New engine rebuild, NO OIL PRESURE!!

[Gearhead1956]

Well this sucks!!

Started cart this morning and no oil pressure, Oil pump would not prime.

pulled oil pump again everything looks ok, pulled the end cover that is also the pump housing, everything looks fine.

BUT! my oil is metallic. so it appears I have destroyed the new rods.
The only good thing is since the pump was not pumping it did not send the shavings to the top half of the engine or the oil passages. There was not even any metallic in the new oil filter.

For the life of me I just don't see why the pump is not working! I did get this cart with a bad rod and not running.
I have never worked on these small engines before, but one would think after years of working on V-8's and tractor trailer engines this would be a breeze. NOT!! LOL

[sonnyk]

Bummer! Sorry to hear that.

[Gearhead1956]

These oil pumps don't seem to be an issue for most. If you look on any parts place they all have pistons, rods valves. but know one has oil pumps. So I would guess most engines never get new ones!

That makes me wonder what the heck is the deal with this one.

[my1423]

Never had one of these engines open myself.
On other small engines with similar issues i have seen the pickup tubes crack an suck air, fall off, plug with stuff, rtv make a straw and suck air, bolts on pump too long and crack the case, cracked case allowing air, warped pump cover allowing air in but not leaking, ect ect.


Can you Take a blow gun and pump air into the galley and see/ hear where it comes out?

[Gearhead1956]

Here are some pic's

As you can see the pump housing is built into the engine cover, The suction tube is built into the cover.
That vertical suction tube mates with a casting horizontal suction tube in crankcase. at the end of the horizontal tube is the oil filter.
The 3 bolt pump cover uses an O ring to seal.

When I got this engine the 3 bolt pump cover looked like someone had purposely hit it with a hammer in the center. Should have been my first clue something was wrong! I did flatten out the cover and used 800 grit sand paper to smooth the inside of cover.

I did check the rotor to rotor clearance at .005

[my1423]

Wow never new they had to suck the oil that far up.
Most small engines they try to keep the pump at oil level since they are smaller pumps and more susceptible to air infiltration on priming..

Is there no screen on the suction side?

.005 is a little worn on most of those style pumps but it should still work. ? Do you mean side clearance or tips of the rotor?
The way this pump works if the case gets to worn it will have issues.
I have seen pumps like this wear the case on the thin separator between the 2 oil passages and be totally in spec elsewhere.

You have to keep a tight side clearance to keep air from bypassing the rotor on startup so it will self prime.
I think your issue stems from that cover.
You sanded it flat but the dent probably made up the clearance that was worn off the case witch had pressed the rotor in farther wearing the case and opening to big a gap for oil film to seal to prime the pump.
I would pull the oring and use a depth gauge to check the inside case for distance all around.
Then mic the rotor width and subtract that from the case measurement.
You probably need to sand the case down 4-5 to tighten the sides up.
On some pumps they make thin steel washers to accomplish this and just shim it up.
Parts store may have something close.

[Dangerousdan55]

I can't​ remember, but, should there be a small O-ring on the filter?

[Gearhead1956]

Originally Posted by Dangerousdan55

I can't​ remember, but, should there be a small O-ring on the filter?

No O ring.
But at that point would be covered in oil so I don't think it would create a sucking air situation.

Thanks for thinking about it.

[Gearhead1956]

Originally Posted by my1423

Wow never new they had to suck the oil that far up.
Most small engines they try to keep the pump at oil level since they are smaller pumps and more susceptible to air infiltration on priming..

Is there no screen on the suction side?

.005 is a little worn on most of those style pumps but it should still work. ? Do you mean side clearance or tips of the rotor?
The way this pump works if the case gets to worn it will have issues.
I have seen pumps like this wear the case on the thin separator between the 2 oil passages and be totally in spec elsewhere.

You have to keep a tight side clearance to keep air from bypassing the rotor on startup so it will self prime.
I think your issue stems from that cover.
You sanded it flat but the dent probably made up the clearance that was worn off the case witch had pressed the rotor in farther wearing the case and opening to big a gap for oil film to seal to prime the pump.
I would pull the oring and use a depth gauge to check the inside case for distance all around.
Then mic the rotor width and subtract that from the case measurement.
You probably need to sand the case down 4-5 to tighten the sides up.
On some pumps they make thin steel washers to accomplish this and just shim it up.
Parts store may have something close.

Thanks for thinking about this.

No engineer here, but that pump does have a long void to suck before it gets oil! Most pumps are made to push or pull, this one has to do both!

No screen on suction side.

The .005 is the gap between rotors as they pass each other.

Going to try to mic. the housing. don't really have a good tools for that. I may try some plastic-gauge? My digital caliper from Harbor freight does not appear to be accurate as it showed my crank to be larger the new! LOL

[my1423]

First i would triple check that the cover is flat.
After that Plasti-gauge might work. Good idea!
I would use 5 small pieces on the ring and 4 on the rotor tips.
Torque the cover down and then have a look.
Clean it all off.
Then use two pieces in the case, one vertical on the little strip center, And one opposite side from that one of the center shaft hole in the large area that looks scuffed.
Should be able to get a good idea from that of any major wear or out of square that the case might be in.