Quick Question Thread

[f350ca]

How about a thread for quick questions that don't warrant a thread of their own
First question,
Was going to change the oil in my compressor, a big old cast iron V-4 two stage. Checked the oil and it looks like the day it went in. Does oil wear out? There's no products of combustion like in an engine, to clutch material like an automatic transmission, no material off the synchro's in a standard or material off running gears, so does it really need changed?

[Dr Stan]

The short and long answers are the same, yes it needs changed.  Over time lube oil breaks down in the case of a compressor from the heat that is generated.  There will also be a small amount of metal from wear in the oil.  If it is not changed this will increase the wear on the compressor pump making its lifespan shorter.

[arvidj]

I'll bite ...

Googled 'does oil wear out' and got lots of irrelevant information about motor oil, combustion by-products, etc.

Googled 'do lubricants wear out' and got lots of [possibly irrelevant, will know later this week] related to lubricants used for sex.

After weeding thru the lubed condom data the theme seems to be that machinery lubricants don't actually break down but they do get dirty.

For my many-year-old two cylinder two stage the process was:

Change it after about 50 hours of use. That way what ever was going on from the cylinder rings and cylinders plus bearings adjusting to one another would be removed.

The next thought was to change it just so I knew how much was in the crankcase, but that thought disappeared with I realized I had bought the optional the low-oil sensor. That will prevent the compressor from starting should the oil level go below a catastrophic level so why not rely on it.

I will occasionally look at the sight glass to make sure I am not loosing oil by it getting past the rings. Assuming the level does not go below the dot on the glass I'm satisfied. I've never had to add oil so ring seal seems to be pretty good.

I admit to having changed the oil several times over the last 15+ years. No reason other than I had the compressor oil on hand and I wanted to change from the original organic oil to fully synthetic compressor oil. And the 'change to synthetic' was motivated more by passion than solid engineering data.

[f350ca]

I can't honestly remember the last time I changed the oil in it, the level has never gone down. I think I have once but guessing thats 4 or 5 years ago. No sign of water but there might be cuttings at the bottom of the base. Guess I'll pick up a couple of quarts and give it a little TLC.
Thanks

[Dr Stan]

I should note my answer was influenced by my time in the Navy where I learned Preventative Maintenance, which of course has been replaced with Predictive Maintenance.

Bottom line, oil is a whole lot cheaper than a rebuilt compressor pump.  There was a oil commercial back in the 60's that featured a "mechanic" saying "you can pay me now, or pay me later" contrasting regular oil changes versus rebuilding an engine.

I have a 60 gallon two stage Champion compressor which I plan to be included in my estate auction.

[arvidj]

I am old enough to remember that commercial.

I also believe in preventive maintenance ... or what ever it is called now ... but I also believe in realistic maintenance. At least for this hobbyist the compressor is not used anywhere near like the Navy might use one.

Given that my dad never changed the oil in the used compressor he bought and the neighbor never changed it when he bought it from my mom, the 40+ years of occasional use with what ever was in the crankcase it suggests 'you sometimes get lucky'.

I will assume that most hobbyist based compressors are like mine and don't have an hour meter on the compressor. Therefore I have no way of knowing how much time it would actually have on it between changes. Nor would have any knowledge of many hours it might have run during any given calendar time period. Therefore 'knowledge based predictive' is not an option. If 'knowledge based' is not realistic then the random 'I have some oil on hand and feel like changing it' seems to be the other alternative ... or not.

[Dr Stan]

I'm right there with you in regard to hobbyist V industrial/military use of machinery.  After I complete the rebuild of my shop I plan to contact Automation Direct to see about a hour meter to install on my compressor.

[Pete O]

Another quick question (I hope); I've been given a recommendation of a steel merchant who is right near where I work and who reportedly takes cash for offcuts at good prices. I plan to drop in there on Monday to see if I can get a chunk of steel suitable for the nosepiece on my frankenmill project. My question is, what types of steel would be acceptable for this part? It will essentially be a version of the piece on the right in this photo- unfortunately cutting the knuckle in half didn't leave enough material on the rear side, so I'll be reproducing the front features- circular T-slot etc- and a flat surface with a circle of threaded holes on the back side. I'm thinking 4140, but if the guy offers me something else I'd like to have an idea if it will suit the purpose. Worst case is the T-slot breaks out in service and deposits the J-head at my feet.
   

[f350ca]

This is above my pay grade Pete, but thinking about it, its a tension load on the T-slots, if cast iron held up, a similar section of any steel should be plenty strong,

[Clifford B.]

Hey Doc. do you remember the 3M system ??
It went hand in hand with the PMS.
MRFA C.Brewer USS Ajax 79-81