Low oil pressure on a honda GX360

[vaultf600]

Hi all,
I was referred here from the smokstak forums. I'm hoping someone can give me some insight as to why my es6500 genset would have low oil pressure before I go tearing it appart. I learned there was an aluminum drive gear on the crank of some of these engines that would start to spin on the crank and give up oil pressure. Apparently from the case number on my engine, I have one with the good drive gear. (#1277694) The thing runs great with no noises, but will shut down the oil safety after its warmed up due to low oil pressure. Here is the thread about how we came to that conclusion.

http://www.smokstak.com/forum/showthread.php?t=143247

Any info by someone who has rebuilt or worked on these much would be appreciated. I'm debating on cutting my losses with this one but I hate giving up.

[HondaG100]

I have never done internal work on a pressure lubed Honda so others will know more but a couple things anyhow... You do not mention what oil you are using. Is it the correct viscosity for your ambient temp? Are you sure you do not have fuel thinning your oil? I have not looked at the IPL for this engine but it may have a pressure regulator that has gone bad.

[KE4AVB]

I too have not work this Honda engine but from experience with autos that use this type pump system it does sounds like a worn oil pump rotors or bearings as your pressure is dropping as the oil thins but then stabilizes.

I would not think the pump drive gear is causing the problem as it is also drives the governor and you would noticed a considerable increase in the governed speed as the engine warmed up and not just a slight up and down changes. Your engine should running around 3600 - 3750 rpm unloaded.

From the IPL it looks like the oil rotors and pump housing are accessible without having go inside the inside and that where I would check for wear problems. You will need at least 2 o-rings and 1 gasket.

And your thought of getting a service manual for this generator and engine is a good starting point too.

[Arkie]

Just a thought.

You mentioned in the other forum that the auto idle does not let the engine idle.
(therefore your 16psi now is at around 3600-3700 rpms. Test the oil pressure at idle and if it stays kinda steady at idle you might have a pop off valve seat leaking. Anyway you need to know what the idle oil pressure is if you get the auto idle operating also. Let us know the cold and warm idle oil pressure?

Try pulling the carb linkage back to idle while watching the oil pressure. That engine is designed for the pressure to stay above 21.3 at idle (probably closer to 28 at idle as minimum) for some leeway) so as the low oil pressure shutdown does not operate below 21.3 psi..
If you get the other engine you mentioned, I would also do this test high low on it before exchanging or swapping any parts.
Also when you pull the pump plate look at it carefully for any wear where the gear runs. Use a straight edge across the plate looking towards a light at 90 degree intervals and if it's not completely flat and grooves, it's bad if you see any light under the straight edge. Take care when re-installing the pump plate and get each bolt snug for no warpage, etc. (one bolt not snug on the machined plate will upset the pump)
It's been my experience with automobile engines most generally if the oil pressure goes to zero or real low at idle most generally the engine is worn out and needs complete machinest attention, new oil pump usually would not get good oil pressure on a worn out engine. (to much clearance on rod and cam bearings)Pressure would start at fair cold and drop when engine warm, sometimes to zero pressure at idle)

[vaultf600]

Ok here is the results from tonight. starting the engine cold and manually throttling it back to idle it was about 30psi. After it was warm it was at 11psi at idle and 17 psi at unloaded full rpm. It has new 10-30 wt oil and new honda filter. I suspected thinned oil thats why I changed it. I dont think the govenor is malfunctioning just from listening to it run. Manually moving the linkage it always settles back to a normal running rpm quickly. I guess the pump is "easiest" to access but still going to be a pain. The situation with the oil cover plate is if there is wear then oil moves past the pump not getting pressurized ? Is that the next step in my mystery? As for the pressure regulator theory.... do I even have one? doesn't the filter have some kind of valve? sorry for all the questions. I appreciate everyone's help!

[KE4AVB]

There is a check valve in the engine but to be honest I know if it is pressure regulation or is just an anti-drain valve. I am thinking the pressure regulator if there is one would be built into the pump housing. I haven't even seen one these engines so this just guess.

As for the oil pump wear if that cover is worn some of the oil would just recirculate in the pump as it just move to next pump chamber of the rotor assembly effectively acting as pressure release. It would be the same if the pump housing is worn in the same way.

[Arkie]

I do not see a spring loaded pressure regulation valve associated with your GX360 oil pump.
IMHO:
Appears you probably need to pull the pump apart for inspection. sometimes a grain of carbon will get inside a oil pump and score the critical areas, cut small grooves in the surfaces, etc. tolerances are close on this type oil pump and don't take much wear to decrease it's output pressure. Note the last sentence.
I left you some info at your thread on smokstak at this link about oil pump gear clearances and a used oil pump on ebay for around $25 and a link to view price of new parts with a exploded view of your motor.
It was more user friendly for me to upload the attachment at smokstak.
smokstak link for members viewing info http://www.smokstak.com/forum/showthread.php?t=143247

Heads Up: I also noticed that the two oil pump gears inside are directional (they have a in and out) Their is a small dot on both gears and the dot faces out or towards the plate. (or away from the engine when they are correctly installed) When re-installing the gears pack the housing inside the gears with a light grease such as Vaseline so as it will prime itself. Monitor the oil pressure and start the engine at idle after working on the pump and if no oil pressure stop the engine immediately.

[vaultf600]

I just took a look over at the smokstak. Thanks for the info and illustrations. I'm going to tear into this pump if I have time this weekend. I will report back with some findings.

[vaultf600]

Well the oil pump is behind the generator....I found this in my searches though! https://www.youtube.com/watch?v=xptxgqcwFCo#t=98 anyone know anything about a oil restrictor?? he talks about in the first two minutes of that video. This guy has an awesome rebuild documented at: http://www.pinellaspowerproducts.com/view/EVTECHINFO/ if anyone is ever in need.

[vaultf600]

I got to my oil pump finally and everything looks fine. the cover as a small shinny spot other then that I can't see anything. The pump gears have .008 clearance. which is within spec. but the outside rotor ring has .005 which is just past the limit according to Arkie's notes....?? Its hard to get a gauge in there but .005 seems close. Its hard for me to believe that a couple thousands of an inch could cause this engine to drop 20psi.