Hi,

I agree with your perspective of diagnosing the rocker arms.

A low cam lobe will show up when comparing each of number three rockers with the adjacent cylinders for movement.
I would turn it all by hand and use a dial indicator to view the results.
If a cam has gone flat there may be more than one or a set of them that didn’t heat treat correctly.

This is why I asked if this was a push rod engine.
When setting the lash clearance it’s easy enough to remove all the low spot needed to close valves.

What I have a problem with is this. Why aren’t the valves closing entirely? Those lobes would have to be nearly round or the lash was set entirely wrong somehow. Even each time must be a clue?

There should be specs of rise and fall with degrees of rotation to clear the cam of any wrong doing.
There is some duration overlap in all of this so the dial indicator and a degree wheel will definitely find a problem, if it is a mechanical one?

There some truth around where he said that switching the head and valve sets within them still came up with number three being or having the same issue.

The wrong head gasket to either head is one I can agree with very easily. Especially in relation to the engines cooling jackets and oil drain passages.

With a carbureted head or having injectors signifying there are head differences would have me suspicious right off the bat of what history this engine has.
I just don’t know anything about these older Volvo engines so I got to stop speculating in that area.


Like I said I’m interested to any conclusions to resolve the thread.

Phil