Hi all,
I'm about to embark on a full service of my 948 - this includes changing the head gasket.
My question is is there any benefit in putting a 1098 head on a 948? I am aware of the 12G295 mod but i have a redundant 1098 awaiting rebuild.
Also - will the valves need sinking - like the 12G mod, or is it a straight swap?
Ps- am thinking of swapping to a 1098 cam as well, I understand the 948 cam is less productive. Same question really, is there any benefit and will it need any work to fit?
Thanks in advance
The cam is well worth swapping- and the head, BUT you will need to have it skimmed by 60 thou first..... And no valve problems. Also use the better 1098 inlet manifold - that's if you haven't found a Mini one and the larger carb to go with it - or even better - an alloy manifold with no 'hot' spot...
Thanks BMC - I guessed it might be you that replied first
1 more question - how 'thick' should a standard 12G202 be then - so I know if mine has been skimmed before.
Bit of a hitch with the manifold/carb. The 1098 I have was in a 948 style minor, so it came with an odd mix of 948/1098 bits. It has a 1 piece cast manifold, but I think it has a 1/4 inch SU on it, it is certainly the same as the one on my other minor (948) and the spare I have. Luckily I'm off to our local scrappy soon, so should find something adequate
Correct! If the manifold is 'one piece' ie NOT bolted together then it is the slightly better manifold. If you want a larger 1.5" carb then you want a Mini manifold. And as before - an alloy unheated inlet manifold with 1.5" HIF 38 carb will be much better - but not inexpensive these days unless you fall lucky.......
Bringing up an old thread
About to do this swap, just need to fit larger (8 inch) drums and overhaul the 202 head.
Can I ask why the head needs 60 thou off it? Is it because of the compression ratio? Just it's a fair old whack to take off and makes it difficult to use on a 1098 in the future
Last edited by chesney on Sat Dec 01, 2012 10:18 pm, edited 1 time in total.
1098 head (12G202) has 26 cc combustion chambers as standard. The chambers in the 948 head are around 24 cc as standard. Swapping heads with no skimming will drop the compression ratio.
Will the drop in CR make a difference? All cylinders at around 150 on a 950 engine. I don't know much about these things, but will 2cc per cylinder outweigh any performance gain? Ta LiamMonty
Just done 'the Maths'- it's actually 1.6 cc difference between the head chamber sizes according to Vizard (24.5 cc on your current head, 26.1 on the 12G202). Your engine should, as standard, be 8.3:1 CR. The extra 1.6 cc chamber volume would take that down to 7.86:1, which isn't that much higher than the low compression engines in LCVs and some cars (7.5:1). I think these engines were about 5 bhp less than the high compression ones. If your engine has 150 psi compression, it sounds as though it's in OK condition, and to be honest, unless you were going to skim the new head before fitting, I wouldn't bother with changing it, as I reckon you'll lose more power than you gain!
One of the main reasons I'm changing it it because it has a temperature sender as standard. I had no idea fitting a 1098 head would be so prohibitive to power! It will be skimmed as a matter of overhauling it but 60 thou is a lot!
It's no trouble- I've just had that much taken off a 12G295, and I had 100 thou taken off another 295 head a couple of years ago without problem. Worry not! The 12G202 heads are 10 a penny should you ever want to get another to put back on the 1098 engine.
I could do with some 8" brakes for my 'warmed up' 948, but they're getting harder to get hold of- I reckon everyone else has had the same idea too! Hope you find some OK.
You've just made me feel old at 36 (though still younger than quite a few MM owners ). I think the insurers will be OK- you're just making the car more like a 1098 car, which would cost the same to insure. I changed the engine in my old Series II about 6 years ago (after the 803 blew...) to a 948, and the insurers weren't bothered, as it was still a standard Morris Minor spec (albeit a 948 one!). I think you'll be fine. TBH, I wouldn't think it's necessary to declare the head change to the insurers, though I don't know the legalities of it- you'd only be talking a couple of bhp improvement, and it's still going to be well under the 'power' of a 1098.
liammonty wrote:You've just made me feel old at 36 (though still younger than quite a few MM owners ).
Agreed
I think I'll call the insurers and see what difference the brakes make. If they say no, or add a huge amount to my premium, then i'll forget it, but as you say it's unlikely
I hear what your saying about the cylinder head too - the only external difference is the temp sender (?) and anyone can tap one in. In fact, all our moggies are a long way from being new, so for all I know it could 'always have been there' and I'm oblivious
Cheers!
Do what you think is best but don't confuse the issue by telling someone who may not know the ins and outs of what you are doing, you'll then open a can of worms! You don't want them wondering if it's a tuning thing for example. why not pm Dave from fj and see if he thinks it's an insurance issue.
Apologies if that's how it came across,it is the only spare head I have and if it is to be fitted it may as well be fitted to its best advantage. Wasn't aware of Dave from FJ - will search his user
No apology necessary, I was just thinking if you told the insurer they may not fully understand that the different head was no big deal and then maybe make more of it than need be
). I think the insurers will be OK- you're just making the car more like a 1098 car, which would cost the same to insure. I changed the engine in my old Series II about 6 years ago (after the 803 blew...) to a 948, and the insurers weren't bothered, as it was still a standard Morris Minor spec (albeit a 948 one!). I think you'll be fine. TBH, I wouldn't think it's necessary to declare the head change to the insurers, though I don't know the legalities of it- you'd only be talking a couple of bhp improvement, and it's still going to be well under the 'power' of a 1098.