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        Help! Removing crank shaft OS 55 AX

#1 Dale 813 Feb 08, 2013 08:01 AM

Removing crank shaft OS 55 AX
 
Need help. Need to replace engine case. Got everything out except crank shaft. Not sure how to remove it.

#2 Hemikiller Feb 08, 2013 08:13 AM

If you haven't done it already, remove the prop drive washer and the thrust washer behind it. You should then be able to push the crankshaft straight back out of the case. If it's stuck, put the tip of the crankshaft on a block of wood and push down on the case, or rap gently with a rubber mallet or block of wood. Whatever you do, do not hammer on the end of the crankshaft without protecting it with a wood, aluminum or brass block.

#3 earlwb Feb 08, 2013 09:17 AM

Besides what is mentioned above. What you do is heat the crankcase up good (I like to use a heat shrink gun, but many people use a oven or a propane torch too). Then using a brass hammer I tap the crankshaft out. The crankcase expands slightly when heated making it easier to remove the crank and bearings. Sometime the bearings can be in quite tight and you might need to reheat the crankcase to repeat the process to tap out the bearings too. I use a 1/4 thich brass rod to catch the inside race lip and tap the bearings out evenly by working the tool around the edge. The brass rod develops a lip on it making it easier to do too.

You should always replace the bearings whenever you remove the crankshaft for any reason. Do not try to reuse the bearings.

Here is a video that can give you a idea on how it is done
How to change model airplane engine bearings (part 1 of 2) (10 min 41 sec)

#4 Dale 813 Feb 08, 2013 01:14 PM

Thanks guys. Awesome vid. Question about the bearing replacement. This motor is brand new. Was on a maiden flight for 25 seconds when the elevator failed and it crashed forcing the carb into the case cracking both. Being as new as it is, is it still necessary to replace the bearings ? I was going to junk the motor but I found a used carb for $40 and a new case for $60.

#5 earlwb Feb 08, 2013 01:36 PM

You tend to invariably damage the bearings in removing them from the case. But in odd situations where the bearings fall out easily like shown in the video, then no you don't have to replace them. Usually the bearing balls get indented into the races, so if you reuse the bearings and reassemble it, you can feel the indentations as you carefully turn the crankshaft over.

Yeah it is a bummer to crash a engine on its maiden flight. But lots of us have been there and done that too.

#6 Dale 813 Feb 08, 2013 02:33 PM

Yep. No biggie. I learned a good lesson. I couldn't find my Radio south hinges and was in a hurry to get a plane together and used the crappy hinges that came with the model. I noticed that the CA didn't get sucked in like the radio south ones. I didn't think nothing of it till it took a Dirt Nap. Elevator came out on the down out of a dive. :) won't happen again. I just ordered more Radio south hinges. Ps I appreciate the help guys

#7 gerryndennis Feb 09, 2013 12:22 AM

G'day Dale,

Bad news about the crash but good that you are repairing your engine.

If it hit hard enough to break the carb off then you will probably need to check that your crankshaft isn't bent. A friend with a lathe and a dial test indicator is needed here. They are reasonably easy to straighten.

You will more than likely have damaged the front bearing so definitely change that. While you are at it it's probably worth changing the rear as well, I believe they are reasonably cheap from rcbearings (.com?) or boca bearings.

Just to clarify what Earlwb said, I prefer to push the crank out first cold then heat the case. If you heat first the rear bearing may come out with the crank, then it's a pain to get off the shaft. The video shows it correctly I think.

Searches here should give you all the info you need. Go carefully and you will be fine, if you get stuck ask here before getting out the vice grips and hammers. It's all fun and learning.

Dave H

#8 DarZeelon Feb 09, 2013 12:27 AM

1 Attachment(s)
Dale,


Whatever you do, never heat the crankcase in the rear bearing area, before the crankshaft has been removed from the engine.

If you do, it could come out together with the rear bearing (since they are both steel and expand at the same rate); and then it will be very difficult to separate them...


Also, I prefer to remove split drive-cone mounted prop-drive washers; using a suitable puller; not with a hammer.

After its removal, you will only need your fingers to push the crankshaft out.


#9 kbozarth Feb 09, 2013 12:37 AM

Quote:

Originally Posted by DarZeelon (Post 24079426)
Dale,

Whatever you do, never heat the crankcase in the rear bearing area, before the crankshaft has been removed from the engine.

If you do, it could come out together with the rear bearing (since they are both steel and expand at the same rate); and then it will be very difficult to separate them...


Never has been a problem for me, or those I learned from. Once the crank is out with the bearing, hitting the bearing with a little heat again allows the bearing to slide off.

Not a "never do" thing.

Kurt

#10 DarZeelon Feb 09, 2013 12:58 AM

Quote:

Originally Posted by kbozarth (Post 24079474)
Never has been a problem for me, or those I learned from. Once the crank is out with the bearing, hitting the bearing with a little heat again allows the bearing to slide off.

Not a "never do" thing.

Kurt

No, it does not, Kurt.

It is a problem and many who did that needed to reinstall the crankshaft+bearing in the crankcase, in order to separate them.

Doing it that way is wrong.

And why would one need to solve this problem, if he can prevent it happening in the first place, by first removing the crankshaft and then heating the crankcase to remove the rear bearing?


Even if someone has the ingenuity to solve a problem he created, wisdom means not creating that problem in the first place; don't you think so?

#11 earlwb Feb 09, 2013 07:25 AM

I have had a bearing come out on the crankshaft a couple of times. No big deal. There was a layer of old varnish and or corrosion on the crank that had built up over time. A little cleaning and the bearing slid right on off. The rear bearing just fits onto the crankshaft, a almost perfect fit. So just a little bit of corrosion or castor oil residue can make it harder to get off. But usually a little judicious cleaning of the crank will let a new bearing slip right on OK.

#12 Dale 813 Feb 09, 2013 11:25 AM

All done. Only had to heat the case to remove the front bearing. But being only $5 for both front and back, I'll get new ones. The crank being bent is another story. If it were bent. Wouldn't it be very difficult to turn ? I'll try to find someone that can check it.

#13 DarZeelon Feb 09, 2013 12:55 PM

Dale,


Regarding the rear bearing, I'd recommend that you install one with a plastic cage (Phenolic or Polyamide).

If this metal cage 'goes' from corrosion, or excessive RPM, it will grenade and possible cause a lot of damage to the piston and/or the sleeve.

That's hefty damage...

#14 earlwb Feb 09, 2013 06:41 PM

You can put the crank down on a piece of plate glass and slowly rotate it and watch the tip and see if it moves up and down any. A very tiny bit of movement is OK as there is a bit of runnout tolerances allowed during manufacture. But the runout is pretty miniscule though. I forget at the moment what the measurement would be. Anyway if the tip moves up and down then it got bent. You can straighten them if you want to. The worse that can happen is it breaks off the threaded portion. But if you got it to straighten out then you didn't have to get a new crank then.

#15 Hemikiller Feb 12, 2013 07:58 AM

Quote:

Originally Posted by DarZeelon (Post 24079426)
Dale,


Whatever you do, never heat the crankcase in the rear bearing area, before the crankshaft has been removed from the engine.

If you do, it could come out together with the rear bearing (since they are both steel and expand at the same rate); and then it will be very difficult to separate them...


Also, I prefer to remove split drive-cone mounted prop-drive washers; using a suitable puller; not with a hammer.

After its removal, you will only need your fingers to push the crankshaft out.


The 55AX has a D-drive for the prop washer, so it should slide right off. Regardless, that puller is a lifesaver.

http://www.amazon.com/Lisle-54150-Ba.../dp/B000I14RY6


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