Projects Air Compressor Making loud Knocking noise

Hey guys,

I've got a small 60 gallon 6.5 hp Coleman Powermate Air compressor, two cylinder single stage, aluminum case pump with iron cylinder liners. I've run this little compressor for over 10 years as my daily runner, I fire up a bigger one for blasting and big air needs.

Its been knocking for quite awhile, and until lately it hasn't gotten any worse and I continued to use it. Sounds like a rod knock and has been getting much quieter after about 100 psi or so is in the tank.

Lately it has gotten so noisy that I thought it was self destructing, and I figured the rods and the crank were going to be toast. I opened it up and measured everything, I can't find the knock. Everything looks good!

This thing is in amazing shape for the abuse I've put it through over the years, I'm sure the rings are even re-usable. Just gaskets and I could put it back together.

What on a compressor can cause a seasoned engine builder to believe it has a rod knock when it doesn't???? Reed valves? Tank check valve??

Before I put it back together I'd sure like to hear from you guys if you have any idea's.

Thanks very much!

Mm

 

Maybe you should switch to premium gas?

The devel made me say it.

 

i've got a 80 gallon 5hp 2 stage compressor that does the samething, its 5 years old and it knocks so bad it blows my mind it even works but it seems to be fine, oil is good, pumps up fast, etc.....

After it warms up or like mentioned gets 100+psi it quiets down...... i don't have an answer but i've got one just like it

 

Its just too expensive around here, nearly $4 a gallon. Don't these newer contraptions have a knock sensor or something that stops that?

Sorry, I just sorta went along with it

 

four dollars for premium? ... sheesh, 4.20 for regular just across the border in CA ..... I cant afford to drive my compressor!

 

We had a similar compressor head that was making a hell of a racket and found nothing wrong - except the ring gaps had somehow all mysteriously lined up.

After alternating the gaps and putting it all back together it was running like a champ again. This was about a year ago and its been fine since.

 

Loose pulley?

 

Just ask your compressor .... "who's there?"

 

is it taking longer than it used to to fill the tank? got one doing the same thing.

 

Mine was knocking really bad and thought it was gonna blow up. All it ended up being was the hub on the plastic fan on the motor was starting to wear out.Put a new one on and its nice and quiet again...Jim

 

The pulley was for sure tight, and its seems to pump up as good as its ever done. Of all of the reading online, check this or check that, I'm just not finding the source of all the noise I was hearing.

 

That one would be easy to check, motor is sitting there by itself with power still hooked up. If its noisy by itself than that's it.

Thanks

Mm

 

yup, thought mine was on the way out it was banging so hard, found the belt shield had broken a couple of mounts and was making the noise, fixed the mounts and it quieted right up

 

All it said was "Knock, Knock, Knock"

 

Reed valves?

 

I think I would adjust the timing, sorry just had to.

 

Does it knock when the pressure goes over 10psi? Probably the boost retard is not working, and premium fuel won't fix that...

On a more serious note, my Quincy had a nasty rattle on startup that turned out to be the unloader sticking. Sounded like it was the pump, made the whole tank ring. All it turned out to be was the valve hammering until the differential pressure shifted & it warmed up a little. A good cleaning & a little lube solved the problem.

B

 

Have you seen the reeds make a bunch of noise? To me they look fine but there isn't much to see. The actual part that is the little flapper valve is under a strap so I can't see the actual area where it seals.

Can't tell if they are bad or not by looking, or at least I don't know how.

Mm

 

One time the waste gate was a little sticky and man did it get noisy that time!

 

That was going to be my first guess as well and yes I have seen some old compressors with really noisey reed valves.

 

You mentioned rods and crank being okay, but I didn't see you mention wrist pins. Did you check them for wear?

 

Mine was making one hell of a racket, took the filter off and no more racket. Replaced Clogged filter.

 

I had a noisy one but it had a broken reed in it, turn the shop radio up that'll fix it! Or just leave it alone it will self diagnose!

 

add a little lucas oil treatment

 

The pins, skirts, bearings, crank pins, everything measures good.

 

How about side clearance? Also check the safety valve that is mounted on the tank check valve as well as that valve. I have had some wierd pumps that have had these things cause "knock". One more thing to check is the case main bearings, some times a pump that is outdoors or has been outdoors for awhile can have condensate build up in the crankcase as well as be drawn in through the air filters, I have seen pumps running with more water in them than oil! The case main bearings ended up pitted from the moisture and caused it to sound like a knock as well. Not knowing the history on your unit weather its been outside or not just something to check if you havent.
Drawing it in through the air filters is only from rainy or really wet conditions the pump case itself usually cannot heat up enough to get rid of the moisture thats why it remains inside the pump.

 

If you have ever heard an engine run with a rod bearing that is so bad the piston comes up and smacks the head. Its a loud most times a double knock, but loud! Not saying this compressor had a double knock, but it sounded the same otherwise.

Just thought I would say that. I thank everyone for their input, waiting still for that guy to come along that has had the exact same problem, yea right. Well........

I check the valve going to the tank, one way valve, seems fine although not sure what to look for. Push pull test seems good.

 

Is it a belt drive or a direct drive. I have seen the couplers on a direct drive cause the noise you are describing.

 

Not sure if this has been done already, but if its a belt drive, can you remove the belt to isolate whether the noise if from the motor or compressor?

 

Not only is the belt removed, the pump is ****tered all of the work bench. I left the power hooked up to the compressor, so I turned it on without the pump being installed. The motor sounded fine, had quite a hum to it but it ran without any knocking noise.

Mm