Converting a 998 Cooper to 1098 – would you??


  1. imported post

    In my time during the 60s and 70s I hadnumber of BMC cars – Morris 1100, MkII Cooper, MkII Cooper S and several Clubmen. The 998 Cooper was the best and most free-revving.

    (My S in 1969 was El Paso beige EVX 898H which is still on the road,if anyone admits to ownership?)

  2. On the back of another thread…….. I've had a couple of 1100 engined Minis and they were very good. One (the original 618AOG when it was a red/white Cooper rep) had a low mileage 1100 Clubman Estate engine and box. I fitted a skimmed Cooper head (12G295) and rejetted the 1.5 inch SU. It went very well indeed and was pretty close to a stock 1275GT. It revved well and I never found any of the higher rpm roughness.

    So – if you were rebuilding a 998 Cooper engine – would you fit a 1098 crank and pistons? You would never know from the outside as the blocks are the same. Personally I would do it for the extra torque and 1098 Midget pistons are still available from places like Brown & Gammons for about £150 a set. I think these were flat top.

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    1) I had exchanged my1098cc for a 998cc Cooper as the old unit was using a lot of oil (2 liters on 600 km or something like that) but I wanted to have similar power/torque. In the end, the 998cc Cooper performed a lot better than the 1098cc unit. It was built up with a single HS4 (Inno 1001 Specs) and A+ gearbox with 3.1 final drive but standard for the rest. It went like hell and could reach 160kph and 6700 revs in second gear.

    2) I don't think that 1098cc crank and pistons will immediately fit a 998cc block. Since the stroke is longer, you will end up with the pistons comming too far out of the bores when at the top dead point. You would need other pistons that have a shorter distance between the pin and top. Some have suggested that Hillman Imp pistons would do the trick.

  4. imported post

    Thanks for starting this thread 618AOG.

    I went to pick up a 1100 crank yesterday for sticking in a 998 engine.

    When I went to pickup the crank i not only got that but the rest of the engine too (clubman 1100). It has had a rebore done not too long ago, new pistons fitted (not flattop) and the crank was ground and balanced too.
    I wanted to check the condition so everything came out and looks very clean and new.

    But like mentioned the pistons are different for a 1100 engine. The crown height is smaller so the pistons don't hit the valves.

    In comparison to the 998 crank a 1100 one has a bigger stroke so revs should be less.

  5. imported post

    The 1100 crank is supposed to be the weakest part – but in reality they are fine. Doing 6700 in any road going A Series is asking for a blow up.

    A 998 will not outperform an 1100. It's 100 cc down for a start and there is no substitute for cubic inches. A standard 1100 has 48 bhp compared to 34 bhp of a 998. The torque is also a lot better and it's torque that really accelerates a car, not bhp. The 55 bhp of the MG1100/Midget/Riley Kestrel is about right but 55 bhp from a 998 Cooper is optimistic. More like 45-50 bhp, yet BMC claimed 55bhp for both.

    Very early Austin/Morris/MG1100's used overbored 850 blocks and some used the horrid pinch bolt conrods. From 1963 when the 998 Elf/Hornet arrived the 998/1098 had it's own block. The 998 was arrived at by combining the bore of the 1098 with the crank stroke of the 948 Minor/A40.

    The 1100 crank has the same stroke as the 1275 so it's hardly excessively long. The later thick tail cranks are very tough. Properly built, an 1100 will take 5500-6000 rpm without drama. In a Cooper I would be using the extra torque to pull a 3.2 or perhaps 3.1 final drive.

  6. imported post

    [b]618AOG wrote: [/b] “The 1100 crank has the same stroke as the 1275.”
    Stroke for 1098cc is 83.72mm and for 1275cc it is 81.33mm.

    I should have pointed out that my comparison between1098 and 998 Cooper was for the old tired 1098 and the brand new rebuild 998 Cooper. Indeed, the torque was consumed by the3.1 final drive and I think that it was around 48 – 50 bhp.

  7. imported post

    here is what keith has to say about the matter:


  8. imported post

    Mini4Ever wrote:
    “I should have pointed out that my comparison between 1098 and 998 Cooper was for the old tired 1098 and the brand new rebuild 998 Cooper.”

