I thought about that tonight too Jim, I’m pretty sure I measured the tubes to be 34mm and the innards seem to be consistent with earlier forks. I’ll double check tomorrow. Odd thing is, after I installed the new seals and reassembled the tube and damper to the lowers, the tube slid very freely into the lower and in fact would fall and collapse with gravity. The issues I’m having are after the springs are installed and oil has been added.
Yes they were quite the stretch to get on. I thought they might be sticking and leaving the marks so removed them from the lowers and slid them up high on the tubes. The black marks still came back.
I would not buy "Yamaha" seals they don't make seals, just add a couple layers of markup to whoever manufacturers the seals. 50 years on they are using "meets spec" venders, not necessarily the company that built the seals that went in the bikes when new. Does Yamaha have higher engineering specs than All Balls? prolly. The good news is seals are pretty standard, so about every 34mm fork uses seals with all the same dimensions. Fresh stock is easy to find.
I'm thinking the dust boots are your problem. I've had issues with 34mm boots just falling apart. Bad or non existent vulcanizing? Once that rubber gets smeared on the tubes, it gets down to the seals and mucks up the sealing. Bummer dood. looks like they are coming apart (again). Doncha just love redoing work cuz of defective brand new parts?
I've done pretty good with pyramid brand seals (parts) They are not expensive. My go to is dusting/coating the just out of the box dry seals with titanium dioxide before any grease or lube. That stuff has a high affinity for rubber and turns it silver. then lithium paste type grease between the lips before assembly. Usually have to wipe off some grease a time or few after riding.
Honestly I've got several tubs of tan lithium grease but still not the "paste type" of my dreams.....
While looking on line for oil seals I found this comment in a blog - interesting (FWIW - only one guy’s opinion)
Interesting point - when I first replaced the seals, I used ones from XS650 Direct. I damaged one so that necessitated replacement one again (after I had ridden a bit). That’s when I used the Alls Balls seals. Now I recall when I installed the first set, they too were sticking to AAAND I had the black marks on the forks as well. Common element - the new dust boots!. I think @gggGary you may be right on this one. I did keep the boots I removed from the bike and may reinstall if they pass my inspection. The OEM boots look very expensive
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I did a quick search for NOK seals and seems there’s many variants. Will need to further research to make sure I find the right seal for the application.
I've bought them through a fork refurb specialist company in the past to be sure I get something that works. I enquired about NOK seals for the 77 650D (35mm) and they worked out similar order of cost to the Yamaha seal. I'd have happily used them and have done in the past.
