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Honda GX670 blowing oil

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Honda GX670 blowing oil

Postby BLES » Fri Mar 08, 2019 7:27 pm

Honda 24hp GX670

Starts and runs really well. After about 5 minutes, starts to stumble and blow smoke from one cylinder real bad.

Oil level is good. New oil and filter. This is similar to when crankcase floods with fuel, but oil level is good and it's only on one cylinder. Compression is good on both cylinders.
Any ideas?

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Re: Honda GX670 blowing oil

Postby KE4AVB » Fri Mar 08, 2019 7:50 pm

I would think it would be a valve stem seal and or valve guide if white smoke. Also check the oil drain back for clogs. As the intake valve seal there should oil in the intake around the valve.

Another test you can do since this is an OHV engine is to disable the valve train then do a leak down test at both TDC and BDC. I recently had a Tecumseh that had good compression was still smoking a few a after start up. It had a very tapered cylinder that fail the BDC leak down test.
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Re: Honda GX670 blowing oil

Postby BLES » Fri Mar 08, 2019 7:53 pm

Yes, that's what it's like, but there is no seal on exhaust. Also, it started suddenly.
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Re: Honda GX670 blowing oil

Postby KE4AVB » Fri Mar 08, 2019 7:59 pm

Normally there is not a seal on the exhaust as the exhaust is pressurized when open during running but the intake side is under vacuum and suck oil in.
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Re: Honda GX670 blowing oil

Postby BLES » Mon Mar 11, 2019 8:31 am

I pulled the head and there does appear to be excessive clearance on the exhaust valve/guide. Mysterious why it started doing this so suddenly and only on one cylinder.? I'm wondering if I should pull the other side, too, and repair or replace both heads.? BTW, I had pulled head before I read the recommendation to leak down. Exhaust port was full of oil though.
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Re: Honda GX670 blowing oil

Postby KE4AVB » Mon Mar 11, 2019 9:34 am

I would check the other head just out abundance of caution. At least the valve guides are replaceable on these heads.

I am however wondering why it stumbling. Worn exhaust valve guides can cause the valve to not be operating correctly and may be causing a loss of compression seal once it heats up as the valve hangs up.

Let us know what you find as it will help others and me too.
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Re: Honda GX670 blowing oil

Postby BLES » Mon Mar 11, 2019 9:38 am

I'm thinking the stumbling is just from the abundance of oil in the combustion chamber.? Oil is thicker in start up, but stumbling starts when it warms.??
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