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Author: Subject: changing auto advance springs
pptom
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[*] posted on 6-8-2012 at 12:36 PM
changing auto advance springs



So, I got hold of a second hand 10Deg auto advance unit from a well known supplier, however, dissapointingly the springs are absolutely useless, so I need to replace them before fitting.
Obviously the end on the outside of the unit just pops off the post, but I can't work out how to get the 'inside' end off the posts. it looks as if the unit needs to be stripped to give enough clearance - anyone have any advice?
Also, could someone furnish me with the correct part numbers for the springs please? 10 deg unit - points in side. My parts manual is for dizzy models only.
Tom




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Raggles39
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[*] posted on 6-8-2012 at 02:23 PM
Springs



Hi Tom

Here's an exploded view of the unit

The springs for a T20 &T20SH :- Part number 425768
'' '' '' T20SS :- Part number 54415640

Jim

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[*] posted on 6-8-2012 at 02:41 PM


Thanks Jim, no obvious way of No4 securing to No7 then - i take it that the cam (No4) should just slide off?



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Chris Foster
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[*] posted on 6-9-2012 at 01:18 AM


Tom,
My Cub was a "dizzy" model but I remember damaging the delicate advance / retard springs when refurbishing the dizzy. I found the easiest way to stretch springs to hook over posts was to attach a length of sewing thread to spring ends then pull on that to stretch[gently!]. Snip off thread when spring in place.
Chris
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Raggles39
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[*] posted on 6-9-2012 at 01:47 AM


Tom, as you say, the cam No4 slides off No7

Jim
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[*] posted on 6-9-2012 at 02:40 AM


Thanks chaps, didn't want to force it off if there was something holding it on - I'll have a go later.
Tom




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jinx
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[*] posted on 6-9-2012 at 05:17 AM


If memory serves ...I had the same trouble...think someone used the wrong washers ?? under the center bolt + over tightening, and somehow caused the shaft to bulge a bit on the end ....it came off with a little heat and lube.
:cool::D
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[*] posted on 6-19-2012 at 09:51 AM


Fed up with this..
the supplier did send me some replacement springs as he said he forgot to check them before sending it out.
I've been trying for the last hour and a half to remove the cam, but to no avail, its rock solid in there.
Double checked what i was doing with my old 5 deg unit and that slides off a treat.
I've tried everything i can think of, including heat and filing the end in case it was bulged. I think the only thing that might do the job is some gear pullers under the cam, but to get them to fit would require grinding the ends to match the recess, so that will render them useless for the future.
In my last ditch attempt I've damaged the unit slightly, It could be repaired if taken apart, but I've given up.
That takes me back to square one, I could fit the 5 deg unit back in, but wouldn't it affect performance - as i thought they were only for the ET system which mine no longer has. I would rather use a 10 if I could find one as this was the sports cub spec, which my engine basically is, or would I be ok going with a 12 which are more plentiful?




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[*] posted on 6-19-2012 at 12:26 PM


File out the bob-weight slots ;)

I have the 12° unit which I have sourced for my Sports Cub build,which I`m giving a bit of a trials treatment(doesnt mean I know what I`m doing though,I only started with a frame for that project....damaged at that :))

If your aim is a bit of a trick tuned motor which is quick to respond for a bit of off-road stick,won`t that extra advance help?
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[*] posted on 6-19-2012 at 03:02 PM


now I'm getting confused - I gather the lucas auto advance unit is pretty universal, so a 12 degree unit for example will fit a triumph twin / single, BSA etc, with the only difference being which way the bob weights point.
The parts diagram that jim posted above shows that when the cam is turned clockwise the weights move outwards.
However, my 5 degree unit is the opposite to this and so is the replacement 10 degree unit from a well known cub parts supplier. If I'm going with the readily available 12 degree unit, which orientation do I need? as per the parts diagram above or as per the picture below?
http://i156.photobucket.com/albums/t40/PeePeeTom/elc47.jpg




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[*] posted on 6-20-2012 at 04:09 AM


Perhaps some strange quirk linked to the Energy Transfer Ignition.

Here`s the 12°unit to back up the exploded diagram Jim provided.Photo not so clear,auto-focus out of kilter.....will submit better photo when I find another camera.

