Oil change

[Aussie_1]

Greetings from downunder.
Having recently purchased a C170A I now need to do an oil change (C145 engine). I note from a number of posts on this subject there are two filters (suction and pressure) and it appears that I need to remove and clean the pressure filter. However (and excuse the silly question) do I drain the oil via this filter or is there a separate oil drain point

[Bruce Fenstermacher]

There are actually two drain plugs in the engine sump. The one to the rear is the one you would drain the oil from. The one in the front is nearly impossible to get to with all the baffling installed and is not the lowest point while our aircraft are at rest. Remember this engine was designed to be used in many airplanes and the front plug might have been used in them.

I always removed both the suction and pressure screen and cleaned them. The suction screen will only stop parts big enough to display part numbers and your not likely to find anything there. But that is were I found a section of an oil ring and others have stuff I'm sure. I suppose you could drain all the oil out the lower suction screen but the drain pointing down has just worked nicely for me.

The pressure screen is very fine. I usually pull this and dump it into a mason jar with some solvent (100LL) and swish it around to clean it. Then I examine the screen and use a fine wire brush as necessary to brush the remaining particles from the screen. I then drain the dirty solvent through a paper towel and examine the crude. Most, hopefully all, of it will be carbon that you can crush with your finger. You may see a few fine metal particles. This is fine though it is disturbing. How much metal is OK is a matter of opinion. I've heard flakes totaling a 1/4 teaspoon to be about the limit. That is a lot of metal and I would be changing oil early and watching it,trying to figure out were the metal may be coming from If I saw half that amount.

[interstellardust]

Hi Bruce, et al,
I just changed the oil in my 1955 170B (0-300-A) and am now chasing a leak. It looks like it is leaking from around the crush washer for both screens. I used AN900 crush washers I just got from Aircraft Spruce. I tightened the pressure screen more, but it was still leaking so I took the pressure screen out and put a second new washer in. Still leaking. It seems like it could use the next size smaller (-27). Do you think that might help or do I just have a bad batch of crush washers?

Also do you know where I might find a new adapter nut that screws into the back of the pressure screen plat to hold the temperature sender? I ordered one from Spruce, but it is not the correct size either. I was back ordered a long time so I suspect they had it made.

[GAHorn]

Dusty... you should examine your present temp-sender nut to determine it's size, thread-count...and MOST IMPORTANT....which oil temp gauge it actually serves. If it's a Rochester then it will have a different flange than if it's a Scott. If it's a Scott...it will depend on if it's a NEWer Scott...or and OLDer Scott. Spruce should be able to guide you on the selection...but in a "nut"-shell...: (Hint: If you have a Continental engine it's a 5/8-18 thread nut...BUT...keep reading):
Old Scott gauges (prior to 1998) used a probe with an adaptor-nut which had a "flat" interior surface.
Later Scott gauges (post 1998) used a probe with an adaptor-nut which had a "conical" interior surface.

You MUST use the correct adaptor-nut or you WILL have a nasty oil leak and MAY even lose all your oil IN FLIGHT!
When installing a gauge your MUST use the gauge, probe, and adaptor nut supplied with the gauge. DO NOT install them separately or mix them. See Scott-Tyco Service Instruction Letter SIL-77-01, available from them.

Our MX Library also contains a copy of this Service Instruction Letter, and a copy of Neal Wright's excellent article (used by permission) he wrote for the 120/140 group on this subject. (One must be a full Member of the Int'l Cessna 170 Assoc'n to access the MX Library.) http://www.cessna170.org/forums/viewtop ... =26&t=8967


The An900-28 is the correct size crush-washer. Inspect your sump cover and screen-base to be certain there's not some reason (such as a crack or cut) that is preventing sealing of that crush washer. (It's also possible that yours isn't leaking at all and that oil is hanging in that area having been blown there from somewhere else.)

[Bruce Fenstermacher]

AN900-10 is the smaller crush washer used under the oil temp adapter if you have a plug on the course scavage (suction) screen. A AN900-16 goes under the scavage (suction) screen. A AN900-28 goes under the fine oil screen as George has pointed out.

[blueldr]

It appears to me that an oil leak problem as is discussed here is an incredibly simple problem. If the problem seems to stump the guy trying to solve it, maybe he shouldn't even fool around with it. Perhaps his mechanical ability and aptitude is a few degrees below what is needed to SEE what is required. Everyone is not mechanically inclined to the degree necessary to accomplish all of these maintenance
items without hands on assistance. Thats why they have licensed "Aircraft Maintenance Technitians".

[Bruce Fenstermacher]

Bl your point is well taken. But when faced with a seemingly simply problem that I just can not find a solution, eventually I have to ask myself the simple questions like am I using the wrong parts. So I wouldn't fault someone for doing the same thing.

I say eventually I ask myself this question because with my superior mechanical intellect and ability I rarely read instructions and tend to just re-engineer stuff that doesn't work the way I think it should. Sometimes it just takes a bigger hammer or a larger Vise Grips pliers .

[15A]

I have to agree with BL!
Sometimes it takes a 'trained eye' to solve even a simple issue. There is no substituting experience!

