Surprise number two today! Where's my nut??

[smg65]

First, the PMA installation the PO told me nothing about. (And no timing marks.). Now I see that there is no lock nut on the cam chain tensioner. Guess a squirrel must have taken it! Grrrr. Darn PO. Can someone tell me what size it is, so I can get another? I DO need it... right???

 

[5twins]

'76 through '79 adjusters had no lock nut so what you found would be correct. The acorn cover nut locks the adjuster down. Not one of Yamaha's better ideas I feel. What's to stop the adjuster from turning and changing your adjustment setting as you tighten down the acorn nut? Right, nothing. As you can see, Yamaha used a lock nut on all the adjusters before your type, and went back to using one on the next assembly .....

 

[smg65]

Thank you, 5twins. At least that is correct, if perhaps a bad choice by Yamaha. Now I need to figure out the PMA that's "new to me".

 

[XSLeo]

Yes you need one. About the only place to find what you need is maybe on here, Ebay or a salvage yard.
I don't know what year your bike is so I can't be more specific about what you need. They changed the cam chain adjuster quite a few times over the years, but this chart may help.
I seem to have trouble on this end, can't upload the chart.
Mike's has a cap nut but no lock nut.
Leo

 

[smg65]

Thanks XSLeo. My bike is a '76 C. I suppose that even if it never had one, it would be a good idea to install one. As 5twins said, and had occurred to me also, tightening the acorn nut would probably change the setting. If I can't find the size here, perhaps I'll do a trial and error fitting using the billions and billions of old nuts and bolts that I never seem to get a handle on.

Thanks guys. Turning out I need more help than I thought I would!

 

[XSLeo]

5twins posted the chart I was trying to post.
Just any old nut won't work. The lip on the body of the adjuster sticks up and a regular nut will hit this lip. The nut has to have a turned down portion. You can see this on the chart. Type E.
Leo

 

[smg65]

OK. Thanks XSLeo. I'll start my search soon.

 

[smg65]

There's a place about 40 miles away called The Rice Paddy. Never been there, but I understand you can find a lot of used stuff there. When I was researching calipers, they said they had a pile of Yamaha calipers I could look through. Maybe I can find my nut, and other "treasures".

 

[5twins]

You may not have room on the adjuster for both the lock nut and the acorn cap nut. Yamaha used a longer plunger on the later tensioner. That allowed the adjuster screw to be out more which made room for the lock nut. So, if you're scrounging parts at the Rice Paddy, you'll need both the lock nut and the later longer plunger. All the other components are the same (spring, housing, acorn cap nut, adjuster screw). Take a metric ruler along with you. You'll be looking for a 100mm long plunger with a 14mm thick head. Notice your current one only has a 6mm thick head .....

 

[smg65]

Thanks, 5twins! I've received a lot of good info today... it's greatly appreciated!

 

[XS650DL]

'76 through '79 adjusters had no lock nut so what you found would be correct. The acorn cover nut locks the adjuster down. Not one of Yamaha's better ideas I feel. What's to stop the adjuster from turning and changing your adjustment setting as you tighten down the acorn nut? Right, nothing. As you can see, Yamaha used a lock nut on all the adjusters before your type, and went back to using one on the next assembly .....

5twins,
I always enjoy your comments. You clearly have more 650 experience than most. I have a '77 which I bought new. It has the acorn nut which locks the tensioner as you mentioned.
When it is installed, it turns quite freely until the o-ring touches. I don't think it causes the adjuster to turn when tightened. If it does turn any, I feel it would be negligible.

Again, I enjoy reading your posts

Regards, Dan

 

[5twins]

That's the thing. There's no way of knowing if that last bit of tightening on the acorn cap is turning the adjuster screw with it. That's what's so cool about these bikes. There's so many little updates, improvements, and "fixes" you can do to them. I consider this one of them.