Compressor repair and mod

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cor
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Compressor repair and mod

Post by cor »

Hi all.

So my air compressor stopped working. When I turned it on, it just gave a mild hum.

It was a free gift from a guy I built some models for, but was still less than a year old. Cheap Chinese junk at its best.

I decided to have a go at fixing it.

First of all, the 4 bolts holding the cylinder head on were very loose, they have spring washers but these are made out of chinesium, and are totally flat. The compressor would make a horrible rattling sound at times, so I think the loose bolts were the issue here.

Took apart cylinder and cleaned up the grease and oiled the bearing.


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Next moved on to the motor side of things, where the problem was more or less obvious.

The capacitor, also chinesium, had exploded.

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This is a pretty cheap fix, so I'm glad I can get it running again. It actually works , as after I turn it on and it hums, I give the piston a nudge and it starts pumping.

The best bit is that I can now play with it to get it working better. Re-greased the cylinder, oiled the bearings, tightened up all the fittings.

I will also clean up the mess of wires and add a cooling fan for the motor.

One other thing I found was the tank was full of brown water, quite a lot.

So just wanted to encourage anyone out there to have a go at servicing your own gear. Prolong the life and get it working better.
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digger303
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Re: Compressor repair and mod

Post by digger303 »

Good all round repair. Might be iffy on how long the tank lasts given how much water has been in it for a time, but then mine has been going for yrs ( plenty of water in it) and apart from one pin hole it's been good.
:th: :th: :th:
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Re: Compressor repair and mod

Post by Twokidsnosleep »

You are a better man than I. no way I would try that level of surgery
My water trap valve is failing on my Grex compressor so it won’t hold any pressure
Got a re-placement regulator/water trap from Amazon, but its quality is questionable.
I just plugged the leaky valve with beeswax and will ask Santa for a Sparmax this Christmas
Scott

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Re: Compressor repair and mod

Post by digger303 »

Twokidsnosleep wrote: Thu Sep 11, 2025 2:20 am You are a better man than I. no way I would try that level of surgery
My water trap valve is failing on my Grex compressor so it won’t hold any pressure
Got a re-placement regulator/water trap from Amazon, but its quality is questionable.
I just plugged the leaky valve with beeswax and will ask Santa for a Sparmax this Christmas
I wouldn't have known that little square thing was a condenser and so wouldn't have known what part to chase down. I'm used to condensers being bigger and more round in shape.

:cheers2:
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Re: Compressor repair and mod

Post by cor »

digger303 wrote: Thu Sep 11, 2025 5:58 am
Twokidsnosleep wrote: Thu Sep 11, 2025 2:20 am You are a better man than I. no way I would try that level of surgery
My water trap valve is failing on my Grex compressor so it won’t hold any pressure
Got a re-placement regulator/water trap from Amazon, but its quality is questionable.
I just plugged the leaky valve with beeswax and will ask Santa for a Sparmax this Christmas
I wouldn't have known that little square thing was a condenser and so wouldn't have known what part to chase down. I'm used to condensers being bigger and more round in shape.

:cheers2:
I took a photo of the square box and used google to search images. it came up with the answer. Pretty nifty. I've ordered a new one plus a fan. Bit of a project but I think the end result will be a better compressor and i now know how to service it.
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Re: Compressor repair and mod

Post by digger303 »

Not a search method I use and I should , I'm so used to searching text based.
Well done.
:th: :th: :th:
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Re: Compressor repair and mod

Post by runnerUA »

right on! Thanks 4 the tip. I love taking things apart.
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Re: Compressor repair and mod

Post by cor »

digger303 wrote: Thu Sep 11, 2025 2:36 pm Not a search method I use and I should , I'm so used to searching text based.
Well done.
:th: :th: :th:
:cheers2:
Yeah, I poo poo all that latest ai stuff, but in this case it told me what the thing was. So, pretty cool I guess.

runnerUA wrote: Thu Sep 11, 2025 4:27 pm right on! Thanks 4 the tip. I love taking things apart.
Its good to make the little improvments that the guy in the factory doesnt have the time or inclination for.

Twokidsnosleep wrote: Thu Sep 11, 2025 2:20 am You are a better man than I. no way I would try that level of surgery
My water trap valve is failing on my Grex compressor so it won’t hold any pressure
Got a re-placement regulator/water trap from Amazon, but its quality is questionable.
I just plugged the leaky valve with beeswax and will ask Santa for a Sparmax this Christmas
Its pretty easy with these fairly simple machines. I learned to repair camera lenses thanks to a guy in new york who gave me the confidence to do it, whereas before I wouldnt dream of it.



And heres the wires nice and tidy. Waiting for the capacitor to arrive next week, cost $15, then will put the fan in (using a perspex cover so I can drill the holes) when the slow boat from china docks. After that it should last another year at least...

The capacitor will be moved to the outside of the case - so the fan can fit and to keep it cooler.

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Re: Compressor repair and mod

Post by cor »

The compressor is working properly now. The capacitoris on the outside of the engine case, so it should keep cool. The fan hasnt arrived yet, but I may not install it.

One thing that has happened is that the compressor will stop the motor at a certain pressure, then restart once pressure drops a bit.
There is a sensor attached to the cylinder head which regulates this on off. It did not work like this before. I dont know if its the new capacitor, or if I caused it when I moved the sensor around in its thread with a spanner a bit.

either way, its in pretty good condition now.

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Re: Compressor repair and mod

Post by digger303 »

You probably corrected it's position and it all works now, damn good job.
:clap: :clap: :clap:
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Re: Compressor repair an

Post by Twokidsnosleep »

Ya I would say your mods made it work correctly now. Nice job :th:
With my leaky trap valve my compressor just runs and runs and doesn’t build up to the psi I want.
Thus it would get really hot quickly
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Re: Compressor repair and mod

Post by Stokesy44 »

Twokidsnosleep wrote: Thu Sep 11, 2025 2:20 am You are a better man than I. no way I would try that level of surgery
My water trap valve is failing on my Grex compressor so it won’t hold any pressure
Got a re-placement regulator/water trap from Amazon, but its quality is questionable.
I just plugged the leaky valve with beeswax and will ask Santa for a Sparmax this Christmas
Reading this thread I did wonder when the word 'Sparmax' would gallop into the conversation! :lol: :lol:
Its been tried and tested, it works! So don't blame the system if you're no good. :doh:
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Re: Compressor repair and mod

Post by Stokesy44 »

Well, I would just like to offer my sincere thanks to everyone who has contributed to the thread.

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Its been tried and tested, it works! So don't blame the system if you're no good. :doh:
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Re: Compressor repair an

Post by digger303 »

Twokidsnosleep wrote: Tue Sep 16, 2025 3:23 pm Ya I would say your mods made it work correctly now. Nice job :th:
With my leaky trap valve my compressor just runs and runs and doesn’t build up to the psi I want.
Thus it would get really hot quickly
That's the down side to oil less compressors, you just can't run them continuously.
I've had to replace the pressure switch on my el cheapo compressor after about 5yrs, fix a hole in the tank after 7yrs and 12 yrs old now it's still going. Not bad for a 100 dollar unit.
So you might find the dodgy looking replacement part actually works long enough to extend the life of your compressor.
:D
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