582 UL 99 Cylinder head rubber ring replacement

I am no 582 expert by any definition but, In looking at the Parts catalog it would appear that you have the correct part number.

There could be many reasons or the profile change, some intentional and some just supply chain issues.

The smaller inner Ring is going to be sealing against the full heat and pressure if the combustion chamber.

The larger rectangular ring is only a coolant seal for the head.  It will never see more than 20 psi.

If it has any deficiencies, the result will be a coolant leak to the outside world.  Hardly a disaster scenario, and easily detected.

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It is always a good idea to lube any O-Ring when installing it.

The idea is to add a little friction reduction, Don't drown it!!!

When using Oil or Grease, just enough to give the ring an oily sheen is all that is needed.

There is no need to fill the groove with grease/oil and then bury the ring in it.

Less is better.

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In all cases be sure to use the proper compatible lubricant.

Motor Oil or Grease would NOT be recommended in this case.

A Drop or two of Anti-Freeze would be the lube of choice.

Hi admin, thanks for the info.

Still the question remains, is the ring I received, part nr. 850040, 152.5x2.5x5, the right ring and why is it different from the original one?

Can I use the new, slightly different ring, just like that?

Gr. Peter

Your engine is 20 years old! Are you sure that the ring you are replacing now is actually the original factory part, and not something someone improvised as a field repair in the past?

The correct 850040 part is indeed a  simple 152.5x2.5x5  

( example:  https://www.leadingedgeairfoils.com/head-gaskets-152-5x2-5x5.html )

Hi Admin, yes, build 20 years ago, running since 18 years and appr. 500 hours in all these years. We don't fly that much.

And yes, I know it is due to an overhaul, according the manual. But it is running very smooth, never had any problems with it.

The reason for the ring replacement was that I noticed some "sweating" between the cylinder and cylinder head. I just didn't know whether this was serious or not so I decided to replace it. Perhaps not necessary.

The part I ordered is the original Rotax, I ordered it from a Rotax service company in the Netherlands so I expect it to be right and it is exactly the part the link, you send, shows.

It is just that the ring that came out looked different, that's why I'm asking.

I took a picture of the ring where you can see the shape.

When I look at it closely I can imagine that the ring, after 20 years, has the shape of the bed or groove where it has been for all that time.

I just want to be sure that I didn't miss something.

For the rest it is a great engine, never a problem in all these years.

Peter, 

I am confident that the new O-Ring will do the job as intended.

After 20 years, we all tend to look a little different

I would install it with a little Antifreeze for lube and if it doesn't leak, what more can you ask?

There may be an initial seepage the first time until the engine gets Hot and the pressure seats the ring in position.

Be sure to let us know the outcome after you get an hour or so of flight time on it.