Gosh, I hope this goes well then.
Before getting into this, let me start by saying, it's a good idea to take your time. We're not in a NASCAR pit crew and we don't have to get this thing back on the yard in record time.
Look things over good before, and during the disassembly. Have a good idea of what things look like, where they're at, and how the different parts fit and work together before taking them off.
You may want to clean things up a bit before beginning the disassembly. After all, this is a piece of outdoor power equipment, and you can expect it to be dirty, but we don't want to get or leave any of that dirt in it as we put it back together. Besides, it's always more comfortable to work on something that's at least fairly clean.
As you take things off, put them somewhere out of the way, and in a place you know you'll be able to find them again. Nothing worse than tripping and stumbling over bits and pieces of the engine you're working on other than stepping on something and either bending or breaking it when it could have been out of harms way.
So, let's get started. Now, this engine had already been removed from the mower, so the list of tools necessary might a bit longer than what I'm showing here. The list of tools you need for the engine is actually pretty short, and other than a torque wrench, nothing specialized.
10mm socket for most everything. 12mm socket to remove the head bolts and a 19mm socket to remove the flywheel nut.
I actually use a 1/4" drive ratchet wrench for most everything. A 3/8" breaker bar to get the head bolts to loosen, and I'll admit, I cheated and used an air impact to get the flywheel nut off.
You'll need a #2 phillips screw driver and a flat bladed screw driver, and a pair of needle nose pliers for the carb. Honda has published a darn good video of how to clean one of these carbs, so I'll just reference it rather than go into it in this rebuild.
A set of feeler gages to set the valves, a plastic mallet to help separate the oil pan from the block, and I used a small chisel at one point, and a length of rope. I'll try to remember to mention how and why when I get to those last two.
First thing obviously is to strip the engine naked, so to speak.
The air cleaner, shroud and dip stick tube come off first. The recoil is attached to the shroud and comes off with it. I can tell you that one of the hardest parts of this whole process is getting the shroud up over the fuel filler neck. There is a rubber grommet on the shroud that fits up next to the filler neck that seems intent to holding onto the shroud on everyone of these I've worked on.
Next, I remove the control, as Honda calls it. It's that part on the side of the engine that the throttle cable attaches to. You see the link to the choke on the carb in the picture above. What you don't see is a coil as it had been robbed from this engine for another before I got it. The engine shut off switch is also on the control, and the wire from that switch to the coil has to be removed if yours still has the coil on it. Two bolts holds the control to the block. Remove the governor spring at the bottom of the governor arm and the throttle control and set it aside. Removing the control also makes it easier to get the choke rod off without having to bend or twist the rod, or worse, break the plastic choke arm. You can just finagle the control around to get it disconnected.
Next you can slide the carb out away from the head. It might take a pretty good tug, and you may actually have to put a lever behind it to get it to budge from the engine. Pull it out until the governor rod and the slot in the top of the throttle lever line up, then you can lift the governor rod up and out. Use a pair of needle nose pliers to turn the end of the anti-surge spring up and out of it's hole in the throttle lever.
Yes, this carb will need to be cleaned, and here is the video that shows you how much better than I could. In case this gets lost in translation, go to the drop down "service" menu, choose "service videos" then "GX series cleaning guide." Don't expect any sparkling dialog, because there isn't any. Just somebody's hands showing you what to do.
Honda Engines Europe EEC
Next up, remove the valve cover. There's your overhead valves. Spin the flywheel around until both rocker arms are loose, then you can easily push down on the springs and move the rocker arms to the side a bit and pull out the push rods. There are 4 bolts holding the head to the block. Two outside and two inside with the OHV.
Usually a fairly gentle tug gets the head off, and the head gasket comes right off too. It's up to you if you want to remove the two dowel pins. Sometimes they slip right out, sometimes not. The remnants of the head gasket are easy to remove with a single edged razor blade.
Note the arrow on the top of the piston and the direction it's pointing. The elongated hole on the right side of the picture is where the push rods go and that arrow points toward that hole when you go to put the piston back in later.
Now you can flip the engine over and get ready to remove the oil pan. There's seven bolts that hold it on. Two of them are right at the bottom of this picture. The other five are in the dirt and crud on the bottom of the engine. Normally I'd recommend starting with one of the bolts and going clockwise around the pan as you remove them, and lay them out, left to right as you set them down. The reason being that sometimes the pan bolts are of different lengths, and in removing and arranging them this way, you can just reverse the procedure during reassembly and they all fall into the right hole. In this case, they're all the same length on the GXV120, so you can just remove the willy nilly and throw them in a drawer together.
You can try to lift up on the oil pan after you get all the bolts out, it might just separate from the block. In case it doesn't, use a plastic mallet and lightly tap the pan where it over hangs on either side of where the dip stick tube goes. That's where the two dowel pins are.
Once you get the oil pan off, this is what you see. As I had said, this engine is from an HR214SXA, which means it has a shaft driven two speed transmission. You see the plastic governor and the drive shaft in the oil pan. The drive shaft is driven off of the spiral gear on the cam shaft that is still in the engine block.
Make note of the two dots you see in this picture. Those are the timing marks that you will be lining up when you put things back together. The small one is on the crankshaft, and sometimes it's just a small "O" that you really have to look for. The heavier mark on the right is on the cam shaft.
The cam shaft just lifts out. Since this cranks shaft is bent, I had to remove the flywheel nut, pull the flywheel first, then the crankshaft just pulls out.
Here's one of the two dowel pins in the block that line the oil pan up. It's easier to get the old gasket off if those are out of the way, but this one was the only one of the two that came out.
You see that black plastic thing with the sort of crown shaped end on it just tot he right of my thumb? That thing is called an oil defense pipe. It sticks out from the bottom of the block when the oil pan is out of the way, so be careful and don't break it, or you oil defenses will be gone when you put the engine back together. I know I said this should be an Q and A, but don't ask me what the thing does or why, I don't know. It's just supposed to be there and it must be important to get a name like oil defense pipe. Those things are supposed to be locked in place, but this one lifted out, and they only fit in one way if yours comes out too.
O.K., so everything else is out of the way, time to pull the piston out. Rotate the crankshaft around until you can get a socket wrench with a 10mm socket down in there to remove the two connecting rod bolts. Note the line on the left side. They're like an arrow pointing you in the right direction during reassembly. Remember the arrow on the piston? When the piston is in correctly, the line on the top end of the connecting rod assembly will be there, so just line up the line on the bottom end, and life is good.
We've gotten everything out of the block, and here's one of the things that makes this engine special. The top end spins on a bearing. One of the other things is the cast iron cylinder sleeve that makes this rebuild possible.
So for now, let's take a break and we'll start the reassembly later.