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BMW K100 DOHC FI head on 1275 block

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twas_brillig

Jedi Knight
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I've just run into the above swap (installing the cylinder head from a 4 cylinder 'K' series BMW motorcycle onto a Spridget/Mini block, to get either 8 or 16 valves and double overhead cams and fuel injection/carbs) - does anyone have any first hand experience or can suggest additional web sites?

There are two suppliers of kits/full engines that I've found:
Specialist Components in the UK:
https://www.specialist-components.co.uk/cnb/shop/sconline?op=merchant-welcome-null
Morspeed Performance Tuning in the UK:
https://www.morspeed.co.uk/latest-newspage.htm

There's a nice photo of an installation in a mini about 3/4 of the way down on this web page:
https://www.miniregister.co.uk/200703TheRegister.html

Specialist Components sells their installation guide separately for about 20 pounds; Morspeed outlines their installation at:
https://www.morspeed.co.uk/Build%20guide%20page1.htm

I dropped a note to Specialist Components asking if their installation would fit under a Bug-Eye bonnet without modifications, and they replied:

"Thanks for the enquiry, as far as we know it will, it certainly fits under a Midget bonnet. We don't know of anyone who has done this conversion on a Frogeye Sprite yet, but the K100 cam cover is only 10mm higher than a Minispares rocker cover on a 5 port engine, so we can't forsee any problems with clearance."

So I'm dreaming of winning a medium sized lottery, and getting a 1275 DOHC FI engine with a 5 speed Datsun all synchro box in a Bug Eye with BIG front discs and Lord knows what for a rear end! (Specialist Components suggest 105 hp with an 8 valve head; +120 from the 16 valve; Morspeed mentions +140hp)

Doug
 
I have no personal experience with the conversion but it is frequently discussed on "The Mini Forum". If you post your inquiry there in the "Problems, Questions and Technical" section I'm sure several people will be able to provide first hand information and additional links.

Basil does not like us providing links to other forums. I hope in this instance he will accept the re-direct.
https://www.theminiforum.co.uk/forums/
 
The K-series isn't a motorcycle engine. It is the engine fitted to the last-gasp family of vehicles from Austin-Rover (formerly British Leyland) which BMW acquired and later dropped, retaining only the Cowley operations and the MINI name.

I think the K-series was fitted to the last Metro as well, although not to the last classic Mini. It came in 8-valve and 16-valve versions, and from 1100cc to 1800cc.

There were probably some significant similarities between the the A-series and the K-series, but AFAIK they are not similar enough to permit head interchangeability. I think a complete K-series replacement of the 1275 in a Spridget might work, but with some significant metalwork.
 
Chris:

This is the K-Series BMW bike engine, not the K-Series Rover engine. Confusing, I know, but different animal.

NOTE: ~Click Here~ to see my post on this subjest last week.
 
<span style="font-weight: bold">BMW K100 Motorcycle engines</span> – In the late 1970s, following several years of declining sales, BMW motorcycle engineers began work on developing a replacement for the aging flat-twin engines. The design team was led by Josef Fritzenwenger and Stefan Pachernegg.

The design team eventually developed a design based on a Peugeot car engine, in which a four cylinder engine was laid on its side across the motorcycle frame. This is known as a longitudinal four because the crankshaft is in line with the direction of travel of the motorcycle. Unlike the flat four engine, however, which is also longitudinal, the cylinders of the K engine were not divided by the crankshaft, as are the pairs of cylinders on the flat four engine found in the Honda Gold Wing.

The original engine has its four cylinders arranged so that the crankshaft is on the right-hand side of the motorcycle, with the cylinders, pistons, camshafts, injectors and sparkplugs on the left-hand side. This arrangement keeps the centre of gravity relatively low, which benefits handling. In addition, since the crankshaft is now on the right-hand side, access to the engine becomes much easier than in a conventional design, where the crankshaft is at the bottom (hence the term "bottom end"). This configuration, although technically not new for motorcycles, had not been seen for many years. It had certainly not been used by any major motorcycle company, let alone one as conservative as BMW, which had been using the flat-twin ever since 1923.

