Cutting open oil filters

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Simon Clifton
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Cutting open oil filters

Post by Simon Clifton » Tue Oct 27, 2009 11:41 am

Rotax maintenance schedules say you should inspect the filter paper inside old filters.

Do people really do this in practice?

If so, anybody know of an effective way of doing this without necessarily spending 50.00 quid plus on a special 'can opener'.

I appreciate using a hacksaw is not recommended because it leaves bits of metal behind, but are there any other proven methods I could try?


Simon C

Dave Hall
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Post by Dave Hall » Tue Oct 27, 2009 11:30 pm

There was a drawing in a recent EAA Magazine of a device that a guy made using a couple of cutting wheels as used for pipe-cutters. These were mounted on axles at a suitable height above a base-board, and a curved saddle to suit the filter size was set up with a threaded screw and knob to advance the saddle and oil-filter towards the cutters. Rotate the filter and use like a large pipe cutter. The saddle had a recess to accept the rolled edge of the filter

Whether the couple of hours or so making it is worth £50 to you is a decision you would have to make. It may be that a single cutter wheel would work fine, and a couple of plain wheels on the saddle might make it more like the commercial pipe cutter.

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Post by gasax » Wed Oct 28, 2009 12:39 pm

I use one of those antique tin openers - the ones with a sharp point and blade. With luck a single thrust opens a hole and rugged use opens up enough of the shell to get the contents out.

By no means sophisicated so if anyone has an easier way I'd be interested to see it!
Pete Morris

Bill McCarthy
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Post by Bill McCarthy » Wed Oct 28, 2009 1:26 pm

Get hold of someone with a lathe. Tape over the oil ports and machine a sliver from the circumfrence (but not all the way through) and use a filter wrench whilst it is still in the lathe to snap off the shell.

Brian Hope
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Post by Brian Hope » Wed Oct 28, 2009 4:25 pm

Wouldn't you rather have a Continental? They have a screen with a mesh so coarse that it only stops parts large enough to have a part number on them but it seems to do the job OK. Are Rotax's really that much more likely to shed lumps of bearing that every filter change has to be cut open and inspected?

Barry Plumb
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Post by Barry Plumb » Wed Oct 28, 2009 6:26 pm

Actually its not a bad idea to open them up once in a while. I do not have a Rotax, but I do have a Jabiru. A few years ago I was returning to Hinton from Popham when I noticed that the oil pressure was a little lower than normal. As the flight progressed the pressure dropped even lower and I diverted into Bicester. I could find no fault, and the oil was up to the mark on the dipstick. Having let the engine cool down for an hour I started up again and the pressure was high enough for the 10 minute hop to Hinton.
When I removed the filter to check the PR valve (located under the filter unit on the Jab) I found a slither of metal jammed in the PR valve. So I cut open the filter to discover that there was a large amount of both aluminium and steel particles in the filter.
Further investigation revealed that one gudgeon pin circlip had come out of a piston and gone down into the sump. This is possible in a Jab because they are fitted with slipper pistons where the gudgeon pin part of the piston is narrower than the crown. Result was that the gudgeon pin was steadily marching out of the piston and scraping metal off the main bearing saddles inside the crank case.
I daresay this had been going on for a while, and if I had cut open the filter at the previous oil/filter change, I would probably have saved a bit of a worrying time in the air.
If an engine is shedding metal into the filter, find out why.
Actually I think even a Continental oil filter would have caught these bits, as two of them did have part numbers on.

Kind Regards, Barry Plumb

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Post by gasax » Thu Oct 29, 2009 8:45 am

Actually Brian this is simply 'good maintenance' practice. The one thing that kills small Continentals is loos of oil pressure - usually from bearing wear.

This is why there are so many after market filters for these engines. If the oil is properly filtered then the engines last a great deal longer.

Finding debris in the filter is unlikely to come from general wear - the particles are simply too small. However if any components are failing prematurely then the particles from them are likely to be bigger and hence visible. The obvious example would be Lycoming camshafts and followers - notorious for spalling and if Lycomings had a decent filter fitted it would be very obvious.

My Rotax is fundementally better engineered than the Continentals I've owned, along with that better engineering keeping an eye of the filter internals is simply better maintenance practice.

The coarse screen on the Continental actually does nothing apart from protect the pump, if you want the engine to last adding something like an F&M cartridge makes a heck of a difference to the state of the oil after 25 hours. and yes I opened up that cartridge as well!!!
Pete Morris

Brian Hope
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Post by Brian Hope » Thu Oct 29, 2009 9:29 am

Hi Pete, my post was somewhat tongue in cheek, I have had a filter conversion on my C90 for many years and change the oil every 25 hours, but I do not open up the filters. At one of the Jodel seminars in the nineties, a guy from Yorkshire Light, now Multiflight, came to talk about looking after small continentals. Based on many years of experience, he said the best way to get your engine to run to TBO was to use W80 oil and change it every 25 hours. His experience showed that multigrades and synthetics were not as reliable as good old W oils. The vast majority of the engines he would have been talking about would not have had cartridge oil filters fitted. I accept the risk of not opening up my filters because I think it is very small, but I do inspect the oil that I drain for any sign of metallic substances. A C90 though, does not have to work anything like as hard as a 912 to produce its power.

Ian Melville
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Post by Ian Melville » Thu Oct 29, 2009 11:02 am

I cannot remember off the top of my head all the details but that would sound right to me. They are measuring two different things, which one happens to be double the other.
There is an article in the last Flyer magazine on oil grades. Very good and will be kept for reference.

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Post by macconnacher » Thu Oct 29, 2009 11:42 am

W80 is not a straight oil it is an ash disperant oil. We only use straight oils such as 80 for running in.
Stuart Macconnacher

Rob Swain
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Post by Rob Swain » Thu Oct 29, 2009 1:16 pm

Brian Hope wrote:Wouldn't you rather have a Continental? They have a screen with a mesh so coarse that it only stops parts large enough to have a part number on them but it seems to do the job OK.
Old Lycomings (Lycosaurs?) have the same approach.
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.

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Post by steveneale » Sat Oct 31, 2009 8:30 am

The parts manual we have for our Lycoming shows a full flow spin on oil filter. That particular manual was printed in 1984. I don't think the Rotax 91X series was even in production then. We open our filters at every change. This is SOP for certified engines. Not sure why anyone would wish to do less because an engine isn't certified?

If something is making metal I prefer to find out on the ground certified or uncertified.


Brian Hope
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Post by Brian Hope » Sat Oct 31, 2009 9:07 am

Hi Steve, it certainly cannot be argued that opening every filter is a bad thing to do, it is simply a question of degree in my book. For ten years or so, at least 1000 hours, I operated my engine without a spin on filter, so there was nothing to look at except the gauze screen and the oil. Generations before were in the same situation, and many still are as they have not modded their engines. I now have a spin on filter, but in my estimation the likelyhood of a problem with metal in the oil is very small so I do not split the filter for inspection. A purely personal assessement of risk. May I ask why those that do split the filter do so rather than send it for spectographic analysis by somebody who actually knows what they are looking at? In this way you will get earlier warning of an impending problem because by the time you personally can see lumps of metal it is too late anyway, the damage is done. I suspect the answer is because in your estimation that is a step too far, again a personal assessement of the actual degree of risk that you perceive exists. There are others that do not change their oil at 25 hours, their assessement is that it will last 50 with no additional increase in risk - I do not agree with them but that's their business.
Maybe I am foolish, but in over twenty years and probably a hundred oil changes, my assessement of the risk and the adoption of an operating methodology that suits that assessement, has proved satisfactory.

Steve Brown
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Post by Steve Brown » Sat Oct 31, 2009 9:09 pm

FYI Shell 80 oil is SAE 40 and Shell 100 oil is SAE 50 and the SAE numbers equate to the automotive values ie 20/50 or 10/40 etc

The Shell use of W denotes the addition of anti wear additives that would inhibit break in of a new engine so straight 80 or 100 oil (no W) is used for that.

I use the recently introduced Shell 80WPlus in my O-200 which has anti corrosion additives in it which help protect low hours aircraft engines from rusting internally.

The Shell multigrade uses this anti rust additive too but as a conservative user of 'Plus' single grade oils, I think I thus get the best of both worlds.

I personally don't like (say) 15/40 multigrade oils in Continental a/c engines since the base oil is very thin (SAE15) with non-oil thickeners in it to get it to act like a SAE40 at high temperatures.

If you assess the temperature ranges of Shell 80 and 100 specs for use in this country's temperatures, I don't think 100 is justified even in summer. So it is Shell 80W Plus all year round for me

I agree with Brian - 25hr oil changes are very cheap engine protection, and a full flow paper filter an additional protection bonus.

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