Anyone Experienced with the Honda GX620? Engine Smoking

vasteve

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  • / Anyone Experienced with the Honda GX620? Engine Smoking
Hi everyone,

I just bought a stump grinder with a Honda GX620 engine and it smokes a lot from of the exhaust when I use it and it has trouble starting after I stop it. There is oil residue in the carb and the plugs were covered with carbon when I removed them (I'm surprised they still worked). I ordered new head gaskets, but they both appear to be fine. Is it possible the rings are worn? If so, what is the best method for testing them? Does anyone have experience with this engine or ideas of what I should be looking for?

Thanks!Engine Piston.jpg
 

tadawson

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  • / Anyone Experienced with the Honda GX620? Engine Smoking
Have you checked compression? I would think burning oil would have left carbon in the cylinder, so unless you cleaned thingnup before taking that photo, it is at odd with burning oil.

But yes, rings or valve guides are the likely culprit. A basic check I did on a GX was to remove the piston and top ring, and check end gap both in midbore, and where the cylinder is unworn at the bottom. The change in gap will let you determine cylinder wear with circumference=piDiameter using the delta in gap to get change in diameter. The end gap in the unworn section will give you a feel for ring wear. (This is assuming you don't just have tools to measure the bore . . .) If wear in the cylinder is low, a hone and re-ring ought to clear it up . . . Not sure the year of your engine, but (at least in the smaller ones) Honda had also used a one piece cast oil ring that wore quickly had has now gone to a three piece set. Check valve guides for play, and also the vent valve in the case that allows gases back to the carb . . .
 
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jp1961

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  • / Anyone Experienced with the Honda GX620? Engine Smoking
Hello,

In looking at your pic, the bottom pushrod (the area around 5:30ish),,,is that a crack in the aluminum or not?

Regards

Jeff
 

vasteve

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  • / Anyone Experienced with the Honda GX620? Engine Smoking
This is great feedback about the checking the piston rings. I'll check compression too after I get the new head gaskets on. I'll also check the crankcase breather.

Jeff,
I never noticed that possible crack until you pointed it out. Great observation! I'll try to look down there with a better light tomorrow! That does look like a crack, but I'm really hoping it is not!
 

vasteve

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  • / Anyone Experienced with the Honda GX620? Engine Smoking
It turns out that there aren't any cracks near the valve, just some dirt that looked like a crack (Phew)! I replaced the head gaskets, adjusted the valves, cleaned the carb, and put on new plugs, air, and fuel filters. The engine is better, but it still runs rough. I need to replace the valve cover before I can move forward; it is currently discontinued and unavailable to buy (Part Number 12311ZJ1000). Mine is broken in two spots and the JB weld did not hold up. Any recommendations?
 
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