Advance Range - Am i missing something

[wherearewe]

Well, here is where the mystery comes into the scene. People will pay $500 to $700 dollars to paint their gas tank. They will tear down their engine and spend another $600 putting it back together because it had a minor oil leak, but when the advancer has gasped its last breath after 35 or 40 years, they will not spend $65 for a new advancer. Instead they peen the weights, cut the springs and screw with it for two weeks instead of just buying a new one.

Too true BUT - Mikes XS Unit. Is it any good? It strikes me that if you buy that unit, and have to a: cut the springs, b: use your old springs etc, is it actually any good? Opinions please! A OEM unit costs 175 US plus 45 US to ship to me. From my local dealer, 270 US. Mikes one would cost me 90 US (with shipping), so i don't see any reason not to at least TRY and screw with it for two weeks before i bite the bullet.

 

[pamcopete]

wherearewe,

Well, what you say is true as well, but the one thing you cannot fix in an old advancer are the pins that the weights pivot on and the corresponding holes in the weights, and that is where a lot of the sloppiness comes from that screws up the advance timing. The point I was trying to make is that you would pay $300 or more to fix any other engine component, but we all try to skimp on the advancer, even though it is also a legitimate engine part. The effect of a worn out advancer is akin to a worn out timing chain, but we would all have that engine torn apart by now if the timing chain needed to be replaced.

I have a MikesXS advancer in my '81/H of necessity and it's just fine. Yes, I had to fiddle with the springs to get it right, but it has been right for a few years now. I developed the PAMCO so we could all ride our bikes on Saturday morning without having to screw with the points, but now we are screwing with the advancer instead!

 

[5twins]

We just like to tinker, Pete, lol.

 

[wherearewe]

Thanks Pete. Anyone else got any opinions / experiances about Mikes vs OEM ATU?

 

[retiredgentleman]

I have no experience with the ATU that Mikesxs sells, so can't comment.

I can't understand why you can't get your OEM ATU to work in the correct range. If the weight's tiny ears are a tight fit in the slotted disk, the range should be close to correct, unless you have large wear elsewhere.

My ATU which is original, has 30,000 kms on it and I keep it in the correct range by peening the tiny ears that fit into the slotted disk.

Yes, Pete, I'm a cheap (frugal) guy that believes in repairing first, and replacing only as a last resort.

 

[wherearewe]

I have no experience with the ATU that Mikesxs sells, so can't comment.

I can't understand why you can't get your OEM ATU to work in the correct range. If the weight's tiny ears are a tight fit in the slotted disk, the range should be close to correct, unless you have large wear elsewhere.

My ATU which is original, has 30,000 kms on it and I keep it in the correct range by peening the tiny ears that fit into the slotted disk.

Yes, Pete, I'm a cheap (frugal) guy that believes in repairing first, and replacing only as a last resort.

Yeh im sorta scratching my head too. I think the wear might be cumulative - worn slots, ears, damage to the atu stop. Im not 100% sure. I would love to get it running right at least temporarily with a 'mr fix it' approach so I KNOW its the ATU and not something else, although im not sure what else could be involved in extending advance range to be honest. Then i can go ahead and replace if needed. Im going to do one last round of messing about today and see what comes out.

 

[aldo5468]

RG, your last paragraph nails it. That's why I went with a Boyer Brandsen system.

 

[Purplezinger]

I've been following this saga and frankly I'm stumped. Even if your mechanical advance unit was totally worn out, you should be able to limit the advance using shims or heat shrink over the tabs, as described earlier. This makes me wonder if the problem is elsewhere, could the cam be off by 1 tooth? Is it possible that somehow you are checking/measuring incorrectly? I would NOT attempt to bend the tabs, they are brittle and can break.

 

[5twins]

Here's what I've observed on mine. I've borrowed a cropped out section of Gary's excellent close-up pic to illustrate. It seems the sharp corners of the disc slot are slowly cutting notches into the arm tab where indicated .....

This is allowing the disc (and hence, the advance rod) to turn back (retard) more and turn forward (advance) more. My total advance amount is slowly growing. I'm not sure peening the little tab at the end of the weight will fix this unless you are inadvertently peening up a bit higher and widening the notched area as well. Maybe the fix is to wrap something around that notched area to widen it out again? Like maybe a narrow strip of stainless? And to combat the notching effect in the future, maybe you could file the sharp corners on the ends of the slots down a bit?

