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Current Racing Project

National Hill Climb Association - www.nhca.co.uk

79 x 100 (490cc) Engine Development

Last Year (2011) 17 year old Jack Bennett started his racing career at various British Hill climbs. He managed to participate in 3 different hill climbs over the course of the year.

Over the winter the iron head and barrel were replaced with an aluminum head and barell also Jack lightened many parts, reducing the weight from 322 lb to 300lb.

2012 Engine Spec:-

Fuel - Methanol

Bore and Stroke 79 x 100

Compression ratio - 13.8 (using an omega piston)

Inlet valve 46mm

Exhaust valve 38mm

Roller rockers were fitted

Cam Technical Information:

1471 Inlet Cam (323° Duration)

1503 Exhaust Cam (304° Duration)

1 3/8" Amal GP5 Carburettor

1300 Main jet

125 needle jet

7 slide

GP6 Needle (centre position)

Inlet tract length from cylinder head to end of bellmouth - 6.5" (Std amal GP)

Total length of exhaust pipe + straight through silencer - 47"


Many hours were spent welding and poliishing the ports and finally it was flow tested with some impressive results:





Prescott Hill Climb - 2012:

Jack had a poor start to the season with a very cold and wet Prescott.

This was the least of his worries as the clutch cable broke.

Overall Result :-

Classic / Vintage Class combined- 7th



Wiscombe Park 2012:


Wiscombe park was the next event with conditions looking a lot more promising with a scorching hot day!

Jacks first participation at Wiscombe Park


Result: 8th overall







   Ramsey Sprint 2012:

Next up for Jack was the Ramsey Sprint in the Isle of Man

Again conditions were poor with heavy rain, but this ended up helping us!

As the other competitors sheltered from the rain, Jack's spirit and determination enabled him to clock in 28 runs resulting in a 1st Place victory!


9.42 seconds

1st Place





Dyno: June 2012:

When we arrived back from the Isle of Man we finally took the bike to the Dyno.



The Dyno produced some very dissapointing results : -

1. We found that up to now jack had been using the bike with only 37hp (Red line above)

2. The engine was running rich as a 1050 main jet increased the power to 40hp (Blue line above)

3. After 6000rpm we had a terrible mis fire (believed to be caused by weak valve springs)

4. As the engine wouldnt rev over 6000 a long inlet tract was fitted (10.75" from head to end of bell mouth) resulting in more low down power and 41hp (Purple line above)


The valves were believed to be bouncing at 6000 so to remedy this we went to Jerry Goodwin (Jawa / Jap expert) who supplied us with some stronger springs.

These seemed to cure the problem at the next event.



Epynt Farm Hill Climb 2012:

At this event rain was there as usual!

This was a new hill climb only recently being made avaliable by the M.O.D. for the Port Talbot motorcyle club, who did an excellent job.

This hill was found to be very steep and demanded a lot of power


2nd in the Pre War Class (4th overall including classic bikes)


Dyno: July 2012:

Our second trip to the Dyno was a much more sucsessful one with far greater results.


We now have 46.5 BHP at the back wheel, which allowing for 10% losses through the gearbox/ chain etc = 51 BHP at the crankshaft .

The power below 4500 RPM is very poor because of the megaphone, so our next challenge is to try and improve this as we do not think it is possible to improve the maximum power.

Loton Park 2012:


Loton Park was an eventful outing for us

Unforutanatley Jack managed to fall off for the first time on the Norton,

this was partly due to the rain, an oil spill or the new back tyre??

But even all of this couldnt dampen his spirits!

Resulting in an overall 5th place finish




August Dyno Test: (2012)


This time at the dyno we fitted some 280deg cams (in 1564 & ex 1563) hoping for better low down power.

Cam Technical Information

The results were very dissapointing as the graph above shows.

We lost 6Hp at the top end and gained practically nothing low down, but it helped cure the megaphoneitus around 4000 Rpm resulting in the bike feeling nice to ride at low Rpm.

Obviously with this new information the old cams will be fitted back again for the next race!


Hartland Quay

Hartland Quay was our last outing of the 2011/2012 season with the Norton.

This was Jack's first time at Hartland on the Norton

Luckily the rain held off for Sunday which was a relief for us all.

Jack managed to better his times each time he went up the hill eventually ending up with the time of 30.04 seconds.

Resulting in a 5th Place finish



Season Overview

After a very enjoyable first season for all involved, Jack managed to finish the year in an impressive 9th position in the championship standings. After attending 5 of the 10 Hill climbs throughout the season.

Probably Jack's most successful stint on the bike came at the Ramsey Sprint where he really enjoyed participating with him clocking in 28 runs!

Eventually all of that enthusiasm payed off with him winning!

The overall Classic Championship Table: