Whats wrong with this air compressor?

Tom Baugues

Member
Messages
2,636
Location
Lafayette, Indiana
A neighbor was throwing out an air compressor the other day. I grabbed it and brought it home just to have a "project" to mess with. I didn't really expect it to run and sure enough it was locked up. I pulled the crank case apart and found the connecting rod seized to the shaft. Got it apart, cleaned up the parts and put it all back together. IT RUNS....however it is spitting oil out of the crank case plug. This plug is where the oil is added. The plug has a hole in it which I assume it to allow the case to breath but why would oil spit out of it like the video shows? Stumped. Thanks for any help you can provide.
 

Attachments

Brent Dowell

Administrator
Staff member
Messages
15,027
Location
Reno NV
So, I'm going to guess air slipping by the rings pressurizing the crank case.

If they rod had seized, I'm guessing they ran it out of oil, it over heated seized the crank and probably damaged the rings.

NAM (Not a Mechanic), but just want to see what the experts say and see if my guess is even close, lol.
 

Tom Baugues

Member
Messages
2,636
Location
Lafayette, Indiana
The piston was not seized. The bottom of the connecting rod was seized onto the crank. It didn’t take much effort to pull it off though. I simply cleaned up with emory cloth and reassembled. Yes I’m thinking that pressure is building up in the case but not sure how. Piston rings “looked” ok but maybe not?


Sent from my iPad using Tapatalk
 

Charles Lent

Moderator
Staff member
Messages
297
Location
Central North Carolina
Is the cylinder scored? Are the rings blued from overheating or have score marks in their edges? Did you put the piston back with the gap in each ring on opposite sides of the piston? Is the crankcase over filled with oil? Any one of these could cause oil coming out of the vent when it's running.

Charley
 
Messages
6,756
Location
North West Indiana
If the rings are not broken they will look okay. The only way to tell if the rings are bad is to remove them from the piston, place in the cylinder (not at the very top of the cylinder) and measure the gap with a blade type feeler gauge. Then find the specs for that set of rings and see if the ring gap is to large. How did the cylinder walls look? Were you sure you had the correct amount of oil in it? Not overfull? Possibly this is why the motor failed to begin with. Blow by pushed the oil out to the point no lubrication (lack of oil) and it seized. It definitely looks like a project worth some time based on what you paid for it. If nothing else, if you have a compressor of this size, remove this motor and plumb this tank in and will increase your work time with air tools.
 

Tom Baugues

Member
Messages
2,636
Location
Lafayette, Indiana
Is the cylinder scored? Are the rings blued from overheating or have score marks in their edges? Did you put the piston back with the gap in each ring on opposite sides of the piston? Is the crankcase over filled with oil? Any one of these could cause oil coming out of the vent when it's running.

Charley
Charley, you may have mentioned something here. The ring gaps being all together. I remember spinning those rings and leaving the gaps all lined up with one another. In fact they are almost lined up in the photo above. Never thought about that causing an issue. I’ll disassemble tonight and rotate them opposite of each other. There are three rings. I would hope it’s as easy as that. Thanks for that advise.


Sent from my iPhone using Tapatalk Pro
 
The ring gaps being all together. I remember spinning those rings and leaving the gaps all lined up with one another. In fact they are almost lined up in the photo above. Never thought about that causing an issue. I’ll disassemble tonight and rotate them opposite of each other.
Sent from my iPhone using Tapatalk Pro
That's the issue for sure
 

Tom Baugues

Member
Messages
2,636
Location
Lafayette, Indiana
Well, I removed the head and the piston rings were NOT all in line however two of them were pretty close. Anyway, I re-assembled with them all rotated differently. I also removed the oil fill plug and upon closer inspection realized that it separated into two halves. I had read that there usually is a piece of foam or material inside to still allow it to breath but stop any oil blow back so I cut a small circle of material I had in the garage and inserted it inside the plug. Turned the compressor on and now it runs without any spitting at all. So for $5.95 for a tube of sealant for the crankcase, I now have a 2.5HP 21 gallon air compressor that runs well and does not leak oil. Thank you all for your advise.
 
Top