OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Honda GXV 120 smoking/overhaul help please

I have a GXV 120 Honda engine from 1987 on a HR214 SMA mower. We have had it since new and has been used regularly every year. It has been getting worse at smoking and now smokes like crazy when started cold. The smoke finally tapers off but never stops completely. It also is down on power since it will die if you engage the blade before it warms up for a couple of minutes.

I have taken it apart and it was very clean inside except for carbon in the exhaust ports and cylinder head. Everything else looks very good. As best as I can measure the bore it is 6.00 mm. Ring gaps are top .016 middle .022 oil .045. Valves have very little play in the guides and the valve seats are narrow at .035". Valve stem diameters are still standard. Valve lash was .012' on intake and exhaust.

Except for the smoking and loss of power the engine appears to be in excellent condition for it's age.

I plan on putting a new set of rings in it along with new seals and gaskets. I have a ball hone that I plan to use on the cylinder. What would be best for a fluid to use with the hone?

Also the lining on the blade brake/engagement disc is about .10" thick. Does anyone know what the new thickness is or what the service limit is?

Any help tips or suggestions would be appreciated. There is a small piece of steel mesh in the oil breather area. I'm not quite sure where it is supposed to go. I think it should go down and cover the hole that leads to the air cleaner. is this right.

Hi Terrys, welcome to Outdoorking.

First, your oil ring is worn well past the service limit of 0.039" and would certainly cause the engine to blow oil smoke, which is blue. Note that either white or black smoke would have a different cause. Your replacement ring set should have two thin steel rail oil rings with a ring expander. Do not accept a ring set like your old cast iron one, which wears out too quickly due to not being chrome plated on the outer surface of the rings. Ensure that the top (compression) ring is also chrome plated, as the original one was. Put the first and second rings in the right way up (there will be a mark on the rings, and it faces upward). Do not remove the piston from the connecting rod, or there is a risk you'll put it back on the wrong way around.

There would not normally be a carbon build-up in that engine, but since it is burning oil, that would account for it.

The cylinder should not require honing, though it is good practice to break the glaze in the cast iron liner when replacing piston rings. I normally do that with some 400 grit abrasive paper or cloth, applied to the bore with my finger tips, using a circular motion with a diameter of about an inch. Unless the bore is damaged (visible vertical lines in its surface), I believe the use of hones usually does more harm than good. Carefully clean the bore after breaking the glaze, and ensure no trace of abrasive is left behind anywhere in the engine.

Your engine was running with grossly excessive valve lash on both valves - perhaps it has been run for years without adjustment, but if not, someone has made a mess of it. Bear this in mind when sourcing future servicing, in case you are employing someone unreliable. The correct clearances are intake 0.004", exhaust 0.006".

The positive crankcase ventilation valve for the engine is underneath the flywheel in a sealed compartment. In the compartment is a brown (phenolic-impregnated cloth) disk, which is the valve. Inspect the disk, which will show some wear on the upper side where it strikes the compartment's steel cover once every revolution. If it is deeply indented by wear, replace the disk. Check that there is no build-up of crud in the port underneath it. There is also a folded piece of plastic mesh (not steel) in a vertical compartment within the PCV compartment. Remove and wash the mesh, and while it is out, carefully push a 1/16" drill bit back and forth through the drain hole in the bottom of the vertical compartment, at the opposite end to the port where the breather tube attaches on the outside of the engine. If that tiny drain hole blocks the PCV compartment will flood with oil, which will then go through the breather tube into the air cleaner and from there through the intake port into the engine, where it will burn and possibly cause additional smoke.

You should service the carburetor while you have the engine apart. I suggest you watch this video, which shows the correct way to do this for your engine:


Bear in mind that many owners make a mess of the carburetor cleaning operation and get poor results afterward. Also, on older small Honda engines like yours, the black fibre gaskets on both sides of the carburetor insulator (between the carburetor and the intake port) always split when you dismantle the engine. They cannot be reused when this happens: use new gaskets on both sides of the insulator.

