breaking in a honda gx390

The motor guy · Jan 20, 2014

I bought a generator with a Honda gx390 engine on it and I noticed that Honda makes their own oil. I think it's called GN4 10w30 and it's SJ rated. This engine does have a flat tappet tappet valve train.I was thinking about getting some and using that for the first few changes and then switch over to the amsoil ASE small engine oil after the engine has around 100 hours or so. Can you run regular SM rated oil in this engine? The compression ratio is 8.5:1 This engine is expensive so I don't want to take any chances.

Doog · Jan 20, 2014

I would look up the owners manual spec for oil if you are not sure. If you cant find one then I would run a HDEO 10w30.

The motor guy · Jan 20, 2014

I downloaded one and it says SJ or later spec. I don't believe in using SM rated oil to break in a flat tappet engine though. I went to walmart and all the had for heavy duty engine oil was rotella 10w30 and that's semi synthetic.

Doog · Jan 20, 2014

I have been using Rotella T5 10w30 in all of my OPE for a very long time. Never a problem. But I do a few 1-2 hour OCIs when the engine is new. Once you get the metal out they usually purr.

I run it in a Honda power washer, B&S Lawnmower, Chonda generator, B&S 9HP leaf blower.

Chris142 · Jan 20, 2014

That little honda dont have much spring pressure.sm oil will be fine,its not an old cam eating 396!

user52165 · Jan 21, 2014

I will guarantee you Honda does not make oil. Been using many Honda OPE for over 30 years without a problem. Honda GX engines are very forgiving about oil - any good 10W-30 is fine.

Be much more concerned about gas. Use non-ethanol if possible, or fresh gas with Stabil or similar, and keep tank full. Drain carb or use at least once a month.

Useful link - any of these places near you:

http://pure-gas.org/index.jsp?stateprov=TX

SuzukiGoat · Jan 21, 2014

Vr1 works well if you don't feel like running gn4.

The spec for their basic oil is actually pretty goo d. Thy SJ rating is because the oil is for wetclutched bikes.

If it were me, ID run gn4 for 10 hours with low load. Drain, fill with mobil1 5w40. And never look back.

And in another life...I was a certified Honda tech. And...that's essentially what I do for my aircooled Honda bike motors...which DO run heavy valve springs...really heavy valve springs. The only difference being I switch to motul rather than mobil1.

Honda oil is pretty robust...though I'm not sure who they get to make it for them these days.

Don't over think it. Just do a drain somewhere around ten hours and pick your favorite oil and run it.

05ChevyI5 · Jan 21, 2014

I've got a couple and Rotella T or T5 does the job. Been tempted to try some Amsoil ACD though.

The motor guy · Jan 21, 2014

That sounds good Suzuki. I'll use the gn4 for a few hours and then switch over to amsoil ASE. I used it in my lawn mower and the oil consumption practically went to zero when switching over from conventional oil.

Rand · Jan 21, 2014

everyone talks flat tappets..

but its a combination of flat tappets with high valve spring pressures that requires special oil

SuzukiGoat · Jan 21, 2014

Out of curiousity...what's considered high?

My valve springs in one of my built motors are well over 100lbs to compress?

friendly_jacek · Jan 21, 2014

I googled and this showed up:

Wilhelm_D · Jan 21, 2014

Originally Posted By: motor_oil_madman
I bought a generator with a Honda gx390 engine on it and I noticed that Honda makes their own oil. I think it's called GN4 10w30 and it's SJ rated. This engine does have a flat tappet tappet valve train.I was thinking about getting some and using that for the first few changes and then switch over to the amsoil ASE small engine oil after the engine has around 100 hours or so. Can you run regular SM rated oil in this engine? The compression ratio is 8.5:1 This engine is expensive so I don't want to take any chances.

Honda makes its usual recommendation for "API service category SJ or later" and "SAE 10W-30 is recommended for general use".

SJ was higher in zinc and phosphorous than the current API service category, SM.

I work on the assumption that oil is cheap, engines expensive, and use SJ-rated motorcycle or recreational vehicle oils in brands like Mobil 1 and Amsoil, in weights like 10W-40 or 5W-40.

The motor guy · Sep 23, 2016

is 15w40 ok to use in this engine?

Serge · Sep 23, 2016

Rotella T5 or T6 if you cant sleep at night.

bubbatime · Sep 23, 2016

Originally Posted By: motor_oil_madman
is 15w40 ok to use in this engine?

15W40 is IDEAL for your engine. For your climate, you would be crazy to use a run of the mill 10W30 oil. Just not enough margin for error there with a 10W30.

I would honestly break the engine in on 15W40 conventional and then switch to Mobil 1 10W40 high mileage or Mobil 1 20W50 after break in.

The motor guy · Sep 24, 2016

I think 10w30 is just to cover all the basis. That way if the engine is shipped to New York it will be ok and still ok in the south.

user52165 · Sep 24, 2016

Originally Posted By: bubbatime
Originally Posted By: motor_oil_madman
is 15w40 ok to use in this engine?

15W40 is IDEAL for your engine. For your climate, you would be crazy to use a run of the mill 10W30 oil. Just not enough margin for error there with a 10W30.

I would honestly break the engine in on 15W40 conventional and then switch to Mobil 1 10W40 high mileage or Mobil 1 20W50 after break in.

I'm sure those CRAZY Honda engineers who have been selling these for 40 years and Millions of engines in all the worlds climates will be glad to hear your amateurish comment. 10W-30 which they recommend is fine for their OPE.

Cujet · Sep 24, 2016

Originally Posted By: user52165
Originally Posted By: bubbatime
Originally Posted By: motor_oil_madman
is 15w40 ok to use in this engine?

15W40 is IDEAL for your engine. For your climate, you would be crazy to use a run of the mill 10W30 oil. Just not enough margin for error there with a 10W30.

I would honestly break the engine in on 15W40 conventional and then switch to Mobil 1 10W40 high mileage or Mobil 1 20W50 after break in.

I'm sure those CRAZY Honda engineers who have been selling these for 40 years and Millions of engines in all the worlds climates will be glad to hear your amateurish comment. 10W-30 which they recommend is fine for their OPE.

Honda engines are generally excellent. I had two fail in short order while using penzoil 10-30. Both were 24/7 water pump engines, used to de-water my average property in hot n sticky south Florida. I thought there was something wrong with the first one. It was covered under warranty. The second one failed just like the first. After a bit of research, I learned about air cooled engines and oil temperatures. I moved to higher viscosity synthetics.

After the Hurricanes here in Florida, there were thousands of generator engine failures. Most of them were oil related issues due to overheated oil.

dave123 · Sep 24, 2016

All my high end hard working OPE spec for 30 gets Amsoil ASE 4stroke 30/10w30 I believe the best it gets for OPE

breaking in a honda gx390

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