Hello all
A new first for me.  Clutch movement interference! 
The background:  the bike underwent a full  restoration that was completed in 2020.  At the time there was an issue with what I thought was a rather stiff pull on the clutch lever.  It was doing this when the bike was acquired.  the clutch handle lever couldn't be pulled through its full range of motion and was only able to pull in about 1/2 way to the handlebar before it would resist an further movement/pulling.  The bike has never been ridden since the restoration and has remained on static display other than a few times being wheeled to a vintage show.  It would be started utilizing a nurse bottle to give the motor a warm up, but never attempted using the clutch or ridding it.  I'm now finally getting around to addressing the issue.
Here's the facts I've established thus far:  All clutch parts are as they should be - the heavy clutch plate 1, the spacer plate, the 6 friction discs and the seven clutch plate 2's.  The rubber cushion rings are also all in place.  All are installed in the proper order.  The clutch basket is seated properly as evidenced by the driven gear at its rear aligning properly with the mating gears.  When the right side cover is off the motor, the clutch movement is perfect.  Put the cover on, and it's back to the interference.  So, the cover is somehow preventing the pressure plate from expanding outwards.  But how?  There's no damage to the cover such as it being pushed inwards.  I've gone as far as matching up part #'s for the parts involved in the event the previous owner worked on the clutch and put in later model parts that wouldn't necessarily work on a 1968 - but the part #'s are consistent.  The only thing I've observed that has become the focus of my attention at this point is that on the inside of the side cover, there's a small "tit" that looks as it it would be just about dead center to the pressure plate when the cover is installed.  I'm wondering if the pressure plate is pushing up against that when moving outwards.  But what doesn't make sense is that the bike was used for years prior to the previous owner storing it away before  I acquired it.
I've got a bit of a mystery here and would appreciate knowing if anyone has ever experienced the same situation or hearing some logical suggestions that I may have not thought of yet.
Thanks all

This is a photo of a new, imperfect one available from CMSNL in Europe - how does this compare to yours?

  OC-0001.3878: Cover, Crankcase (r.h.) Yamaha , an alternative for 214-15431-01-00 - buy item at CMSNL

That was a good thought.
I'm not at home, but appears to be identical.  The little "tit" I was suspecting is seen on this one as well.... it's within the "m" on their water mark.  So there's probably no chance that the cover is wrong.  I will compare it directly to the picture when I go home for lunch in a little while.
Also, there's no signs of any rubbing around the perimeter of the area of the cover that fits over the clutch - so I believe the focus remains on the center portion of the pressure plate pushing up against something - but why?  And how to prove out?

It wasn't clear to me if the problem occurred before or after the restoration?  In any case, my first thought is that the plates might have been replaced with the wrong thickness?  For example, 4mm frictions instead of 3mm?  Or steels are supposed to be 1.6mm from the parts diagram.  How does the clutch pack height look compared to the pics in the 68 service manual?

Second thing that I've come across is aftermarket cover gaskets...  I had a clutch hit the cover when lever was pulled because the aftermarket gasket was much thinner than original.  Kick start was stiff too unless shim was removed...  but it wasn't as extreme as you're describing.

Good point regarding the gasket, Mark.

That thought crossed my mind as well (a very short trip, mind!  ), but all of the issues that I can remember reading about related to a too thick gasket adversely affecting the kick start mechanism. Same solution, always fit original!

I appreciate the dialogue fellas.  I'm sure I'll (with suggestions) get to the bottom of this.
The gasket is from Partzilla - so OEM.

Mark - the bike had the issue when acquired - just not resolved during the reassembly process.
Last week I took it all apart - removed and cleaned each plate of the clutch thinking there might've been something wrong with them.  Reinstalled with the new gasket, and then same thing.

The cover is off it again now.  I wish I could post a picture showing where the pressure plate sits in relation to the outer edge of the clutch basket.  A visual may help determine if it's out too far from overly thick plates/discs.
I don't have an assembly manual for the DT1.
When I go home shortly, I'll put the calipers to the discs & plates and see what they're measuring.  Perhaps PO put something in that is too thick.
I will report back in a couple of hours.
Thanks guys.  Good suggestions.

Here is a picture of my 68 clutch after engine build going back together. This clutch works butter smooth, easy clutch pull, no slippage. You can compare to yours and see where the clutch pack is relative to the clutch basket.  I might have a different angle picture if needed. 

You can click on the picture on a home PC and it will make the picture larger.

Someone donated a copy of the 1968-specific DT1 Yamaha Factory Service Manual years ago so it should be in the tech library?  If not, I can post very grainy pictures...  looks like the final steel is just a little below the inner hub edge.

One other thought...  did someone replace the clutch actuator worm gear on the left side cover?  If the spiral gear was clocked wrong it might be pressing on the pushrod all the time?  You would not be able to get any internal freeplay with the adjustment screw in the center of the gear if that was the case...  Just that more than once I've seen clutches slipping because the freeplay at the handlebar lever is correct but the "internal" freeplay at the engine is non-existent. 

 "...Just that more than once I've seen clutches slipping because the freeplay at the handlebar lever is correct but the "internal" freeplay at the engine is non-existent."  Thank you Mark.   I will be going back to this to be sure all bases are covered - but I can't see me putting this together and not addressing the adjustment.  I do have a couple of mm of play at the lever before feeling any resistance, but I know that's not the whole story.  it'll be revisited.

Skydancer - I've confirmed my cover is the same as shown in the cmnsl picture.  More on this in a bit.

Additionally, while home for lunch I took sample measurements.  I didn't have time to do every component.
"heavy plate"  3.22mm
spacer  2.3mm
rubber cushion  3.04mm
friction disc  3.04mm
plate  1.58mm

I'll look for the manual on the site.  Hopefully I'll be successful.  But honestly, I'm thinking there's probably nothing there to help me.  But I'll give it a review.

My latest idea is what can I use that I can put on the outer most edge / perimeter of the pressure plate and the center point that'll remain through a quick reinstall of the cover and will leave a mark upon contact with an interfering surface?  I'm thinking maybe a dab of single stage paint?  That tends to take awhile to dry up.
I'm wondering if there was ever an impact on the cover that resulted in an ever so slight distortion - even though I can't see it.
Also, regarding the cmnsl cover, I'm wondering if I could get them to lay a straight edge across the backside of the cover and use a caliper to give me an accurate measurement to the that little "tit" that's dead center.  I'd do the same for comparison to help prove out the possible distortion question.   I keep suspecting it's involvement.  

Skydancer - your posted picture looks pretty much the same as mine when assembled.  Thank you.  Perhaps another pic from a 90 deg angle that'll show the true relationship of where the backside of the pressure plate is in relation to the leading edge of the clutch basket?  If you can without any bother.

So recapping....

• find & review service manual 
• measure all remaining discs, plates, & cushions
• check actuator adjustment
• reassemble according to manual / parts diagram
• match reassembly to new skydancer46 photo (if possible)
• add wet paint (or any better suggested marking material) to pressure plate, put cover on along with gasket and hope that clutch activation leaves a mark

Anything else I should consider for this evening's homework?

Thanks fellas

yamaha-enduros.com/index.php/service-man...8-dt1-service-manual