ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 12-24-2012, 03:52 PM   #16
disston
ShadeTreeExpert
 
disston's Avatar
 
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,771
What you are saying is the advance unit does not have a full amount of advance. It reaches full advance but it is starting half way there. Have you removed the advance unit and cleaned the cam tip and the inside of the advance? There is a special grease for this but a light oil will do for now.

Used points are almost impossible to gap. I also will move the points gap to change the timing but it is for special circumstances or when trying to figure out what's wrong.

(Don't forget to look for the #. tell us what it is)
__________________
.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
disston is offline   Reply With Quote
Old 12-25-2012, 07:30 AM   #17
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Quote:
Originally Posted by disston View Post
What you are saying is the advance unit does not have a full amount of advance. It reaches full advance but it is starting half way there. Have you removed the advance unit and cleaned the cam tip and the inside of the advance? There is a special grease for this but a light oil will do for now.

Used points are almost impossible to gap. I also will move the points gap to change the timing but it is for special circumstances or when trying to figure out what's wrong.

(Don't forget to look for the #. tell us what it is)
I did clean the advance, and inspected it ( actually was inspected by a local BMW Mechainc who said it looked fine to him - cam, springs etc). Did use lube on the felt pad when replacing it. Not sure of the numbers yet as the vie is running fine and I won't be I there for a while... At least a few days.
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.
Captdan is offline   Reply With Quote
Old 12-25-2012, 10:49 AM   #18
disston
ShadeTreeExpert
 
disston's Avatar
 
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,771
Your mechanic may have looked at it and pronounced it fine but if it is working as you state there is something wrong.

If you take the small nut off the tip off the cam, the one holding the advance unit on, you can remove the advance unit. Careful they sometimes don't want to come off if they have not been cleaned in years and this is what we see all the time with these machines. Clean the cam tip and inside the advance unit and put this back together with some light oil but don't use too much as it will just get on to the ignition points and ruin them.

The felt is to lube the exterior surfaces of the points cam to help the rubbing block last a little longer.

In operation the advance unit rotates on the cam tip.

You will most likely need your timing light to get the advance unit back on because they have some play in the D shape locating portion of the cam. It's hard to get them timed right with out the light.

If you are saying you have already removed and cleaned the advance unit then somebody is not seeing something. The idle should be at S and full advance at F. If not then something is wrong.
__________________
.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
disston is offline   Reply With Quote
Old 12-25-2012, 05:33 PM   #19
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Quote:
Originally Posted by disston View Post
Your mechanic may have looked at it and pronounced it fine but if it is working as you state there is something wrong.

If you take the small nut off the tip off the cam, the one holding the advance unit on, you can remove the advance unit. Careful they sometimes don't want to come off if they have not been cleaned in years and this is what we see all the time with these machines. Clean the cam tip and inside the advance unit and put this back together with some light oil but don't use too much as it will just get on to the ignition points and ruin them.

The felt is to lube the exterior surfaces of the points cam to help the rubbing block last a little longer.

In operation the advance unit rotates on the cam tip.

You will most likely need your timing light to get the advance unit back on because they have some play in the D shape locating portion of the cam. It's hard to get them timed right with out the light.

If you are saying you have already removed and cleaned the advance unit then somebody is not seeing something. The idle should be at S and full advance at F. If not then something is wrong.



Thanks for the insight, I do appreciate it. For the time being I'm going to trailer down to Florida and ride over the holidays. Presently the bike starts and runs great. While it may not be technically correct it's fine for the next few days of fun with it. Then after the 1st of the year I'll get back into the actual fix. If need be I'll just buy a new advance and go from there.

Thanks agin and a happy new year!
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.
Captdan is offline   Reply With Quote
Old 01-01-2013, 12:38 PM   #20
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Timing advance number

Today I decided to do a bit of routine maintanace and pulled the front cover off the r90. The advance has this number on it: 0232002012. For those that asked me what number it was, does this tell us anything?

Btw, the bike ran like a top all weekend. At one point doing a 165 mile trip through the countryside with other bike nuts. Now, it may not be timed as per the book, but it sure does run good!
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.
Captdan is offline   Reply With Quote
Old 01-01-2013, 12:44 PM   #21
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Quote:
Originally Posted by Big Bamboo View Post
The bill's in the mail... (just kidding) Glad you've got it sorted out! Just out of curiosity, did you notice what the last three numbers are on the advance unit? Can be 005, 007, 010 or 012
My number is 012....
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.
Captdan is offline   Reply With Quote
Old 01-01-2013, 01:00 PM   #22
Big Bamboo
Aircooled & Sunbaked
 
Big Bamboo's Avatar
 
Joined: Sep 2010
Location: Big Island of Hawaii
Oddometer: 3,178
That's the correct one for /6 & /7.
Big Bamboo is offline   Reply With Quote
Old 01-01-2013, 01:35 PM   #23
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Quote:
Originally Posted by Big Bamboo View Post
That's the correct one for /6 & /7.
Ok, thanks. Now for a dumb question. When holding the advance in your hand how much play is normal? The weights are held back by the springs, but the center section that slides onto the cam has play when holding the unit in your hand and inspecting it. In fact the hold thing seems rather fragile. Also, on the rear of the unit where the weights are connected there are small blazed metal plates near each end. I think someone mentioned those could be custom weights?

I don't really want to buy another of this one is ok. It does advance to "F" when the engine is reved up as indicated by a timing light.
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.
Captdan is offline   Reply With Quote
Old 01-01-2013, 03:42 PM   #24
disston
ShadeTreeExpert
 
disston's Avatar
 
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,771
They do seem flimsy but they aren't doing all that much. They wear in a few places over time. The springs get weak, most of us will replace springs when trying to solve timing issues. The little springs are not cheap either and they sell each not by the pair. 12 11 1 357 627 $10.39 according to Max but there are two different weights of spring and I didn't find another part number so I don't know if this is the one called "heavy duty". I think you want the HD ones. If you decide to get these.

