1275 Head on 1098 engine

[bmcecosse]

I tried a 'test fit ' of this on my 1098 engine. It has an MG metro camshaft - but that has the same lift (unfortunately!) as the standard AEA 630 camshaft. Using an old 1275 head gasket (which measured 36 thou thick) , and setting the valve clearance to zero - with a bit of blu-tack on the block I turned it over by hand. there was no obvious tight spot - but it compressed the blu to virtually NOTHING, so thin I could not measure it - but maybe 5 thou. So this fitment is NOT SAFE - with a 15 thou valve clearance there would be only 20 thou between the exhaust valve and the block. And this was a valve that had been reground a few times and was sitting slightly down in the head - where I had a new valve fitted it was sitting obviously higher in the head, and would have made contact. So there are two options - either sink the exhaust valve into the head slightly (at least 20 thou) or make small pockets in the block with mounted points and an electric drill. The first is probably less hassle, but will lose a small amount of power - but at least it leaves the block standard. With a 948 engine using the standard low lift camshaft - it would 'probably' be ok with the head as standard. The head I used had NOT been skimmed - obviously a skimmed head will mean even less clearance.

[turbominor]

think we have done the 12940 on small block engines several times, a fair few of us have ( inc me personaly) dropped them on with no moddification


I think the bottom line is that some people will have no problems fitting it and do many happy miles. Others will have heads that will need to have the valves sunk in or the block pocketed but I dont beleive there is a blanket statment to cover it..

Try it and see is the only way.

I have done 50-60000 miles in a 1098 with a low mileage early Mg Metro head with the bigger pre unleaded valves on a standard 1098 with no problems at all.

[bmcecosse]

I would say you have been lucky ! The Maths says it can't be done - and my measurement gave only the smallest of clearance - and that only because the vlave I measured has been quite heavily reground into the seat. Maybe some head gaskets are a bit thicker than others - that might just make the difference !

[Alec]

Hello all,
I think it is prudent, as Bmc has done, to do a trial assembly and measure the clearance rather than 'chance it'.
When I had to replace a cracked 12g295 head on a 1098 engine, the only readily available head I had was a 12g940 and I pocketed the block. The reason for that was that I had read (Vizard I think and Owen Burton) that it was necessary, so I did it.
It was relatively easy for me to do as I have a relatively well equipped home workshop and can make up a pilot mandrel and stone to do the grinding.

Alec

[wanderinstar]

Turbo,
The question is what cam were you running.I read an article the other day where someone did what BMC has done with standard cam, and got 1mm of clearance. Obviously the cam does matter.

[turbominor]

I had a 1963 1098cc bog standard engine with the original cam with my 12g940 on it and had about 1mm of bluetack left.

I also had a 12g940 mounted on my last 1098 , a standard '69 engine that i had turbo'ed and had no problems with that

[wanderinstar]

Iain,
I think the thing to note with BMCs first post is "MG Metro camshaft". Obviously that gives higher lift than standard cam, this is a road I,m thinking of going down.
Have a 12g295 that I was going to put on standard 1098, but I want to raise CR due to running on LPG, so there would be a risk of breaking into oilway. Was the power increase very noticeable using standard cam?
Eventually will do spare engine up and fit MG cam and pocket block, but until then will try it with standard cam. I do have 1 3/4" on w/heated manifold at moment, so 940 head should make a decent improvement I,m hoping.
Ian.

[turbominor]

Hi Ian

far as i am aware the mg metro cam has the same lift at the 1098 cam just a different profile so the valve lift should not be any different.

my 1098 with 12g940 and mg metro manifold, HIF40 (1.5") and grumpy's lcb big bore exhaust went very well, and would pull to around 90 much better than her original 70-75

I may get shot down in flames but i beleive the 1098 cam was also used in early cooper engine..

[TerryG]

I always thought early coopers were 998s followed by 1071 (I could be wrong). When i was working on minis I was told that you couldn’t fit a 12g940 onto a 998 block without pocketing it. I may be wrong but the general consensus among mini folk is you can’t do it with the block as standard.

[les]

I always thought early coopers were 998s followed by 1071

I'd say you were right, but there was a 997 cooper first, followed by 998, then 's' variants 1071,970, 1275. It may well have been the 997 that used the minor cam.

[bmcecosse]

No the 997 engine had the 2A948 cam,(and the '948' bit is nothing to do with the 948cc Minor engine !) - and this excellent cam was never fitted to any other A eries engien as standard - but it beame the common upgrade for all engine tuners !! For some strange reason the 998 that followed ( a much better engine) had the slightly less timed AEA 630 cam - same as fitted to 1098 engines of all kinds. A different camshaft with this same timing and lift was fitted as standard to all the Cooper S engiens - but this was just a ruse to keep the warranty claims down - by limiting the revs the engine would pull !! The first thing any 'tuner' did was to upgrade the camshaft and fit twin 1.5" SUs. The MG Metro cam has the '948' inlet timings - with the more widely timed 'Rally' camshaft (731) exhaust timings. Unfortunately the lift is exactly the same as the '948' and '630' cams - but the timings are excellent - and if looking for a value for money cam - this is the one to go for !! The low speed torque is fantastic, and it pulls very strongly to 6000 rpm. The 940 conversion can only be done safely with either pockets in the block - or the exhaust valves sunk into the head by at least 20 but preferably 30 thou.