Peter Le Gros
 

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I originally designed and built 'Sledgehammer' in the late 80's, with John Clift making the frame for me, as that seemed the most important part to get professional expertise involved! Handling and weight shift were fine - based mostly on fortunate guesswork - but a bit more triangular bracing was added a couple of years later when we started making decent power.

Engine is basically a JAWA 500cc speedway single, 1970-ish design 2-valve pushrod type. The engine is strengthened around the crankcases by side plates surrounding the main bearings, connected to a thick dural plate across the head.
Crank is standard but lightened (flywheel diameters reduced) with the crank pin and driveshaft both being welded in. The rod is a standard steel Jawa, although most modern speedway engines have gone the way of aluminium, and pistons are J&E; made to my specification.

The engine is laid almost horizontal and converted to a dry-sump oil system using a Norton pump mounted externally and driven off the cam gears. I reckon I laid it down before anyone had the same idea for speedway bikes. It was simply to keep the C of G down and make engine swaps easier, although converting the oil system to scavenge successfully was a bit of a nightmare.

 

 

Sledgehammer at Avon Park.

 

THE engine revs safely (?) to about 9000 rpm. Blower is Shorrock C75B, and gearbox a Bewley 2-speed. Clutch is based on a Norton Commando but modified to lock-up operation - a conversion Pete Davies used to do for grass-track sidecar outfits.

Fuel injection is all Hilborn, with common fuel loads around 80% nitro. The head is converted to twin plug and ignition supplied by two Interspan plasma-discharge units which both fire simultaneously. These type of units are very effective when using high nitro loads as the long spark duration seems to assist the relatively slow burning fuel. In fact at 6000 rpm the spark duration lasts from 50° advance right up to TDC.
 
 

IT has taken many breakage's over many years to get the right combination!
Best e/t is 8.97 secs, and speed 156 mph.

Nowadays it runs regularly and reliably around the 9.2 mark, and seems to shock quite a few turbo/ nitrous/ Japanese based colleagues. I have enjoyed many sprint (and some drag!) successes and still hold 500cc track records at a few venues. Not Santa Pod I hasten to add; that accolade still belongs to Brian Chapman on Mighty Mouse, who amongst others inspired me as a spectator in the mid 70's.

I have raced in Holland, and the Isle of Man winning the Ramsey Sprint in 1994 and 1995.

 

I believe with a more up-to-date motor, blower and overall lighter bike I could build a 500 capable of reliable mid 8's.
I know a wider tyre would also be needed, so the current conclusion is to build again starting from scratch. I'm considering using an Eaton M45 blower, and would be pleased to hear from anyone who has experience of these.

Whilst in the States recently I was really taken with the lightweight wheels, forks etc manufactured by PMFR (and others) which virtually everyone seemed to be using. So the mental shopping list has already started - don't tell the wife!

 

Special thanks please to my mate Shaun, who's support and help with the bike makes it possible to keep doing it (even if he and his wife do ride Suzuki's!).

Pete le Gros - Sledgehammer racing Fleet Hampshire.