OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Hello Everyone

It was a nice sunny day today, so I started to put the engine back together. Used lots of assembly lube on the journals, conrod/cap, bushes, cam and tappets. Quite thick, sticky and the stuff I used is coloured with red dye. That way you can keep track of which parts are lubed.

Here is a comparison of the old vs new ring gaps, checked using a feeler gauge. All rings were replaced.

- old. new.
compression ring - 0.66mm 0.50mm
oil scraper ring - 0.65mm 0.49mm
oil ring - 0.83mm 0.47mm



The new compression ring doesn't have a 45 degree chamfer on one side like the old one did. Very peculiar.



Using my bare hands I roughhoused the piston and rings into the cylinder. A piston ring compressor would have been handy, but managed to save myself $40. Best way to lift up those tabs that lock the bolts and prevent them from rotating, is to use a ratcheting spanner. Very easy this way. A drive pin punch and hammer is OK for flattening the tabs, that is what I did so I could remove the bolts. According to the manual, the specified torque for the conrod bolts on this engine is 100 inch pounds or 11.3 Nm.





Markings on the cam gear and crank gear were aligned before putting on a new gasket and torquing the sump bolts to 85 inch pounds or 9.6 Nm.




Also decided to remove some of the rough casting from the intake port using some needle files.


The valves, keepers, springs and head will go back in/on tomorrow. I'll Probably reset the points gap, put the coil and the flywheel back on and check for spark. Putting a new recoil spring in too, that'll be fun.

Going to keep my eye out for a cheap 2nd hand engine just like mine. Has to have a crank with a good keyway. Then I should be able to swap them over with out any problems. Until then, I am going to proceed with caution and get pulley key stock and cut it to length. The original is 1.5*0.2*0.2 inches. I'll probably find some at a bearing shop and cut to length at about 2". Then there is no room for the key to move.