Please post some pictures of your engine as you go, and ask as many questions as necessary.

Grumpy, thanks for the quick reply and the tips. The mower was my fathers so I know the valves were never adjusted as we did not know they needed adjustment. How often should they be adjusted?

The PCV disc flipped over when I took it out so I don't know which side was up. But neither side shows any type of marks or wear. Also the PCV chamber was very clean and the drain hole was open. However I did notice a little oil at the end of the hose going to the air cleaner. Maybe this was from excessive blow by from the worn oil ring. I plan to get genuine Honda parts so will the rings be the type you described? Or do I have to ask for them specificly?

The valve seats and mating surfaces on the valves look good. Should I attempt to lap the valves in or just clean the carbon from the exhaust valve and related areas?

The cylinder looks good. No scratches or other damage. You can still see the factory crosshatching. No ridge at the top of the cylinder.

If I can get my camera to cooperate and if I can figure out how to post pictures I will do so.

The valve clearance should be checked when you service the mower, which essentially is when it's due for an oil change.

I agree that with the piston ring wear you had, there may have been enough leakage past the piston rings to carry some oil into the breather tube. The new rings should put that right. Provided the bore is good (no longitudinal wear marks in the bore) the chances are that a new set of standard size GXV120 rings will fit properly: ex-contractor engines of that type that I've seen, with similar ring gaps, have only had 0.002-0.0025" of bore wear, which is insignificant. Of course you should check the gaps in the new rings before you put them on the piston. AFAIK, Honda has switched to the steel rail rings on factory-built engines several years ago, so unless somebody sells you new-old-stock rings, you should get the correct type. However if you just look at them without taking them out of the transparent plastic packaging, you can verify this without being stuck with them if they're the wrong type. It is still possible to buy the old type in unbranded rings from Thailand, but even all the copy-Hondas from China that I've heard of, have had the steel rail rings for several years now.

It sounds as if your project should be no more difficult than resuscitating the average ex-contractor GXV120: new rings, check the PCV (which is usually OK), clean the carburetor properly, inspect the valve seating, and put it back together. The rings alone are only about a one-hour job, but the carburetor takes nearly an hour, and the checking over everything at the end takes perhaps half an hour. In my opinion that is a sweet little engine, and very pleasant to work on.

Trying to order parts. When you say steel rail rings are you saying a 3-piece oil ring?

Yes, the oil ring is assembled from two steel rail rings and a steel ring expander, so three pieces to make up an oil ring. The pieces are separate, you put the expander on first, then put the two steel rail rings on over it. Do it carefully - in particular, do not allow the free ends of the expander to overlap each other.

I understand about the oil rings. I don't expect the parts for at least a week.

Thanks for letting us know, Terrys, and that's fine, we'll leave the thread open.

I finally got the parts. The ring set they sent is Honda part # 13010-ZE6-013. It has a 1 piece oil ring like the one in the engine. However they do not say which is the top ring and which is the 2nd ring. one ring is solid black with. the other ring has a grey coating on the surface that hits the cylinder wall. This ring also has a tiny step on the top of the ring surface that contacts the cylinder.

Can you please tell me which ring is the top and which is the 2nd ring. I believe the 2nd ring is a tapered scraper ring but the taper is so small I can't see it.

Also the valves and seats look very good with narrow contact areas as I said above. However after putting the valves in a drill and cleaning with scotch brite I can just barely make out some very small pitting. I have some lapping compound. Could I use a drill to spin the valves against their seats and try to lap them in?

Thanks.

Were the new rings in a genuine Honda packet, with the Honda logo and name? I haven't heard of anyone but the cheapest non-genuine Thai spares dealers supplying that old-style ring set. Provided your ring gaps are within the specified range you can use it, and it will work well, but the oil ring will wear out faster than the current design. Nevertheless, I think you could have bought chonda rings of considerably higher quality for very little more money.

