Adjusted valves; popping sound and no power!

[hlw49]

Cylinder Head Head Bolt Fastener (torque in 2 increments) fi rst to 22.6 N·m (200 in. lb.) fi nally to 41.8 N·m (370 in. lb.) Rocker Arm Screw 11.3 N·m (100 in. lb.) Rocker Arm Stud (AVT) 11.3 N·m (100 in. lb.) Rocker Arm/Valve Adjustment Jam Nut 7.3 N·m (65 in. lb.) Rocker Arm/Valve Adjustment Setscrew (AVT) 7.9 N·m (70 in. lb.)

 

[hlw49]

Decided to quit overthinking and go old school, quicky diagnostics. Unplugged spark plug from rt side while running. Popping stopped; no change in RPM; actually runs a bit smoother with no spark. Hmm. Unplugged left side, engine stops.

Tons of sparkage from HEI test plug on offending side (right).

Dry compression test: right 95, left 125. Hmm. Valves or head gasket? (even with the exhaust valve compression release they should at least be close together).

The "port" I thought air was poofing from was just the exhaust cap-screw head crudded up so bad I couldn't tell what it was. Lots of hard, crusty black down there. If it were an exhaust gasket leak it would not blow straight down, it would blow sideways. So I'm thinking head gasket.

So, right side has spark. Since popping stops when I remove spark, fuel is igniting in the bad cylinder--occasionally. I have fuel and spark. Compression test suggests valves or head gasket on the right.

Soooo...pulled valve cover. YIKES. The rocker arm stud on the exhaust valve had loosened from the head (I hadn't messed with it!) The rocker arm flipped sideways, jammed the intake rocker, and bent its push rod. LOL

One would THINK "Well, that's GOTTA' be it!" I beat the push rod back into shape to test things until I got a new one. Re-torqued loose stud. Set valves. Starts right up. Runs smooth. NO POPPING!......also NO POWER!! Pulled spark plug wire on good side and it died. You guessed it--head gasket.

So I went from fixing a simple oil leak, to a bent pushrod, to a blown head gasket all in one day!

What did I learn from this?

1. Don't assume coincidences don't happen. They do! This was the perfect storm of FUBAR.

2. This is just like plumbing repairs. You fix joint A, and cause B to start leaking, so you fix B and cause C to start leaking!

3. Apparently, even with both valves closed, it was sucking in enough fuel mix to pop now and then when there was spark. So it quit popping and ran smoother with no spark.

4. That is the most crappy head gasket I have ever seen. Looks like something that would go on a no-name, 3HP push mower engine. Glad they redesigned the new ones. It answers the question "Should I replace them both?"

I think the head gasket had been going bad for a while. It was the "chi--chi--chi" air sound that I would hear when I would start and stop the engine, which I thought was coming from a non-existent compression relief port .

Thank y'all, and does anyone know what the rocker studs are supposed to be torqued to? Not sure I'm looking the correct item in the Service Manual.

Yes it took them over 20 years to fix the problem on the command twin. Finally they put a fire ring on the head gasket. It was a real problem before the did that but very little since they fixed it.

 

[CallMeCHaz]

Pulled heads. Flattened the face. New gaskets. Re-adjusted valves. Runs fine with LOTS of power. Head must have been getting worse little by little. LOTS of power when mowing. Goes through the tall parts of my lawn without dropping an RPM at full ground speed. Thanks for the advice guys!