Rebuilding the Rotax 185 aircraft engine.

The Rotax 185 is still a very popular engine primarily used to power a portable high pressure pump used for forest fire fighting , so all parts readily available. This page is going to deal with replacing the crankshaft bearings and seals, which is recommended every 300 hrs as well as piston cleaning which can be as little as 30 hrs. 

They are quite easily done ,the key is using the right tools for the job, plus there is a few very helpful tips that I learned from a long time local Lazair pilot, that make the job that more enjoyable. 

This page contains many pictures they are not meant to be in any order, some steps considered incidental are omitted,  all have been edited down to size to speed up the download. 

Anyway I got most of the important and helpful procedures. 

On my next rebuild I will fortify the picture collection. 

The right tools for the job an assortment of pullers, from left to right Rotax copy, fly wheel puller, custom made front bearing puller, but available from Rotax (bearing positioned against crank flanges no room for regular puller), typical bearing puller works for rear bearing.

Inspect and clean cylinder, remove carbon from exhaust port and inside de-compressor ally. This job is made easier by soaking the whole cylinder in carb cleaner, removes varnish and softens carbon        

Here I am being a little cheap but it seems to work well with minor build up ,I am brushing on poly stripper paint remover, instead of soaking the piston i n stinky carb cleaner, the stuff I used on my first engine rebuild. 

This stuff worked great dissolved even the most stubborn carbon build up but the odour was permeable it would last for days on your hands and on your clothes, the stuff was hardcore, loads of warning labels.  Anyway one of its ingredients, methylene chloride is also in poly stripper. 

Once brushed on cover with plastic meth chloride is extremely volatile and won't last if not covered  Wait several hours then scrape carbon off  piston crown (Note : try to leave the thin hard carbon film ,this apparently protects the piston crown from heat)

To scrape carbon from the ring grooves ,make a tool from a old p iston ring you can see the shape that's been grinded on the end (check the shadow cast on the white background)Carefully scrape away all traces of carbon in ring grooves ,this job also easier if piston has been soaked overnight.

Now your wife will love this one.
To dis-assemble crankcase insert in oven heated to no more than 210 degrees F, wait till completely heated then rap the case halves with a rubber mallet or a block of wood they should fall apart with relative ease.