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Adjusted valves; popping sound and no power!

#1

C

CallMeCHaz

SV-725 Courage.
Adjusted valves after repairing leaking valve covers. .004/006. Torqued lock screws to 70 in-lb.
Washed oil off of engine with garden hose. Covered carb with plastic bag. No forced spray above bottom of flywheel (did not blast coils).

Ran fine for about 2 minutes. Started loud "popping" (almost a banging sound like a severe miss/backfire) and lost power. Popping is coming from small port pointing downward next to exhaust port on engine (compression release?), right side only. Every time it pops there is a definite puff of air coming from the port.

Pops are very rhythmic--not a rapid-staccato like a wet ignition. More than one pop per second at idle, 2-3 per second at full speed. Feels like a severe miss--you can feel it through the entire mower. Pop...pop...pop.

I hate to pull the valve cover right off to check the valves. Any ideas. First question: is the port a compression release? If so, what could be triggering it in such a rhythmic pattern. If that cylinder were missing, would the port be popping in response? Or is the port a compression release that is popping open?

A miss? Maybe water got in a fuel line? Ignition miss? Or did a valve adjustment slip? I read somewhere that valves out of adjustment can affect the compression release (usually not letting it open.) Thoughts are appreciated before I dive back in tomorrow!


#2

H

hlw49

Kohler engines don't have a compression release. I think I would go back and check the valve adjustment. There is no port where you are talking about. Did it blow a head gasket?


#3

7394

7394

Valves gaped too tightly


#4

H

hlw49

7394 said:
Valves gaped too tightly
Click to expand...
explain what you mean.


#5

S

slomo

Use compressed air to blow off any water that could be shorting ignition parts. Remove top engine shroud.

Clean the cooling fins while you are in there. Yearly job in yours and every other engine manual out there.

All was good until you gave her a bath right?

There are 2 TDC strokes on a 4 stroke engine. Could of set the valves wrong.


#6

C

CallMeCHaz

Slomo: yes was running fine until I bathed her, and before I adj valves. It ran fine for 2 minutes then started popping and losing power.

hlw49: There is definitely a shot of hot air coming from the area of the exhaust manifold at the engine every time it pops. I suppose it could be a blown gasket. Awfully strange coincidence it just happened though.

Looks like I'm going to have to go over the ignition and valves this AM.


#7

C

CallMeCHaz

hlw49 said:
Kohler engines don't have a compression release. I think I would go back and check the valve adjustment. There is no port where you are talking about. Did it blow a head gasket?
Click to expand...
According to my shop manual the Command twin engines do not have compression release. "All other models:...are equipped with an ACR." I believe it works through valve timing at low RMP, not an external release. Not sure what the "port" is I'm seeing (a 1/4" nub in the casting), but it's near the area the air shoots out of. May be a head gasket leak. Checking!


#8

7394

7394

CallMeCHaz said:
yes was running fine until I bathed her, and before I adj valves
Click to expand...
Hope you didn't hit a hot engine with cold water...............................


#9

7394

7394

hlw49 said:
explain what you mean.
Click to expand...
Valves set TOO tightly.. Whern engine gets warmed up the valves do not seat.


#10

C

CallMeCHaz

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.

Attachments







#11

H

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.)


#12

H

hlw49

CallMeCHaz said:
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.
Click to expand...
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.


#13

C

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!


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