Subject: Followup: Valve timing expertise needed
Author: Greg Bender
Date: Jul 24, 2004, 9:46 PM
Post ID: 1717220404
Just a follow up to my valve timing experience...
Taking Brett's advice, I downloaded and printed a copy of a degree
wheel. It was easy enough to mount on the crankshaft (using the three
pulley bolts to secure it in place).
Sure enough, when I checked my valve timing, it was way off. The exhaust
valve on the number 2 cylinder is supposed to start opening at 122
degrees after top dead center. Mine was starting to open at 158 degrees
after top dead center. So, following the instructions in the workshop
manual, I set the valve timing correctly. Afterward, it was very
satisfying to verify the opening and closing positions of the intake and
exhaust valves with the degree wheel and the values given in the book.
The engine started right up and ran well after a quick adjustment of the
ignition timing. Ah...that really felt good!!! :>
***The only part of this experience that remains unsatisfied is not
knowing why my timing was so far off when I used the timing marks from
the other two sets of timing gears.
All this and I didn't even have to remove the engine from the frame to
get at the flywheel! Two things made this technique possible: (1) I used
the degree wheel suggested by Brett; (2) I used a piston stop to
determine top dead center.
About piston stops: Until yesterday, I had never heard of a piston stop,
so here is what I know now.
THE PROBLEM: It is easy to determine top dead center by looking at the
flywheel side or by looking at the arrow on the timing case cover and
comparing it to the pulley markings. However, when the flywheel isn't
accessible and the timing case cover is removed, top dead center has to
be obtained via an alternative method - the piston stop. [note: when
adjusting the valve clearance, I just use a blunt screwdriver to
determine top dead center, but that method is far too crude when timing
the valves.]
THE SOLUTION: A piston stop is a device that prevents the piston from
going all the way to top dead center. Although ready made piston stop
tools are available, I made due with a spark plug that had very long
threads (a Champion RE14PLP5). Here's how it works: with the piston NOT
at top dead center (just feel with a screwdriver), screw the piston stop
(spark plug, in my case) into the spark plug hole and tighten. Next,
rotate the crankshaft clockwise VERY SLOWLY AND CAREFULLY until the
piston comes into contact with the piston stop. Write down the value
that is shown on the degree wheel. Then, repeat the proceedure by
rotating the crankshaft counterclockwise. Again, write down the value
that is shown on the degree wheel. Top dead center is the mid point
between these two values.
For those interested, I will be adding a section about valve timing with
more information to my website over the next few days.
Regards,
Greg Bender
1971 Ambassador
2000 Quota
http://www.thisoldtractor.com/gtbender