - and use it.
6 holes in the stat and it will NEVER heat up ! 2 x 1/8" is fine. Indeed in winter I have a higher rated stat with NO holes - makes for a great heater !

[miniman5]

i tihnk you will find youle get valve slap or i think thats what its called! thats where the valves hit the pistons and get smashed to peices!

[philster]

Fit the 295 the 940 is okay on a race engine but a cheap compromise for the road and not the best option imo.
Oh and if you drill 6 holes in the stat it'll never get warm on cold days (as roy said) If you're gonna drill holes you only need to let the same amount of water through as the by-pass or better still don't bother and just leave the heater tap open all the time or if you can keep the by-pass hose and just fit some decent hose to it.

The 295 will need skimming a fair bit to get the compression right but will be less messing than pocketing the block, also you may need to file a bit off the top pulley as it can catch the bottom of the head but best just to try it and see if it fits.