Two months ago I timed my air pressure build and I remember it being about 1:45 from 90 to 125 psi.
Since then I have driven about 5000 miles and changed my engine oil. It was really thick black but an oil analysis said it was consistent with having been driven 9100 miles. (that was the first oil change since I bought the bus) I put in NAPA 40W oil and filter.
Now I think it takes at least twice as long to build from 90 to 125, though I haven't actually timed it.
My bus holds pressure fine once it's fully aired up.
My first guess would be compressor seals. What likely causes are there that would affect the pressure build time? What should I do to investigate the cause?
Thanks.
Check for oil at tank drains. Some have a small muffler tank off compressor with a drain petcock also. Check there for oil also if yours has one.
Also look at the exhaust port of your air dryer for signs of oil contamination. You could be due to service your air dryer.
Most MCI 5 have a separate air cleaner for the compressor check for the filter and replace it,check the intake hose if you have one for kinks if the compressor doesn't breath they don't air very fast
My compressor has two unloader pistons. They recently both stuck open and the compressor stopped putting out any air. I am now confident that the longer air build time happened when the first unloader piston stuck open.
wonderful, please confirm after checking out. sounds like you did get it though!
miles. (that was the first oil change since I bought the bus) I put in NAPA 40W oil and filter.
Not to start another oil thread but check to see if that oil meets the spec for 2 stroke Detroits.
It's been a long time since I did the research but the NAPA item number is 75118. 40w conventional heavy duty diesel motor oil. Comes in 5 gallon pails.
Edit: The pails say "NP75118", and something like "Meets cf-2 standard... Approved for 2-stroke Detroit Diesel 71/83/92". The description on the NAPA website says something completely different.
Quote from: hogi6123 on June 27, 2021, 04:42:32 AM
My compressor has two unloader pistons. They recently both stuck open and the compressor stopped putting out any air. I am now confident that the longer air build time happened when the first unloader piston stuck open.
I replaced the unloaders (I could have cleaned them but new ones came with the compressor gasket kit). Tested them and they moved correctly, so reinstalled the compressor. Fired up the bus and compressor works again. It took 1:40 to build from 90 to about 130 psi, with Fast idle on.
Can you replace the unloader valves without removing the entire air compressor or does the head need to come off?
Quote from: Jsrcaptain on July 04, 2021, 09:03:32 PM
Can you replace the unloader valves without removing the entire air compressor or does the head need to come off?
The head needs to come off to remove the unloaders. That means the coolant needs to be drained.
If the in-floor engine access hatch is usable, the compressor does not have to be removed from the engine.
Replaced mine on my 700 Compressor. Though the access hole in the rear floor by removing the rectangle cover on top of the compressor about 2" x 1" and taking the two unloaders out with needle nose pliers and then inserting the new one close it back up and done in my 5C
Quote from: Dave5Cs on July 05, 2021, 07:33:02 AM
Replaced mine on my 700 Compressor. Trough the access hole in the rear floor by removing the retangle cover on top of the compressor about 2" x 1" and taking the two unlooaders out with needle nose pliers and then inserting the new one close it back up and done in my 5C
My access hatch is covered over, so I had to remove the compressor from below to see what was going on (unloaders are on top by the floor). I had the compressor head off already so I didn't try taking unloaders out the side. The manual doesn't mention the possibility either but it makes sense that the unloaders can be plucked out as you said without removing the head.
After some investigation, the valve on one cylinder is stuck open. Not the unloader. I'm thinking there may be something stuck under the valve keeping it from sealing. I'd like to avoid taking the head off. Any ideas? A blast of compressed air?
Edited
Can you watch both unloader pistons move up and down completely? A blast of air shouldn't hurt anything. Remove the unloaders. The valve stems should slide freely. There are light springs pushing down on the valve disks, you should be able to see/feel the force when you push up on the valve stems.
The input valve disks ride up and down in a small cage. The valve disk could could be hanging up on the cage. Can you remove the valve stems through theCo intake hole? Then you have direct access to poke a wire up in there and feel around.
Taking the head off would make the troubleshooting fast and easy LOL. Just have to figure out how to store the coolant and get it back in.
Do you know if it's input or outlet valve that's stuck open?
I'm pretty sure it's the intake. I took the hose fitting plate off and ran the engine. I'm getting a blast of air from the aft valve. The unloader is moving freely. Something is holding the valve open. I'll take the unloader out, blast some air in there while I'm pushing the valve open. I wish I had a boroscope. Hard to see in there. If that doesn't work it's off with the head!
Quote from: hogi6123 on July 05, 2021, 01:59:24 PM
Edited
Just have to figure out how to store the coolant and get it back in.
Good point. That's why we always carry two 5 gal. Buckets and a 5 gal. Oil drain pan. Has come in handy on needed occasions...
Just spit balling... have you confirmed the air supply hose isn't collapsing inside from the suction?
I hate using tools...
Happy coaching!
Buswarrior
New hose. Doesn't work with the hose off.
Does anyone know if the head kits for the TF500 through TF700 are the same? I have a TF600.
According to these web pages, they are the same, but you can't believe everything on the Internet.
https://www.amazon.com/gp/product/B00KH540K4
https://www.ebay.com/itm/Parts-for-Bendix-500-700-1000-Tu-Flo-Air-Compressor-Head-Set-Gasket-kit-NEW-/272167157698
Thanks. At least with Amazon, you can usually return stuff easily.