Rotax 185
Piston de-carboning
Bearings re & re

TheRotax 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 easly done ,the key is using the right tools for the job, plus there is a few very helpfull 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 ment 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 helpfull procedures. On my next rebuild I will fortify the picture collection.

Dis-assembly procedure

I will type this in from the manual when I got time and include some pictures in the mean time I think you can find these posted on Dave loveman's page ultralight news
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, Don't buy a cheap one of these,its not worth the frustration.. 

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


Here Iam being a little cheap but it seems to work well with minor build up ,Iam brushing on poly stripper paint remover, instead of soaking the piston in stinky carb cleaner, the stuff I used on my first engine rebuild Ill tell you this stuff worked great desolved even the most stubborn carbon build up but the odor 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.
pic 2 once brushed on cover with plastic meth chloride is extremely volitile and won't last if not covered 
Wait several hours then scrape carbon off of 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 piston ring you can see the shape thats been grinded on the end (check the shadow casted on the white background)

Carefully scrape away all traces of carbon in ring grooves ,this job also easier if piston has been soaked overnight.

If engine is not too dirty ,you may choose not to remove the piston,this quickens the job as it eliminates the need to pick out the wrist pin retaining clip ,this can be frustrating.

Scrub out crankcase, I use cheaper paint thinner than varsol just as well 
a 10" plant pot tray makes a great solvent holder

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 halfs with a rubber mallet or a block of wood they should fall apart with relative ease.

Here Iam pushing in new oil seals, with a homemade 1" pvc tee and socket tool
works good for removing also.

Now heres the fun part. The bearings are friction fitted to the crank, here is a way you can put the new ones on without a press,this works slick, toss the crank in the deep freeze, put the bearings in a small pot submerged in motor oil and heat till hot when every thing is as hot and cold as its going to be whip the crank out of the freezer,grab the bearings with pliers and slip them onto the cold shrunken ends IMPORTANT do not forget to replace all the shims and spacers in there correct positions


To re-assemble crankcase.Into the oven at 210'F goes the case halfs and back into the freezer goes the crankshaft with new bearings wait (be patient) till they are up/down to temperatures

When ready whip the back crankcase half out of the oven and place on a block of wood, whip crank out of freezer and carefully and firmly press crank assy into rear case.(make sure to put magneto end of crank into this side)
POSITION case gasket then quickly remove front case from oven and place over crank and press down to bring halfs together.
Notes  you must me gental at first to make sure bearings align with there sockets in the cases to prevent jaming also check gasket placement 

Replace the 4 crankcase bolts and torque down to correct value, remember to use cross sequential incremental torqueing .
At this time you will usually find a little resistance when the crank is turned over, This is normal before the anealing step. Put the unit back into the oven to again  bring all parts up to uniform temperature, remove crankcase from oven then rap both ends of the case halfs and bearing housings with a 2X4 block or wooden mallet,this will settle the bearings into there proper place. Recheck bolt torques when cooled 


Use ring expander to re-install piston rings, some say that you must use new piston rings every time , I don,t think its necessary myself especially if I am de-carbonning every 50 hrs ,Id probbably replace them after 200-300 hrs

Install gaskets, cylinder and head
Torque to proper values
Special Notes
Cylinder head placement is important, you will notice that the top of the combustion chamber has a defined shape,make sure that the shallow lobe that assists the removal of exhaust gasses is placed over the exhaust port side.
also regarding the cylinder head gasket, myself and others I know re-use it several times, as long as you replace it in the original position, I have never had a failure and I put lots of hours on my engines.this is especially handy for just routine combustion chamber cleaning and inspection.

Reinstall magneto. If you did not put a referance scribe mark on mag and case you will have to reset timing using a dial gauge inserted into the spark plug hole. Its a good Idea to fill all electrical connections with silicone to exclude any moisture
This is also a good opportunity to check or replace the points.

Engine Specs