Bearing Replacement - OS 1.60

 by Bob Pastorello, and a mix of others from

the NSRCA Mailing list in July, 2003!!!

Update April 25th, 2005 - I've run three OS 1.60's on the Stainless steel bearing from Boca, with and without shields left intact.  Evidently, there is little if any difference in the performance.  The "good news" is that you only need follow this procedure on a new (or very low run time motor).  As soon as you can, get that original steel bearing out of there, and replace it with the Stainless steel version.  You'll not have to use after run oil, or do any maintenance at all for a VERY long time.  All I have done is consistently run the engine out of fuel, and I've had some pretty long breaks between sessions.

Also - the "bearing air scoop" deal - DO it!  If you are a purist about appearance, buy some of the really slick, neat-o fairing-type scoops.  If you're like me, and lets function drive form, I actually make a little plywood (1 /32" thick) three-sided scoop, angled appropriately to direct the main air about 2" back from the spinner ring.  This gets a LOT of air moving over the lower part of the crankcase, and can result in spinners being COOL to the touch upon landing, even after a hot flight.....it is a worthwhile exercise to do the "bearing scoop".

It's been awhile since I had the glow motor bearing blues, but recently, I purchased a used motor that was in excellent condition, other than an unbelievably-rusted main bearing.  So, a few posts to the NSRCA list, and the guys there provided their favorite recipes for replacement.  I read it all, looked around my workshop, and created my own procedure as a mix of theirs.  Many ways to skin a cat....

So, here are the steps, in the order I did them, and no photos this time - there WILL be another chance soon, so I'll add photos then...Here goes!!!

1. Make a CLEAN workspace, and get something to put the various parts in; I used some plastic cups...
2. Clean off the exterior of the motor.
3. Remove the thrust washer, and be SURE to get the woodruff key out, and make a note of which way the squared part faces.  Mine faces forward.  Behind the woodruff key on the crankshaft is a black shim.  Probably the MOST important part of this whole process.  If you don't reinstall this - you will have SERIOUS trouble.  Don't loose it!!!
4. Disconnect the line from the remote needle valve to carb.  Remove the carburetor by removing the two screws on either side.  They tighten into threaded holes in the carb throat base.
5. Remove the two backplate screws holding the remote needle.  Remove the needle valve assembly.
6. Remove the other two backplate screws, then the backplate, taking care to inspect the O ring carefully, and inspect the screws.  This is a good time to inspect the backplate for scoring from the crankpin/conrod bushing.  If you use starters a lot, as the bearing and the lower conrod bushing wears, it will allow the crankshaft to push back VERY slightly, and sometimes enough to rub the backplate.
   1. This level of where is SERIOUS and can be indicative of wear on the UPPER or LOWER end of the conrod; wrist pin, piston.  If there is scoring, be sure to make a note to inspect all those parts as you pull them out.
7. Remove the head.  You may have to get aggressive to get all six screws out.  Be sure to inspect the glow plug hole/threads, and all the screws.  There is a head shim; it may stay with the head, or stay on the sleeve, but either way - make sure you FIND it, remove it, clean it, and remember which way it was installed.
8. Heat the crankcase evenly, and thoroughly in the area of the main bearing and the carb/intake window.  Many recommend a medium-heat oven (350 degrees for a 5 - 10 minutes), some a soft flame from a torch, but ONLY if you are experienced and can heat evenly.  Use the method that works for you....
9. Remove from heat, and gently grab hold of the sleeve top flange....it should pull upward VERY easily.  Remove and place aside in your clean workspace.  If it doesn't, you don't have the case hot enough.  Be sure to note the orientation of the exhaust ports, even though there is an indexing system to PREVENT you from improperly reinstalling the sleeve.  There is also a VERY small NOTCH in the center of the REAR of the sleeve top flange, that matches an equally-small PIN in the crankcase.  REALLY, REALLY important to remember that!!!
10. With the sleeve out, there is enough room to work the piston/conrod assembly off the crankpin.  Be gentle, and don't force.  A "high time" motor MAY have buildup on the crankpin around the bushing chamfer; if so, gently chip that away, or scrub on it with an acetone wipe...DON'T scratch or damage the piston, and be mindful of the ring, now expanded, that probably does NOT align with it's index pin in the ring groove.  You'll align that on reassembly.  After the conrod/piston is removed from the crankpin, you're ready to remove the crankshaft.
11. Don't waste a lot of time, here, because the crankcase can cool down enough to NOT let you get the crankshaft and main bearing out pretty rapidly.  As soon as the sleeve is out, you SHOULD be able to gently press on the threaded end of the crankshaft, and it will drop right out.  Usually, it will leave the bearing in the crankcase, but sometimes it will stay on the crankshaft.  With LUCK, the bearing will stay on the crankshaft, leaving you to figure out LATER how to get it off.  If the bearing STAYS in the crankcase, you need to get that bearing out.
12. If you have a fancy-shmancy bearing Puller, use it NOW.  If you do NOT, do what the 99.8% of us do...rap the crankcase vertically against a flat, hardwood block or workbench top.  Be very careful not to distort, or strike the crankcase at any kind of angle.  The backplate screw bosses should ALL leave a slight imprint from the strike.  While holding it with the front end UP, rap the rear of the crankcase against the block.  The bearing should drop out of it's main housing area, but usually will NOT fall out of the crankcase.  It will be in there flopping around crooked.  That's okay, don't panic.
13. With the bearing sort of catty-jawed in the crankcase, insert the crankshaft in the bearing just far enough to align the inner race on the large journal of the crankshaft and get the bearing partially on the crankshaft.  Now, gently retract the bearing/crankshaft out the back of the crankcase, and the whole thing will be out in your hand.
14. Let everything cool down, while you're finding the new bearing you already have.  The correct bearing is 42mm OD, 20mm ID, 12mm thickness.  It's a MR-6004, anyway.  Here's the Boca Bearing Page (6004)  I recommend stainless steel, but if you can't get them, at least get a high quality replacement bearing.  Some say Boca Bearings aren't very good, but I've had good experience with them.

