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Ignition timing and Tappet gap setting for a BSA F12 Sloper engine

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Mr. E Thu, 19/04/2018

I have read the Norton Villiers F12 Manual which has been put onto this website with interest.  I am looking at buying a mower which has a BSA F12 engine on it - I take it that BSA took over Norton Villiers and produced the same engine?

My technical question is how do you set the engine to 0.125in BTDC so as to set the Inlet and exhaust tappets with a clearance of 0.006in?  I can set the tappet clearance on my 1955 Land-Rover 4 cylinder 2 litre engine, but that has timing marks on the flywheel and I use the lamp method to set the distributor for the ignition timing...the F12 must be simpler to set up?  In anticipation of learning from a Guru...!

Mark the novice!

 

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wristpin Thu, 19/04/2018

The BSA and Villiers F12s are basically the same engine. 

Ignition timing. The flywheel is keyed to the crank so unless someone has had it apart and moved the magneto stator there is nothing to worry about other than setting the points gap to 18 thou.

Valve clearances are set with the piston positioned  quarter of an inch down the bore past top dead centre on the power stroke. That gives you both valves shut and they can then both be checked without having to turn the engine for individual checking.  If the clearances are way too small you will need to remove the valves and carefully grind or file metal from the end of the stem - very little at a time. If the clearances are way too large - say over ten thou you may consider refacing the valves or recutting the seats to “ loose” metal and reduce the clearance.

I say “may” because those engines are pretty tolerant and if it is running alright I’d leave it alone.

Mr. E Thu, 19/04/2018

Many thanks for the advice.  It seems as if it is best to leave well alone and set the points gap, unless it is running rough...

 

Mark

wristpin Thu, 19/04/2018

Should just add that you can clean and set the points through the “window” in the flywheel without removing the flywheel itself which should only be done with a puller bolted into the three tapped holes provided ; not with a legged puller acting on the rim.