Favorite ways to "lock" the motor

t ingermanson

t ingermanson

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When doing assembly and maintenance on your vintage bike, what's your favorite way to "lock" the motor, in order to tighten or loosen things like pinions, cam nuts, rotor bolts, etc?

  • 4th gear and friend on the brake pedal
  • 4th gear and stick in the spokes
  • Extra, loose pinion in the timing gears (Triumph and BSA, etc)
  • Head off, plate bolted across bore(s) onto the piston crowns
  • Rope down the spark plug hole on compression stroke
  • Handful of gravel in the gearbox
  • Stern looks
 
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One of the first two options depending on availability of assistant and/or tightness of thing being loosened or tightened.

If at engine assembly/disassembly stage and barrel is off, a stout bar that's a good fit in one of the balancing holes in the crank.
 
I vaguely remember pouring a quantity of castor oil through the spark plug hole and refitting the plug on the J.A.P speedway engines. But that was 50 years ago, so it might have been water or some other liquid instead. Same procedure but more liquid than when we measured compression once a week after taking off and check the head. Should be between 14 and 16 depending on next track.
 
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I feed a length of clean, soft, 1/2" rope in a spark plug hole at bottom of stroke then turn the engine against it.
When you've finished whatever job just turn the engine back a bit, pull the rope out and refit spark plug.
Cheers

Edit: ...just make sure you leave the end hanging out ;)
 

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