Air Compressor knock and tear down, with pictures

[250]

Recently I noticed that my quincy compressor sounded a little different as it got up in the compression range >110psi or so. I started poking around and could hear a very metallic 'tang tang tang' as it went along, and while I could only hear it well when listening though the tank, it was a sound that was new and not good.

Talking with a couple of the local compressor shops, all they were interested in doing was to activate the Quincy head trade in program... more money than I'm interested in. Thus with nothing really to loose, I opened her up, took a look and some pictures. I've never tackled a project like this, so the questions will be basic.

It looks like I probably need new connecting rod inserts (bearings)?
IMG_2318 by david koenig, on Flickr

IMG_2331 by david koenig, on Flickr

IMG_2325 by david koenig, on Flickr

Crank shaft bearings. I don't see anything obviously wrong, replace them since I'm here? Can these be removed with a normal bearing splitter?
IMG_2324 by david koenig, on Flickr

High pressure piston, new rings needed.
IMG_2320 by david koenig, on Flickr

High pressure cylinder. Some staining where the wrist pin rides. There is nothing that I can catch with my nail in there.
IMG_2323 by david koenig, on Flickr

The low pressure cylinder. I wasn't expecting the wear to the piston skirt. I'm not sure what caused it, I'm guessing something is worn and allowing slop as it sides up and down. Its pretty concentric around the skirt.

IMG_2317 by david koenig, on Flickr

IMG_2316 by david koenig, on Flickr

The low pressure cylinder, honing marks up higher, smooth lower from what I believe is the cylinder rubbing.
IMG_2322 by david koenig, on Flickr

And there we are.

I haven't taken the connecting rods out of the pistons yet, in case there was something I should check first. I'm expecting some replacement bearings and rehone the cylinders, and perhaps a trip to a machine shop? If so, I'd like to go in not completely ignorant and know what service to ask for on what parts.

Anyways, hopefully the GJ community can give me a hand. Thanks,

-david

 

[MacMcMacmac]

Plastigauge the crank bearings, but I'm confident you will find them in spec. Your bottom end looks fine to me. Bearing splitter will work. Getting the race out of the oil pump end is the hardest part if you don't have a welder. Seriously though, I wouldn't bother.

High pressure wrist pin bearing is probably the most likely culprit, or a loose valve in the head. The tank check valve might also be going south, if there is one.

Don't mix up the rod caps. They won't interchange.

 

[250]

Thanks Mac.

I went through the head first, given that I've had a valve get stuck before, but the sound remained. What I found interesting is that when I listened directly to different parts of the compressor during operation with a scope, I couldn't find the noise anywhere in the head.

I'm happy to leave the crank bearings alone.

I haven't taken the wrist pin out of the high pressure cylinder/rod assembly. Is there something I should do at this point to confirm a bad pin?

And what are your thoughts on the low pressure piston skirt wear?

-david

 

[Trey T]

If it's just knocking, just replace the bearings and clean up the rings. Put it back altogether and run it with some full synthetic 10w30. Run the oil pressure about 20-25psi.

I wouldn't put anymore than couple hrs and whatever the cost for new bearings into it.

Overall, just from the photos, the internal is in a really good shape

 

[MacMcMacmac]

Just hold the hp rod in one hand and rock the piston side to side in line with the pin and see if there is any appreciable slop. If there is, you should replace the bushing.

 

[American Locomotive]

None of that wear looks too abnormal to me. Even the connecting rod bearings seem pretty serviceable.

 

[250]

This is encouraging news.

I looked at the HP assembly again, and while I'm not 100% I'm testing correctly for slop, I did notices that the wrist pin can move a little with in the piston, maybe 1/32-1/64th along the long axis of the pin. This if I push on the pin itself. I believe I feel this movement when try to 'rock' it as well, if I've been rocking in the orientation you've described.

 

[250]

Alright, got some parts last week and I'm ready to put it back together. Any reason I specifically need to use Quin-Cip oil?