 

[wherearewe]

I've been following this saga and frankly I'm stumped. Even if your mechanical advance unit was totally worn out, you should be able to limit the advance using shims or heat shrink over the tabs, as described earlier. This makes me wonder if the problem is elsewhere, could the cam be off by 1 tooth? Is it possible that somehow you are checking/measuring incorrectly? I would NOT attempt to bend the tabs, they are brittle and can break.

Not planning on bending the tabs. It's possible im measuring wrong i suppose - Timing strobe, watch mark on rotor, give gas to 3k, watch mark on rotor advance. Study its' speed (linear vs sudden) and range. Thats pretty much it right?
I didnt get a chance to test it today with shims etc but i will do tomorrow. My neighbours will hate me! My gut tells me its combination of worn parts and best thing to do is replace the unit.

 

[wherearewe]

Ok to conclude this thread so if people with a problem ever search it has and end!

I solved the problem. However I am going to replace the ATU. But now i know what was going on. My advance range was too great as a cumulative result of worn slotted disc, worn weights and a most importantly a damaged stop. While one weight would hit the stop, the other could open another 1-2mm. The wear to the weight tangs and disc allowed the cam to turn a few more degrees.
Previously i had tried to restrict weight opening by peening. While you think that might work, under centrifugal force peening alone will not stop them from expanding to hit the stops (i clearly underestimated that), and if you did peen it enough to do so you would likely screw the advance curve up big time.

I determined the problem by placing a blob of JB weld on the outside of one of the weights to restrict how much it could open. I was surprised at how much was needed. I added the jb weld to the weight that would hit the damaged stop and id say i added about 3 or 4 mm thick layer. I moved the idle timing to fight over F, and now at 3k it is maybe 8-10 mm from the max advance line.
The he extra weight of the jb weld changed the advance curve, it would advance much faster than before. Therefore i would try the soda pop can method suggested in this thread or like Pete says, simply REPLACE the unit. The relationship between bob weight tang size, their weight, the distance they open, the spring tension and the disc slot size ALL play a part to determine the advance curve.

I also hope all you east coasters are safe and your bikes arnt under water!

 

[Austblue]

Can anyone chime in with an opinion on the quality of Mikes ATU or recommend another source? Shipping to Australia is $35!

 

[Punkskalar]

Can anyone chime in with an opinion on the quality of Mikes ATU or recommend another source? Shipping to Australia is $35!

I have 2 here that do not advance enough, right out of the box from MikesXS. They were supplied with Pamcopete ignitions. They are well built enough, but may require some filing or fine tuning to get just right. I ended up pulling them off, and using old used ones with new springs and they were just fine.

I should have taken a pic/video but the MikesXS Advance Units really do need to be checked for making full advance before using them too much.

 

[Austblue]

I've sent you a PM Hugh

 

[XSLeo]

I have been running one in my 75 and it works well. My stock advancer advanced to much. Don't recall exactly but was going to the Pamco, so ordered the kit with an advancer. I Had to tune the springs. It is just a bit wide. At idle I'm set to just to the right edge of the right F line. At full advance it comes to right at the left side of the full advance line. Neither is off the lines just right at the outer edges.
I might pull it apart and check for tightness at the disc notch and weight tip. If they seem to be a bit on the loose side I can peen them to a snug fit.
Oh also I did this before I read about the tip peening or I might not have gotten the new advancer.
Leo

 

[wherearewe]

I ended up getting a new OEM unit. Problem fixed. I found some damage to the back of my old unit when i removed it a had a close look. Im not at home at the moment but when i get back ill post a pic for those interested.

 

[Austblue]

For $200+ or did you find a cheaper source?

 

[wherearewe]

Cheapest i found was powersports for 170. I choose OEM cause i didnt fancy spending half that and messing about with it to make it work correctly, plus I am someone that prefers to use original parts where i can.

 

[weekendrider]

Brought this back to top because I found this old part.
The reverse of what wear 5twins was seeing on the bob weights.
The weights have worn a groove in the advance disc.
Now I have an interesting spacer washer.

 

[retiredgentleman]

WER..................that amount of wear is just incredable. Hard to believe that amount of wear could happen...........................must take a ton of kms or miles to do that.