Rotax Rebuild

[Shannon]

Guys following the forum closely know Karl suffered a crankshaft failure as the result of faulty flywheel. He is currently rebuilding the engine with a replacement crank assembly and has run into a bit of a problem. For the benefit of those who will be rebuilding at some point here's a description of the problem as relayed to me in an e-mail from Karl. (hope you don't mind the repost of your e-mail Karl)


"Hi Shannon,

I have a little puzzle. After rebuilding and re-assembling my motor that
had the broken crank, the new crank seems a little stiff to turn. It is
smooth in rotation, with no binding, but takes a pound or so at the end
of a 6" wrench to turn. If I slack off the crankcase bolts, it then
frees up so I can turn it by finger. I measured all the thicknesses, and
it should have given me about .010" of free play end to end. If my
measurements were off, I guess I need to remove a shim. Or is it normal
to be stiff until it is run in a little?

Karl"

The clues that Karl has provided indicates the crankshaft bearings are probably over-shimmed. If during reassembly you find the crank hard to turn STOP right there and go no further. The article provided here at LazairForce(http://lazairforce.central5.com/) "fun with shims" should assist with finding proper end-play in the crankshaft assembly.

As I've experienced myself an improperly shimmed engine will run at idle and mid-range yet be incapable of developing full power. This is due to "squeezing" together of the crankshaft asssembly and engine case halves as heat builds.

Shannon

[gdewsbury]

There is another thing that can happen. When replacing a bearing I had the same experience of the engine being stiff to turn. Pulled everything apart and rechecked the shim measurements and they looked OK. Took a bit of head scratching to figure this out. What I found was that I hadn’t got the bearing fully seated in the aluminum housing before installing on the crank. Pulling the engine halves together would not seat the bearing in the housing. What I did find was a small burr where the bearing had stopped moving. I must have started it a bit crooked causing the bearing to bite into the aluminum and dragged the burr to the bottom of the bearing seat. Cleaned out the burr and reassembled without any further problems.

Glen

[flyalaz]

Hi Shannon,

I don't mind at all. Anything to help the cause.

I followed the Lazairforce and Ultralight news instructions to the letter, and following those instructions had no problems at all.
I installed the bearings onto the crank first, then into the rear crankcase- which just dropped into place following the heating and cooling of the respective parts. No hammering of parts at all. That might help avoid the problem that you had Glen.
It's probably a measurement error on my part that is causing the binding. I'll be working on it this week and hope to have the problem solved. I hope the bearings come off as easily as they went on!

Karl

[flyalaz]

More progress:

Separated case halves. Of course the bearing won't come off easy! I figure I am going to have to get the special bearing puller to remove the rear bearing. Last time I had a rotax dealer remove it, but he charged a base amount for the "work", and the ga$ it took me to get there and back makes getting one a better proposition. I know I'll be needing one in the future anyway. Might as well get some more odds and ends while I am at Wildfire. They are getting too used to my face

Karl

[Shannon]

To pull the rear bearing you need a "Bearing Splitter" and two-leg Flywheel puller.

[Shannon]

Pic 2

[flyalaz]

Hi SHannon,

Thanks for the pics, When I said "special" I meant the rotax puller. The Rotax dealer used the type of puller you are showing here, but it seemed to me he frigged around an awful lot with it. It popped off a couple of times, and didn't pull it up evenly. These are new bearings I put on, and don't want to warp the races. However, having said the above, if you say that this is what you use, it's good enough for me. Probably cheaper to buy as well.

[Shannon]

Karl, I do not have any experience with a Rotax puller so I can't say if it's better or worse. I've had no problems however getting bearings (new & old) off using the splitter and puller together.

Shannon

[flyalaz]

I haven't had any experience using this type of bearing splitter. I take it that after tightening it (2 long bolts)around the bearing, you screw in the two vertical bolts down onto the face of the crank lobe until it is high enough to get the two or three jaw puller under it (or the bearing)?
Or do you just tighten the 2 long bolts until you can get the puller in?

[Shannon]

This is the set-up I used Karl. First get a 4x6 wood block and drill a 1" hole in it say 4-5" deep. This holds the crank assembly steady for bearing removal. Some red rags dress it up a bit for the photo shoot.

Place the bearing splitter on each side of the bearing and tighten up the bolts. This causes beveled edges of the splitter to go underneath the bearing outer race subsequently lifting the bearing up from the crank lobe. Once the splitter is well beneath the bearing grab under the heads of the bolts sticking up verticle with the flywheel puller. A few turns and the bearing will start walking up the shaft.