Question Bauer Junior Slow to Fill and Not Reaching 3300 psi

[stammster]

I’ve got a 1997 Bauer Junior J2B that has worked flawless since new. Regularly maintained. Honda engine.

2 weeks ago it worked fine. Yesterday I went to top up some tanks and it seemed the fill rate was about half of what it normally is, and maxed out about 2700 psi (vs 3300 normally).

I don’t hear, feel, or see any leaks. No odd noises when running. Also there seemed to be a little more oil than normal discharged when I dumped the water from the draincock between the 2nd and 3rd stages. Normal is mostly water with a trace amount of oil. This was more like oily water being drained.

I pulled the head off the first stage and all looked good there. I also pulled the 2nd stage and the piston ring closest to the crank was broken in 2 pieces. The other 3 were fine. Would this be enough to cause the issues that I am experiencing. New rings should arrive next week.

I’m looking for a little advice (I.e. should I be tearing into the 3rd stage?)

 

[Mudbags]

Definitely worth checking the third stage. Pull out the floating piston and liner and make sure it's a nice tight fit with no internal scoring or wear marks. Even the slightest mark will cause air to pass the piston into the crankcase, which means you won't get full pressure at the outlet (this is called blow-by, you can test it by running the machine with the oil dipstick removed and looking at how much air comes out of the crankcase, it should be very little or none at all).

99% of pressure issues are either a leak at the condensate drains or a worn third stage floating piston.

You've done very well if you've lasted 26 years without replacing the third stage. Don't be too sad when you see the replacement cost of the part!

 

[stammster]

I pulled apart the 3rd stage today and nothing looked out of the ordinary. There was a little scoring on the bore of the crankcase piston, but I assume that doesn’t have any effect since it doesn’t seal pressure.

The floating piston and floating piston bore looked pristine. That’s an amazingly tight fit.

It’s 26 years old, but probably has less that 500 tank fills.

 

[Angelo Farina]

I pulled apart the 3rd stage today and nothing looked out of the ordinary. There was a little scoring on the bore of the crankcase piston, but I assume that doesn’t have any effect since it doesn’t seal pressure.

The floating piston and floating piston bore looked pristine. That’s an amazingly tight fit.

It’s 26 years old, but probably has less that 500 tank fills.

So other possible point of failure are the valves of the third stage. Particularly the output valve. It should impede to compressed air to flow back towards the piston. If it does not seal properly, you get a flow back and you cannot reach the max pressure.
Luckily valves are not so expensive. And often you can simply overhaul them...

 

[stammster]

I just wanted to follow up.

My compressor is actually a 1987 Purus model. Other than the frame, it’s identical to a late 1990s Junior model.

I had a lot of air entering the crankcase. This could be heard and seen when removing the oil dipstick. The 2nd stage would blow down to zero pressure in less than 20 seconds. Max pressure I could reach was 2700 psi - and it took a long time to get there (100% longer).

I was also getting a lot of oil discharge out of my air trap - due to aerating the oil in the crankcase and sucking it into the air intake (clear hose from the top of the dipstick to the 1st stage intake).

After a second look, I found a little slop on the floating piston and cylinder, and the cylinder would easily slide/fall out.

I replace the cylinder and piston with a new one, and now everything works as normal. Charge times are now back to normal (2.9 scfm) and reaches my pop of pressure at 3300 psi.

The new piston and cylinder were very tight - and clearly formed a better metal-to-metal seal. $500 including shipping from a shop out of Florida.

 

[Mudbags]

Nice work, glad you got it sorted.

This is a good thread for others to read. Your description of the issue is a textbook third stage piston failure.