Finally the bottom end rebuild is complete. What a milestone this was getting the engine back in the frame. There were times during the last couple of months where the project had really slowed down and I am really glad to have made this progress at last.
Sump and Oil filter
The oil filter I used is the one piece paper filter. On the /5 the filter goes in the housing and the round filter housing lid is installed with no o-ring (the rubber end of the filter itself engages the groove on the lid. This is then torqued to spec. The triangular oil filter cover plate takes a paper gasket, however this needs to be replaced after the engine is back in the frame as the frame clearance is too tight with the cover installed.
The oil pickup strainer can be replaced- on the /5 there is a single paper gasket between the strainer and the pickup tube. Then the sump gasket is replaced- I used a thin even smear of Hylomar blue and then installed the sump. The bolts should be torqued in a crisscross sequence as shown in the manuals.
Engine breather
The engine breather apparatus is a spring loaded plate. This was later changed to a reed valve which is probably better but in the interests of keeping things original I replaced the old valve. There is a paper gasket under the housing which I replaced.
Connecting Rods
At this stage I re-installed the connecting rods. I had measured the connecting rod journals on the crankshaft when I did the bearing journals. They are 47.98 which is in spec. The measurement can actually be taken carefully with a micrometer with the crankshaft in the case. The old connecting rod bearing shells were removed (put the rod in a vice and a gentle tap on the edge of the shell knocks them out), and new shells installed. There is a groove meaning the shells can only be installed one way.
Be sure to install each rod back into the side it came out of as they are accurately balanced. When installing the rods, the connecting dowels are towards the front of the engine.
First a light even smear of assembly lube (Honda Moly Paste) was applied to the crank journal and the inside of the new shells. Then the rods are installed with new bolts and these are tightened down in stages ensuring the two halves of the rod are seating correctly. Then they are tightened to spec. The side clearance of the rod in the journal can be measured with a feeler gauge and should be less than 0.3mm It’s common to have quite a bit of clearance and lateral movement in the airhead engine.
Replacing the Engine in the Frame
Finally the rebuilt engine is ready to go back in the frame. This is a two person job and Mrs GFP helped out. I positioned my jack in the centre of the frame and applied a lot of towels to the frame with gaffer tape to prevent any scratches of the fresh frame paint. Then we tilted the engine gently into place and rested it on the jack. Then the rods were inserted into the front and back. The back rod is simpler (it just has two round spacers which sit between the frame and the engine) and it’s slightly longer as it has the two foot pegs attached outboard of the frame.
The front engine mounting rod is a little more complicated as it has the two brackets for the side stand and centre stand springs. These little brackets have essentially been welded to two round spacers similar to the rear mounting rod. The larger bracket goes on the left and (kickstand side) and the round spacer points towards the engine on both sides).
