The Mechanical (centrifugal) Advance

[3Phase]

Inspecting and servicing the mechanical advance is easy, it's just not as not as sexy as triple cleaning the carburetors. It's also very messy but it's necessary or the mechanical advance will eventually die.

Please note that the cracked mechanical advance in these pictures is from Bush, my salvaged '79 Special, not from Columbo!



The XS1100 mechanical advance assembly ready to be serviced with the snap ring removed. All 1978 to 1980 Yamaha XS1100s have a movable reluctor mounted on a shaft with spring-loaded weights.





The XS1100 reluctor with its inner grease reservoir that should be filled with high-temperature grease to lubricate the reluctor, the mechanical advance shaft and its bushings.





The XS1100 mechanical advance shaft and its bushings. The reluctor slides onto this shaft and the reluctor's slots engage the posts on the mechanical advance weights at the base of the shaft.

The upper bushing is fixed and does not move. The lower bushing rotates freely on the shaft. It can also move axially on the shaft below the upper bushing.

To grease the lower bushing and shaft, pack grease into the upper slot while turning the bushing to allow the grease to move between the shaft and the bushing. Move the bushing axially and pack more grease into the lower slot. Repeat as necessary until the grease has been worked in place between the bushing and the shaft.


Unfortunately, this mechanical advance is junk but it can be stripped for parts. There is a large crack in the lower bushing from wear and fatigue caused by lack of lubrication and you can see the 'witness mark' left on the upper bushing by the reluctor's obviously empty grease reservoir.







Fill the grease reservoir in the reluctor body with high temperature grease and reassemble the mechanical advance.

Before putting the snap-ring back on the shaft to hold the reluctor, make sure the reluctor tip aligns with the slot in the base of the mechanical advance shaft or the reluctor will be 180 degrees out of time.





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[DGXSER]

Scott,

The 81 models did not have a mech advance, only vacuum advance. The "mech" advance was built into the 4RO TCI programming.

[IanDMacDonald]

Scott- I'll be using this post this weekend when the advance arrives. Thank you!

[3Phase]

Scott,

The 81 models did not have a mech advance, only vacuum advance. The "mech" advance was built into the 4RO TCI programming.

D'oh! You're right, Don! Maybe a mod' can fix it because it's too late for me to edit the post.

Man, I knew everything was going too easily.... I can only watch so much paint dry and sniffing wintergreen oil while cleaning and reconditioning old rubber parts gets old pretty fast too!

I have two more posts written for setting the air gap on the pick-up coils and servicing the vacuum advance but I don't have the pictures yet to go with the steps in captions. I Copy/Pasted the first part of the mechanical advance description from the vacuum advance description and forgot to change the final year.

Scott- I'll be using this post this weekend when the advance arrives. Thank you!

Ian,

When you install the advance use some blue (medium strength) LocTite to hold the assembly in the end of the crankshaft, then torque it down. If the screws holding the pick-up coils to the timing plate still have the factory locking paint blobs on them then just leave them alone! You can check their air gaps after the timing wheel is torqued in place but you'll have way too much fun trying to adjust them.

The mechanical advance is a close fit with a locater pin but it can wobble and shift around a little when it's not bolted to the end of the crankshaft. When you take out the bolt and remove the timing wheel to try and set the pick-up coil air gaps, the feeler gauge will push the advance assembly and the reluctor away from the pick-up coil. LocTite will help hold the advance assembly in place and keep it from moving when it's not bolted down.

On top of that the pick-up coils themselves are magnetic and they love steel feeler gauges. If you can avoid setting the air gaps -- do it!


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[IanDMacDonald]

Scott- I plan on just swapping the advance right on. I will use my pickup coils that are already on the bike, therefore no gap setting required.

[DAVINCI]

Re-install the bolt with a nut for a spacer and the mechanism won't move on you.

[3Phase]

Re-install the bolt with a nut for a spacer and the mechanism won't move on you.

Randy! How's it going!

Using a nut for a spacer on the bolt works fine for setting the air gaps while the bolt and nut are tight. As long as you remove the snap-ring first or just make sure the nut doesn't cinch down on the snap-ring or the reluctor you can even use the nut to turn the crankshaft and check/set the gaps on both pick-up coils.

But! after you remove the bolt and the nut to put the timing wheel back on the advance assembly will move slightly and it may or may not bolt up in the same position it was in when the gaps were set. It's the "may not" part that can get aggravating.

A little LocTite keeps that from happening unless you just go all hog wild and break the advancer loose from the crankshaft while you're messing around with the air gaps.

I've also had one slightly bent bolt here that made the advance move around and shifted the reluctor tip with the bend in the bolt. When I was trying to set the air gaps they kept changing after I set them and reinstalled the timing wheel. The nut I used and the timing wheel were not exactly the same width so the advance/reluctor tip would be in a different position when the bent bolt was tightened down. Once I found it I got rid of that bolt but it was not obviously bent. I think someone put the timing wheel on 180 out and then reefed down on it with a 1/2" drive breaker bar or something because the offset slot in the timing wheel was messed up too.


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[IanDMacDonald]

Just to clear things up for me dummy brain, I DO NOT need to mess with the air gaps if all I.am doing is swapping out the advance, right?

[3Phase]

Just to clear things up for me dummy brain, I DO NOT need to mess with the air gaps if all I am doing is swapping out the advance, right?

Erm, "It depends."

Are the factory paint blobs still intact on the pick-up coil screws? If they are then Scott didn't change the air gaps and you'll probably be alright. That is why they are adjustable... if the paint blobs are gone then you should check the air gaps. The air gap is important but it's pretty forgiving if it's not dead-solid-perfect.

Any time you remove the timing wheel -- not just when you replace parts -- you should turn the crankshaft by hand with a wrench to make sure the reluctor doesn't hit the pick-up coils before you press the Start button and rip the pick-up coils off the timing plate.

If you have to change the air gaps, check them again after you install the timing wheel.


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[IanDMacDonald]

BRING-ON THE OTHER TWO POSTS!!! lol.

[XS1100 Newbie]

Yes Scott, a step by step procedure for removing, and installing the centrifugal advance mechanism, and associated parts.

[3Phase]

Yes Scott, a step by step procedure for removing, and installing the centrifugal advance mechanism, and associated parts.

The problem with doing the photos is that some of the tricky parts really should be video. I don't want to do video. I don't want to post a bazillion pictures with dissertation-length captions either.

Let me finish putting Columbo back together and make a 1,000 mile test ride out to Arizona so I know everything's working and I'll get back to it when I get home.

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[alaskey2]

Can anyone replace the pictures here? I want to pull my advance and put all new wires in and clean it up, but I'm hesitant to do anything without seeing what I'm getting into first.

[3Phase]

I'm sort of in the middle of putting my engine back together, Alaskey, but I'll find them and re-upload them somewhere "not Flickr" for you.

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[mack]

Scott

You still need a 78 E governor?(mechanical advance)? I can pull one from my spare motor.