Normally there is a small mark on the top of each ring, right near the ring gap. It will probably be a tiny letter.

You lap the valves against the seats by applying a special suction cup on a wooden shaft, to the center of the top of the valve head. You can get the device at any auto spares shop.

Yes the rings came in a sealed package from Honda and all have a .014" gap. The rings do have a letter on them indicating the top side. Can you tell me which is the top ring and which is the 2nd ring? I will try to find a valve lapping tool.

Since they are genuine Honda, the top ring is chrome plated on the outer (wearing) surface and the other rings are not. There is also a slight radius on top and bottom edges of the wearing surface of the top ring.

Here is the illustration from the manual, showing what the rings look like:

I could not see a taper on the black ring until I held it up against a square and then I could see a very slight taper like the middle ring in your picture.

My other ring has a grey coating on the wearing surface but it does not look like chrome to me. Also it has a tiny 90 degree step at the top outer corner of the ring.

I talked to the service manager where I bought the rings and he said the black ring goes on top and the coated ring with the step is the middle ring.

Yes; it's a 'scraper ring'. A good [though it does have gaps] online reference on piston ring types is HERE .
That's because it's 'hard chrome' plating, as distinct from the decorative 'bright chrome' you'd be familiar with.

Oh dear. Grumpy's reference is correct; that service manager isn't. The top ring works the hardest; that's why it's an advantage to provide it with a hard main wear surface, expensive though that is. In comparison to a plain cast iron ring, at any rate.

At this point I don't understand how those old rings were even available for sale, but I am not closely familiar with Honda's sequence of design changes. Perhaps they continued to make the old design available for some reason I'm not aware of, or perhaps you have been sold New Old Stock rings.

I won't say anything about the service manager in the interests of fairness since he hasn't had a chance to explain himself.

The service manager seemed very willing to help and spent some time cleaning the valves. In fairness to him I had asked him about a week ago and he may have just forgot the correct sequence. They are a very busy shop and many service people around here won't give you the time of day let alone stop what they are doing to help with something for which they are not getting paid. He was very helpful in getting me the specifications for the blade clutch lining wear. So I will chalk it up to an honest mistake.

For what it is worth my top ring has a step like the stepped ring in the link you provided except it is on the top outer corner that contacts the cylinder wall.

I have no doubt it was an honest mistake, but it does seem to mean you need to check the accuracy of information you get from him. I also agree that a helpful service person is very much more pleasant to deal with than an unhelpful one.

As you can see from the diagram from the Honda manual, the original design of the top ring did not have a recess, and the current ones with the steel rail oil rings do not have a recess either. I do not know what design evolutions Honda may have followed in between those two steps. For what it's worth, all I would do myself is make sure the rings were clearly supplied by Honda and have the correct part number (which they do). On that basis I would be sufficiently confident to use them without feeling any concern. There are many designs of piston ring, and it is not unusual for an engine manufacturer to change from one to another as they acquire more service history data from engines in the field. The use of recesses relates to how the ring twists under compression pressure in a running engine, and when you consider the range of speeds and compression pressures (the latter depends on how far the throttle is open at that moment) that may be experienced, it is no simple task to arrive at a design.

Sure, with Honda's 'continuous improvement' process, it can be easy to lose track of parts supersessions.

It needs to be remembered that Honda's technology in the field of pistons and their sealing is world-leading; especially their Formula One race car, and Grand Prix racing motorcycle, engines - e.g. the NR500 racebike used oval pistons!

And this does trickle down to their more mundane products, such as OPE engines. So advanced design features, which other OPE engine makers don't use, can occur.

Ok I finally had time to get back to the engine. I found a valve lapping tool and got the valves lapped. I seem to remember something about spacing the ring gaps 120 degrees apart. Or should they be 180 degrees apart?

One more thing. I forgot where the screen in the breather chamber goes. I think it is supposed to slip down in the bottom and be pushed as far as it can to cover the hole that goes to the out side of the case where the rubber breather tube connects. Is this correct?