YonHeng ready for maintenance service - how to?

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bigHUN

bigHUN

Member
Jan 16, 2020
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Canada/L4G7X4
In a past one year I was always just topping up the tanks from not less that 200 bars so I have a feel for that timing needed, but,

Unfortunately I had to empty completely my two larger SCBA tanks, and filling now from zero, after some two + hours total running time it still didn't got to 250 bars yet. This may be an indication that better me to replace the high pressure piston rings. I have about 30ish hrs so far with a stock compressor (2 oild changes), and I don't want to wait until the rings break or completely wear out either side of the material.

Looks like now is a good time to take it apart and refresh the piston rings. During this one year I collected all the spare parts and kits from ali, and hoping now I did not missed any critical parts.

What is a best sequence? I didn't look at youtube videos yet, but based on my knowledge with small engines:

- I would remove the front "oil pan" only, but seeing that the "low pressure + high pressure assembly" is longer, may happen that I have no room to pull all out from bottom?

- if possible I would like not to separate the head assy's.

Best tips?


 
Guess it could possibly be the rings but most often it is a small leak somewhere. Lots of places for it to leak main ones I have had to deal with are the o-rings in the foster fittings, the o-rings in the filters, The gauge and then the dowty seals at the top of the head and one of the cone shaped seals in one of the stainless fittings. I am at near 30 hours as well and it just keeps pumping up to my 4200psi self imposed limit.

If I was going to do that job I would just take off the second stage cylinder and leave the stainless lines attached. Don't think you need to disassemble much else. The top two rings on the second stage piston just unscrew and the new third ring goes on tight.

Sambo Cotton has some of the best rebuild vids. Pulls the second stage cylinder and head at about 6:40 min in the vid.



https://www.youtube.com/watch?v=YjsBcKSVeGk&ab_channel=sambocotton



You can get the whole first and second stage cylinder and head assembly, stainless lines included, for under a hundred dollars shipped so if things go south you are in good shape. I managed to get mine replaced but getting the bottom ring on was a pain. The rest was a breeze though. The plus is I got to take it apart, a second time, and file a little off of the top of the new cylinder as it was a bit to tall and made quite the racket when I fired it up after the install. Got it right though and have the twenty plus hours on it since that problem originally caused by poor QC from the factory.

https://www.aliexpress.com/item/1005002043512865.html?spm=a2g0o.detail.0.0.574b7b8bel3SmM&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.169870.0&scm_id=1007.13339.169870.0&scm-url=1007.13339.169870.0&pvid=a686c4a5-8838-4d91-bbcf-d5e23bbffd9b&_t=gps-id:pcDetailBottomMoreThisSeller,scm-url:1007.13339.169870.0,pvid:a686c4a5-8838-4d91-bbcf-d5e23bbffd9b,tpp_buckets:668%232846%238107%231934&&pdp_ext_f=%7B%22sceneId%22:%223339%22,%22sku_id%22:%2212000018527342364%22%7D


 
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I have all the parts ready, the two piston kit plus one separate upper piston kit as well and all the gaskets and a bunch of spare rings. I am just trying to save the "head gaskets" these are nicely holding tight.

No leak at my machine, I am turning off frequently, waiting for some 15 or so minutes to cool down and when I am back still holds the last pressure. I just turn it off now @ 4000 psi, and planning to push it to a full 300 bars, a hair beyond is the auto shot off.

What I was planning (without seeing the internals first) to separate the upper high pressure brass piston from the lower aluminum piston, but if I remember correctly this not going to work if I open it from top (aluminum blocks) because a screw is holding it from bottom.
 
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I just removed the last block bleeding screw to clean the gunk and saw inside a small green chunk of oring, turns out the second stage check valve oring disintegrated and bits and pieces were clogging up the port to the exit block. This much surgery for today, tomorrow I still have one more scba bottle to fill. I have tree bottles and I want to have all full for case of any incident I can survive until parts arrive.

I was looking into my full box of spare parts, I am guessing I shall be able to remove the pistons assembly from bottom, kind of messy job diving into oily parts but this how I grew up in my 20-30s racing motorcycles :) (and then somewhere about there I got married and all stoped)

good old times
 
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It sounds like the check valve O-ring was the problem. It is common and should be the first thing to look at after checking for leaks. If you still want to change the rings you will need to remove the top end but you won't have to remove the front sump cover. If you remove it you will more than likely need to replace the rubber gasket because of shrinkage. The pistons and rod do not need front access to the crankpin to be replaced.
 
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I have a Yong Heng Clone I got off ebay May 2020. Used very lightly, I bet there isn't 2 Hrs run time total. 35 sec's to fill my Gamo Urban from 1000 psi to 3000 psi, The Airforce Talon SS about 1-1/2 min. Suddenly won't go past 2000 psi. I have taken it apart and cleaned very small amount of carbon grit From the metal check valve. Always used Royal Purple Syn since new, I have ordered the Mobil 827 compressor oil from ebay as suggested. My Question do I lube the second stage piston seal on reassembly ? The knowledge here is astounding, Thank You. Bill
 
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