Which A-series?

[chrisryder]

Hi there, I've got a project in my garage that will be a fairly tamely modified 2-door. 5 speed, discs, teles, alloys, the usual easy bolt on stuff. But i'm torn with engines. I've got an MG Midget to break for its engine, 5 speed, and diff. It's the 1275 engine which currently pours a fair bit of oil down the side of the block, hopefully just the head gasket. it runs, and it's mot only expired a few months ago, so it's perfectly useable.

I also picked up a 1098 Midget engine, engine number starting '10CC', which makes it the larger main variety i believe. This engine has done 0 miles, only ever run on a test-bed from when it was tuned (supposedly by MG themselves) when it was bored out to +060 (so it's 1147cc i think), fitted with 'Hepolite Cast W Type' pistons, that normally have 5 rings, but had only been installed with 4 (as, according to vizard, 5 rings makes too much resistance). Other mods include a '5A' camshaft which i believe to be from a Mini, which (according to vizard again) improves top end power in an 1100 without too much being lost at the bottom end. The flywheel has also been lightened from 7.1kg (standard minor) to 5.8kg. It originally would have had a 12G295 head, but it came without a head fitted, and just a rusty 295 head missing valves and springs and everything (not much use really). I took this engine apart when i got it, as it had been stood for a while, and to attempt to find out what mods it had. So it would need assembling and sourcing a head to make it useable.

Whichever engine goes in, it'll have an HIF38 carb (to give nice fast flow at the choke area ) breathing through a K&N filter, all fitted on a Titan Motorsport inlet manifold. And will either have a Falcon or Maniflow LCB manifold with a homemade system from there.

So the question is, should I rebuild the 1098 engine with all it's mods (and would you recommend doing anything else to it?) provided i can get a head. Or do I just chuck the 1275 engine in (if i whip the head off, clean up the chambers valves and ports, and fit a new gasket) and run with that?

The 1275 should be torquier as it has the bigger displacement, but apparently the long stroke makes it quite an agricultural way of getting there. With the 1098's larger capacity it should be getting closer to 'squareness' which apparently is condusive to smoothness. But would the 1275 be more reliable than the tuned (more stressed?) 1098?

I've not ruled out the idea of tuning the 1275, and i'm open to throwing the 1098 back together and selling it on to make a quick buck.

You see a lot of 1275's in Minors, a midget 1098 might not turn heads (hardly anyone would notice that it's not just a minor 1098) but at least it would be different!

Just looking for a few differing opinions if you wouldn't mind

[chrisryder]

Oh, by the way, i'm not looking for out and out power, it'll be an every day car so i want it to be useable, and happy to cruise on the motorway (5 speed and midget diff should see to that hopefully). I'm looking for about 75-80bhp, then i should have 100bhp/tonne, and that'll keep me happy

[Mogwai]

I would personally go for the 1275 as 70- 80 bhp is not difficult to achieve & will still be road friendly whereas to get the same power from the smaller engine will make it a lot more peaky
my 1275 was measured about 90 bhp on a RR session, has a good spread of power & really wakes up over 2500-3000rpm

[hotrodder13]

was urs a standard 1275 ??
cheers tom

[Mogwai]

not quite but nothing to radical. still std bore but with a Kent 266 cam, have worked the ports/ chambers etc in the head & fueling through a hif44 /maniflow exhaust system

[chrisryder]

hmm, camming the 1275 sounds doable. if i built up the 1098 and sold it i'd easily afford to mod the 1275. does the cam still drive low down the revs ok? not too lumpy?

and may i ask if your cam was expensive?

[Mogwai]

Its on the milder end of the choice if performance cams so is quite tractable low down & idles smoothly. other factors that will affect this will also depend on what you do to the head. Whatever your budget or how far you want to go maybe worth concentrating on that first

I got the cam from minispares along with a load of other bits I needed. some of the cams come as a kit with followers & springs so may be worth looking at if you go down that route.

[hotrodder13]

how can you tell what cam is in a engine ?

[chrisryder]

the vizard book helps, mainly in identifying standard (bmc production) camshafts. a lot depends on lobe width, rings on the shaft, and numbers stamped in the front face (the face you would see in the middle of the timing chain gear if you took the timing cover off). It's been a while since i looked at the Mini cam that came in my mg 1098, but i recall that had 5A stamped in the end.

[bmcecosse]

I've no idea what a '5A' cam is........ and the 1098 is longer stroke than the 1275! If the 1275 is in good condition - use it. Oil down the side is unlikely to be the head gasket...........maybe just the rocker cover gasket ?? For either engine an MG Metro camshaft would be ideal.

[chrisryder]

the 1098 is longer stroke than the 1275

i assumed, i've never had a 1275 apart. i had always thought that all the bores were largely similar and that the extra capacity was made up by stroking. but it makes sense now, as 1275's need larger head gaskets so they must have considerably bigger bores.

I think i'll go for the 1275 then, and i'll keep my ear to the ground for bits to tune it. is suppose the HIF38 is plenty? or will it stifle it at higher rpm?

[Kevin]

Just a thought but quite a few 5 speed gearboxes fitted to modified cars keep the 4.22 diff ratio as it gives a good performance with the new gearbox ratio's, but with the midget diff it might stunt the performance so I would try it without the diff upgrade first and you can always try the other diff later.

