Yes! This is a "Blanking Plug"!!!

[YAM277]

Sorry! Gotta go to the last pic, to see what it is.
Putting my cases back together and I did remember the F'n "Blanking Plug"! I also used the recommendation of HondaBond by two other Gurus, here on the forum. Here are my pics, which include the upgrades of the 5th gear overdrive and rephase. Enjoy!

 

[grizld1]

That hole is a spot where Yamaha's engineers changed their minds a time or two. Some motors came with the solid plug, some had an O-ring there, and in my experience it hasn't seemed to make a difference. It must have been an early and retroactive change, as the parts books show it listed as "Gasket," part no. 256-15395-00-00, from the XS1 manual through the H, and the illustrations show the O-ring type seal. Maybe TwoMany can chime in on the history of that change and the thinking behind it! Anyhoo, nice assembly pics.

 

[Higgy]

Thanks for the pics and words, YAM277. I also will be rebuilding my '81 this winter. That plug... available to buy somewhere?

 

[YAM277]

Partsfish.com has clear schematics, but I would think you should make friends at your local Yamaha Parts Dept.
Keep in mind, not all years have the Blanking Plug!

 

[TwoManyXS1Bs]

Huh, what? (*blink* *blink*)...

Oh, that goofy blanking plug. Apparently, there were some teething pains in the evolution of the early cases and lubrication system, and the original o-ring was replaced with that disc. Since there's no inner support (like from a hollow dowel), there's a risk that the o-ring would squeeze into the hole and stop sealing.

See upper half of this service bulletin:

 

[grizld1]

I knew you'd know the history, TwoMany. But there's still a bit of a mystery here. Yam277's photo shows a plug--no hole. I've seen the same more than once in motors that hadn't been opened before (and relax, 277, none of them showed any sign of lube failure when I took them down, and none failed after I put 'em back together with the same plug in place). Any idea what that's about?

 

[TwoManyXS1Bs]

Yes, that's right, Griz, a plug with no hole in it. There's no mating oil gallery in the other case half. So it's just there to prevent oil seepage between the halves.

These 2 pics show the flat/blank mating side of the bottom case.



But you're right about the 'mystery' here. I can't remember any probing of that area on my other cases, been too long ago. So, I've been collecting pics of that area for awhile, and that entire left side oil gallery situation definitely needs a hard second look.

This pic shows the typical left gallery situation in the upper case half, with an entrance notch/groove into the left main roller bearing and clutch pushrod bushing. Is there a hidden or missing connecting gallery in there?



But, this pic of a case upper, that has been ground to give clearance to a hydraulic clutch mod, seems to reveal a hidden/covered gallery plug, for a possible horizontal gallery hole to deliver oil to that mainshaft bearing.



Then, there's this pic of a later 80-up case upper that shows a cast-in gallery for that mainshaft bearing.



There were 5 revisions of the early 70-71 cases, only one I could find documentation on, which was the change to that mainshaft needle bearing diameter. We do know that there were some changes during then to the front gallery oil jets, but no details of that evolution.

One of my suspicions, in light of the shifting and neutral-finding issues, points to insufficient lubrication delivery to that left mainshaft bearing area. Which would deliver lubrication, per the manual documents, down/alongside the clutch pushrod, to the mainshaft oiling holes, clutch, and shift fork guide shaft.

Maybe this left gallery oiling was an oversight of the case processing, or intentially eliminated.

Maybe a mod, involving cross-drilling a gallery through that web, would restore lubrication and eliminate the shifting/clutch/neutral-finding issues?

This is something for the guys in the field, working on these things, to contemplate...

 

[Higgy]

Maybe a mod, involving cross-drilling a gallery through that web, would restore lubrication and eliminate the shifting/clutch/neutral-finding issues?

A strong point to ponder, TwoMany. Now I ask you: What, if anything, would it hurt to drill a galley in that spot? This winter, my plan is to rebuild my motor, and I want to do it up - all the way up - polished gears and everything. If I drill that hole, what would it hurt?

Mine is an '81, so probably has that cast-in plug.

 

[TwoManyXS1Bs]

Hey, Higgy. Yeah, yours may already have the cast-in gallery. Something to look for.
The early XS1's had smaller oil pumps, maybe an oil insufficiency debate occurred, I dunno...

 

[angus67]

Back when this forum was new , '09, or there a bouts, it was curious why there was not oil jets pointing up to the under side of one piston, while there were jets for the other piston. Someone here threaded in carb main jets into the unopened passage to do the same to that piston.
....... I........miss.....John.
I think it was xsjohn that did this, may have been in inxs.
In either case could it be related? A passage blocked off due to low to no oil pressure?