Topic: Engine case gurus Q?

[Don R]

 I have a blank pad replacement engine case, the head/cylinder wasn't original. I'm curious what year the case might be correct for. It had a diecast head and cylinder that were pre 26,000 due to the lack of a front center bolt.
 Just for fun, what might any production year tells be? I'll post a pic of that spot.
 One might be, the transmission vent tube is close to the case but not as tight as some I've seen.

[Don R]

 I see 70 and 71 has the same size and location trans vent, 73 is also the same, 74 and 75F0 have the same small size but its raised, later F and 76-up K got the bigger vent tube.   
 That makes this case 70 to 73. It's stamped on the back, K774 top and bottom rear. I think that's the case match numbers.
Any other changes 70 through 73?

[HondaMan]

On the inside, lower case below the kickstart shaft hole: the K0-K2 (and some K3) versions have much less web below the shaft's hole than in later engines. This area got beefier when the offset kickstarter arm of the F0 and later bikes came out, too.

The little sliver of (bottom case) aluminum in between the 3-4 main bearing supports, which is supposed to help hold the loose (not assembled yet) cam chain onto the crank sprocket while the top end is disassembled, got thicker in the K4 engine (and later), too. This web was often found broken in the early engines when the chain was loose and someone turned the crank, or when the chain got too loose in operation and the engine backfired for some reason.

By the final drive shaft: is there 3 of the 6mm bolts under the sprocket cover (in front of the sprocket), or just 2? If 2, it is the K0.

Look at the oil pump's feed tunnel from the middle oil pump port over to the (left) shifter area: is the hole where it ends at the left side round (so it can receive the round oil plug) or is it "D"-shaped where the passage turns upward to feed the countershaft's outer bearing? The latter don't have this plug (and the tranny covers often leak right there for it). The K0/K1 bikes have the "D" shaped hole and all later ones have the round hole for the rubber oil plug. This particular item has long been an identifying factor for the pre-K3 'New Factory' engines, when both factories made the bikes: the Old Factory engines, all the way thru to the K3, often got old, reworked cases (like my own bike) where this hole was made round after the fact and the oil plug doesn't quite fit slightly recessed as in the later cases. On the plus side, though: this lets the side cover press harder on it and makes it seal even better!

[mark ward]

Hondaman, are there any sources for those 'D' shaped plugs, which seal that oil galley, at the tranny side cover gasket?  And, are any round plugs still available? During my last rebuild, 2018, I had to replace my engine cases for my K1, and the replacement cases had a different shape hole in that area. So, I assembled without a plug, using just gasket, with sealer. It eventually started to leak oil.
    Perhaps I can try just using a 'gasket maker' black RTV (THE RIGHT STUFF) instead, on the tranny case?  Would that stuff hold up to the oil pressure, which would try to squeeze out along that gasket-surface?

[HondaMan]

Hondaman, are there any sources for those 'D' shaped plugs, which seal that oil galley, at the tranny side cover gasket?  And, are any round plugs still available? During my last rebuild, 2018, I had to replace my engine cases for my K1, and the replacement cases had a different shape hole in that area. So, I assembled without a plug, using just gasket, with sealer. It eventually started to leak oil.
    Perhaps I can try just using a 'gasket maker' black RTV (THE RIGHT STUFF) instead, on the tranny case?  Would that stuff hold up to the oil pressure, which would try to squeeze out along that gasket-surface?

There never were any "D"-shaped plugs, but just before the holes became round in production some of them got the round plug stuffed into the "D"-shaped holes. I have had better luck with tapping the hole and then turning down a screw head to fit into the hole, then filing it all down so it is also flush. The threads are real short (I think it has room for just 2-3 threads) so it doesn't block the flow, which turns 90 degrees there to go up into the countershaft bearing's housing. I have also done it with 3 different screw sizes, the 3rd one because the hole was broken out by someone into a 'V' shape toward the right as you look at it, and I used a bigger screw to fill in the area. It's not a critical thing, as the pressure there is about 2-3 PSI, but being hot oil from the crankcase it will usually melt away any form of sealant.

I also met one that an owner had made from a tapered rubber plug he got at Ace Hardware: it worked fine, too. He was smart enough to cut the inner tip of the plug off at a 45-degree angle so it sort of helped "turn" the oil upward while also giving the plug more grip. When I pulled off the side cover it popped partway out, but went back in OK and worked fine.