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I could see part of the repair from the front, but the back of the repair gave a better idea of what it was and why it was. When I removed the barrel this is what I saw[Figure 1.]. Until I removed the timing cover and it's contents I couldn't be 100% sure, but from a look at the pics in the manual and where it was, it was most likely to be something to do with the cam followers.
When I pulled the timing chest off the first thing that was obvious was the, badly, enlarged drilling's in the oil passage bosses
in the timing cover. So oil could freely be pumped into the timing chest instead of squirting to the places wanting oil; turned out
it didn't really matter;-) The cam support plate looks like it's been welded and ground down, I am guessing this was done to relocate
the hole for the cam follower spindle bolt. When the cam support plate was removed I could see the "repair" in all it's glory. The
cam follower crankcase spindle boss has been replaced by a brass boss brazed to a thin steel plate which is screwed to the case.
Figure 2. Repair from inside the timing chest.
The repair is screwed in with thirteen 4BA screws. The screws are around three sides of the repair. The back edge of the repair and the crankcase didn't meet and the gap was covered with the big wodge of epoxy. The cam and followers are pretty badly worn [that's the metal I found in the oil tank]. The pump must have sent the metal back to the tank! The timing chest and timing cover show some odd signs of damage, looks like bit's have been chiseled out in places? The valve lifter has been ground away so the cam follower would touch the cam! The crank pinion has a big part of a tooth missing and the idler and cam drive gear have some damage. The oil pump pinion and worm are really worn, I wouldn't put either in a motor.
The cam has a lot of duration and it was only when I started looking for a cam I found it's one usually run with lifters with much larger radius. I can only speculate the small radius might have contributed to the cam and follower wear. The advance gear looks intact, but it has a lot of metal buried in it so I am going to have to replace the gear. The advance gear was infact running out enough to cause 'tight spots', I didn't notice till I reassembled the bottom end, I think the gear hub had been distorted when a new gear had been riveted on, so a new ATD hub had to fitted. Someone had been in the timing chest since cam/follower wear started, to grind the valve lifter away.
The timing cover had the cam oil way countersunk so all the oil would have been squirted out into the timing chest, well as the crank was blocked it didn't really matter. This was fixed and a cam spray bar was added, the cam support plate I bought came with one so I presume the later engines had one, the time it took to get decent cam and followers I want them kept well slippery. The oil feed quill had been almost cut through by the mushroomed end of the crank!
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