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[*] posted on 6-20-2012 at 08:59 AM


Thanks Crusty, so does that mean that the 10 degree unit was not only seized, but in fact, the wrong one for a cub anyway?



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[*] posted on 6-20-2012 at 10:52 AM


Hi Tom

Your photo of the ATU is the correct type

i.e. the weights operate outwards when the cam turns anti clockwise

There are other ATU's out there which operate clockwise but are not for a Cub

I would say that the one supplied by Greystones also your 5 degree unit are the correct type for a Cub

Jim
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[*] posted on 6-20-2012 at 10:58 AM


Hi
Now you've done it. I had to go and dig thru old parts to see what's up,.... reliving all those evil ET system memories...... The unit in your fuzzy pix has it's weights facing in the wrong direction. I "think" it's for a twin. Don't use it as it will retard the Cub ignition instead of advancing it. In my picture, if it shows up, you'll see two advance units both 10d. The one on the right has the usual "lobe" on it and the other has instead a "flat" spot. Right (normal) one has the points closed thru most of the revolution and opens momentarily for the spark. The other is just the opposite and keeps the points open thru most of the revolution only momentarily closing them for the spark. I got both of them on engines with ET ign systems...neither worked properly. The bottom pix shows the underside of one of them and the "oval" opening that determines how much spark advance it will supply. If you fill part of that hole with braze for example, you can limit the advance to whatever you like, or open it up more for a greater advance.. If you're trying to use ET, the less advance you can employ, the better chance you have of not pulling all your hair out and the more beer you'll have left...:D:D:D:D

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crusty
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[*] posted on 6-20-2012 at 02:35 PM


Jinx,Tom has ditched his ET.

Jim,my fuzzy pic matches your exploded diagram....both illustrate bob-weights moving out in the same direction.....yes?

What does Scott say?
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[*] posted on 6-20-2012 at 03:12 PM


Hi
The bible doesn't seem to get into much detail. That diagram appears to be from the "owners workshop manual" page 70. If you look at the facing page 80, clearly on a side points engine, there are two actual pictures of the advance mech and the weights face different from the direction shown in the diagram and the fuzzy pix...,.Based on the fact that all of the ones I have face the same as the pix I sent, I think the person doing the illustration may have had the wrong part in his hand when he did the drawing. I haven't touched a dist points engine in 50 years so don't remember if it could have come from that. :D
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[*] posted on 6-20-2012 at 03:49 PM


You are right Jinx,I`ve been sold a pup and Toms is correct....just looked at the Haynes manual and like you say the illustration is incorrect,but on the opposing page(71)it clearly shows the weights facing the other way.Never noticed that in the 30-odd years I`ve had this manual.

In future don`t listen to me if it`s anything to do with ignition ;)
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[*] posted on 6-21-2012 at 03:28 AM


Apologies for any confusion Crusty as I only used the illustration so that Tom could see the actual breakdown of the parts ............... I should have added at the time that the Hayne's drawing was incorrect and that the ATU operates anti clockwise

Jim
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[*] posted on 6-21-2012 at 10:42 AM


The Haynes manual is incocerrect as is the triumph parts manual, I have the cub engine posters and they are also wrong, the 5 deg unit is the better one it helps to stop back firing when shutting the throttle back quick, I have just removed a 5 deg unit from an energy transfer system on my French army cub and fitted Boyer 12 v system but not having much luck getting the bike fired up. I have set up the timing valves etc but she still wants to fire back throught the carb and kick back, so I will have to move the rotor to 3 o'clock position tonight and see if this helps
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[*] posted on 6-21-2012 at 10:53 AM


Is the Boyer system the one that replaces the points with two tiny coils? and runs off a 12v battery, NOT the alternator rotor? I ask because there seem to be more of these systems than I thought. If it's a straight battery system, moving the rotor has no bearing on the problem....., if it's the system that runs off the alternator, then rotor position is very important. I run the battery system and once the timing is dialed in it seems no further tinkering is necessary. Unless the battery voltage is very low, (-10v) and then the timing seems to go full advance when you kick it and it spits and kicks back. :D
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