Subject: Valve timing expertise needed
Author: Greg Bender
Date: Jul 23, 2004, 7:33 PM
Post ID: 1717216163
This is a little long-ish, but please bare with me as I explain the
situation.
The camshaft timing gear on my 1971 Ambassador broke as I was riding
about 70 MPH (I've since learned that this is not as rare as one would
hope). I replaced all three timing gears with a complete set of
replacements. I also had the valves and pushrods checked (amazingly,
neither the valves nor the pushrods were bent). There are no holes in
the top of either piston. When I installed the new gears, I was careful
to follow this procedure:
1. I made sure that the number 2 cylinder (the one on the left when I
sit properly astride the motorcycle) was at top dead center (both valves
closed) while on the compression stroke.
2. The keyway in the crankshaft pointed toward the number 2 cylinder.
3. The camshaft dowel was at about 10 or 11 o' clock (as I was facing
the engine).
4. Then, I inserted the gears, making sure that the painted marks were
aligned properly (both the crankshaft gear/camshaft gear paint marks AND
the camshaft dowel/camshaft dowel hole paint marks).
With this complete and the engine reassembled (with the valve clearance
adjusted properly and the ignition timing set properly), I started the
engine. It ran extremely rough at idle, but smoothed out somewhat when I
get the revs high enough.
A compression check revealed that both cylinders were pumping out a
whopping 65 PSI (prior to this incident, both cylinders were at about
145 PSI). Adding 1 squirt of oil to the cylinder did not raise the
compression of either cylinder at all.
So, I've ruled out the following:
1. pistons and rings are fine
2. valves are fine
3. ignition timing is fine
This leaves me to highly suspect the valve timing itself.
I started counting teeth on my timing gears and comparing them with
other sets of timing gears as well as information I could glean from
other sources (spare parts catalogs, knowledgeable individuals, etc.). I
learned the following:
1. Early V700's had really fine teeth on all of the gears. I do not have
a count, but the number on the camshaft gear alone was well over 100.
2. Later V700's, Ambassadors, and Eldorados had the following gear
count: Oil - 29 teeth; Crankshaft - 25 teeth; Camshaft - 50 teeth.
3. Early V7 Sports with timing gears had the following gear count: Oil -
31 teeth; Crankshaft - 26 teeth; Camshaft - 52 teeth.
My Ambassador had the *typical* V7 Sport set of timing gears. I have no
idea whether or not the cam itself is from a V7 sport or not.
I've tried both a set of *typical* V7 Sport gears AND a set of *typical*
Ambo / Eldo gears. I get the same results in both situations.
In Guzziology, Dave Richardson recommends a quick check of the valve
timing by checking that "the point at which both valves are equally and
just slightly open should occur just a few degrees before top dead
center" (version 5.2, page 5-23). Using the push rods as a visual guide,
mine appear to be correct.
Help!!!! Can anyone help me figure out this situation? If I have to pull
the engine and use a degree wheel to get the valve timing correct, I
will. But, I'd rather avoid yanking the engine out if I don't have to.
Thanks in advance for your suggestions.
Regards,
Greg Bender
1971 Ambassador
2000 Quota
http://www.thisoldtractor.com/gtbender