Thursday, 30 June 2016

One month to go and popping pistons !

 . . . yes, only three weeks till I fill up my transportation crate and fly my 250cc pushrod off to the United States for Speed Week, Bonneville.
   And in true time-honoured tradition, as time runs out for the preparation of my machine, what can go wrong is going wrong,  and is manifesting itself in a succession of blown pistons.

But it's OK because thats the way it goes, and like Burt Munro the Bonneville legend, if you don't have an alter of 'sacrifices' to the gods of speed in the form of broken engine components, then you are either very lucky, or just not trying hard enough.

I look at it this way,    . . .  rather a load of problems before I go, than no problems till I get there.

You see my point ?

With the significant additional stresses on my engines due to demands of competition, individual components are increasingly stressed in pursuit of more speed and performance.   This can lead to components failing under test and for my bike it is manifesting itself in the form of 'popped' pistons.
This is where the heat during operation around the spark plug gets so high (600 c+) that the aluminium based alloy of the piston starts to over-heat,  soften then tear removing all compression in the chamber and causing failure.

Establishing the exact cause is not so easy as various factors are influencing this situation,   but I have some great engineers who will fix things,   and that makes all the difference.

popped piston in a cylinder.
earlier offering to the gods of speed !

Sunday, 12 June 2016

Lapping the valves and other jobs.

 . . . with not long to go (six weeks) till Bonneville Speed Week in Utah preparations are ongoing with getting my engines ready for the event.    All of the work on both the frame and the three engines have been done by my Team-mates Chris and Richard who have shown considerable patience with my lack of skills in this field, but as I spend more time with the machine, I am gradually making more sense of it.
    Recently I tackled some wiring installation and have been checking clutch plates and ajusting brake shoes,  and with supervision have been introduced to 'lapping' which involves a smear of different grades of grinding paste onto the lip of the valves which is then rotated in it's engine location to ensure absolute even seating into the casing.    
Lapping !

I have seen traction engine builders with the little tin of grinding paste with lids at both ends, one end for course grade, the other end for fine grade and at last, I know what the stuff is used for.   Like most jobs relating to engines it cannot be rushed and requires both patience and precision to be done right.
  The results are simply a better performing engine which is just what I need for the demands of world record attempts.

Another job has been bedding in the traditional drum brake shoes which when new have a shiny surface which can make braking more difficult.    By lightly roughing the surface with a file or sandpaper the ability of the brake surface to perform is improved.   There are many other jobs to do yet, but it's all coming together and I am learning a lot from the experience.