Reassembly Steps - everything cleaned, inspected, and ready to go....

1. If you aren't messing with the front bearing, get the new rear bearing ready to install on the crank.  You can do this at room temperature. 
2. If you have a drill press, get a piece of old wing tube, pvc pipe, old teflon coupler, whatever will be "just right" to allow you to place pressure only against the inner race of the ball bearing.  NEVER apply pressure, or tapping motions to the bearing, or it's outer race.  This causes very small dings in the race and the balls, and will result in VERY premature failure of the bearing, no matter what else you do.
3. Spray the crankshaft lightly with WD 40, or equivalent, and spray a bit on the bearing inner surface of the inner race, too.
4. Hold the crankshaft, and 'start' the bearing by gently pushing on the pipe piece.  You're just getting it started.
5. On a flat surface, like the edge of a workbench, put the counterweight area flat on the surface, with the threads UP.  Hold the crankshaft, and gently align and gently push the bearing installation fixture (that piece of header pipe, wing tube, whatever), and pushing ONLY on the inner race surface (NOT the ball race, nor the Outer race), push the bearing home on the crankshaft.
6. Making sure the bearing is properly seated, now heat the crankcase just like above.  When things are properly heated, push the bearing/crankshaft assembly into the crankcase.  Some say "hold the crankcase, and drop the assembly into it"; personally, I think that damages the balls and race, so I just push things in gently.  It should insert solidly, and go all the way forward. (You DID thoroughly clean and lightly lubricate the entire inside of the crankcase, didn't you?)
7. While still hot, right NOW, get the piston/conrod assembly just barely inserted into the top of the crankcase.  You will have to gyrate around with the conrod, and be turning the crankshaft slightly to get the lower conrod bushing to engage.  
8. After the conrod bushing is installed, making sure the ring is properly indexed and compresses easily, push the sleeve PART way down on the top of the piston.  Just a bit...to make sure you have everything aligned properly.   
9. This sounds harder than it is; as long as the ring is properly indexed on it's groove pin, the sleeve will easily slide onto the piston, because the bottom of the sleeve has a chamfered step that permits the sleeve to compress the ring.  Once it does PUSH THE SLEEVE absolutely perfectly straight down, aligning the little pin and index groove on the flange we found out about above.
10. Rotate the crankshaft, and make sure things are smooth, easy to turn, free, not binding....
11. Let it all cool down.
12. Check the rotation once again, and then install the backplate.  Take care to not pinch, deform, or damage the o ring.  And be sure to reinstall the needle valve bracket where it was when you started. 
13. Install the head shim on the top of the sleeve.  While keeping it centered, install the head.  I always use the cross-torquing method, tightening the head bolts down uniformly, in two groups of three.  Sort of like 1-3-5, then 2-4-6.  It works very well for me, and prevents warping.
14. Install the carb.  Inspect the O ring prior to assembly, and be sure the groove in the crankcase it fits in is perfectly clean.  Coat it lightly with a little oil.  Reconnect the line from remote needle assembly.  DON'T overtighten those two screws!!! Don't ask me how I know this....it wasn't very pretty, and costs a "carb body"  Learn from my mistake!  Fortunately it was a few years' ago, and I remembered.
15. Remember that black shim?  Find it, insert it on the crankcase, then the woodruff key.  Be sure it is oriented so that the groove in the thrust washer fits without forcing or wobbling it on.  If it doesn't slide on easily, it's not aligned.  DON'T force fit this.
16. Put a piece of tubing on the crankshaft, and the propwasher and nut...just to hold things together while you're reinstalling.

Because you've had the ring, and sleeve removed and re-fitted, it will feel low on compression.  Don't worry about that, after the first couple of tanks, everything will refit itself, and the motor will be better than it was when it had the bad bearing.

Suggestion - DON'T let rough bearings go unattended-to until the rpm drops.  At that point, there is risk of the bearing seizing momentarily while running at full bore, and this will "spin" the crankshaft.  If THAT happens, and doesn't get addressed, the crankshaft itself will have to be replaced.

Use a very good after run oil.  There are a lot of opinions about this, but personally, I use Amsoil "MP-1" Metal Protectant in a spray.  Open the carb barrel fully, give a couple second squirt in the crankshaft intake window, then turn the motor through.  If installed in the airplane, use the starter for a second or two, then repeat.

You will be amazed at how much lubricant this throws inside the motor, and will really protect bearings.  And it sure doesn't do any harm for the conrod, wrist pin, journal, crankpin, etc.  If you're faithful to do this at the end of each flying session, NEXT time you tear it down, you'll see shiny, oily parts that look great.

But ONLY if you use clean fuel, run it out dry at the end of the day, AND - MOST IMPORTANTLY - Don't run it lean!!!

There's a growing body of anecdotal evidence that cowling scoops which direct air onto the lower crankcase around the main bearing area dramatically cool the motor in flight, and consequently, lengthen the service life of the bearings.  I believe it.