Hill MK4 pump problem

Instead of 005 oring on pump piston I used a 006 which is one bigger.  Is that the problem.  It fit in the tube without marring the oring.

I have the same problem but with a different pump. If there's a small bleeder hole under the piston o-ring, check to see that it's not blocked with gunk. Also check the passage ways, below the check valve, going to the bleeder screw to if there blocked. And check where the check valve seats, to see if the surface has been eroded and pitted.

Thanks for your input James.  I think your right on the check valve.  May have to do a little more polishing, etc.  

Cleaned everything up again. Checked check valve, orings good, passages all clear, relubed. Same thing? Very Frustrated with a 5 year warranty pump. I'm 2nd owner. First owner never used it. I have used it very little. Can i send it to hill or talk to someone and see what i can do?

It is the small high pressure green o ring.  Did you use silicone grease on it?  Even the grease that Hill provides will make the pump very hard to use.  In my ecperience it works well everywhere EXCEPT the small green o ring.  I'd take it back apart, clean the o ring and the tube where the o ring slides and then use silicone OIL on them.  The grease is just too thick...

Yes. The green o-ring was fine. Used silicone divers grease. But still replaced o-ring with a new one. Pump handle pushes down with ease but springs back up?

I've thought the pump handle, springing back up was a check valve issue, either a pitted o-ring  seat, or a bad check valve o-ring. The worst issue I've seen is pitting at the bottom of the first stage tube.

I can't remember if I put a new oring on the check valve.   That MAY be the culprit.  Thanks.  🙂

Well I've had it apart 6 times or more!!!!!! I friggin give up. Anybody want to give it a shot I'll make it worth your while. Or send it back to company????

Try cleaning the 2 rubber ball valves with alcohol and the holes they go into, no grease needed.

Sounds like they're getting stuck open on the upstroke.

Could be.  I haven't thought of or tried that.  Thank you.  Yes sounds like it's not sucking in air on the upstroke.  Thanks again. 

When the handle is lifted the 2 rubber balls moves up to let air into the first stage.

On the downstroke the 2 balls need to drop to close off the air to compress the 2nd & 3rd stage.

If it's lubed it can get sticky and not full drop down to make the seal.

....... more here

https://www.tapatalk.com/groups/yellow/graphical-explanation-of-a-3-stage-hand-pump-t188586.html#p1918764

Thanks GKU.  

Tried cleaning rubber balls and passage with alcohol.  Still No luck!

   This two minute fix works on the Axsor pump and should work on the Hill pump as well.

   Set the pump upright and stand over it looking down. See the two screws on the bar between the two handles? Loosen these screws a few turns. You should now be able to push the handles all the way down with the air exhausting through the loose screws. retighten screws. Done.

I will try that.  But I don't know that there's two screws on a King of the Hill.