Subject: Left push rod / head problem reveiled
Author: Ian Adkins
Date: Mar 15, 2004, 6:19 AM
Post ID: 1716302823
Hey All,
Finally got around to pulling the left head on the Ambo. Before doing so Ed
and I measured the compression in the cylinders. Right side was
170-180....left side was 0.
Whene we pulled the head...noticed that the intake valve was bent.....and
not seating. Probably a 1/16 inch gap. Piston had a little nick where the
piston had struck the valve.
So what caused this? Here is what Ed and I deducted:
I will start by assuming that the push rod bending started the failure of
the cylinder. How the rod bent is another story....will pose that question
later on.
When the rod bent it immediately caused the rocker gap to increase. In doing
so it allowed the push rod to come out of the rocker cup and catch on the
edge of the cup (there were marks on the rocker and push rod cup that
supported this). So for a moment the push rod pushed the valve in excess of
where it should be and in doing so the piston struck the valve...bending it
and shutting down the cyliner. The little nick on the piston indicated this.
So what bent the push rod? Either it was a "dormant failure" of the rod or
some excessive force on the rod did this. The only thing I can think of is
that when I was leaving the shack.....I had to rev the engine and play the
clutch to keep from rolling back on the steep road. With the clutch on the
70 Ambo being so tight (compared to the other bikes) the bike "lurched a
couple of times" while I was trying to hold the bike from rolling backwards.
Could this rapid accel/decel have caused the stress in the rod?
At any rate I will pull the valve and inspect the guides. If the guides are
ok then I will replace the valve and hopefully that will be the end of it.
Hopfully the guides and valve seat will be ok too. If not I will likely
rebuild both heads. Any good thoughts as to where I should get this done?
Any input would be welcome....thanks...Ian