[Bruce Fenstermacher]

Joe that is another good point. You have got to know your limitations.

There are lots of mechanical people who have never used a crush washer. Doesn't make them less mechanically capable. Just means they've got to be smart enough to ask questions before grabbing a bigger pipe wrench when the crush washer leaks and they hadn't expected it to.

[GAHorn]

It may help to keep in mind the reason for existence of these forums... to promote maintenance of our airplanes, assist our participants and Members with their Mx questions, ...to further our association friendships, ....and to attract new ones to our group.
We all know people who should never be trusted with a screwdriver or vise-grips (Ol' Gar, Harold (according to Caroline), and apparently, Bruce... ).... but when someone comes here for the first time looking for answers and the collective knowlege-base...it can be discouraging and appear downright inhospitable to criticize their curiosity or search for info. It surely appears unfriendly and that's not the way any of us are in reality.

If someone truly does display a lack of talents in this area, it's a good oportunity for us to educate them on the finer points or complexity of the matter and thereby steer them towards qualified assistance....and gain a new friend while enhancing our own reputation as a resource.

Discovering a leak while an owner is performing authorized preventive maintenance like an oil change is not disqualifying, and I applaud "dusty's" efforts to seek answers. (And it's easy for us here in the states to forget... obtaining parts, service, and info in the Land of Oz is not a simple matter!.... I can't imagine how much more difficult it is intergalactically! )

By the way, Dusty.... yes, if you remove that suction or pressure oil screen ....it will drain all/most of the oil out of your engine. But you won't like the mess it creates! The best method is to get a large 5-gallon plastic bucket and place it beneath your sump and remove the rear drain plug (found just aft of your carburetor between it and your suction screen. There's another just forward of your carb but it's difficult to gain access to due to the carb air box, so most folks don't bother with that one and accept the few ounces of dirty oil that remains there as a consequence of the design.
Also...it's not a good idea to place TWO crush washers beneath that sump-filter housing. They will not seal well and may dislodge, which could prove disastrous in flight! Only ONE crush washer, OK?
(Besides....I doubt that's where your leak is coming from. I imagine it's only a drop of oil hanging there which has migrated from somewhere else. Get a aerosol can of "GunK" engine-wash and spray your engine down, then wash it with a water hose and let it dry. Compressed air may help speed the drying process. Try not to get your carburetor wet ...Water can enter your carb thru it's accelerator pump shaft and corrode it internally. Taping a plastic bag around it while washing may help.
Let the engine sit without running for a few hours and I'll bet that crush washer isn't leaking. Chances are it's coming from above...like the starter, generator, magneto or pushrod housing area. )

Aircraft Spruce and others sell a fine product known as a "quick drain" which I recommend installing while you do this job.
The one for the O-300 engine in C-170s is Spruce PN 07-00880 (Saf-Air S-1000). When performing an oil change I simply slip a 3-foot section of 3/8" hose (PVC works fine) and with an upward push-and-twist...all that dirty oil drains down into the bucket.
Simple, eh?



http://www.aircraftspruce.com/catalog/e ... Valves.php

[15A]

No critizism intented.
When it comes to getting information for the 170, this is one of the ONLY places to go.

[Larry Holtz]

I have a leak like yours and I believe it is from the generator seal. I put in a new seal last year and it still leaks. I will probably tackle it again next winter and see if I can see what I have been doing wrong. I also have the pull starter and will check that out also. Never thought about it being the starter.

Larry

[blueldr]

The "Dryest" radial I ever flew behind, and most of them leak, was a P&W R-985 on the first DeHaviland Beaver that the Air Force bought for service test in February 1951. We picked it up at the factory in Downsview to take it back to our unit, the Cold Weather Test Unit at Ladd AFB in Fairbanks, Alaska. That engine did NOT leak even ONE DROP all the way to Fairbanks.
The Canadian mechanics used a water mixed white paint in the manner used in NDT with a dye and a developer. They speayed the engine with the white paint and allowed it to dry. When they ran the engine up, any oil leak showed immediately in the porus white paint. It was the most effective method I've ever seen.

[3958v]

George Removing the large screen (pressure screen I believe) on my C145 drained very little of the oil from the sump. I did this last weekend because I had a broken quick drain which would not release properly. The largest portion of the oil did not come out until I removed the quick drain. I got a new drain today and plan to install it over the week end. I don't use a hose on the quick drain as it is real easy to clean up the mess on the lower cowling. Bill K

[GAHorn]

George Removing the large screen (pressure screen I believe) on my C145 drained very little of the oil from the sump. I did this last weekend because I had a broken quick drain which would not release properly. The largest portion of the oil did not come out until I removed the quick drain. I got a new drain today and plan to install it over the week end. I don't use a hose on the quick drain as it is real easy to clean up the mess on the lower cowling. Bill K

Yes, it's possible that hyd/air-lock of the system can occur preventing draining action. Even if no lock occurs, it's a slow process at that point, and why the press. screen is not the normal way of draining oil. (Suction screen has an entirely different effect.)