Honda GXV670 smoking

[Mr Mower Man]

This GXV670 TAE2 GJAH-1012351 engine is on a Land Pride ZTR. It has sat for a couple years while the owner hired someone to mow his grass, but he recently decided he wanted it back in working order so he could start using it again. I put on a brand new carburetor (customer's request), and I found a complete used air cleaner assembly on ebay, as the original air cleaner had been hit and broken off.

So the engine ran fine after that, except it smoked. The crankcase was overfilled, and when I changed the oil, I noticed that the oil was especially thin. So my assumption was that after I had fresh oil in the crankcase, at the proper level, the smoking would go away. Well, it didn't. It smokes pretty profusely sometimes, and it eases off at other times. I asked the customer if the engine had been ran any length of time without the air cleaner in place, and the answer was "No, not really."

I have not done a leakdown test yet, but I did do a balance test between the two cylinders, and it checked out fine (3440 vs 3480 RPM's).

I also did a crankcase vacuum test, which yielded some troubling results. With each cylinder running by itself, there was vacuum in the crankcase, except for a brief loss of vacuum when I put a load on the engine by shoving the throttle control up. (Not good. When I see this type of result with a Briggs single cylinder OHV, I know there's a head gasket failure.) With both cylinders firing, there was vacuum in the crankcase sometimes, but also there would be slight pressure in it at other times, particularly at low idle. So the crankcase vacuum test results were never what you want to see, but they were worse with both cylinders running than with either cylinder by itself, which leads me to suspect that the cylinder walls probably have wear in them, equally. Or else both head gaskets have failed, which doesn't seem very likely.

I'm thinking I need to remove a cylinder head and look around if I really want to know what's going on inside that engine.

Problem is, the customer does not remember this engine smoking the last time he used it. So what happened to it? I suspect the customer just has a bad memory.

What do you all think?

[KE4AVB]

Or you could ran a leak down test with the valves disable looking for a cylinder problem such as a taper cylinder by cycling the cylinders through their compression stroke. Might save some tear down time.

As for the running vacuum results I have never did one on a small engine so I am of no help there.

But on the over filled crankcase I do it puts a lot of oil in the exhaust system which can take 15-20 minutes running at full throttle to clear the exhaust after the problem is resolved especially on these ZTRs larger mufflers.

[Mr Mower Man]

But on the over filled crankcase I do it puts a lot of oil in the exhaust system which can take 15-20 minutes running at full throttle to clear the exhaust after the problem is resolved especially on these ZTRs larger mufflers.

That's what I was assuming was going to be the case here. But as this engine runs, the smoke sometimes is very bad, and then it seems to clear up. Then it starts smoking bad again. It's intermittent. There's clearly something wrong with it. And I can smell it. Clearly an oil burner. Skeeter fogger!

[KE4AVB]

That sounds like a Tecumseh OHV60 single on a go kart I had here late last year where it had a tapered cylinder where the smoke came and went. It had passed a standard leak down test with the piston locked at TDC compression. It actually had only had a 10-15% leak down but when I disabled the valves and tested it was dropping to 60% at near BDC I torn the engine down and verified the problem. It was so worn that it was non-rebuildable.

Strange though that it only smoked idling long term [several minutes].

[bluemower]

your comments:
as the original air cleaner had been hit and broken off
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Take a look at the broken air cleaner to see if there is any dirt past the filter. Also look at the old carburetor for any dirt located on the carb inlet and choke area. Pull the intake manifold and look for signs of dirt.

[Mr Mower Man]

Well, I removed cylinder head #1 for inspection. I found a nice shiny cylinder with no trace of cross hatch, except at the upper 1/8" where no compression ring reaches. I wiped the cylinder dry with a rag and then turned the crankshaft by hand 1 or 2 revolutions. After the piston had traveled up and down the cylinder 2 or 3 times, there was an oil film left on the bottom of the cylinder, which I could rub off with my finger and see the oil gathered on my finger. So I'm thinking this oil control ring isn't doing much of anything. If it's leaving an oil film in the cylinder with just one revolution, how much is it going to burn at 3600 RPM's? No wonder it's smoking.

So I'm thinking new engine. What do you all say?

[bgsengine]

So I'm thinking new engine. What do you all say?

Me, I would say compression test results plus leakdown test results would have told the tale to 98% certainty what to expect when popping a head off, but sounds like you'd have discovered low compression and considerable leakdown , if you find a smooth bore (do you got a ridge at top of cylinder where cross hatch is?) I'd say do a cylinder bore measurement and check for out of round and taper , probably find neither is in spec, in which case, you wouldn't even need to ask whether new engine or not.. but I'd probably say re-power time.

[Patrickbat]

Why are you leaving those 2% chance that it could be something else btw? What else could it be?

[KE4AVB]

There is always a chance it can be something else but bad leak down results it most likely a worn cylinder, BGS or me either have the engine in front us so we troubleshooting based on the info provided.

I have seen on some Briggs engines that smoke heavily to either valve stem seal or worn valve guide but they passed the leak down test. It can be even a bad head gasket or just a bad oil scraper ring. This why we do leak down and compression tests. These tests can save a lot work troubleshooting a problem.

Plus well experience knows what baseline results are for a good are. We in professional shops just don't the time to completely tear an engine down just for investigation purposes when the non-invasive tests indicates it is bad. Borderline engines are sometime savable but are seriously out spec are just not worth the effort as most overhauls cost as much as a new engine.