Low oil pressure on a honda GX360

[HondaG100]

I am no oil pump expert but .005 seems like it could very easily cause your amount of pressure loss.

[bgsengine]

I am no oil pump expert but .005 seems like it could very easily cause your amount of pressure loss.

Hoo boy, will it ever.. When it comes to internal engine parts and oil clearances .005" difference is about the same as the difference between Mount Everest and a molehill in your backyard.

.005 is huge amount of clearance when it comes to oil pumps and will absolutely cause you pressure problems and the limit tolerance is just that- a *maximum limit*

- the tolerances in hydraulic pump motors are even smaller - a groove the depth of a human hair (not even .0005" - half a thousandth) in the slipper blocks on a hydrogear valve block will make all the difference between a tractor that can pull a car along your driveway, and a tractor that can't even make it up a 15 degree incline when its warmed up.

- The main thing I would want to be looking at is how much clearance the gerotor will have between the block and the cover plate, and also inspect for any grooves worn or scored into the block where the gerotor runs - if you get a groove dug in between the oil inlet and pressure outlet passage by some dirt getting caught between rotor and block and cutting a groove in the aluminum across to the other side, you've got yourself an oil pressure bypass that should not be there, resulting in a huge drop in oil pressure especially when it gets warmed up. - If the groove is bad enough you gonna have to replace that cover (Item #1 in the posted photo)

[KE4AVB]

Ahh had register @ smokstak to se what Arkie posted.

There is some clearances which BGSengine referred to that can be only be checked by using plastigauge. This is the clearance between the rotors and the cover plate slip area and between the rotors and the pump housing back slip area. To check these plastigauge is place in these areas and the cover plate bolted back on.
Excessive wear in either these areas which cause lost oil pressure as the oil thins.

Maybe Arkie can post that spec for you. I got an idea that one is close to .001 or .002". I know it got to be fairly tight.

[KE4AVB]

This is image of testing the clearances that I wrote about; although, I still think the plastigauge method would best. The following is of testing an automobile version but the principle is the same for the multi-lobe rotor-type pump.

[vaultf600]

OK I'm going to show you all how deep I'm in this...




As for the oil pump....I have .001 or maybe .002 thousands of and inch over on the rotor clearance where it meets the aluminum housing. Its the bottom measurement of this pic Arkie posted at smokstak. Sounds like you all think that a thou over spec isn't good.

[vaultf600]

So I have decided to tear down the motor and have a look... now that I'm this far in. I checked the main and rod bearings with plastigauge when I was tearing it down and it was at the top of spec limit according to http://www.pinellaspowerproducts.com/view/EVTECHINFO/ this guy. I did find out that this engine does have an oil pressure regulator, its in the bottom of the case.

Here are a few pics of the oil pump. I still need to check it with a straight edge.

[vaultf600]

So aside from some nasty oil and being over one thousandth over spec on the oil pump rotor and the aluminum housing I haven't found anything really alarming.

[HondaG100]

- the tolerances in hydraulic pump motors are even smaller - a groove the depth of a human hair (not even .0005" - half a thousandth) )

Human hair is about .0025. Snug fit on a good micrometer. All depends on how much product you put in it to!

[KE4AVB]

Rotors and cover plate looks to be in good condition from the photos.

Oil pressure regulator picture; OK then that the check valve I was looking at in the list is the pressure regulator. I kinda thinking it was; just wasn't sure.

Since you have this engine completely disassemble don't forget check the oil orifice (oil flow restrictor) between the the head and block. Items circled and location note below.

[Arkie]

Very good videos you found!!!!!!!!!
Appears about everything you have checked is at the max spec for oil clearances which is not good.
Keep in mind that the guy is doing MM (millimeter) specs for crank clearances as .02 min=.0007874 inchs and .04mm max = .0015 inchs max is .0007874 inchs tolerance specs between good and bad. (.04 minus .02mm=.0007874 inchs tolerance)
The guy also said that 28 lbs psi is min oil pressure spec and he says most engines actually run at 40psi minimum when in good shape, this would also be the engine idle specs.


I would have tried another set of oil pump gears on it before tearing it completely down, (oil pump specs are critical)
but now that it's down and all is at max specs for oil clearances, appears it needs main bearings, oil pump gears, Rod bearings maybe?? and the oil restrictor and it's associated o ring seal needs to be checked to see if they are intact.
May need to keep ear and eye open for another engine!!!!!
Everything just little bit bad which indicates not any one item can be replaced for now[/color] and expect it too be fixed[/color][/b]. (unless the oil restrictor is completely missing which is not likely, but need to be looked at. If Bubba had removed the head and not re-installed the restrictor or maybe it's o ring the top of the engine would rob too much oil pressure from the bottom end.

I've been into vehicle engines similar to these specs and symptoms and had to go thru all including cam bearings to expect any long term useage and get good stable oil pressures from low to high rpms'.