Honda GXV120: Valve Adjustment...which one is intake vs exhaust?

[nobb]

Hi guys, I'm doing a valve adjustment on an old Honda HRA214 mower with the GXV120 engine. Browsing the shop manual and internet...it's not clear which valve is the intake an which is the exhaust. How do I figure it out?

On the GCV120 engines, the exhaust is closest to the muffler and the intake is closest to the air cleaner. As you can see in the pic of this GXV120, the orientation of the valve pairs is perpendicular to the intake & exhaust sides!

 

[Silverado12]

I'm going to guess the top one is the intake.

 

[FowVay]

If you can see them then the bigger valve is the exhaust. Follow the intake and exhaust ports and see which ones line up. As a last resort take the plug out and spin the engine over. You'll have an intake stroke with the intake valve opening followed by a compression stroke where both valves are closed, followed by combustion down stroke and then you'll see the exhaust valve open. This repeats itself over and over. Intake-compression-combustion-exhaust...

 

[Silverado12]

Bigger valve is intake.

 

[Lolvoguy]

Originally Posted by Silverado12
Bigger valve is intake.

+1

 

[nobb]

Maybe I'm blind but I actually can't see a "bigger" or "smaller" valve.

 

[bobdoo]

Take the muffler off, and look.

Where the [censored] is the intake manifold?! Weird design.

Why is hll censored?

Turn the engine over. Intake opens, compression stroke, combustion stroke, exhaust stroke.

 

[Rand]

try some compressed air in the muffler, with one valve open if no air comes out its the intake.

 

[Slick17601]

Originally Posted by Lolvoguy
Originally Posted by Silverado12
Bigger valve is intake.

+1


+2

 

[Linctex]

Originally Posted by Slick17601
Originally Posted by Lolvoguy
Originally Posted by Silverado12
Bigger valve is intake.

+1


+2


+3... Some very old engines have them the same size,

but everything built in the last 50 years or newer always has a larger intake valve!

 

[Linctex]

Turn engine so one rocker is all the way open.

Put a vacuum cleaner hose to the exhaust port on the muffler and feel for air sucking into the spark plug hole.

If no air sucks into the plug hole, you've got the wrong rocker.

I'm "guessing" intake on top, exhaust on the bottom.

 

[mk378]

It looks like the bottom one would be intake. There must be some sort of pipe from the carburetor across to the intake valve, but it could be part of the casting.

Turn the crankshaft by hand the same direction it runs. The exhaust valve will open first, then the intake, then they will both be closed for one full turn of the crank then they cycle repeats.

You want to have the crank turned to a bit past the middle of the "both closed" part when setting the clearance. That is the power stroke. There's likely a compression relief bump partway up the compression stroke which could interfere with setting the exhaust valve.

 

[bubbatime]

Im seeing bottom one as the exhaust and top one as the intake. Look to where the carb is bolted to the engine, and follow the casting to the valve. Same thing with the exhaust, look to where the muffler is bolted to the engine, thats your exhaust port. Looks like the bottom valve to me. More pictures at different angles would confirm.

 

[Tman220]

Originally Posted by bubbatime
Im seeing bottom one as the exhaust and top one as the intake. Look to where the carb is bolted to the engine, and follow the casting to the valve. Same thing with the exhaust, look to where the muffler is bolted to the engine, thats your exhaust port. Looks like the bottom valve to me. More pictures at different angles would confirm.

quoted for emphasis! I agree with this assessment. look closer at the head, where the carb attaches to the head and where the exhaust enters the muffler. Another clue that the exhaust valve is the lower rocker is that the valves are located on the left side of the head which is most likely the exhaust port because that would allow for a shorter exhaust port. The shorter the better on an air cooled head for obvious reasons. Also look at where the spark plug is located.. at the top of the head, there is no way you could have an exhaust exit left from the top rocker.

wow some of you on here know just enough to be dangerous, there is really no way to knowing which valve is larger without removing the head and checking

 

[nobb]

Thanks for all the replies. On the intake side I don't see any porting but on the exhaust I do believe I see some porting to the lower set of valves.

 

[Linctex]

It was hard to see in the first photos,

But with these new phots you can see very clearly the bottom is the exhaust.

 

[FowVay]

Here is the parts diagram and the reason I commented on the valve size. From the looks of the drawing the exh. valve is the larger of the two. I suppose it's possible that this is not drawn to scale:

 

[Kamele0N]

It is clearly stated that 7 is VALVE IN (intake valve) and that 8 is VALVE EX (exhaust)...

 

[FowVay]

Yes, and no. 8 (ex) certainly looks larger than no. 7 (in) to me.

 

[Lubener]

Originally Posted by Silverado12
Bigger valve is intake.

That has always been the case from what I dealt with.