The Mechanical (centrifugal) Advance

[3Phase]

Looks like you and me both found one today Scott. Fellow forum member is sending me an "E" timing wheel, advance and vacuum pod.

Out'a sight and blemish free!

Do you have a small handheld scale you can use to measure the advance spring tension when you get the parts and before you put them on the engine? Crazy Steve made the Interchange Tech Tip but didn't delve that far into it. I want to at least try to measure the spring tension of the different advance assemblies when they first start to allow advance and when they're 'all in'.

For the rest, the '79 and '80 timing wheels are marked in 5 degree increments. Any of them can work with the 10 degree setting for the '78 ignition but the 'F' mark will be off by 5 degrees so the '78 wheel is much more cooler.

It may or may not be true in the real world but the graphs in the good book of Yamaha show that the '78 and both '79 models use the same vacuum advance pot:
Min. 0 degrees advance @ 1.96 inHg (50 mmHg)
Max. 16 degrees advance @ 5.9 inHg (150 mmHg)

You do not want to know what they did for the '80 and '81 vacuum pots.

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[3Phase]

REPOST: The Mechanical (centrifugal) Advance

REPOST again with working pictures.

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, my 1980G!


MechAdv1: 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.




MechAdv2: 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.




MechAdv3: Fill the grease reservoir in the reluctor body with high-temperature grease.




MechAdv4 and MechAdv5: 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.
EDIT: The lower bushing is bad, it's pressed on and should not move.


To grease the lower bushing and shaft, pack grease into the upper slot while turning the bushing to allow the grease to move in 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, then reassemble the mechanical advance.

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.





MechAdv6: 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.




This is the mechanical advance from my 1979F parts bike.