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XK100

XK100

I understand from a recent magazine article that Jaguar recently found 50 four cylinder XK engines (destined for the XK100 version of the XK120, which no one ordered). Anyone have any more information on this find, and what Jaguar intends to do with these engines (I believe they are not complete - only engine sets)? It would be interesting to build an XK100 and see how close it came to the 100mph mark. - regards Jon Garde.

Not a lot of takers on this one, so I rechecked my facts. The article is from the most recent copy of The Jaguar Magazine, and the source is Howard Davies the Manager of JDHT who writes: "...we recently had a startling and very welcome find while clearing out our former engine building plant at Radford which is only several miles from Browns Lane. "When the XK120 was advertised for sale in late 1948 the brochures included the alternative of an XK100 - a four cylinder XK version. "The XK100 did not go into production (the six cylinder 2.4 [sic] litre engine getting the nod), only a few of these smaller engines were built and even less were kept for display purposes - until we discovered 50 engines or engine sets at Radford! "We are not sure what to do with the four cylinder 2.5 litre engines - but we will have a lot of pleasure deciding that!" John Elmgreen - maybe you could check this story out while you are at Browns Lane? Hmmm. In addition to building the mythical XK100, I wonder if one of these engines would fit into a Mark V? Sure to have more power than the two and a half litre Standard engine. - regards Jon Garde.

Jon Garde, I recall seeing the XK100 engine story too, but I will not have time to chase down that sort of detail at Brown's Lane. Maybe when I retire, if by then the story has not already been written. By the way, the new Philip Porter book is apparently in the UK but not yet in the bookshops. 144 pages, c 250-300 pics, should be good. Only UKL 20. - Regards, John Elmgreen

I believe a supply of MGA Twincam engines has just been found! I owned a basket case 1958 Twincam MGA many years ago. You are correct the 4 cylinder version was dropped and my research discovered Jaguar sold(?) the engine to Morris Garage. It was used with MG embossed cam covers for the production Twincam MGA's. I believe it would not be suitable for a Mark. - L J Haithcock, S830794DN, XK-150S OTS

My recollection of stuff I read 20 years ago is that MG bought the twin cam head design from HRG who were more or less defunct. I would be surprised if it had any parts in common with the XK100, which was probably based on a Standard engine layout. - regards, Mike Morrin

Well, this sure is news to me - but unfortunately not true IMHO. My MGA Twin-Cam engines are DISTINCTLY UNLIKE like the pictures of the XK100 engine that I have seen and are UNLIKE the Jag XK engine. Also, just about every MGA history book (for whatever that is worth) goes into great detail on the development of the Twin-Cam engine and doesn't reveal any DIRECT Jag heritage. Yes, the basic concept of the Twin-Cam engine follows the pioneering XK engine (as well as some others) and may even have benefited from some reverse-engineering of the XK100 engine (and the production XK 6-cylinder engine). But, the Twin-Cam engine has a mildly modified BMC 'B'-series block under the alloy DOHC head. There is NO way that a 4-cylinder XK-equivalent head will fit onto that relatively small 'B'-series block. - Dave Quirt, 58 XK150S OTS (S830465DN), 59 MGA Twin-Cam (YD3/1426)

For what it's worth.... The XK-100 had the same bore (83 mm) as the XK-120, but the stroke was shorter (91 mm vs 106 mm). Capacity of the XK-100 engine was given as 1970 cc & developed 105 bhp @ 5000 rpm. The head was a 70-degree twin OHC (same as the XK-120). Crankshaft rode in 3 main bearings. Don't know if any of this has any relevance to the XK-100/MGA Twin Cam discussion, but there it is anyway. - Mike Plechaty

Concerning the lineage of the XK-100 vs MGA Twin Cams. If I remember history correctly, there were at least two separated designs looked at for the TC engines. One was the modified B series engine chosen and another was a design that looked suspiciously like a 4 cylinder XK engine although I believe that the book gave the design credit to Morris. This engine was fitted to several racing MGA-s and, in supercharged form, one of the MG record cars. I don't remember all the details but the B series version was chosen because the other version did not show enough (if any) increase in performance to justify the all new design. Although the alternative engine did look a lot like an XK engine, I am not sure it was an XK-100 motor because I believe that it was under 1600cc in displacement for racing class purposes. - Regards, Bill Eastman

I saw the Xk100 at the Cunningham Museum before it closed, and thought it would make an interesting alternative to, and fit nicely in my Healey 100. To have put that engine into the MG would cause major fitting problems, not in length, but in height. They would have had to put a king size bubble in the bonnet to get the lid closed. Plus I would think that the weight, and added potential power would have caused some major handling problems. just my observation. - Ron Yates -"Dipstick Digest" P.S. I would still like to have it for my Healey 100

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