    So an utterly useless comparison then……………:D

    My Mini book is wrong as it lists the 997 Cooper as having an 83mm stroke. I didn't think that was right, but I've no other reference. Thinking back, the 997 and 1275 have the same stroke with the 997 havingf a stupid small bore.

  9. imported post

    I am a great fan of the much underestimated 1100 engine. Which is in my opinion by far the best all round small bore A series of the lot.

    It will of course NEVER outperform any of its big boire brothers, but if you are prepared to do a carefull build using sensible well known mods you can end up with acomparitivley powerful, economical, fast road engine for a Mini. You will lose some smoothness when compared to the 998, but the torque you gain more than makes up for this.

    If you are looking for a bit more power than is atainable from a 998 using SENSIBLE tuning mods, then the 1098 is in my opinion the way to go. I look forward to following your progress.

    Good luck,


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    Have got the 12G295 head to go on it, my mistake then.

    The engine will go in my daily driver to run it in and after that will go in an other project.

  11. imported post

    I used a 998 Cooper for one year and 5000 miles, and it never held up any traffic.

    The 998 auto Mayfair I also use is also caned.

    With the news that speed limits are to be reduced on country lanes to 50mph, and 20mph in villages, there's even less need to tune cars.

  12. imported post

    I have decided to use the 1100 block and parts for the build.

    In the meantime I have an SW5 cam for it and and a set of twin HS2's. The head will be a standard 1100 head, all will be sitting on a rebuilt gearbox with a 3.1 FD
    Maniflow LCB with an RC40 exhaust.

    Any suggestions and/or remarks are welcome.

  13. imported post

    has anybody got the specs that speedwell used for the 1152 conversion?
    this was one of their options as anupgrade from a 850 or a 998.
    A copy of the info sheet sold only recently on ebay and I got outbid 🙁

  14. imported post

    [b]masnarda wrote: [/b] “has anybody got the specs that speedwell used for the 1152 conversion?
    this was one of their options as anupgrade from a 850 or a 998.
    A copy of the info sheet sold only recently on ebay and I got outbid :(”
    mk1's site is usually the place to go for stuff like this. Haven't confirmed it, but try here: [url=][/url]

  15. imported post

    hi Dave thanks for the link, I know Mark has got numerous Speedwell documents online.
    But the back of the specs sheet isn't online which contains all the technical details.

  16. imported post

    Just had a look, confirm spec sheets as listed only have front page. However, did you check the '64 catalogue pages? Try under 'Complete engines' and 'Price lists'. Complete engines seems to indicate why Mark didn't bother putting in page 2. Price list seems to list all parts and machining operations but doesn't includethings like cam specs, presumably so that competitors had to at least buy one to find out what it was!

  17. imported post

    You don't need a speedwell build sheet. 1152 is @ a +60 rebore on a 1098. You just need a 12G295 head, a cam of around 270 degrees (although a 285 will really motor), around 10.0:1 compression – I would stick with the 1 1/4 SU's as well to start with. No reason why it won't do 70 bhp with plenty of torque.

  18. imported post

    Back in the seventies I used to mess a lot with minbins, doing engine swaps and a bit of tuning. :cool:Engines I tried were 848, 998, (basic and Cooper),1098, (basic and MG), and 1275S. The sweetest and smoothest, (but not obviously the most powerful), were both versions of the 998. My friend's dad had a mini van with a 998 so smooth that it would tick over all day so slowly that you thought it would stall. :). Only thing I cant figure is why, having brought out the 1098 in the big saloons in 1962, BMC went onto de-stroke it to put in the minbin, producing less power. I'm sure I,ve posed this question before on other forums. Does anyone have an answer? Steve.

  19. imported post

    thanks for finding me the info 618AOG!

    Am progressing quite well, carbs have been rebuilt, engine has been cleaned (it's in my living room) pistons have been fitted.

    still need to order the oil pump and cam followers, head needs to be converted to unleaded too.

    gearbox is going to be rebuilt in two weeks

    will try to post some pics soon

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