Valve issue, what causes this?

[jjdlc]

I'm a chainsaw guy, don't have a lot of experience with 4 strokes, but sometimes get conned into working on one. This is from a Honda GX160 on a wood splitter that a buddy asked me to look at. Engine starts easy enough, and runs pretty good, but blows grayish white smoke. Compression was a little on the low side so I tore it down expecting to find it needing rings and maybe to be bored.

When I got inside the rings, piston, and cylinder looked a lot better than what I expected, but the head was another matter. The exhaust valve was caked in carbon. I pulled the valve and took a wire brush to it to see how bad it was, but I found the following, what I though was all carbon buildup is instead metal. See the pics, wish I had thought to take one before I started cleaning the valve.



My question is, what would cause that? Is it metal extruded from the valve itself? The valve seat and the valve itself neither have a nice beveled edge like I would expect, instead there is a groove worn in each. At this point I'm thinking a new head is probably in order, since I'm not really sure what all is salvageable on this one. I'll probably go ahead and put new rings in while I'm at it.

Anyway, thanks in advance for any insight, always eager to learn new stuff.

 

[Wonkydonkey]

Is that just sh!t loads of carbon build upon the valves, prolly from never cleaning the air filter. If you google gx160 valves and look at the images, you should see what they should look like.

Wasn’t there a way to check if it were the rings or valves with low compression. ?

Summing like check/get compression reading, then put some oil into cylinder and check compression again.
Iirc... the oil helps seal the rings betterer thus you can dejuice if rings or valves are the prooblem,
With all that carbon, the valves prolly not seatin right. So a clean/quick bit of lapping and a check.

It’s up to you I guess...see what else someone else chirps in with..

Cheers

 

[Wonkydonkey]

Just another thought, have you looked at the piston and rings. ? With all that carbon, the rings could be full, thus allowing to much oi” pass the rings. Hence the carbon...? Or even broken oil ring

Just thinking, as I can’t looky from here..

 

[jjdlc]

This is what remains after I removed the carbon, it's apparently metal. I'm guessing the engine was running hot and deformed the valve, but like I said I'm not real experienced with 4 stroke stuff. I'll have to read up on the oil thing, would make sense, if its rings you should see an increase in compression, but probably wouldn't if it was a valve problem.

The piston and rings are in pretty good shape given the carbon buildup, I was surprised how good honestly.

At any rate, I haven't ordered any parts yet, but looking the head over I'm not sure a simple lap will do. The valve has worn a nice groove in the seat, and vice versa, there isn't much left there to lap. The valve seal on the exhaust valve is pretty rough, which I figure is the source of the burning oil.

 

[Stump Shot]

Check the bore carefully it most likely is wore out and you are seeing it crusted on your valve. Check the bottom end and see if it's full of metal as well. If so more likely than not a replacement engine will cost less than parts to repair. Look twice before going down the rabbit hole is all I'm a saying here.

 

[jjdlc]

I'll check it out good, I'm borrowing a good set of calipers so I can measure the bore too. I didn't notice any play in the crank, but I'll check it more thoroughly.

 

[srcarr52]

This is what remains after I removed the carbon, it's apparently metal. I'm guessing the engine was running hot and deformed the valve, but like I said I'm not real experienced with 4 stroke stuff. I'll have to read up on the oil thing, would make sense, if its rings you should see an increase in compression, but probably wouldn't if it was a valve problem.

The piston and rings are in pretty good shape given the carbon buildup, I was surprised how good honestly.

At any rate, I haven't ordered any parts yet, but looking the head over I'm not sure a simple lap will do. The valve has worn a nice groove in the seat, and vice versa, there isn't much left there to lap. The valve seal on the exhaust valve is pretty rough, which I figure is the source of the burning oil.

That is heavy carbon build up, you'll be able to scrap it but a wire brush won't take it off. It even takes time with a bead blaster to get that amount off.

It has definitely been burning a lot of oil, check the ring gap when you get the piston out. Maybe someone overfilled the oil and ran it that way for a long time. Ring gap should be something like 0.008-0.014" on the top two rings.

Oil doesn't usually come from the top end of these engines until the valve guide is extremely worn. If it was you'd have a lot of carbon build up on the backside of the intake valve.

From what I can see of the valve face in the last picture it doesn't look that worn. I've seen much worse. The seats only have a 45deg face cut on the square insert from the factory, no 3 angle seats on these. So they always look terrible when you pull them down but they are not really that bad. You could probably get away with lapping them. If not, a loaded AM head is $30 and they work fine. I've used the AM 160 head and valves up to around 18hp on alcohol kart motor, anything more than that the cam profiles needed break the retainers or valve stems.

Oh, and that is a good looking pup you got!

 

[huskihl]

What Shaun said, I bet it's carbon buildup on the valves also. I bet it has a couple hundred hours on each oil change and they don't use a quality oil when they do change it. The Rings get stuck in place on the piston from carbon and it starts blowing oil by the rings

 

[Wonkydonkey]

Cheers for chirping in

 

[jjdlc]

Thanks for the input, going to check the ring gap and measure the cylinder this weekend. Told my buddy he should just go get a Predator from Harbor Freight, but he really wants to keep the Honda if possible.

 

[Fish]

Do you have any pics of before you started knocking carbon off of things? Any pics of the head/head gasket?

 

[Fish]

Looks like running one with a leaky head gasket.....

 

[jjdlc]

Ok, pretty sure I found the source of the burning oil. Pretty sure the ring gap on these top 2 rings is bigger than 0.014" .



I really don't see any signs of a leaky head gasket.



Measured the cylinder 3 times at multiple depths, and got 68.0 mm on the dot, so it's in pretty good shape. Piston shows a little wear. Found a kit with AM head, piston, con-rod, rings, and all that with good reviews, figure I'll order it, should put this motor in good condition.

Thanks again for the advice.

 

[isaaccarlson]

Holy smokes! Yeah, put a new head, piston/rings and send it home. Those rings are garbage!

 

[jjdlc]

Got her put back together yesterday with the new parts, and she runs like a new motor. Thanks again for the help, srcarr52 hit the nail on the head with the ring gap.

 

[srcarr52]

Got her put back together yesterday with the new parts, and she runs like a new motor. Thanks again for the help, srcarr52 hit the nail on the head with the ring gap.

Glad I could help.

 

[FergusonTO35]

I say it's always a great idea to replace cheap parts any time you have something apart, provided you havent found a reason to write off the whole thing. Often times, new rings/bearings/lap the valves will breathe enough life into it for a few more years or longer.