Snapped pushrod

[DRWDRW]

So which valve's pushrod is dying?

It's on the inlet side. The exhaust has the steel rod.

 

[DRWDRW]

Measure the height of the valve guides, they should be the same.
What is happening is the pushrod is dropping into the engine then the cam comes around & breaks it
The push rods jump off because the valve lash gets too big
The plastic guide that is there need to be replaced , where is the other one ?
Do not reuse the old head gasket.
There is way too much oil in your head so most likely the valve stem oil seal on the inlet valve is gone ( none on the exhaust ).
Were both of the lash caps on the end of the valve stems ?
If one dropped off
1) it will be in the engine somewhere
2) puts the rocker at an angle where it can hit the valve spring which can cause the push rod to drop off.

I've measured the heights and they're identical (which surprised me, because they didn't look it).

The plastic guide from the inlet side had popped off the plate. It was floating around in the rocker cover, along with the bit of pushrod and lash cap.

The exhaust lash cap (I mistakenly referred to them as shims) was still in place, and the clearance appeared to be normal (I didn't check it).

On the inlet side, I decided to check the clearance before disassembly - I compressed the spring and dropped in a new pushrod. It was then tight against the rocker (little or no clearance) even without the lash cap in place. This is what made me believe the valve clearance had closed up.

I recall setting the clearances a year or two ago, and noticing the rocker on the inlet valve was sitting at an unusual angle. But the clearances tightened up okay, so I assumed to be acceptable. Is this actually my problem?

 

[DRWDRW]

I've attached another photo here - this taken prior to disassembly but with a new pushrod trial-fitted to check the clearance.

 

[bertsmobile1]

IT is sounding more & more like a loose valve guide.
Give each one a LIGHT tap using a drift to prevent damaging the end.
If the inlet moves even the tiniest amount then it needs to be repaired.

Walt has a system that seems to work fairly well, or just replace the head.

 

[ILENGINE]

I've attached another photo here - this taken prior to disassembly but with a new pushrod trial-fitted to check the clearance.

Looks like the rocker retainer nuts are different between then intake and exhaust. Could the larger looking nut be causing binding of the intake rocker leading to excessive wear on the intake aluminum push rod.

 

[DRWDRW]

Looks like the rocker retainer nuts are different between then intake and exhaust. Could the larger looking nut be causing binding of the intake rocker leading to excessive wear on the intake aluminum push rod.

One of the nuts was replaced a few years ago when the thread failed. It's the correct B&S part - or so I was told - but I could swap it to the exhaust side and see what happens?

 

[DRWDRW]

IT is sounding more & more like a loose valve guide.
Give each one a LIGHT tap using a drift to prevent damaging the end.
If the inlet moves even the tiniest amount then it needs to be repaired.

Walt has a system that seems to work fairly well, or just replace the head.

A light tap didn't budge it the guides at all.

Unfortunately, a ham-fisted idiot (me) making a heavier tap with the drift did move the inlet guide and damaged the end... :ashamed:

 

[Tinkerer200]

The valve guide should not exceed 1/8 inch above the head casting. It is quit normal for the aluminum push rod to wear thin and bend when not rotated end for end periodically on this engine when adjusting valves which should be done every year per B&S but a couple years at most. Replace it when the push rod shows heavy wear. As said above, many have replaced the aluminum push rod with the steel one with no apparent problems. Note that the later version of this engine uses a different assembly support method eliminating this wear problem.

No clearance when new push rod installed - check that the push rod is seated in the recess in cam follower, tappet.

Walt Conner

 

[DRWDRW]

The valve guide should not exceed 1/8 inch above the head casting. It is quit normal for the aluminum push rod to wear thin and bend when not rotated end for end periodically on this engine when adjusting valves which should be done every year per B&S but a couple years at most. Replace it when the push rod shows heavy wear. As said above, many have replaced the aluminum push rod with the steel one with no apparent problems. Note that the later version of this engine uses a different assembly support method eliminating this wear problem.

No clearance when new push rod installed - check that the push rod is seated in the recess in cam follower, tappet.

Walt Conner

Thanks. The thing with this engine is that the pushrod was new last season, after suffering a similar break last year; until then it had been fine for a dozen years or more.

I've now replaced the whole cylinder head with a good second-hand part, and it seems to be working perfectly. Interestingly, the rocker (which was previously at an awkward angle) is now level.

 

[Tinkerer200]

Thanks. The thing with this engine is that the pushrod was new last season, after suffering a similar break last year; until then it had been fine for a dozen years or more.

I've now replaced the whole cylinder head with a good second-hand part, and it seems to be working perfectly. Interestingly, the rocker (which was previously at an awkward angle) is now level.

Probably due to a problem with the covering on the metal push rod support, missing or worn thru allowing push rod to ride on the bare metal. I expect a new rub block would have cured the problem.

Walt Conner