Suunto marine compass repair

In our 1999 Bavaria 50 Cruiser, both Suunto compasses (model F-116/Sail) started leaking mineral oil at about the same time. After doing some research, I found out that this was not an uncommon problem. Unfortunately no replacement parts were to be found as this is an older model (and also regarded by some as a sealed unit and not repairable).

The (repaired) compass

The general consensus seemed to be to buy new ones. But new units are expensive, and didn’t seem worth the price for how little use they get.

Luckily, using my 3D printer I were able to produce tools to make it easier to disassemble it, as well as designing a replacement for the broken bellow. Since disassembling the original unit requires a vise and special tools, I designed new parts to make it easier to reassemble with only a screwdriver. I also made a small holder for a red LED-light, as ours only had an old light bulb glued on.

Printed replacement bellow. These are printed in polyurethane, and are chemically resistant to mineral oil, very tough and flexible. They should last longer than the original part, made of much stiffer plastic that cracks.

Getting the old compass apart is best done by dipping the lower “cup” in boiling water for about 30 seconds to soften the plastic, and then placing it in a wise with the 3d printed tools. This way the cup is squeezed off the compass body, and will pop of rather easily when enough pressure is applied.

Compass in a vise (with older version of the tools)

Cup off. Add some paper bellow to absorb any oil spill.

Vise-tools for applying pressure to the cup.

After getting it apart, clean all parts before starting to assemble again. I rinsed them in water, and cleaned them up with lint-free cloth. To not touch the compass dial though, this is very delicate and can easily bend. Any white spots or discoloration on this that shows up when it dries are invisible when the compass is refilled, so don’t worry about them.

Then its time to reassemble. Putting the new bellow on, ensuring that it fits well, the newly printed part to ensure a tight fit is put on and tightened with a screwdriver, using A4 stainless screws which are not ferromagnetic.

New bellow in place

New part to replace cup. Easier to tighten and ensure a good seal than original part.

For replacing the old mineral oil, fragrance-free baby oil were used. A syringe were needed to get the oil through the small refill-hole. Filling the compass and refilling the syringe takes time and patience, so one can save some time by filling the compass nearly full before putting on the clear acrylic dome. Then the rest of the oil is filled through the fill-port, tilting the compass so one can get the last bubble of air out before replacing the seal.

Everything ready for compass repair

Refilling of compass using syringe

Turn it around some times to make sure there aren’t any small bubbles stuck under the dial or elsewhere. My experience is that very tiny bubbles will dissolve after a day or so in the mineral oil.

Two newly repaired compasses. The right one has some oil spill on the outside of the dome.

Mounted in the boat with new LED-holder.

Compass with LED light on

So both compasses are now good as new. Hope this can help other who have given up hope on these compasses.

Due to there being some demand for these, the drawings are available at thingiverse. Since printing these are somehow difficult, and not everyone has access to a 3D printer you can now buy the complete kit from me

7 comments

  1. HI, i also have a Suunto compas on a bavaria 37 that has lost its fluid.. Am about to dismatle it to try and replace the bello that i suspect is dammaged. i am intrested in one of your replacement bellows to repair the compass as spares are not avaliable as you alreqady know. Please let me know if you are able to post a replacement to me on the Isle of man where we are based. I look forward to hearing from you and my compliments on a great write up to this problem.

  2. Hello together!
    My suunto compass just lost almost all oil (bought the boot recently Bav 31 1999) i do not see any cracks on the below part and also no signs of oil where glas is connected with black plastic. Only place where stil oils is coming out is the lowest part , where is a hole. I ‘ve tried to check what is inside ,looks a rubber gasket or membrane. If I stick this hole with oil resistant glue (or clean it properly the surface) I think can refill the compass with baby oil..😉 Do you think it will be a solution or even if I do not see cracks or damag on the plastic this make no sence? Thx Mate-Hungary

    1. Inside the plastic cover there is a membrane, and these fail from old age. That’s why I designed and printed a new one. I do not think plugging the hole at the bottom will work, as a flexible membrane is needed to let the oil expand and contract due to temperature. I guess it will start to leak again after a few temperature cycles.

      1. Aah no I got it. And Your poliurethane materiel is flexible enough instead the original hard plastic + membrane inside
        Thx

  3. Hello Njal:
    I have a question regarding an order i placed and the repair process for the Suunto compass.
    Thank you very much for contacting me via email.
    Best regards
    Bert

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