Hi guys- been away for a bit again but back at working on the '68 DT1 (earlier VIN- 001717) with the strap under the fuel tank to mount the tank.
My bike came without the strap but I have acquired and am looking to mount it soon. I see the 2 little bumps for the tank mount are 6mm, and they are clean and good (odd that when I see photos of them online they always appear to me to be a 12 or 13mm head but maybe that is just the closeness of the shot?).

Here is my puzzle: What holds the strap to the frame??

There was a rubber bumper still on the round protrusion from the frame rail, but I have never seen a photo of a fastener in that spot, ever. The parts books I have seen online and in paper do not call out a bolt or screw there that I can see. Not sure if there is actually any threads there at all! Neither 6mm nor 8mm bolts will thread in. 

What gives? Tension between the rubber frame mounts between the tank and frame?

Would appreciate any tips from the early DT1 experts!! 

I wonder, but doubt, if they ran a version of those rediclous exhaust studs on some bikes that are 6mm stepping up to 8mm. Surely they wouldn't be that stupid in the 60's "only the "70's" or was it 80's haha. What size hole is in your strap that goes across., or did I muss that. Our first gold tank DT1 in '68 never had the strap nor did my white tank one which I think was just an old stock 68 or 69. Both square swinging arm models. Most likely answer is there's special expensive 6mm nuts with a 12 or 13 hex head. Do they have rubber inserts in the bracket strap. OK i'll go & look. Strap idea sounds good, was it just another expense they wanted to avoid in manufacture. I feel deprived seeing ours never got that lol.

Early bikes have 6mm threaded bolts, later production bikes were updated to larger 8mm bolts. The strap center hole fits in the round frame stud on the lower frame tube. The metal strap is spring steel and holds the tank in place. I also added a thin rubber grommet where the strap fits on the frame to keep it from making noise. 

 

Skydancer thanks very much for that photo as well as the info regarding the fastener size. I confess to some relief that my eyes have not completely gone bad. My tank does have the 6mm threaded boss so that is what it will get.

So, apparently when assembled there is sufficient tension created between the tank resting on the 2 frame bumpers, (at the rear of the tank and the front (where mine were anyway)) and getting pulled down just a bit by the strap below. My bike also had some pretty ratty foam rubber glued to the top frame rail as well, possibly anti-rattle material. I anticipate needing to do that as well.

Phew. I was and am relieved as I was fearing some unobtanium special bolt was missing!!

Thank you again for the information, especially the photo!!

Cheers! 

Your welcome,
You are correct that there is slight tension when you bolt the strap onto the tank. Be sure to use the correct length bolts. Mine also had the large foam glued to the top of the backbone frame. I think all these Yamaha enduro's do or at least did. All the 68-73 bikes i owned had the foam on the frame.