I'M working on my sons Ariens riding mower with a B and S engine 31C707-0603-G1 and suspected a bad head gasket. Ordered it and when removing the push rods I noticed one was bent. It was the lower which I think is the intake. Pulled the head, replaced the gasket, which looked fine and ordered new push rods. Question is the bent one is aluminum while the top is steel. Why aluminum and why did it bend. I was thinking about this on the way home and am wondering if the valve is stuck. New push rods should be here in 3 days so I will check to make sure the valve isn't stuck. Seems strange to have one aluminum rod.
#2
Scrubcadet10
I would check to see that the intake Valve guide hasn't migrated upwards in the cylinder head.
Theory
The aluminium one expands at the same rate as the alloy barrel ( not quite true ) so the valve lash remains the same
The exhaust valve runs red to yellow hot so tends to stick in the guide thus requiring a steel rod.
Those with their hands in their pockets & silly grins will talk about reducing the reciprocating mass which is insignificant on a low tech mower engine.
Do as Scrubbie advised and check the valve guides.
They sit at the same heights from the head floor so the two guides and when fitted the two valves should be at identical heights.
When I have to replace on, I only fit steels as the alloy ones wear thin where they rub on the plastic guides .
And for this reason, push rods should be inverted from time to time.
The do break apart & fall into the engine.
Thanks for the replies. My son checked the valve guides and says they are firmly seated flush with the head casting. I have no idea why it bent but I have received the new push rods so I will be installing them tomorrow. Question: do I find TDC and then back the flywheel counterclockwise so the piston drops 1/4" and the set the valves. I guess that is BTDC.