[chrisryder]

i want the car to be happy on motorways. i drive a mog with standard running gear, but slightly smaller wheels. and it's so out of puff on the motorway that i only got a mph or two faster than the lorries on the road. i know the right size wheels would help. ok a 5th gear gives me a slightly better top end, but the midget diff would help that too. i'm not after out and out speed, but keeping the revs down at a sensible motorway speed will keep it quiet, use less fuel, and put less strain on the engine.

the midget, with it's engine and diff, would have had (effectively) a minor box. so that diff can't be all that bad with the extra grunt of the 1275.

technically the midget diff would hinder acceleration, but if it means i can go faster in each gear, that can improve acceleration. that only works to a point. a very low ratio would indeed have a negative effect on acceleration. but it's just as important to have the right gearing for your engine.

i understand what you're saying, as the minor diff is still in my casing then i might aswell give it a whirl with that diff first, see how i get on. but i can see myself changing to the midget one after not very long. i'm almost considering putting the midget diff in my every day car just to put the legs back on it. the engine is tuned, and in flies up to 60 like a scaulded cat, so it would cope with the more stretched out gearing the midget diff would give... but that's another story!

[bmcecosse]

For a decent 1275 you will need an HIF 44 (or HS6) carb. Yes - put Spridget diff in your normal car. Fitting a 5 speed box won't make much difference - it won't go any faster because it will run out of puff in the 5th gear - but it will drop the revs back although you will then have to run with wider open throttle to maintain speed. And you will likely have to change down to 4th for M/way hills........
Interestingly you could put the 1098 crank in the 1275 block (and machine down the 1275 piston crowns slightly) and get something like 1330cc - going up to ~ 1400 cc with an overbore..... Trouble is - the cylinder head still limits the max power - but low rev torque will be much better!

[chrisryder]

i guess that only works in my case as i've got the 2 inch mained 1098. a very interesting proposition, hadn't crossed my mind. darn, now i've got more options!

i suppose it's also possible to put the 1275 crank into the 1098 block, and have a lower capacity engine. as that would have a shorter stroke, which could make it smoother too. only trouble is, the pistons wouldn't reach the deck so i'd have p*ss poor compression... ok maybe not such a great idea!

thanks for your wise words

[chrisryder]

Been thinking about that crank swap idea today. Sounds good, but it would effectively use up two engines. if i put the 1098 crank in the 1275 i'm left with a 1098 with no crank. As i said before, i couldn't really put the 1275 crank in the 1098 block as the pistons wouldn't reach the top! I suppose the only way i could do that would be to fit 1275 pistons in the 1098 block. effectively turning that into a 1275. that would ofcourse require a hefty rebore of that block. would it cope with such a big bore? and if i was to go to that extent i would just aswell keep the cranks in their respective engines, and bore the 1098 to take 1275 pistons and face them down as you say!

so unless i find that the 1098 block is scrap (which i doubt) i think the cranks will stay where they are. i dont know whether to build up that 1098 and keep it in stock as a spare though. aren't they worth a bit?

[bmcecosse]

Oh yes - I was just pointing out the possibilities. Build up both engines into working order - the 1098 is not really 'valuable' because most Spridget owners would rather upgrade to the shorter stroke (= higher revving) 1275 engine...... However it is a 'stronger' version of the 1098 and so will fit in a Minor etc and still retain the original capacity but with the potential to take a bit more stick than the standard engine ! I think at the time some of the Competition classes (including Formula Junior ??) were for engines up to 1100 cc - and so this was the engine BMC hoped would be used. The block was also the basis of the original 1071 cc Cooper S engine which for similar reasons was aimed at the 1100 cc class...... It was then short stroked to 970cc (with longer con rods) and then long stroked to 1275cc ( with extra 'meat' on the deck to accept the longer stroke).....as the Competition classes evolved into 1000cc and 1300cc limits.

[chrisryder]

learn something new every day! i think i will just build up the 1098 and keep it in stock. we run so many minors, we're bound to need a good 1098 one day. and you could bet, as soon as i sold it, i'd find i need it!

i think i'll do as Mogwai said, and stick a 266 cam in the 1275. I've found the kit on the mini spares website. not as pricey as i feared! I was thinking i could run with standard cam for a bit and put a cam in if i felt it needed it. but is the midget block that doesn't have tappet chest covers?

i'll breathe on the head as per mr vizards advice too. any other good mods i can do that'll make it a bit better but keep it reliable?

[bmcecosse]

Not really familiar with the '266' cam - i prefer to stick with the BMC/Rover cams. So I would go with an MG Metro cam. It is better to do the cam swap while you can turn the engine upside down - but it can be done in situ. Timing chain with tensioner is the way to go. Otherwise just build it up carefully. Start with a big valve head - one on ebay at the moment but not cheap...... I used to pick these up for £10 to £20 !! Not now though.......

[chrisryder]

I may know of a big valve head i can put my hands on. a friend of mine swapped it for a different one, as the valves were so big he couldn't get unleaded seats put in it! though you're about to tell me that unleaded seats aren't worth it, and to set my inlets to 12 thou and exhaust to 15. I'll give him a call and see if he's still got it