In recent years the BMW K100 2valve and 4valve engines, as well as the later variants the K1100 and K1200 4valve engines, have provided Austin/ Rover classic Mini and MG enthusiasts with a cylinder head that closely matches the bore centers of the age old Austin Rover 'A' series 1275cc engine. In fact three of the originally head studs of 'A' series engine block line up with those of the BMW cylinder head. Miss alignment of the chambers from a 'bolt on' stand point, is only around 1mm front to back, and 2mm end to end. The cylinder head itself needs slight modification so it can live in an upright orientation, and converted to run a sychronous belt to drive the camshafts from the engines crankshaft. The engine block needs further modification to accept the new stud pattern of the BMW cylinder head.

Popularised by a handfull of companies, this conversion has seen power outputs so far in excess of 230bhp by forced induction, from only a 1.3 litre engine. Thats more than 175bhp per litre. Most however are of similar power outputs of the engines these heads are taken from.



<span style="font-weight: bold">Rover K-Series engines</span> - The K-Series was introduced in 1988 by Rover Group as a powerplant for the Rover 200 car. It was revolutionary in that it was the first volume production implementation of the low pressure sand casting technique. This works by injecting liquid aluminium into an upturned sand mould from below. In this way any oxide film always remains on the surface of the casting and is not stirred into the casting structure. This production technology overcame many of the inherent problems of casting aluminium components and consequently permitted lower casting wall thickness and higher strength to weight ratios. The aluminium engine blocks are fitted with steel cylinder liners that were manufactured by GKN's Sheepbridge Stokes of Chesterfield.

The engine was introduced initially in 1.1 L single overhead cam and 1.4 L dual overhead cam versions. The engines were unique in being held together as a sandwich of components by long through-bolts which held the engine under compression. As a result of the loss of Honda engines on the BMW takeover of Rover, an enlargement of the K Series design to 1.6 and 1.8 litres was carried out. This was done by using larger diameter cylinder liners and also increasing the stroke. The change required a block redesign with the removal of the cylinder block's top deck and a change from "wet" liners to "damp" liners. This change reduced the block stiffness and made the head gasket interface unstable.

The two types of head that were bolted to the common 4-cylinder block were designated K8 (8 valves) and K16 (16 valves). A later head design also incorporated a Rover-designed Variable Valve Control (VVC) unit (derived from an expired AP patent). This allowed more power to be developed without compromising low-speed torque and flexibility. The VVC system constantly alters the inlet cam period, resulting in a remarkably flexible drive - the torque curve of a VVC K-series engine is virtually flat throughout the rev range and power climbs steadily with no fall-off whatsoever until the rev limiter kicks in at 7,200 rpm.

By comparison, the V6 engines are more conventional engines that do not make use of the through bolts to hold the head to the block.

The 1.8 litre versions are often used in kit cars and are starting to be used in hot rods, especially as a popular swap into the MG Midget, Morris Minor and the Caterham versions of the Lotus 7.


<span style="font-weight: bold">Honda K-series engines</span> - The Honda K series engine is a four-cylinder otto cycle engine. The K series engines are equipped with DOHC valvetrains and use roller rockers to reduce friction. The engines use a coil-on-plug, distributorless ignition system with a coil for each spark plug. This system eliminates the need for spark plug wires and distributor as well as the problems associated with them. It also allows the ECU to precisely control the ignition timing based on various sensor inputs. The cylinders have cast iron sleeves similar to the B-series engines, as opposed to the FRM cylinders found in the H-series.

Two versions of Honda's i-VTEC system can be found on K series engines; variable timing control (VTC) can be found on the intake cam of both versions. The VTEC system on engines like the K20A3 only operate on the intake cam; at low RPM only one intake valve is fully opened, the other opening just slightly to create a swirl effect in the combustion chamber for improved fuel atomization. At high RPM, both intake valves open fully to improve engine breathing. In engines such as the K20A2 found in the Acura RSX Type-S, the VTEC system operates on both the intake and exhaust valves, allowing both to benefit from multiple cam profiles.
 
Nial - thanks for referencing your last week's note. I thought I'd done a search so as to avoid redundancy (and to profit from other's efforts), but obviously I messed up on the search criteria.

Doug
 
Got dreaming of DOHC again last night...

Has anyone priced out a conversion, using the KAD or the BMW approach?

Anyone know if such a conversion would fit under a bugeye bonnet?

And are there any more DOHC converstions out there (since this thread started in 2009), as I thought a saw a reference to something from Honda.

Thanks,
Doug
 
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