Our Mate Mr Ed, loves buying old motorcycle magazines, so he couldn’t resist picking up a few at last Saturday’s Kempton Park auto jumble. On the way back to East Kent in the car his voice kept chirping up from the back seat with fettling tips from several 1950’s editions. Some of them were really barmy and had us falling around with laughter (not a wise thing to do on the dreaded M25 London Orbital motorway!).
Of the many zany tips the prize surely must go to this one, which I summarise below:
“To find top dead centre (TDC) first take an old spark plug and remove the ceramic part. Then plug the metal base with plastocene (modelling clay) and make a small hole in the centre by means of a nail or rod. Screw the plug base back into the head and take some soapy water and form a soap bubble on top of the hole in the plastocene. Turn the engine and as the piston rises the bubble will inflate. Keep turning the engine gently until the bubble reaches maximum size - you are now at TDC. If you go past TDC the bubble will start shrinking again.”
Spider saw a chance here for a cartoon so here goes:
Hey Lannis, How does your 'soda straw' method cope on machines where the spark plug is angled in from the non vertical position?
The whistle method sounds just as barmy as the soap bubble method. How one would accurately set the timing with either of these makes the mind boggle! The fact that the magazine even published the bubble method is a bit worrying! Mind you, after listening to some of the other fettling gems from the same source I'm not really surprised.
funny, I used a similar idea to know the compression stroke, if not the actual TDC. an old rubber glove finger over the plug body with a hole in the tip, it would inflate on the compression stroke, and deflate after. I had a small ring clamped to the oil feed on the A10 to hold the stick straight on the angled plug hole.
================= /1957 BSA A10 Spitfire Scrambler (in a friend's shed) /1960 BSA Super Rocket Basket Case (in the attic!) /1987 BMW K100LT nekkid