# Honda GX340 Rebuild Questions. Specifically The Head.



## orangputeh (Nov 24, 2016)

The lower end blew from either low oil/excessive heat and I have a lower end rebuild kit coming.

My question is about the head here. It appears perhaps high heat around the exhaust spring . Not sure if valve is toast. I think the picture can show evidence of high heat. There is also soot and tar like oil.

Do you think this is worth the work to rebuild the head? What caused this? A leaking valve? Could this contribute to the lower end blowing?
I'm thinking of not taking any chances and just getting a brand new complete head.

Thanks. 

I have done minor head work before , lapping valves, seals , etc but not sure what work needs to be done on this one.


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## tadawson (Jan 3, 2018)

Which side sits up? Looking at the pic, it looks like the gunk may have come from the bolt area. In any case, pull the valves and check for guide and seat wear. If that looks good, myself, I'd probably reuse it.


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## orangputeh (Nov 24, 2016)

tadawson said:


> Which side sits up? Looking at the pic, it looks like the gunk may have come from the bolt area. In any case, pull the valves and check for guide and seat wear. If that looks good, myself, I'd probably reuse it.


this is upside. what do you think caused this? It seems like it is leaking. I'll pull the valves.


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## RIT333 (Feb 6, 2014)

I agree with TADawson. If it looks good once you pull out the valves for inspection, I would reset the clearances and give it a go.


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## contender (Jan 18, 2018)

Is this crud and tar since you had it running after the rebuild, a day or two ago??


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## JnC (Feb 21, 2014)

Disassemble the head, clean up everything, lap the valves, check for play between valve guides and the valve, the crud is common for 240/270/340/390 engines NBD just a bit of blow by due to the motors not having any valve seals. Check the spring height and confirm its within acceptable range, put it all back together and you are good.


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## tadawson (Jan 3, 2018)

orangputeh said:


> this is upside. what do you think caused this? It seems like it is leaking. I'll pull the valves.


Not really anywhere for oil to come from to come up the exhaust guide . . . I suspect that is just due to the lube in the valve train and the normal heat on the exhaust side, esp. if run hard. If the vwlve/guide fit isn't loose, call it good . . . (I note that as the GXV variants evolved, Honda added a rubber seal to the intake to stop oil from being pulled _in_ through the stem, but nothing on the exhaust side . . . Unless the engime was really ragged out when you started, there sho8ld not be any oil on the exhaust side.


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## orangputeh (Nov 24, 2016)

tadawson said:


> Not really anywhere for oil to come from to come up the exhaust guide . . . I suspect that is just due to the lube in the valve train and the normal heat on the exhaust side, esp. if run hard. If the vwlve/guide fit isn't loose, call it good . . . (I note that as the GXV variants evolved, Honda added a rubber seal to the intake to stop oil from being pulled _in_ through the stem, but nothing on the exhaust side . . . Unless the engime was really ragged out when you started, there sho8ld not be any oil on the exhaust side.





contender said:


> Is this crud and tar since you had it running after the rebuild, a day or two ago??


This is another engine. Thanks everyone. Took it down the shop to let them inspect/advise and they said it should be good to go after disassembling clean up etc. I just like to cover all the bases to be sure.


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## Michigan Paul (Dec 20, 2021)

That is coked oil which is right on top of the exhaust port looking at 2nd pict seeing a thick gasket and exhaust studs. Remove the valves/spring/retainer and locks and give all good cleaning with carb cleaner then wash with HOT soapy water and dry. Get some lapping compound to re-bed in the valve seat surface. Replace the valve seals and reassembly. If head surface is questionable spray glue crocus cloth onto a piece of glass and with WD40 as lube figure 8 the head on the crocus. I see nothing wrong with the head as long as the piston didn't kiss the head.


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## orangputeh (Nov 24, 2016)

Michigan Paul said:


> That is coked oil which is right on top of the exhaust port looking at 2nd pict seeing a thick gasket and exhaust studs. Remove the valves/spring/retainer and locks and give all good cleaning with carb cleaner then wash with HOT soapy water and dry. Get some lapping compound to re-bed in the valve seat surface. Replace the valve seals and reassembly. If head surface is questionable spray glue crocus cloth onto a piece of glass and with WD40 as lube figure 8 the head on the crocus. I see nothing wrong with the head as long as the piston didn't kiss the head.


Thanks. Local shop agreed with you and others here. Just wanted to make sure. I got a killer deal on this blown 1132 and was willing to buy a complete new head. S it just needs some cleaning and maintenance. The rod/piston needs replacing. Inspected the case yesterday and it's in good shape. The crank looks good. Gonna hone the cylinder .

Put it altogether and give it a go as soon as parts come in.


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## harry398 (Jun 22, 2021)

I have seen this on various engines. I think this occurs due to various reasons, primarily poor maintence. I have seen it on briggs inteks as well, and when you see it there...the valve guide is already loose in the head. The Hondas are usually fine...but they eventually blow up when 0 maintence continues....exh valve gets hot....lash expands........and eventually pushrod comes out of the rocker...Boom. bent valve

I think some of these were run with the carb really junked up, and the engine running very lean....which in turn creates alot of excess heat in the chamber on the exh side....

I now also think the engines being run lean from the get go with small jet also creates this.....


these engines Dont use a exh valve seal.


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## ST1100A (Feb 7, 2015)

That looks like an exhaust valve guide starting to wear a little bit.
That can also come from using the wrong type oil - Automobile Oil. Another cause can be oil that is too light a viscosity for the temperatures it is operated in.
Small air cooled engine oil is designed to tolerate much more heat than Automobile Oil. Even the best Synthetic Automobile Oils are not designed for the abuse a small air cooled engine will give it and will not last very long and degrade much quicker, break down and lose viscosity a lot quicker than oil specified for Air Cooled Small Engines, then you will have deposits in the engine shown by Orangputeh.


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