Post in the equipment and tools under John Deere.

 

Moved to the Equipment subforum.

@Golivarez

 

Do a compression test?

 

do a leakdown test to be sure..might be a bad valve that needs adjustment/replacement or just simple carb adjustment for white smoke..

 

o.k. thanks. I have discovered that the valve on the exhaust side was covered in carbon deposits (especially on the underside of the valve), which appears that it may have been sticking at times.

 

o.k. thanks. I have discovered that the valve on the exhaust side was covered in carbon deposits (especially on the underside of the valve), which appears that it may have been sticking at times.

If the exhaust valve was sticking, it would run terribly, if at all. I highly doubt this is why you're getting smoke.

If you have run the engine longer than 20-30 mins and are still getting smoke, then I'd temporarily disconnect the crankcase breather line at the intake. If the smoke clears, then you're likely getting excessive blow-by, which will be obvious once you disconnect the line. You would also see a heavy accumulation of oil in the intake tract and the new plug will show signs of oil fouling pretty quickly.

 

So if this is the case, is there fixing any excessive blow-by? And so just to make sure I'm understanding you correctly, I should disconnect the breather line (while mowing)?

 

A few short interval oil changes might be worth trying if you suspect ring blowby. Fresh oil can do some cleaning.

 

So if this is the case, is there fixing any excessive blow-by? And so just to make sure I'm understanding you correctly, I should disconnect the breather line (while mowing)?

Disconnect while the mower is idling, no need to mow with it. The line is usually just a friction fit onto the air filter intake elbow. But honestly, any small engine I've seen where the crankcase breather is outputting enough oil vapor to emit visible exhaust smoke, has shown obvious problems in the intake tract and it was only necessary to remove the air filter to see it.

As far as fixing the blowby, that depends on the source. Blown headgasket, worn rings/piston/cylinder wall, or excessive carbon build-up in the ring grooves which prevent the rings from sealing properly. Pressurizing the cylinder and listening with the valve cover removed will help narrow down where the leak is. Head gasket/crack issues are usually pretty obvious, ring blow-by will present as lots of flow coming out of the crankcase.

 

Well I've checked the head gasket and it is in good shape, but I have not checked the rings. However I did notice wear on the cylinder wall on the exhaust side;

 

Well not cylinder wall, but exhaust side of head. That maybe what's causing the leak ?

 

Depending on how much material is left on the old valves, you could possibly try lapping the old valves against the seat. If there's not a lot, it shouldn't be hard to find replacement valves.

 

should the valves sit flush, when closed? I cleaned them and there was no major signs of wear or pitting. If I recall they sit slightly raised when closed and by slightly, I mean like they are raised in the very slightest.

 

Most I have dealt with do sit slightly raised.

The valve is the wear component here. you don't want the steel seat wearing so you make the valves of a softer material so that they can be replaced. Hence if you have enough material a valve lapping job may be enough for fix the issue if it is the problem.

I personally wouldn't put the valves back in after cleaning the valve and the seat without a light lapping/reseating of the valves, but YMMV.

Edit for clarity. Everything on the top of the valves is mostly irrelevant, it's the underside where they contact the valve seat that really matters.

 

o.k. thanks I appreciate the info.

 

So if this is the case, is there fixing any excessive blow-by? And so just to make sure I'm understanding you correctly, I should disconnect the breather line (while mowing)?

Disconnect while the mower is idling, no need to mow with it. The line is usually just a friction fit onto the air filter intake elbow. But honestly, any small engine I've seen where the crankcase breather is outputting enough oil vapor to emit visible exhaust smoke, has shown obvious problems in the intake tract and it was only necessary to remove the air filter to see it.

As far as fixing the blowby, that depends on the source. Blown headgasket, worn rings/piston/cylinder wall, or excessive carbon build-up in the ring grooves which prevent the rings from sealing properly. Pressurizing the cylinder and listening with the valve cover removed will help narrow down where the leak is. Head gasket/crack issues are usually pretty obvious, ring blow-by will present as lots of flow coming out of the crankcase.

have you done a leak-down test? this would narrow down where to look for leaks.

 

So if this is the case, is there fixing any excessive blow-by? And so just to make sure I'm understanding you correctly, I should disconnect the breather line (while mowing)?

Disconnect while the mower is idling, no need to mow with it. The line is usually just a friction fit onto the air filter intake elbow. But honestly, any small engine I've seen where the crankcase breather is outputting enough oil vapor to emit visible exhaust smoke, has shown obvious problems in the intake tract and it was only necessary to remove the air filter to see it.

As far as fixing the blowby, that depends on the source. Blown headgasket, worn rings/piston/cylinder wall, or excessive carbon build-up in the ring grooves which prevent the rings from sealing properly. Pressurizing the cylinder and listening with the valve cover removed will help narrow down where the leak is. Head gasket/crack issues are usually pretty obvious, ring blow-by will present as lots of flow coming out of the crankcase.

have you done a leak-down test? this would narrow down where to look for leaks.

I second this, as an ex-pro, we generally do a compression and leakdown test (which is pretty much what I describe above, which is fine if you don't have an actual leakdown tester.) BEFORE disassembly and after reassembling to diagnose, and verify repairs.

 

Well not cylinder wall, but exhaust side of head. That maybe what's causing the leak ?

That actually looks like the head was cast that way to unshroud the exhaust valve and improve flow. Lay your head gasket in place on the head. If the anomaly falls entirely inside the area the gasket contains, I wouldn't worry about it.

 

Thanks MasterMech; I don't have an actual leakdown tester. So I will follow your advice on testing, but just to make sure I'm clear..... (if I remove the breather line and still see smoke, there is internal problems? Are there any available and reliable videos online that display a leakdown test?

 

Thanks MasterMech; I don't have an actual leakdown tester. So I will follow your advice on testing, but just to make sure I'm clear..... (if I remove the breather line and still see smoke, there is internal problems? Are there any available and reliable videos online that display a leakdown test?

I know it's not real helpful, but - it depends. :bd: I'd be looking for heavy oil vapor coming from that breather line. Heavy oil vapor flow = problems. There is normally some air flow in this line, but the job of the breather is to keep the oil in the crankcase and let any pressure in/out to a controlled outlet, which is the engine air intake in this case. When it gets overwhelmed, you get oil vapor entering the engine air intake, and in turn - smoke. If the oil deposits in the intake are very heavy, then the smoke may not clear up immediately.

Leakdown testing videos are out there, but mostly on automotive channels which is not terribly helpful for a small engine.

Here's one, but there's a bunch of extra steps and I can see this being intimidating for a novice -

Leakdown testers are available for about $30-$300. Perhaps your local auto parts store has one available as a loaner. Without a test rig, all you need to do a quick and dirty check is the spark plug hole adapter for a compression gauge.
Often, this hose has a quick disconnect fitting that plugs right into an air line. Don't worry about the numbers. The engine needs to be immobilized somewhere on the power stroke (valves closed). And all you're doing is listening to where the air is going. If everything else checks out and all you hear is air in the crankcase, then that leaves the rings by process of elimination.

At that point, I'd consider replacing the engine. You can buy a complete Honda GX120 for ≈$300 and swap the lighting coil over from your old engine. You can certainly fix it if you want but the time and tools required to ascertain the remaining life of the engine block and other components exceeds the cost of a new engine. You could disassemble and if you find a broken ring or other obvious problem, you could buy rings and a gasket kit and put it back together, taking a chance on the condition of the cylinder block.

 

Thanks a lot, this helps me tremendously. This is my first reel mower; I definitely enjoy the cut, but I'm learning the in's and out's of it as I go along.