Piston replacement,Yong Heng

[far_shot]

55 tins of pellets and the Yong Heng started to struggle to get over 200 bar. Lower piston looked great, but the high pressure piston rings apparently were worn down too much. Piston bores looked great. Ordered a new piston and rod assembly for $25.00 from Ali. Took about 3 weeks to arrive.
Pulled the complete top end off in one piece and saw there was some debris in the bottom of the crank case.Took off the front cover and rinsed it out with Brakleen, Watch out for that front cover preformed gasket/baffle. It shrinks and was difficult to get back into it's groove. Yep, assembled and it felt great,running in the four bolts......but it had partially slipped at the top groove and allowed a small oil leak. Off it came and what little it ran under no load, there was some new metal in the oil. Rinsed it out again and pulled and stretched the gasket(hot water)....but it just returns to it's shrunken state Clamped it in place dry for a couple hours and it stayed put long enuf to assemble it. Ran it several times with no load and now works good again. No leaks and dead heads quickly to over 300 bar.

Cover removed to clean out wear residue.

Dry gasket clamped in place at the corners

Gasket stayed this time. Grease wouldn't hold it

Top piston ring wear.

Bottom piston rings are barely worn.

 

[sendler2112]

Thanks. hope my Yong Heng lasts. I wonder if we could remove the inlet filter and spray a couple drops of airgun oil inside once in a while and then crank it over with the bleed open?

 

[lennyk]

I just changed my rings couple weeks ago, they were also very worn and struggled to go above 4000psi.

Had to use the boiling water method to get them on, they are very tight now, unit is running a little hotter 52c vs 45c with ice in bucket.

but it is building pressure real quick now, better than when new.

I also have the upgraded piston with rings already installed but wanted to try my hand at swapping them myself.

I changed all three but I prob could have gotten by with just changed the top two.

 

[far_shot]

I just changed my rings couple weeks ago, they were also very worn and struggled to go above 4000psi.

I dealt with industrial pneumatics for 20 years. I had some real pickles with some of those systems. Might try that with the old piston just to have a good spare

 

[lennyk]

I just changed my rings couple weeks ago, they were also very worn and struggled to go above 4000psi.

I dealt with industrial pneumatics for 20 years. I had some real pickles with some of those systems. Might try that with the old piston just to have a good spare

They will stretch for sure and more than the factory installed ones

you need to heat them back up in boiling water and with oil push them back into the piston carefully to resize them into the piston

the piston has a little bevel so you can see if the ring is pinching and could get nicked

use a flat blade screwdriver to guide them into the piston

Once you can get the piston/ring into the piston it should go in subsequently just becareful.

 

[MMCM13]

What do the new rings look like compared to the old worn ones?

 

[Queequeg]

I keep a small rare earth magnet on my drain plug to catch any worn iron and it does grab some powdered stuff and keeps it out of circulation.

 

[lennyk]

What do the new rings look like compared to the old worn ones?

They are the ones on the narrow brass piston above, made from a type of plastic.

however under the ring there is also an oring which adds some expansion to them.

 

[Jayson]

That’s so funny! I gave up on that damn gasket and sealed it with Ritestuff, the clamp idea is brilliant! But now my oil level is pretty violent when running with no splash guard, lol. Curious, did the new piston assembly come with the spacers for the cam rod? Or did your compressor have them? One of mine did and the newer one didn’t? Thanks

 

[far_shot]

Curious, did the new piston assembly come with the spacers for the cam rod? Or did your compressor have them? One of mine did and the newer one didn’t? Thanks

None with the compressor or the new parts......./