Rebuilding a '68 250, and find the clutch springs seem sacked at 34+/- mm, with spec at 36 mm. Looking at OEM, but I read on another rebuild thread that Barnett springs are being used with a 39 mm length. OEM pretty reasonable $$, and this bike probably won't ever get really beat on (by me anyway), so I could go that way. Not sure where to get Barnetts. Any clues there?

Second question: I could not find the torque setting for either the clutch nut or primary gear nut on the crank listed specifically. I did find a general list for different shaft sizes at the end of my original shop manual, with the 17mm shafts getting 45-50 ft/lbs, so I used 50 ft/lbs for both. Is that sufficient? It seemed low, but the last couple of bikes I worked on in this area were my 2 XS650s, which I seem to recall were a bit more.

Appreciate any thoughts!

Hi Steve...I put the info out there about the Barnett frictions and Barnett HD springs. I found on my 360 and 400 bikes I was getting a little slipping at peak horse power. The Barnett frictions and HD springs cured that. I don't know if the 250 will generate enough torque or horse power to slip the stock parts? I'll be watching others input as I'm starting my 68 DT1 as well and that will be a question I'll come to this summer. I believe the parts books call for one less friction on the 250 vs the 360 and 400. They use a steel spacer to make up the difference. I posed the question here awhile back about putting in an additional friction in place of the spacer for more grab. I think only RT325 responded with "why not if it will fit". So not sure what I'll do yet. I do know I did not appreciate having to take the clutch covers back off of fresh restorations to upgrade the springs and frictions so probably will start right from jump with the heavy duty parts. For getting the Barnett parts just search Ebay. I think they are the same parts as my RT1B...and the same as many of the 70s enduros. One final comment on the rubber clutch rings...I'm a purist so I put all new rings in the RT1B but when I changed to the Barnett parts I removed them. Experts here say they can even contribute to clutch slippage. I put about 500 miles on the RT1B before I switched to Barnett and pulled out the rubber rings. Riding it afterwards I noticed no I'll effects without the rubbers. No extra chatter or anything. I won't use them on the 68 either. 

For your nut torque questions...I use 50 ft lbs for the output shaft sprocket nut, primary gear nut and clutch hub nut.

I would say similar for the flywheel but man the 68 has short threads and standard size nut. Later bikes had more threads and about 50 percent thicker nut...so IDK there. I'm playing mine by ear. 

Steve.

Appreciate the input Steve. I will check on eBay and see what I can find. 

Interesting about the rubber rings. I do believe that at some point in it's life someone had been in there, but not sure about the clutch. Everything shown on the parts page was there (in order even!!). Right now the clutch cover is off while I decide on springs, and now, friction discs.

Glad our torque specs are in agreement on the right side.

And the flywheel spec..... yeah. Not real sure what I will do there as you are quite right. The early '68 has a smaller shaft end and just a regular nut. Don't want to strip that baby after all the work I had done to make it useable. Still scratching my head as to why I went that route and not use a later year crank/mag assembly, other than a strong desire to stay as close to original as I could. You cannot see any difference at all once the cover is on. Dumb/stubborn... take your pick.

On that one I will probably follow dad's advice: tight's tight... too tight's loose again.

So, apparently Barnett does not now sell clutch springs specifically for a DT1/DT2/3. I was able to go to the Barnett website, where they have a down-loadable parts listing. For the DT1 they do not show a part number at all. I take that as an indication that they do not now sell them. The disc part numbers and required # are shown. It's actually a lot of information in one place. I bookmarked the site.

Barnett Tool & Engineering (barnettclutches.com)

Well, a funny thing happened on the way to the parts store.... to paraphrase an old joke. I ordered a new set of OEM springs, part # 90501-20124. But while I was on eBay I got a set of Barnett springs for a later YZ125/IT200 as well. 

What I found was that the OEM springs were essentially the same 34.5+/-mm as the old ones. Curious, I measured the Barnett YZ springs, and they measure 35.5 +/-mm. The diameters of the springs are close as well, with the OEM diameter measuring 14.5mm and the and the Barnett YZ spring measuring 15.5mm. The diameter of the wire is essentially the same, 2mm.

In both the OEM Yamaha manual and the Clymer manual the spec for the spring is 36 +/- .5mm. At this point I am getting confused as to what is correct, and what I should use. Are both books wrong, but the parts I got correct?? I don't want to overthink this. I'm really tempted to just use the new OEM parts and see how it goes.

The pic shows the 2 springs, with the OEM Yamaha on the left and the Barnett on the right.

 

The original OEM springs have been superceded .
The new spring free length is shorter than the original spring , so the manual spec no longer applies .
They seem to work fine in practice . I put a new set in my DT1 , and have had no issues .

Here is some more info on my recent experience rebuilding clutches.

I recently ordered new springs from various sources.

Yamaha part # 90501-20122 is 32.5mm in length.

Yamaha part # 90501-20124 is 34.5mm in length.

And springs I removed from a high mileage heavily abused RT3 clutch are 35mm in length. They were probably a little longer when new.

NHSTEVE mentioned in his original post that Barnett had springs that were 39mm. I'd be leery of those as they may put more strain on the clutch actuator nylon spiral.

Appreciate the confirmation of what I was seeing! I was getting confused as both manuals I had gave the longer spring length. Your DT3 springs measuring longer does give evidence that perhaps early on the springs supplied were indeed longer.

Regarding the 39mm length, I was referencing a different thread and member. 39mm seemed too long to me as well. I'll be using the new OEM parts.

Thanks all!