Lost one cylinder on my 425!

[frischtr]

I was out mowing grass for the first time this year, and after about an hour of mowing the engine lost power all of a sudden, and dramatically at that. I've been running it all winter moving firewood and plowing snow, so its not a winterizing issue with the fuel. Also, today was rather chilly at about 45 deg. out, so I'm not thinking it was overheated. I've cut grass for hours in 90+ deg. heat with no problems before.

First pulled spark plugs, one was dry and tan, the other darker, but dry. Check spark, both looked good. Did compression check, one cylinder good, one has 0 compression. Pulled valve covers, everything looks normal. Stroked engine and watched rocker arms, also appear to function normally. Also, there is oil backing up through the carb, leading me to believe that I have lost a head gasket. Or maybe one of the valves is sticking, despite the action looking normal.

All maintenance has been performed as required, and the machine only has 70 hours on it (purchased April 2010). What else should I try before tearing it apart? Thanks in advance.

 

[frankhinde]

Pressurise the dead cylinder with compressed air (use an air to spark plug hole fitting available at NAPA).. Listen at the exhaust pipe, oil filler tube and cab (with throttle wide open).

In one of those locations you will hear a much louder hiss.

if the exhaust = exhaust valve
Carb= inlet valve
oil filler= rings/hole in piston.

You can try tapping the tops of the valves (where they should be closed) to reseat them..this tells you its the valve seat..not very useful as the head has to come off anyway.

Frank

 

[SixHoeBob]

Have you thought about re-powering with a Kubota diesel?

 

[Gravy]

Double check the valve clearance. Mine tightened up well before the recommended adjustment interval.

And Sixhoe Bob, a Kubota engine won't fit. (not even close).

 

[frischtr]

Double check the valve clearance. Mine tightened up well before the recommended adjustment interval.

And Sixhoe Bob, a Kubota engine won't fit. (not even close).

I'm kinda new to working on 4 strokes, can you explain that like you are talking to a fifth-grader? Valve to piston clearance? Or something else?

 

[J_J]

Valve clearance represents valve timing.

The intake and exhaust valves in an engine are timed to ingest air and fuel, and let out exhaust. They are opened and closed in a sequence, based on the rpm , and the cam provides the timing for this. If the valves are bent or broken, no compression. Valve adjustment has to be correct for proper operation.

You could also have burned a hole in your piston. You can hear this at the oil filler tube. The engine might even try to run on one cyl, with the other cyl completely dead. One way to find which cyl is bad is to short out the spark for a cyl.

 

[frischtr]

Valve clearance represents valve timing.

The intake and exhaust valves in an engine are timed to ingest air and fuel, and let out exhaust. They are opened and closed in a sequence, based on the rpm , and the cam provides the timing for this. If the valves are bent or broken, no compression. Valve adjustment has to be correct for proper operation.

You could also have burned a hole in your piston. You can hear this at the oil filler tube. The engine might even try to run on one cyl, with the other cyl completely dead. One way to find which cyl is bad is to short out the spark for a cyl.

I know which cylinder is bad because it has no compression, the other has 150 psi. The engine does run, barely. I had it running long enough to limp the PT back to my garage. I can't see anything out of the ordinary through the plug hole. The engine should be under warranty, but I'll bet the shop will want me to remove it from the PT if I have them work on it. Guess I'll be calling them tomorrow.

 

[KMA]

I had a similar problem... see my thread here: http://www.tractorbynet.com/forums/power-trac/184578-pt422-engine-shaking-sputtering.html

My engine was out of warranty and I've ordered a new one to replace it. I plan to get the current engine fixed to sell/reuse.

 

[J_J]

It may be as simple as a stuck valve. If you take the valve covers off, can you see if both valves are moving as you try to start .

 

[KMA]

Yeah, I removed both plugs and stuck a dowel into the spark plug hole on the "bad" side, then turned the crank. You'd expect the dowel to move up and down, but the bad piston my machine did not move. If it does move, that's good news and could be a valve or similar as others have suggested.

 

[PTWannaHave]

... The engine should be under warranty, but I'll bet the shop will want me to remove it from the PT if I have them work on it. Guess I'll be calling them tomorrow.

Who are you supposed to call for warranty...? PT or Robin? (Does PT automatically refer a customer back to engine manufacturer for engine problems while tractor is on warranty...?)

Might be faster to deal locally than with Virginia anyway...

Cheers,

 

[FAZTRAC]

You have probably got a hole through the piston or broken oil control and compression rings if oil is coming out of the carburator, with a new engine either one could be the result of dropping a valve which often promptly makes a hole in the piston crown and simultaneously destroys the cylinder head and the little pieces get the rings. Or maybe you just broke a ring.???Either way you're covered under warranty. Oil is probably coming out your breather/rebreather tube from the crankcase as well and flooding the air cleaner carb inlet. Pretty low hours for a catastrophic failure. Be curious what you find. Let us know.

 

[frischtr]

The piston moves, so the con-rod is at least intact. The rocker arms seem to move normally watching with the valve cover off. Even with the engine now stone-cold, I still have zero compression in the bad cylinder. I have talked with the local Robin service center, and I am taking the whole machine in tomorrow. Unfortunately they are backed up 2-3 weeks, but its under warranty so I'm not going to mess with it myself. I'll keep you posted.

I described the symptoms to the engine tech there on the phone and he said it sounded like a blown ring. We'll see...

 

[Gravy]

The piston moves, so the con-rod is at least intact. The rocker arms seem to move normally watching with the valve cover off. Even with the engine now stone-cold, I still have zero compression in the bad cylinder. I have talked with the local Robin service center, and I am taking the whole machine in tomorrow. Unfortunately they are backed up 2-3 weeks, but its under warranty so I'm not going to mess with it myself. I'll keep you posted.

I described the symptoms to the engine tech there on the phone and he said it sounded like a blown ring. We'll see...

You could loosen the adjustment on both rocker arms about 1/4 turn. This would eliminate any likelihood of a tight valve. If you then have compression, you can adjust them properly. If not, you haven't hurt anything.

 

[frischtr]

You could loosen the adjustment on both rocker arms about 1/4 turn. This would eliminate any likelihood of a tight valve. If you then have compression, you can adjust them properly. If not, you haven't hurt anything.

I'll try that tomorrow before I take it over, but if I remember correctly, there was a gap between the rocker and the valve stem at TDC. I guess could still possibly be a stuck valve, or maybe the valve is shut and the gap is correct. I'll look at it...