Since returning from the Lake the Cliff Stovall, the Technical Director at Triumph Australia has been busy rebuilding the engine. After much analysis we believe the cause of the engine failure was a faulty injector. The follwoing images show some close up deatil of the damage done to the piston and bore.
We were running the injectors very hard as the increased capacity of the engine, coupled with the highly modified head demanded a lot of fuel, the injectors we were using seemed capable of meeting the demand for short bursts on the dyno but over a long race run we feel we may have exceeded the duty cycle of the injector in the RH cylinder. Ironically we were running a air fuel meter on the bike but were taking readings from the LH cylinder, had we been using the sensor in the RH cylinder we may have had some warning before the motor partially seized. A close inspection of the whole engine revealed very little damage considering the failure, the head, valves, cam and crank were all in great condition. The only parts that required replacement were the piston, and bore in the damaged cylinder. The following series of images show some a small glimpse into the internals of the race engine…
We get lots of questions about the specifics of the modifications made to the engine, here is a summry from Cliff;
“The brief way to describe the performance mods is: we took a 40hp 865cc Bonneville air cooled parallel twin, we built a 6mm stroker crank that went from 68mm stroke to 74mm stroke, and increased the bore from 76mm to 92mm in order to accomplished 998cc. That was the first line of design of being able to fit within the rules in the class we were running it.
From there we contacted Andrew from Hallam Racing who had built Bonneville cylinder heads all the way from mild to wild in the past and he knew we wanted to go “wilder”.
We increased the valve diameter on each bank by 3mm. We then had to increase the bucket size due to the lift and duration of the cams, to stop the cam falling off the edge of the bucket. This involved designing a totally new valve bucket and shim system to accommodate the wild cams. The artwork alone in the machining was impressive but to create a 62mm inlet track was phenomenal – you have got to understand the original intake track is 34mm…
Fuel was delivered through standard Bonneville fuel injection which included, injectors and throttle position sensors but mounted it all on to a set of Harley-Davidson throttle bodies. We mapped the bike using a power commander and managed to go from 40hp to 108.67 @7700rpm.
For the exhaust we contacted cone engineering and ordered all the 2 inch bends that we needed and then Ross and I decided that we were going to design and weld up the pipes in one day. It was a combination of optimal power and fitting within the DLRA rules which state the exhaust cannot be: pointing at the wheel, pointing at your feet or not pointing at the salt. As you can imagine that leaves you with a limited window on a small bike!!
Other bits and pieces where a Mule Motorcycles hydraulic clutch and oil cooler these were chosen because they remove the frame rail and reduce the frontal surface area of the bike.”