Honda Gxv120 Rebuild-mystery part?

Boats.net came through on my Honda parts a little more than a week after ordering them. Not bad, and they really did seem to have the lowest prices. So today I picked up some assembly lube, a piston ring compressor, a 3/8ths torque wrench and went to work. First came putting the piston back into the cylinder-not too bad a job, just be VERY careful to align the rings with the mark facing "up." My mark was a "N" instead of a "T" but I think I got it right.
 
Next was the crankshaft (lube it up, drop it in the bearing) and the the connecting rod cap. When you tighten the connecting rod bolts, make sure you are using a torque wrench! The space you have to work in is really tight so I actually went and picked up a new one for the occasion. The sears store only had a 3/8ths drive, but a 1/4" probably would have worked even better if I had thought ahead and ordered it online.

After the crankshaft and piston are back together, move on to the camshaft. Make sure the dots line up, the lifters are back in their slots, and drop it in. I didn't mark the lifters as I took them out...but they appear to have no wear and be identical.

So far so good...until I found a mystery part! Shit, I hate it when that happens! Here is a picture of the little sucker:

This little guy shows up in the parts sheet on boats.net as a "pipe, oil defense" in the cylinder head parts diagram.  Unfortunately, it shows up nowhere in the manual, and in the parts diagram it is off in the corner by itself...no clue to where in the cylinder head it lives. Hmmm...so dear readers, anybody know where things thing goes?

Tools used to reassemble the gxv120 piston, crank and camshaft:

1/4-Inch Torque Wrench
Piston Ring Compressor
Engine Assembly Lube

Measuring the gxv120 Cylinder Bore

After I got the gxv120 cylinder honed I began to have doubts that the cylinder was still within spec. After all, this engine is pushing 30 years old (!), and was running super high revolutions when the tear-down began. So I decided to do some rough measurements with a telescopic bore gauge and calipers that I borrowed from a friend. Luckily the hr214 shop manual had the specs for the bore, and after taking some measurements it looks like my bore has about .05mm of wear, but is still well within spec. If anybody wants to do a tear down on one of these hondas and take the measurements, you need to take your time and do multiple measurements. I followed the directions from the video below:

Tools used in video:

Telescoping Bore Gauge Set

Digital Caliper

Dial Bore Gauge

Like Jaf says in the video, the dial bore gauge is the best solution if you're building a serious engine, but for a lawnmower engine that is measuring so far below tolerance with the telescoping bore gauge set, I think I'm fine. I ordered some parts from boats.net too...hopefully next week the rebuild will start.

Honda hr214 lawn mower engine tear-down

And so it begins! I spent the majority of sunday tearing the gxv120 down. I used the official honda manual for the disassembly, but didn't necessarily go in the order prescribed.

Tools: No special tools required, just a wheel puller and a strap wrench to remove the flywheel. Beyond that, I have a motley assortment of metric wrenches and sockets. I would need some special measuring tools if i was going to check out engine internals myself, but for now we're OK since I'll be sending the block out for honing before I drop the new rings in. Oh, and a digital camera to take pictures as you go, and some baggies to store the parts.

Manuals: Just some youtube videos and the official honda hr214 manual. I'll use the parts manual from planopower.net or boats.net to order the stuff, but it wasn't necessary for the take apart.

Steps: I should have removed roto-stop assembly from the bottom of the mower, then taken the engine off the deck. Instead I left the mower on the deck, too it apart until I was down to the block, and then removed the roto-stop assembly. My back is killing me from all the bending over, even though the mower was on saw-horses.

So what does the inside of this small engine look like? Really, not fantastic. No metal shavings, but the bore is as smooth as glass, no cross-hatching in site. Ergo, definitely a hone job before it gets put back together. I'll also have the machine shop check the bore to make sure I don't need an over-size on the piston/ring set, but I would guess I'm ok there.

3800 rpm Honda gxv120!

So after posting my "before" tear-down  video of the smokey hr214 mower, some of the guys over at "My Tractor Forum" said that Yoshimi was running a bit fast...like a thousand rpm fast! Whoops. So I ran out to Northern Tool and picked up a digital tachometer like this one and hooked it up. After a little  learning curve, this tach was pretty easy to set up; red wire gets wrapped around the spark plug lead, and the white lead gets grounded to the frame. The hr214 sparks every revolution (even during the exhaust stroke), so i left the stock settings in place, but you can also set it for different types of motors (distributor vs. non, etc).

So what did I find? Holy crap, this thing was about to fly apart! The specs for the gxv120 call for about 2,000rpm at idle with the blade disengaged, and I was up around 3200 at idle, and around 3700 at top speed.

Hmmm...after reading the manual, it looks like the idle gets adjusted at the carburetor via the throttle stop screw, but no dice! Long story short...the breather hose was actually broken off a the block  and had pressed the governor arm as far as it would go-keeping the engine running at top speed. After seeing the breather hose venting to the outside world, I decided to go straight to the tear-down, and spent most of today taking the gxv120 apart. Video of my rev-happy Honda below: