Unacceptable oil useage

[jdmcbean]

Before making too many assumptions.. please do a leak down test (AKA compression test) This will help identify rings, or valves...

If you are running Auto Fuel it may pay to run 100LL for 20-50 hours.. Some may even suggest a little MM (Marvels Mystery Oil) in the oil.

[Dave S]

Hi Keith,

Lots to be said about correctly diagnosing things before diving into a major/costly repair.

I once flew a plane with an HP lycoming engine where the owner considered a quart an hour acceptable consumption.....guess everyone has their standards....now you know one of the reasons I went to a Kitfox homebuilt where I can be the repairman

If you can get some info from the person who put in the modified pistons, you may be able to rule out or confirm certain potential problems.

One issue with the rotax engines is they are not continentals or lycomings.

If a rotax has a piston or ring change using conventional cylinder wall prep; or no prep at all if the engine has some hours of use on it before the modification, it is not beyond possibilities to have cylinder/ring seal problems develope.

Rotax engines do not use an iron sleeve or cylinder and cannot be honed in the manner commonly used with iron sleeved cylinders. The rotax cylinder wall is essentially a silicon particle sintered aluminum wall which is great for long term wear. There is a correct procedure (lapping) but, traditional honing will likely create a problem.

If a Rotax has some hours on it before a piston/ring modification; the engine already has a breakin/wear pattern with the existing rings. If new rings are put in without any cylinder wall prep (the correct kind) new rings are trying to become one with a previous wear pattern and that can take a while or possibly never happen.

Just some ideas to throw out there......

As John said.....do your diagnosis first and find out is going on...... cheaper that way

Sincerely & Good luck,

Let us know what you find out.

Dave S

[DAT]

I had a similar problem when I bought my KF 5. It had very little usage, average of 4 hrs per year for 10 years, before I bought it. I had a good friend who is an A&P do a compression test and borascope the cylinders during my prebuy. It had good compression and the cylinders and rings looked clean, no rust. It used oil. Not much, maybe a few ozs every 3 or 4 hours. We thought if I flew it the rings might reseat and it would quit using oil, but it didn't. We checked for oil leaks, and any obvious signs that have been mentioned already. We decided to pull the cylinders and check it out. As long as my friend was going to be tearing it down I decided to go ahead and order the Xtra pistons. When removing the cyl we found that the number one cyl had a broken oil ring. The cyl wall was fine and had no scrapes or scratches. We honed all the cyl, installed the pistons, used the old rings, replaced the broken oil ring, and put it back together. It has been perfect since then and I have more than 100 hrs since the repair/install and it does not use oil. I changed the oil every 25 hours and split the filters. Everything looks fine. I don't have to add oil between changes now. The engine definitely has more power, but I don't know how much hp it's pulling. I have an IVO IFA prop and run full throttle and 5,600 - 5,700 rpms on climb and 5,300 to 5,400 rpms at cruise. The engine seems to like the power settings and everything stays in the green. Good luck.

[WWhunter]

DAT, I am wondering if I have the same issue. This particular plane sat gathering dust for over 11 years. The previous owner bought it, flew it a couple of hours, had a bad landing (bent the landing gear) that I think scarred the crap out of him. He them parked it and never touched it. He tried selling it for top dollar but no one would buy it due to the hard landind and their thinking of hidden issues. Over the years people would 'fiddle' with it. Turning the prop, etc., before I finally bought it. It started right up and after a thorough going over I flew it. Right from the start it seemed to have a vibration which was mostly due to the two blade prop. I changed to a 3-blade Wirlwind and that seemed to cure it. After a few hours it would run rough again. Pulling the plugs and replacing them every few hours were needed due to the fouling.

I am fairly mechanical having done total restorations on cars and done basic maintance on my plane but have not dealt with the Rotax seris of engines. The are still an engine but seem a little more critical than engines of yesteryear.
I have gone over the outside of the engine very thoroughly and see no signs of any leaking. I have a compression tester but not a leak down type. I do remember that a couple cylinders had a little less than the other two. I don't have the numbers handy.
(I am currently in MD and the plane is at my strip in MN)
I only have a few months each year to fly so I would like to get this figured out as soon as I get back to MN.
Anyone have a good (cheapest) source to get a leak down compression tester for the Rotax?

[kmach]

I bought my differential compression tester for the rotax 912 series from ACS was around $80 if I remember right. rotaxparts.net also carry them

[jwlt500]

Just a thought but have you checked the engine for the AD that applied to this motor?

[WWhunter]

Could you please post the AD you are refering to? I am 1500 miles away from the plane and any maintance books right now.

[Av8r3400]

There are literally hundreds of service bulletins on Rotax engines.

The best way to get the information that applies to this engine is to take the engine's serial number and run it through the Rotax Website.

http://www.rotax-owner.com