The "D" shape that indexes the advance unit is worn and the advance can be rotated in advance or retard direction before the small nut is tightened . This actually helps sometimes to get the bike timed. It's just something you have to remember when the plate doesn't seem to move round far enough.

There should be some small fiber material washers and very small E clips that hold it together. A lot of riders will polish the pieces so they can slide easily against each other.

You seem to have a restricted amount of movement to the advance. This could be something done on purpose by a former owner or it might be worn springs. It could also be bent posts, the posts the springs attach too. The small posts I mention should be straight up. If they are then they aren't bent. Another way that Hot Rodders try to customize the advance unit is to weld or braze the hole that one pair of posts is moving in. By making the hole smaller the amount of advance is restricted. If this has been done you should be able to see either weld material or the more common brazing bronze material on the top piece of the advance with the holes in it.

No evidence of modification? Then you probably need new springs.

You have the latest edition advance unit, that is the latest that they made before they stopped making them. It is the one you want to have.

There is another more rare problem that does pop up sometimes. You should check for a double timing image. You will notice that because of the physical arrangement of things the two lobes of the advance unit each fire for one side of the motorcycle. Don't get this confused with the lost spark or extra firing. Both plugs fire at the same time so they fire at every TDC. One cylinder on compression is a working spark and the other cylinder on exhaust is a lost spark. This is checked with a timing light, inductive pick up non advance timing light is about the best, easiest to use. You have to watch in the timing window carefully for a double image of the timing light firing through a wide range of RPM. If the advance unit lobes are uneven or the tip of the cam is bent the firing of the plugs will be uneven. If the light is showing the F mark or the S mark and then it shows the next firing a blank mark it will be difficult to notice because you think you are seeing the mark you want. It sometimes looks like there is a ghost mark. In addition keep inmind that there is sometimes a little irregularity to the firings and the normal mark is not dead steady. Good luck with this. I have tried to make it as plain as I can. Maybe I succeed, it's plain as mud to me.

You are doing well. The bike is or should be rideable as long as the full advance is being observed.
__________________
.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
disston is offline   Reply With Quote
Old 01-01-2013, 04:09 PM   #25
Big Bamboo
Aircooled & Sunbaked
 
Big Bamboo's Avatar
 
Joined: Sep 2010
Location: Big Island of Hawaii
Oddometer: 3,178
I'm holding a brand new advance unit in my hand and yes, they are a bit sloppy feeling. remember, the top plate with the D shaped hole is bolted to the end of the cam, and the other part is centered by the shaft itself. That will eliminate 99% of all "sloppiness". There are two thin plates welded on the bottoms of the weights.

Big Bamboo screwed with this post 01-01-2013 at 04:34 PM
Big Bamboo is offline   Reply With Quote
Old 01-01-2013, 04:47 PM   #26
Captdan OP
Gnarly Adventurer
 
Joined: Jan 2012
Oddometer: 132
Thanks to you both, and others here for the info. The bike runs like a bat right now so I shouldn't really complain, but I'd like to get it perfect at some point. The timing issue naws at me. So, when I have time I dig back into it.... I think I'll order the new springs. Not all that much in cost, and if I don't need them at least I won't be out much cash, if I do need them it's a cheap fix... Can't lose with that logic. ;)
__________________
1965 Cushman super silver eagle, 1968 BMW R-60/2, 1974 R-90/6 cafe, 2008 R-1200 GSA.

Captdan screwed with this post 01-01-2013 at 04:53 PM
Captdan is offline   Reply With Quote
Old 04-20-2013, 03:17 PM   #27
apt13
Gnarly Adventurer
 
Joined: Dec 2010
Location: Athens, GA
Oddometer: 477
sorry to resurrect this, but did you ever figure it out?

i've always had the same problem and have never been able to figure it out, as seen here.

http://advrider.com/forums/showthread.php?t=840445
__________________
----
'78 R80/7
'74 CB360
Airhead Tshirts!
apt13 is offline   Reply With Quote
Old 04-20-2013, 09:32 PM   #28
Brun
Gnarly Adventurer
 
Brun's Avatar
 
Joined: Jun 2012
Location: BorderBurg, South East Oz.
Oddometer: 146
I'll add another thing to test. When I first got my 90/6 and started doing the research I read about the 'double image'. Now I knew that the timing chain was old and slack - I could hear it thrashing around in there - but only had a single image when I shone a strobe through the timing hole. Then one day after adjusting the points using the static timing method the bike ran really badly; popping and backfiring, not running at all well. I borrowed a strobe and pointed it at the advance unit. A double image for sure, but out by a lot ...



I went back to the static timing and rotated the engine to check both sides a few times. Found that they were way out of sync. I made a paper indexing disk, glued it to the alternator and measured the difference to be around 30 degrees.



Clearly, the cam nose was bent, but not by much - it doesn't take much of a bend to make a big difference. You can see by the first pic that the original threaded end of the cam had been broken off and replaced with a bolt. Somewhere along the way somebody had also tinkered with the shape of the points cam. Since I couldn't afford a new advance unit I resorted to reshaping the points cam again, and got it pretty good. O, and I also replaced the timing chain. I now have a comfortably close double image through the timing hole when I use a strobe.

I'm throwing my unusual experience into the mix, just in case it is useful to others out there. If you have a 40 year old bike with stock points and you can't see that second image, look further. It may be well outside the window. Good luck.
__________________
Cheers
Charlie, and the lovely Brunhilde (74 R90/6)
Graduate, Wallace and Gromit School of Engineering and Design (pending)
Brun is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 04:50 AM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014