The o-ring fits in the beveled recess of the primary drive gear. It seals the conection between the gear and the crankshaft so that fluids (crankcase and transmission) stay in the respective areas. Early Yamahas did not have this area sealed this precisely, from my recollection.

The crankshaft end bearings are still available from Yamaha, last I checked. But the seals are more difficult to locate.

Check with Enduronut or DEET for the crank seals. It's worthwhile to get the original dual lip seal that works for pressure and vacuum.

Many sellers on ebay are selling single lip seals that may work but aren't really correct.

Thank you, wasn't sure if I needed it or not. I'll add it to my "need to order" list.

From some of the posts I've read I was thinking that the double lip seals were unavailable anywhere and people were having to use the single lip ones now since there was no alternative but I may have mis-understood. I'll check with those guys and see if they have them. Thanks.

Hi Jack.
I have read the post from start to finish.
Regarding the gears .
If you put them back and you get a failure, i can say from experience you will be highly pissed off undoing all the good work you done
and be saying " why didn't i just replace them".
It's time you don't need to waste. The US is full of cheap spares compared to here in the UK.
Just make sure you have all the info and tools before you take the job on .
It may take a while longer to complete but completed it will be and it will be a first time fix.
A guy i met here at Cadwell park racing circuit had just bought a Kawasaki ZX 7 RR SP cheap due to a gearbox issue.
It didn't select 3rd gear correctly. As he came up the mountain section it promptly seized the gear box and threw him and the bike up the track. Wrecked a perfectly good bike and injured him.
That's extreme but should you be in traffic and get a gear break, it could cause a lock up. Extreme again but do you want to be there?
Replace the parts and swallow the cost now rather than later.
Of course it's your bike and you'll do as you like. Just something you should think about though.

Hi shyted, thank you. I can't argue with anything you said there. You're right of course and I appreciate that you took the time to say all that.
Just to be clear, I haven't made a final decision on replacing the gears in question, or the shifter drum either. I've been checking ebay every day looking for replacement parts. Like you said the gears are out there, some pretty cheap, some not so cheap. But it's not as simple as it seems in that most of the pics aren't good enough to really know what shape they're in. If I took similar low resolution pics of mine and posted them up, not me or anyone else would be able to spot the damage. And the only seller I've found that posted high quality, clear pics of the gears has a pic showing damage on the exact gear I'm needing, it's actually in much worse condition than mine........

In most of the pics I've looked at, the dogs and dog slots aren't even visible. It's likely that some, possibly many, of those ebay gears are in similar shape as mine. Np way to know without purchasing. So say I take a chance and buy them, wait a week or two for them to get here, and then find they're no better than what I have. My options are to eat the cost and look for another, or eat the postage and return them and look for another.
I don't like using the dodgy parts, especialy where safety is an issue, and you're right, the possible outcomes are scary. And if I could find reasonably priced replacements that I knew were in good shape, I'd buy them. But so far I haven't been able to do that.
I hate compromising on parts but it is what it is.

Ok, been doing some more thinking about the gear wear and decided to take some more pics and post em one more time. To me they honestly don't look that bad. Don't get me wrong, not arguing with anyone, just giving you my opinion. But I'm smart enough to know that a lot of you guys know about 1000 x more than I do about it so if I can get you to take one more look at the new gear pics I took today, I'll go with your opinions. I remember RT saying that he could see some ramping going on, I couldn't really see it in the old pics so decided to take some new shots at better angles regarding the ramping. The pics are of the selector gear that pairs with2nd and 3rd. Took 1 pic of each dog. Even after looking at the new pics I still wasn't sure I could see the ramping you were talking about so got out my trusty calipers and took some measurements. I measured the width of the dogs at two places, the base and at the top. I measured all six dogs on that selector and the worst one I found had right at .25 mm difference between top and bottom of dog. You have a very good eye RT. I also found a very tiny chip in one, which I don't think would be a problem but you guys are the experts so let me know if you think it's a potential problem.

Been too cold to work evenings in the shop this week so been working on cleaning up one of the case covers. Made an improvement but still needs a lot of work. Started buffing today but after I got started realized I need to give it one more sanding with the next higher grit before continuing with the buffing. Think it's gonna look nice when I get it done though.

Just found a decent looking set of gears on ebay and bought em.

Been tracking down more parts and turns out Partzilla has all four transmission bearings. But their prices seem insanely high to me, 250 bucks just for those four. One of them is 130 all by itself. Crazy. I'll pay it if I have to but before submitting the order thought I'd check with you guys and see if there were alternatives to any of those bearings out there. I'm not looking for super cheap junk or anything like that, just hoping to save a few bucks while still ending up with good quality bearings.

My cylinder and crank is on a truck somewhere between Missouri and Minnesota. New KOYO crank bearings and lower end gasket kit on it's way to my house. Ordered a complete transmission from ebay with both shafts and all gears, shims, etc which hopefully has a good 2nd to 3rd selector in it. Hoping that everything in it is good and if so I'll just swap out the whole axle, gears and all.

My shifter drum looks good to me but you guys showed me problems with my gears that I hadn't caught so took a couple pics of the drum. Let me know if you see any problems. The only wear I see is the very faint line that runs along the middle of the channels but that line is not a measurable scratch, completely imperceptible to the touch. The high and low points have a flattened area but I "think" that is probably the way it's supposed to be. I may be wrong....