Nathan Twin Cam

The Nathan Twin Cam currently belongs to a member of The Imp Club and is being rebuilt. Development is ongoing. The original twin cam casting still exist, as do the original cam shafts.

	Photos I took at Imp11. Clark Dawson had it with him. He would not say who bought it...
	Piston: Mahle; 72P12++

The Imper who presently 'holds it in custody' contacted me [Thu, 26 Jul 2012] and gave me more photos. He says: "... the rebuild is underway. Judging by the state of the pistons it would appear that this engine has been built and run in the past."
Roger Nathan, whom he tracked down online, gave him quite a bit of information regarding the development. Apparantly Mr. Nathan is very interested in this rebuild project.

Information provided by Roger Nathan

The Imp Twin Cam Head concept was similar to that of the Cosworth TC head for the Ford and was a dead ringer of the Coventry Climax V8 (FWMV). The idea was to obtain more power from the Imp engine as at that time it was not possible to increase the bore/cc beyond 998.
It was intended for Imp use as well as the Costing-Nathan range of sports/GT racing cars.

The head was designed by Ron Burr and Claude Jephcott. Both were at the time working for Coventry Climax engines. Ron later left them and started with Colin Chapman at Lotus.

There were initially problems with porosity in the head castings. These were made by a local company in Clerkenwell, London. It was Coldbath Foundry, they were sand cast. The porosity occurred in the combustion chamber and the porting. Unfortunately this was often only discovered when the machining of the heads was almost finished rendering them scrap.
Nathan eventually commissioned Aeroplane & Motors in Birmingham to modify the wooden casting blocks and produce a far better head.

Eventually this lead to a power test on the dyno; Nerus Works in Rye near Hastings was used for this development and testing work.
Nathan developed all the parts for the head, valves timing chain, gaskets, special bolts, valve seats etc. etc. at the machine shop Dawson and Shannahan, both at Primrose Hill in NW London and another branch in Wimbledon. All work was done by hand by craftsmen - no computer controlled machines in those days.

The twin cam was developed for the 1967 Costin-Nathan Le Mans entry - although this was not the only desired use - and Rootes were rumoured to have donated several Imps for Twin Cam testing.

Various combustion chamber shapes were being tested with a maximum attained output of 125bhp at that time. At this time the project was eventually shelved due to a lack of funds.

There were several issues during the development stages. The blue prints for the twin cam head 'went missing' for a time and subsequently a very close competitor (located next door to Nathan at Lynton Garages) immediately developed an almost identical twin cam head.

Current specifications

Inlet valves: 35.5mm
Exhaust valves: 31.5mm
Plugs: 10mm Ferrari
Mahle 'Domed' pistons
Head has been re-skimmed and pressure-tested
Valve seats re-cut
Cam profile selection/development underway

The Nathan twin overhead camshaft Imp engine fitted with Tecalemit-Jackson fuel injection gave 98 bhp in the 849cc version and 998cc 125 bhp.