Bearing Replacement - Saito .56

[REX1945]

    I finished my Legacy last year near the end of the season and put a couple of flights
on it before letting it sit around the cellar most of the winter. When I fired it up
for the second contest this spring, I knew there was ball bearing someplace that
was in serious trouble.

   My first thought was that it must be the front bearing; but when sending for parts
I purchased both of them since I would have it apart anyways. Good call - it was the
rear bearing that actually failed !  I'm pretty sure it failed due to rust inherited from
the crankshaft. After-run oil never seems to get there (it's behind the valve gear).

    The replacement went much easier than I anticipated.

      o Remove cylinder head ssembly without even removing vale covers
         (don't drop the pushrods on the floor)
     o Remove backplate.
     o Remove piston and rod
        (watch out for wrist pin pads falling out)
     o Remove cam housing assembly.
     o Attach a pair of prop nuts to the end of the shaft.
     o Heat crankcase and the prop driver with heat gun.
     o With the back surface of the crankcase housing resting on a steel plate, tap on the end of the crankshaft.
     o Remove cam pinion and spacer.
     o Drive out bearings with a steel punch.
       (it helps to heat the housing once again).
     o Locate new bearings in counterbores as far as you can by finger pressure.
     o Use dirveshaft (without cam gear and spacer) to drive in the rear bearing first.
     o Re-insert the crank with pinion gear and spacer.
     o Place front bearing over crankshaft and into housing.
     o Heat housing one more time.
     o Use prop, washer and propnut to pull the front bearing into housing.
     o Replace cam housing assembly.
        (make sure timing mark lines up with slot in cam gear)    
     o Replace piston and rod.        
     o Start piston ring inot cylinder bore.
       (be sure to get wrist pin pads in place)
     o Push the cylinder assembly down while working pushrod tube into boots on cam housing.
       (don't get the pushrods in backwards - tapered end toward rocker arm)
     o Make sure all the screws are tight and prepare for bench test.
     o Take valve covers off to verify pushrods are seated.
        (might as well check rocker arm gap with feeler gage)

      Attach backplate, inlet system, and muffler in preparation of test run.

      I worried a lot about getting the cam gear in the "right" tooth. The valve overlap
position is near top dead center.

       Total time was about 1.5 hr, including photos.

       Runs great ! No more bearing noise. Why did I wait 6 months to do this ?

       Does anyone have a good method of verifying the valve timing after the engine is
     fully assembled ?


  PS : Bob Zambelli has the secret for cam timing: http://stunthanger.com/smf/index.php?topic=20227.0

[proparc]

Got ourselves a REAL engine man here. Not only flys four strokes but, does overhauls on them also.

[Jim Kraft]

I always heat the case to install the bearings using a piece of tapered dowel to hold the bearing. If you use the shaft to put in the bearings you are putting pressure on the balls and race. If you are going to press them in, use something that fits the outside race of the bearing. If you put the bearings in the freezer, and heat the case, the bearings will drop right in. Just my 2 cents.