Re: Timing an F-20

Posted by LenNH on October 21, 2010 at 07:16:58 from (24.128.163.35):

In Reply to: Timing an F-20 posted by Tom 43 on October 11, 2010 at 12:28:00:

1. The release of the impulse coupling depends only on the position of the input shaft to the magneto. If the mag has been removed, it is possible to recouple the magneto drive in the wrong position (all those bolt holes in the drive are there to allow some changes in the timing).
2. Here are the instructions from the F-20 owner's manual:
a. Crank until No. 1 piston is on upper dead center of compression stroke (remove spark plug and feel compression), then contine cranking until D.C. No. 1 mark on flywheel is in line with timing mark on flywheel housing. Both valves should be closed at this time.
b. Lock impulse coupling out of engagement (small rod or wire into oil hole--lift up pawl). Set breaker housing cover as high as it will go (that is, lift the spark lever up). Remove housing cover.
c. Rotate magneto clockwise (as viewed from coupling end) until rubbing block in breaker assembly is on high point of cam. Set points to .013".
d. Assemble magneto and drive coupling parts on engine bracket. Insert magneto base screws loosely in magneto (DO NOT use screws longer than the original--they will damage magneto).
e. Remove distributor block and rotate magneto clockwise at coupling until the segment in distributor disc is under the distributor block terminal marked 1 and the breaker points are just beginning to open.
f. With magneto in this position, locate the two holes in the adjustment coupling that align. Insert shims between the two halves of coupling so cap screws will pass through the holes in shims and enter the holes in the tapped half of the coupling.
NOTE: The holes in the coupling are so spaced that only two pairs of holes will line up exactly. DO NOT force the screws or the setting will be incorrect.
g. Tighten magneto base cap screws. Replace breaker housing cover and distributor block, being careful not to damage the brushes.
h. Attach the spark control rod to breaker housing cover.
h. To check the timing:
Retard the spark with the hand control lever.
Remove breaker housing cover and crank engine until breaker points are just beginning to open. DC mark on the flywheel should align with timing marks on flywheel housing.

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