Advance Unit problem

[mudiwater]

I am having a problem with the advance unit sticking. I have new weights and springs. I guess that I am not positive that it is sticking, but when I move the weights out by hand, they either stay, or move back slowly. Is this normal? If not, what steps should I take to get them moving properly? Keep in mind, this is with the engine sitting cold and not running.

[grizld1]

No, the condition is not normal either cold or hot. There are labyrinth grease seals in the camshaft because the advance rod requires grease, and many of these machines haven't seen any since they left the factory. Remove the ATU as a unit by knocking loose the stepped nut that secures it to the camshaft with a flat punch. Move the ATU out to gain clearance as you continue turning off the nut. Against the camshaft oil seal you'll see the pin that aligns the disc which connects the advance rod to the bobweights. It will install in either side of the rod, and if it's reinstalled in the wrong side, timing will be out 360*, so look at the ignition cam on the other end of the rod and note which side the pin is installed in, then remove it. Remove the rod from the left side, clean the hole in the camshaft with solvent (brake parts cleaner or aerosol carb cleaner work well), and lube the rod and bobweight ends with moly grease.

I recommend checking the stepped nut whenever you service the ignition. By far the majority of XS650 engines I've seen with holed pistons also showed a loose ATU nut and a damaged ATU. When the nut comes loose the alignment pin is slams back and forth in its slot and deforms it, timing advances radically, and you have a very small window of opportunity in which to shut down and save your engine. Most try to limp the bike home, with predictable results.

[mudiwater]

Thank you Grizld1 !

[mudiwater]

Grizld1, how do I know when the stepped nut is not tight enough or is to tight?
Thanks for all the good info you put out, I've learned a lot on this site.

[grizld1]

Thanks for the kind words. The nut is tight enough when you smack the flat punch hard with a ball-peen hammer and the nut doesn't move then rap it once more for good measure. It's too tight when the threads in the nut strip, and given the diameter and materials of the nut and camshaft end, that ain't gonna happen with a hammer and drift unless you manage to land a full swing with a 6-lb. maul! Blue Loctite is your friend here.

[mudiwater]

ok, thanks. I was thinking maybe it was to tight, causing the slight drag in the advance unit, sounds like I guessed wrong. One more thing, I changed out the housing on that side due to a stripped out thread that holds the chrome cover on. Could changing that housing be the root of my drag problem?

[grizld1]

You need to think about how the advance unit works. The advance rotor turns with the camshaft, and needs to be secured tightly to it. The advance rod turns back and forth inside the camshaft: when rpms pick up, the bobweights are thrown outward by centrigugal force and move the rod to the advance position by means of the notched disc. Tightening the rotor to the camshaft won't affect the action of the rod, bobweights, or disc. The housing you refer to--the camshaft cover--houses only the camshaft oil seal. This can have no impact on the action of the advance rod. The only resistance you should feel on the advance rod is spring tension from the bobweight springs and breaker points springs. If the action feels sticky, the rod needs to be removed, cleaned, and lubed with moly grease, ditto the bobweight tips where they engage the disc.

[mudiwater]

Thanks Grizld1, yep, once I went back down and looked at it, I realized that I had asked a stupid question. I have it cleaned up and re-greased, problem solved. I am curious though, It seems to me, after having that all apart, that the timing could be slightly off now? Thanks again for all your help!

[grizld1]

Yep, timing will shift with small changes of ATU position. Strobe and adjust at the points.