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Couple ATU questions...
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TeeCat
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PostPosted: October 17, 2009, 1:53 pm    Post subject: Couple ATU questions...

Guys...

Rainy and miserable, so I figured I'd go out in the shop and replace my ATU. I had a heck of a time getting the old one off, as it seems the slotted retainer nut didn't want to slide over the little "cam" that drives the weights. I was a little spooked and thought I had broken something or lost a pin because, after I removed the old weights, I noticed that the whole assembly, from the PAMCO rotor all the way to the cam on the advance side (but not the ATU plate), was turning freely. I was worried that I'd have all kinds of nightmarish timing issues on reassembly, but then I remembered that the little arms on the weights that insert into the little cam are the only thing keeping the rod from turning.

So, I took that little cam off the ATU side, being careful to note whether the pin in the rod was still there, and it was. Similarly, once I coaxed the ATU plate off - with difficulty - the pin for that was there too. There was a tiny bit of oil inside the compartment, but the camshaft seal looks clean and dry.

So, I suppose I'm ready to put things back together, but I wanted to make sure of something first:

- I'll reassemble the ATU, weights, springs and all. Is it possible to press the plate back too far, and how tight should I make the slotted ring... just tap it snug? I don't want to bind anything. Should I use any anti-sieize or grease on the contact surfaces of the ATU and the camshaft?

- On the slotted nut, one side is flat and the other side has a slight raised ridge on the inner diameter. Which side goes against the ATU plate (facing the engine)?

- When I put the little cam back on the ATU end of the timing shaft, with the little pin in it, I have to make sure that the little mark on the cam is aligned with the little mark on the ATU plate, and then I should be okay in terms of NOT being 180 degrees out, correct? I was concerned because the whole assy was turning... that spooked me... but I suppose that if all pins are in place, and the marks are aligned, all should be well. Incidentally, I did NOT take the PAMCO rotor off, so the position of that relative to the ATU side should be okay. Am I right?

I guess I still get confused about the physical link between the rotor, rod, ATU and the engine. I know the rod turns inside the camshaft, but I don't quite get the relationship between the two.

I just want to be careful about not being 180 degrees out.

Thanks -

TC
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pamcopete
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PostPosted: October 17, 2009, 4:09 pm    Post subject: Re: Couple ATU questions...

TeeCat,

1. It's not possible to press the plate back too far. There is a rise in the cam shaft that limits that.

2. Just tap it snug, but, more importantly, tap it all the way around.
3. No grease or anti seize required.
4. The raised edge goes away from the engine. (Edit)
5. You are correct about aligning the marks on the slotted disk (cam?) and the ATU plate, but in fact, it doesn't matter with the PAMCO because it's impossible to be 180 out.
6. The rod does not actually turn completely inside the cam. It only rotates for the number of advance degrees, so that means it turns no more than 20 degrees, at which point the weights have come in contact with there stops and no further movement is possible.

I also file down the pin on the ATU plate that protrudes slightly and interferes with the slotted nut coming in full contact with the surface of the ATU plate.


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Last edited by pamcopete on October 17, 2009, 7:18 pm; edited 3 times in total
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TeeCat
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PostPosted: October 17, 2009, 4:20 pm    Post subject: Re: Couple ATU questions...

Pete, thanks! Based on what you say, I think I'm in god shape, then. I'll button it up tomorrow. And I never knew that it was impossible to be 180 degrees out with the PAMCO! Last time that happened when we serviced the rod last year, I did not yet have the Pamco. One less thing to worry about!

I'll tap the plate home with a carving mallet and hit that little nub with a file if it protrudes at all.

Oh... and why is there a tiny pin on the back of the plate itself, as well as the pin on the camshaft and a slot in its collar (that accommodates the pin on the camshaft)?

Thanks again!

TC
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pamcopete
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PostPosted: October 17, 2009, 4:59 pm    Post subject: Re: Couple ATU questions...

TeeCat,

The tiny pin on the back of the plate keeps the locating pin in the cam shaft from exiting.

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pamcopete
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PostPosted: October 17, 2009, 5:27 pm    Post subject: Re: Couple ATU questions...

TeeCat,

Although I installed the slotted nut with the ridge towards the engine, your question prompted me to review it, and I came across a picture that shows the opposite.



I edited the previous post and I'm going to change mine around.

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TeeCat
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PostPosted: October 17, 2009, 5:57 pm    Post subject: Re: Couple ATU questions...

Ah... received and noted, Pete! I guess we're both glad I asked!

Thanks again!

TC
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tacoswild
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PostPosted: October 17, 2009, 6:44 pm    Post subject: Re: Couple ATU questions...

TC, if you're still unclear how everything is related or connected, it's the ATU plate that provides the connection between the camshaft and the timing rod. The threads that the big tabbed nut go on? Those are actually on the camshaft, that's the end of it poking out. So the ATU plate goes on, gets tightened down by the nut and has a hard connection to the cam, then the timing rod goes through. It would spin free until you connect the disc on it's end to the weights which are mounted on the plate. This is the physical connection between the two, the tabs on the end of the weights fitting into the slotted disc on the end of the advance rod. Seems tiny but there's very little force or rotation here, just the force of the springs really.


Pete, at first I thought you were filing the locating pin right off but I think I know what you mean now, it did seems a little long when I put mine together.
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pamcopete
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PostPosted: October 17, 2009, 7:16 pm    Post subject: Re: Couple ATU questions...

TeeCat,

Yea, well, when you asked the question I went down and checked my '81/H and it had the nut with the ridge towards the engine, so that's the answer I gave you. But I went back and checked my faithful '78/E and it had the ridge to the outside! So I checked further and found the pic with the ridge to the outside.

I have had that ATU off several times. Usually to investigate a question that I'm asked, so I must have just put it back on backwards the last time, but I changed it over now.

The truth of the matter is it doesn't really matter, except that by having the flat side on the plate, there is more metal to metal contact which helps to keep the nut secure, but only if you file off that pin as described above. The purpose of the ridge is to provide more space for threads because they could not make the entire nut thicker due to possible interference with the weights.

Something as small as this really makes you appreciate the work of the 1,000 Yamaha engineers that designed this great motorcycle. Details like this were discussed over and over until they got it right.

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pamcopete
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PostPosted: October 17, 2009, 7:23 pm    Post subject: Re: Couple ATU questions...

tacoswild,

Yes, i found that there was a score mark on the slotted nut where it came in contact with the pin protruding through the ATU plate, so I filed it flush. That allows the slotted nut surface to come in contact with the ATU plate which tends to lock the nut in place.

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TeeCat
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PostPosted: October 17, 2009, 7:39 pm    Post subject: Re: Couple ATU questions...

Guys, I'm more clear on this now. Thanks for taking the time to answer my questions. Once I get this together, I can get on my valves, maybe tomorrow if my life allows.

I'll hit that little nub in the plate with a bastard file... glad you pointed that out.

That old ATU was pretty grody and I'm still hoping that the new one will help to get me toward a better idle and hot return to idle. Hope the new weights return okay.

TC
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TeeCat
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PostPosted: October 18, 2009, 5:47 pm    Post subject: Re: Couple ATU questions...

Guys... FYI, got my ATU in today. I have not started the bike yet as it's too miserable out, but I wanted to tell you that weights on the new unit snap back very nicely with Mike's springs unaltered, whereas the old unit had springs with one coil out in order to make the springs return. I also found two very, very tiny washers on the old unit, which may have been beneath the old weights, and I have my suspicions about the integrity/functionality of the old unit. I still theorize that I may have eliminated at least one variable in my idle quality.

Thanks again for all the help!

TC
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