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MG Midget and Sprite Technical - BMW motor bike Cylinder head for A series.

Anybody already done or considered doing this?

"This kit contains all of the used BMW motorcycle parts usually required when converting your A series engine to the BMW K series DOHC cylinder head and fuel injection, eg: head, cams, valves, rocker cover, injectors, throttle bodies, throttle position switch, fuel rail etc. Kits can be tailored to your requirements eg. with different cams, or without injectors if you are using carbs. Please call to discuss your requirements. Parts are supplied in unmodified, used condition with a limited 6 month warranty. We can also supply any additional new BMW motorcycle parts you require for the job e.g. valve stem seals, shims, studs etc. A 10% discount will apply to any new parts bought at the same time as the kit. We offer full after sales advice and support in regard to the BMW side of the project. Companies such as Specialist Components can supply the special (non BMW) parts and Mini expertise required to complete the project e.g. cam pulleys, seals, belts and head gaskets of varying thickness to alter compression. All of the combustion chambers were designed to work with flat top pistons. All heads have valve seats suitable for use with unleaded fuel. This is the two valve per cylinder head. It was designed for a 67mm bore. Advantages over the 16 valve kits include low cost, simplicity and ready availability. Valve clearances can be adjusted without removing camshafts (shims on top of buckets) using valve shimming tool our part no. TOA14020. This head may be better suited to road cars and turbo or supercharged applications. The bike engine it comes from is rated at approx. 90bhp."

Lawrence Slater

Toby was/is doing it. Don't know how far he's got.
Dave O'Neill 2

Considered it, K series was cheaper.

Specialist components are the people doing it, when I looked into it there was a couple of hundred quid involved in machining the top of the block to get the K100 head to fit. It won;t fit under a standard midget bonnet either.

I bet it's cool though, but by the time I'd priced up the whole conversion, the K series was a much cheaper option and with proven reliability. They claim 127bhp out of their twin cam 16V head, which I guess is a bit much for a standard A series bottom end. Even the 90 bhp one will be stressing the ribcase gearbox some, meaning a gearbox conversion has to be added to the price.

It would be attractive to have a more modern headed A series. But I can't see it being better than a K :p
Rob Armstrong

I bought the manual from Specialist Components.

The finished item looks very impressive, but in my opinion its very complicated in comparison to fitting a Rover K series.
You still need to rework ancilliaries manifolds etc plus to get any major benefit you have to spend a lot on uprating the bottom end of an A series.
It does feel like proper engineering though. Overall, I really liked the idea, but doubted my ability, perseverance and funding to finish the job. But hey! Thats me all over ;)

M Crossley

Hi all, thanks for that.

The ebay add caught my eye at 240. But I guessed it would cost a lot more than that in the end. So ta for confirming my guess.

I agree, not worth doing on it's own and if end result is expensive compared to k series implant, then might as well have a full modern K, rather than a halfway house hybrid.

But, if it were cheap enough -------- ?

Lawrence Slater

Toby has the engine completed and it looks stunning but I think that the arival of a baby has meant that the completeion of the rest of the rebuild has had to be curtailed. Perhaps he might stumble across this thread and update everyone
Gary & Gaps

I think the true attraction for this set up, is the guy that just wants to build it, cause its a cool concept, the big draw back is you got a modern head on a weaker lower side at the end of the day, its still just a 3 main engine, but wow on the cool factor, if i had the space and funds, id certianly build one... It looks like a fun project... And ripe for future devolopment

I understand that Toby has stalled on the plumbing, not because he can't do it but because "other life" has taken over for a while.

As Gary says the engine looks wonderful, Toby will probably be getting on it again soon.

W O N ' T Y O U T O B Y :)
Bill 1

The K100 conversion was developed for Minis, where a K-Series or other conversion is very tricky due to the limited space.

I've seen some pretty well done big engine Mini conversions, but you basically have to space-frame out the whole front to achieve it. A couple of the conversions I've seen with K100 16-valve head can achieve about 160bhp, and it is one of the simplest and cheapest ways to achieve big power, due to the complexity of other options.

But, a K-Series or Zetec will produce more power and be less stressed in doing so where there's space - it's a bit of a 'needs must' case with the Minis.

Agree that a 160bhp conversion will involve a great deal of expense in terms of mods to the ASeries block, gear-box swap etc

I think it's great to have an option to retain the Aseries block for those purists... on the other hand, the cheapest Kseries conversion to date cost only 120 all-in (to put that in context, I've put nearly 100 of petrol into my other car on one occasion!!).

To achieve this exceptional low cost, he used a 1.4 SPi Rover Metro engine (approx 90bhp), and original Midget box and has since recorded 0-60 in 7.9s.

Anthony Cutler

This thread was discussed on 11/10/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.