Help repairing leaking pressure washer pump....

[gerrymoore]

I bought a pressure washer off fleabay..advertised spares or repair...God help me! The 6.5 Honda copy I now have running pretty well but I'm lost with the pump!!

It is a quite well made Chinese copy of the Italian Interpump 51. Solid brass housing with three ceramic pistons. When I stripped it down it was in a very sorry state...the small crankshaft bearing was knackered but the crank and cams seemed fine. I replaced both the small and large bearings anyway. The 'oil' in the pump was full of water so I put in 3 new oil seals. I replaced all the O ring seals by taking measurements off the old seals. I also obtained new flinger washers - 31 on the drawing.

Started up the pump and got about 2000psi pressure but had water pouring from the join between the pump and drive side.

Turned out to be wrong O ring sizes when I checked having got hold of the interpump manual. I replaced the seals again with the correct ones and tried again but still getting a water leak from the join and I think water is still getting into the oil. The only O rings I haven't changed are the ones inside the pistons marked 29 on the drawing. The new ones I've fitted are 6mm x 1.5mm instead of 5.28 x 1.78.

I'm happy to change these if I thought they were the problem but cant see how they would allow water into the oil? I also think the motor is working very hard as it seems to get very hot and when I checked the (new) oil in it is was a very strange light brown colour and milky..is this a sign of overheating?

I haven't changed the 'packing' washers (18,19) in the pump...could these be a cause of leaks? Any help appreciated.

I've attached the drawing and can post photos of the pump if necessary.

 

[Wendelspanswick]

Is there a pressure relief/bleed off/bypass valve that's not working, on electric PW's the motor stops when the lance trigger is off, I am guessing that on a petrol PW there is a relief valve to unload the motor when the lance trigger is off.

 

[Wendelspanswick]

Had a look on the drawing (bit difficult as I am on my iPhone), what are the bores like, looks as if the water is pressurising in the bore as it's supposed to but getting past the pistons into the crank side. Either the chambers are over pressurising (see my first post) or the seals are failing on the pistons.

 

[gerrymoore]

Hi...thanks for your input. The pressure relief valve is working fine I think...when you pull the rigger the motor 'labours' under the load and goes back to normal when trigger is released. The ceramic pistons don't seem worn and they are running in brand new O rings so the seal should be good..but as I said, I haven't got the correct O rings inside the pistons....I must order the correct ones....maybe they are the culprits!!

 

[carbon]

Have you replaced the 'O' rings '21' and '22'. How are you getting water into the pump, direct connection to a tap or suction from a barrel. Also pressure washers do tend to load petrol engines quite well when working.

Did you apply any thread locking adhesive to the nut on the end of the pistons. As this nut is inside the pump it is subject to the high pressure water and as such the water can travel along the inside of the ceramic. If there is sufficient water leaking the flinger washer is not really going to stop much water getting to the oil seals. The oil seals don't stop water getting into the pump they stop the oil getting out. What I'm trying to say is if there's enough water on the outside of the piston on the return stroke some water will get taken into the pump. As the pump is running at approx. 3400 rpm it doesn't take long for the oil to be contaminated

 

[gerrymoore]

Hi Chris..yes those were replaced by the correct items. I understand what you are saying re the nuts on the end of the pistons. I did use threadlock on them but I feel that the internal O rings (actually inside the ceramics) may be the problem so I'll get proper sized replacements for them. I am running the pump from our normal outside water tap but our water pressure is quite high. The pump actually leaks slightly even without the motor running so something is not right! I'll get the O rings, rebuild it again and try with just the tap pressure. If it still leaks then it's head scratching time!!

 

[carbon]

As you have a leak with the tap turned on then it's going to be the incorrect size 'O' rings that you fitted. If a ceramic is damaged its usually fairly obvious as there's a crack down the length of it. An other possibility is damage to the cylinder head, check that the reccess than item '20' fits into is not oval. Whilst its rare for this to occur it is possible and will cause a leak

 

[gerrymoore]

Thanks again Chris...you seem to know what you're talking about!! I'll check the head and order the O rings....as a matter of interest, do you know roughly the cost of a new ceramic piston? thanks again gerry

 

[carbon]

Gerry if a ceramics not cracked or chipped in the middle (never seen one chipped in the middle without being cracked) then its not worth replacing.
Just had a quick look in an old price list, list price for one is £27 inc vat for a 15mm ceramic but would expect to pay less than that.