Stupid question about the swingarm pivot bolt on my '74 DT250 please. The way it's designed it seems is, you tighten the nut (~75lbft according to the manual) against the shoulder step on the bolt, NOT against the frame mounting brackets, correct? I tried using a lock washer but it tightened up before it hit the step, so it was pinching the mounting brackets and binding the swingarm so it wouldn't move. I removed the washer and it tightened up nicely against the shoulder step on the bolt so now it's nice and free with no lateral play. Is this correct?

Wrong.  You may ruin the frame tabs if you ride much like that. 

The 1974 DT250 has a long internal sleeve (#2 in parts list) that is supposed to be pinched by the bolt and held solidly between the frame tabs.. www.partzilla.com/catalog/yamaha/motorcy...m-cushion-chain-case

With that long sleeve secured by being pinched by the tight bolt, the swingarm bushings (#3) pivot on the sleeve. 

Note that there are shims (#4) shown under the end caps.  They are there because you don't want the swingarm to slide side to side on the inner sleeve!  Since yours sounds too tight, you need to remove the end caps and remove #4 shims (if any) until the swingarm moves with bolt tight.  Add shims to remove side to side play with bolt tight.

Damaged end caps (#5), internal sleeve (#2), frame tabs, or bushings, can cause problems.

You haven't mentioned any circumstances either...  like installing new bushings or something?  If you did, make sure they are pressed in all the way and thick paint or powdercoat on the edges isn't making the swingarm wider than it should be.  Sometimes with aftermarket bushings I've had to carefully sand down the outside edges of new bushing flanges evenly to narrow the swingarm width a few thousandths so it doesn't get pinched solid. (Moving with some friction is ok.)

 

MarkT covers it better than I can.  I'll just say is the sleeve through thd bushes seized up or just replaced bushes & sleeve ie spacer. If that's all free maybe remove any shims inside the end caps & tighten it up against the frame tabs then see if move up n down freely & see how much side movement there is. Then decide on adding shims. With the arm on the bench there should be a slight protrusion of the inner sleeve--one piece sleeve right through on those from what Mark is saying, the shims if used sit over the sleeve Not Against, to adjust end play side to side play when in the frame. Sorry-- I went on a bit much there.

Okay, thanks for the reply. There are no shims at all. Just the end caps. It's the original, or at least the same bushings that were in it when I took it apart. If I tighten it to 72-74lbft like that, I can move the swingarm up and down with great difficulty. I have another identical bike here and it's the same situation. The end caps seem like they are okay. Not bent or warped.

Gosh you're fast replying. The caps do get indented especially if the arm mightve been removed a few times in 50 years & just the tightening process does that. I tend to overnighter & don't use a torque wrench but top marks for using one. Just sit the arm on the bench with axle through plus the caps then space up the leftover to tighten nut & see if it revolves free. When in the frame the frame mount tabs have to compress against the caps hence inner sleeve/say spacer for it to work as it should. Last thing you want is for the arm to be turning on the arm axle. I've seen a few of those in my lifetime with flogged out frame plates--not good.

Okay, I'm going to try to attach some photos. You can see the innersleeve doesn't protrude much if at all.

OK will check later but I'm sure you understand the inner must protrude for it all to work.

"]Gosh you're fast replying. The caps do get indented especially if the arm mightve been removed a few times in 50 years & just the tightening process does that. I tend to overnighter & don't use a torque wrench but top marks for using one. Just sit the arm on the bench with axle through plus the caps then space up the leftover to tighten nut & see if it revolves free. When in the frame the frame mount tabs have to compress against the caps hence inner sleeve/say spacer for it to work as it should. Last thing you want is for the arm to be turning on the arm axle. I've seen a few of those in my lifetime with flogged out frame plates--not good.[/quote]
Okay, I'm going to try to attach some photos. You can see the innersleeve doesn't protrude much if at all.

Okay, I'm having no luck posting photos.

Okay I think I understand. So, that long inner sleeve is supposed to go all the way to the outside of the bushings, protrude a little and be stationary with the bolt wen tight while the inside of the bushings rotate on the outside of that sleeve?