Bogged-down compressor

[spavined]

All,

Finally fed up with the lack of capacity my 6-gallon (oil-less) compressor provided, I recently bought a used 5hp 33-gallon craftsman. I bought it off a chiropractor who said he didn’t use it very much and who knew less than I do about it—which is not saying much. He ran it for me for ~30 seconds when I bought it, and it ran well.

After the hour-drive home, I unloaded the unit and plugged it in. It ran well for about 5 minutes, but then something happened and it really started to run poorly; it sounds like it’s getting bogged down, like the motor is having a hard time driving the compressor. I loaded a short video on youtube here: http://www.youtube.com/watch?v=p-toEKTBkLE

The only thing I can tell you that it seems to be losing a good amount of oil out of the bottom gasket, which appears to be shot. I noticed it was even spraying a little bit of oil as it ran while it was running well. This seemed bad, but I’m not sure whether it’s the cause, related to the cause, or unrelated to the cause of the problem.

I’m pretty comfortable with engines and taking things apart (I rebuild old motorcycles), but I don’t know anything about air compressors. If someone could please give me some idea as to what this problem may be and how I troubleshoot it, I would appreciate it.

Thanks in advance – I appreciate any thoughts.

Thanks,
-s

 

[shenion]

Is that running on 220?

Check the bolts on the bottom of the compressor. Mine all came loose.

I have just about the exact same compressor.

 

[spavined]

It's wired for 110. The bolts appear to be tight (though I didn't torque to check just yet)--I'm wary about overtightening them.

 

[shenion]

Yes, it is aluminum, mine were loose. Just snugged them up, a bit more than hand tight.

It should be 220. Didn't it come with a cord with an odd plug. Looks like a normal 120V but one prong is rotated 90 degreees.

It will either be a 20A 110V plug or a 220V one (depending on which prong is rotated.) If 120, will probably bog down on any extension cord unless you use a 12/2 one and it is short.

True 5HP is about 38 amps on 110 and 17A on 220. Mine runs on a 220V/20A circuit.

 

[spavined]

It's definitely wired for 110. Given that I've seen it properly function, I feel like the issue is more one of compression than electrical input.

My suspicion is it has to do with the loss of oil pressure from the blown gasket--or at least I'm hoping. I feared it may be blown rings or who knows what else...again, I'm clueless as the the inner workings of a compressor beyond that it runs on pistons.

Looks like I'm about to find out what the insides look like, though...

Thanks.

 

[shenion]

Could have been previous owner had wired a 220V outlet but used a 110 plug.

There is no "oil pressure". The pump circulates oil by the crankshaft throwing it everywhere.

Do you have the model #?

 

[the snooper]

just watched the video and it sounds very mechanical to me and given the fact it displays the same pattern each time i would be inclined to look at the pullys the motor pully could be slipping wich would cause it to slow down each time it came to a compression stroke

 

[tigler]

I'm inclined to think that it's the motor struggling for power. Check the voltage across the line voltage terminals before switching on , then see if the voltage falls when the compressor is set to run. If it does then the line feed is inadequate. As has been mentioned , oil is simply splashed around the crankcase and cylinder walls by dippers attached to the con rod big ends. If there was a lack of compression it would be easier rather than struggle to start up. Compressors of this type have very simple internals , pistons are similar to an internal combustion engine but much lighter in construction , valves are simply flexible stainless steel discs which flex to open and closed on the relevant stroke.

 

[the snooper]

come on guys if you have watched the video it cant be power related whos compressor sounds like that it sound liske a diesel single cylinder not a motor

 

[brightspark]

just wached the vid sounds like the cranks knacked .take the belt of it and run motor see if its ok. then turn the pump over by hand rocking backwards and forwards if theres a knocking noise its err had it

 

[shenion]

The sound is about right, but the motor is turning way too slow (it is 3550 RPM.)

 

[brightspark]

the crank might have even snapped so motor wont get up 2 speed

 

[the snooper]

it is very odd the way its speeding up and slowing down if i didnt know better i would have thought i was listening to an engine hunting for fuel.
if the crank had gone or snapped you would expect the noise to be constant not up and down.

 

[malcolm]

It does sound like the poor thing is just struggling for power. Well worth exchanging serial numbers with Shenion and seeing if it is indeed intended to be a 220V unit.

Did you happen to test it at the sellers house in a heated workshop? I reckon the change is likely due to cold, but that won't be the source of the problem as they should run at low temperatures.

There's nothing to suggest the crank has snapped! It's probably perfectly good but misconfigured in some way or has bad electrical connections somewhere.

 

[brightspark]

look at the motor when its running its rocking backwards and forwards trying to pull it over take belt of and check

 

[shenion]

That's normal until it get up to speed.

The knocking noise is the air intake. Quite loud on these.

I still bet it is 220V. 110 will not run a true 5HP motor. Probably 2HP with marketing lies.

The specs on the cover are identical to mine: 10.6CFM @ 90PSI. Mine is 220V/16A.

 

[the snooper]

he does state thought it ran well for 5 minutes when he got home

 

[malcolm]

look at the motor when its running its rocking backwards and forwards trying to pull it over take belt of and check

That will be a mode of vibration most likely forced by the compression strokes of the compressor working on some elasticity in a belt or shaft or clutch spring. Most compressors rock a bit on start up, and this one is running at start up speed continuously. The rock wouldn't worry me - it's likely down to the running speed.

But it is exactly the really interesting stuff I used to do for a living before taking up house painting. Have you ever noticed clutch judder in a car pulling away from rest? Exactly the same thing.

 

[shenion]

he does state thought it ran well for 5 minutes when he got home

Probably took that long to build up pressure in the tank.

Takes 6 minutes to fill my tank on 220, but my tank has been replaced with a 60 gal.

 

[eil]

My suspicion is it has to do with the loss of oil pressure from the blown gasket--or at least I'm hoping. I feared it may be blown rings or who knows what else...again, I'm clueless as the the inner workings of a compressor beyond that it runs on pistons.

Looks like I'm about to find out what the insides look like, though...

Thanks.

I'm going to go with that assumption as well, after running short on oil its piston /ring picked up in the cylinder blowing oil out of crankcase, next stage will be ceasing altogether by the sound of it.