Honda GXV120 rebuild

[Hammermechanicman]

If you have a outside micrometer measure the valve shaft diameter up near the keeper area then measure along the valve stem in the area where the stem rides in the guide. If there is any difference i would replace the valves and lap them in. Unless you are planning to race the engine or the like i would not worry about the guides.
Hone the cylinder, new piston and rings, new valves lapped in, seals and gaskets and i bet you will be good to go. As Taryl would say. It's not the space shuttle. ?

 

[Chris Parman]

Hi Chris,

Assuming you have a 0-1.00" micrometer, i'd try to find the largest diameter rod that will fit into the valve guides and then mic your valve stems where they come into contact with the valve guides, if > .001" I'd replace the valve guides. Mine were within 1/2 thou or so (i.e. .0005"). I understand about not having special tools, my Intertec manual says a special tool is needed to install the guide(although a right sized deep well socket would probably work) and they must be reamed after installation, again using a special reamer, however reamers can be purchased at like .0005 increments.

Correction on the cylinder bore diameter,,,the Intertec manual says 2.262-2.363, I believe is a typo (by Intertec, not me) I think they mean 2.362"-2.363. Makes sense as the piston is 2.360"-2.361". Sorry,,,I try to triple check what I type for accuracy.

Jeff

Hello Jeff, I found this online



But I don't understand the clearance meaning of 0.20 +/- 0.02mm (0.008 +/- 0.001 in)

 

[jp1961]

Hi Chris,

Hmmm,,,hard to interpret this chart. I'm guessing for your GXV120 engine the intake should have .15 MM clearance for the intake and .20 MM clearance for the exhaust. Not quite sure if this is the clearance for the valve stem to guide clearance or the amount the valve opens?

If the values in brackets are imperial measurements or inch base,,,,.006" seems very loose for the valve stem clearance, somewhat like a baseball bat in a rain barrel.

Jeff

 

[jp1961]

Hi Chris,

I'm guessing you want as tight a clearance in the valve stem to valve guide clearance, Too tight and the valve stem will bind, too loose and oil will escape into the combustion chamber. Your talking tenths here,,,(i.e. .0001")

Keep in mind as metal gets hot, it will expand, as long as the guide is made from similar material, it will expand at the same rate.

Regards

Jeff

 

[logert gogert]

If you have a outside micrometer measure the valve shaft diameter up near the keeper area then measure along the valve stem in the area where the stem rides in the guide. If there is any difference i would replace the valves and lap them in. Unless you are planning to race the engine or the like i would not worry about the guides.
Hone the cylinder, new piston and rings, new valves lapped in, seals and gaskets and i bet you will be good to go. As Taryl would say. It's not the space shuttle. ?

oh cool, you know who taryl is?
like, taryl fixes all?
if thats who your talking about, i could honestly care about his mowers, i just wanna see how fast he can eat an ear of corn. LOL not really
sorry I'm so mean lol

 

[ILENGINE]

Here some pictures of the Cylinder head and Valves. I clean the cylinder head in a Ultrasonic cleaner and it came out pretty clean except for the exhaust runner and valve pocket, which I already started to grind out the carbon build up. I'm not entirely sure if this engine ever had valve steam seals and I did see evidence of any seal debris in the oil sump. Also, there is quite a lot of carbon build up on the exhaust valve (see pictures) not sure if its due to worn piston rings or valve guide. However, initially when I took off the cylinder head I noticed a small pool of oil at the bottom of the cylinder when the piston was at top dead center. I know I need to oder the GXV120 Service manual (and I ordered the manual today from Honda), I was just wanted your thoughts thus far in the rebuild cycle. As always I appreciate everyones input.

View attachment 50823 View attachment 50824 View attachment 50825 View attachment 50826 View attachment 50827 View attachment 50828 View attachment 50829 View attachment 50830

I looks like the exhaust valve wasn't sealing properly which can cause oil usage. Also oil in the bottom of the cylinder could be cylinder wear, but could also be just oil seepage past the ring while setting.

hey guys, i know this is off topic, buuut lets say i wanted to rebuild a engine, ( which i don't )
HOW do you get those precise measurements, i mean you can't just whip out a ruler and go, alright the cylinder is 3.0001276
like wut?

You need to have a bore gauge and micrometers to measure the bore gauge down to the nearest thousands. I have a dial type bore gauge that measures .0005 but you still need the micrometers to set the standard bore size to calibrate the bore gauge to find out of round and oversize.

 

[ILENGINE]

Hello Jeff, I found this online

View attachment 50836

But I don't understand the clearance meaning of 0.20 +/- 0.02mm (0.008 +/- 0.001 in)

Those are rocker to valve stem clearances. And the .20+/-.02(.008 +/-.001) means the valve clearance for the exhaust valve is .18-.22 mm or .007-.009 inch.

 

[tranchinh]

I'd re-ring and hone the cylinder a little ,lapping the valve then it run good ,never see cylinder that worn out to out of spec on these engine ,Piston sometime need to replace .

 

[steve581581]

Where do you guys buy your parts from? I've got the same engine that I'm rebuilding and my local shop can't get new valve guides or seals and I'm waiting to hear back from them about the gaskets and rings.

 

[Chris Parman]

Where do you guys buy your parts from? I've got the same engine that I'm rebuilding and my local shop can't get new valve guides or seals and I'm waiting to hear back from them about the gaskets and rings.

Hello Steve: It really depends on the lawn mower model and/or the VIN number on the engine itself. For example the GXV120 I rebuilt some 3 years ago was attached to a HR214SX. From what I found on (boats dot net), only the exhaust valve guide is available. Valve seals were never a original part per the GXV120 engine head. Here is the URL -> https://www.boats.net/catalog/honda/lawn-mowers/hr214-sxa-2-vin-hr214-6235981/cylinder-head