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WATCH OUT: New production ignition advancers
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Re: WATCH OUT: New production ignition advancers
Frank.
NYC.
NYC
- schrader7032
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Re: WATCH OUT: New production ignition advancers
James -jwonder wrote: ↑Fri Jul 24, 2020 7:41 pmIf you don't know what I am talking about being able to control the advance, look at the Barrington book and you will see a hack that includes a screw and nut to allow you to control exactly where the advance stops! Since I have the old style advance I do not have that capability which is why I purchased the new one. This hack allows you to set the idle exactly and then adjust the advance exactly where it should be, and its a hard stop.
I thought your "issue" with the new advancer unit was with the unevenness in the cam lift for the rubbing block, resulting in aggravated differential timing. In your video, you do show an old and new unit...I'm guessing that you mean the old one has the question mark as an advance stop while the new one has the u-on-it's-side stop. Initially it seems you were identifying an old OEM advancer unit versus a new aftermarket device.
As for the "hack", I can't find stuff in the Barrington book; it's almost like there's just too much stuff there. But what I think you're referring to is the "Brian Caro" stop screw...that's what I heard mention on the old Yahoo /2 list. I ended up buying from Vech the nut and screw to do that conversion. Allan Atherton has a picture of it on his website:
https://www.flickr.com/photos/roundel/sets/394821/
There are a number of individual discussions on that page about the old and new advance units. The Caro stop screw is the lower left picture.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
- jwonder
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Re: WATCH OUT: New production ignition advancers
Yes, the new one has the cam ground wrong.
Yes, I am showing an original OEM versus the new aftermarket one.
The only reason I even started to look for a new one was that I wanted one with the new style spring on top to put the Brian Caro screw in to have a more exact limit for the full advance. Great link to the picture BY THE WAY, you always come up with these things!
I hope I did not muddy the waters with my last post.
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York
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Re: WATCH OUT: New production ignition advancers
How did you attach the arms of you dial gauge holder to keep it steady?
Thanks.
Frank.
NYC.
NYC
- jwonder
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Re: WATCH OUT: New production ignition advancers
I have a magnetic dial indicator holder (the one pictured below) that I have my dial indicator mounted on.
I then got a nice thick, and heavy, piece of angle iron (I believe it is 2 inch) and drilled a hole in it on one end. I put a bolt through the sidecar lug on the right side of the frame and tighten it so it is secure. I then mount the magnetic holder to that and and adjust as needed.
It is not perfectly secure, and you will see that when I am rough on the kick starter it jumps a bit (a couple thousands), but its accurate enough for what I was doing. It does allow you to get the nose of the magneto straight and lets you know how your lobes are.
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Long Island, New York
- jwonder
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Re: WATCH OUT: New production ignition advancers
He asked me to: "add something about the meaning/consequences of your findings". And, that is what I am doing in this post. If I miss something please add as needed.
This picture sums it up:
Even if the above picture didn't happen from pre-ignition you would still have the following problems.
- To say that the timing would be grossly off is an understatement. One cylinder would be fine and the other would be advanced greatly. This throws off the idle timing, but also the maximum advance which is scary!
- Even if you split the difference, the timing would be so unenven that acceleration would be quite poor.
- The motor would not run smooth.
- The motor would be grossly down on power.
- The engine would generate far more heat than normal and the risk of seizing would be higher.
If you want to add to the list please feel free, but I think the point is that it would be BAD and that its not worth the risk!
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York
Re: WATCH OUT: New production ignition advancers
1974 R90S
Re: WATCH OUT: New production ignition advancers
After seeing your video I measured and the difference in lift of the lobes is 0.2mm! While the runout on the shaft it's mounted on is less than 0.05mm.
Looks like the problem exists from a long time ago.
Edit: Friday I called a supplier who is selling the advance unit for R69S, R50 etc with part number ...113 instead of the ...112 in my original parts manual. On questioning him about that he just said that was with a "wrong" cam grind. He just sells these advance units without mentioning that on their website, and covers his ass by small print "customer should always check if the part number is correct".
On further analysis of my "new" advance unit with a cam degreeing wheel there seem to be more issues:
1. The advancer lobes have pins which attach to the small springs. The shorter pin hits it's limit earlier than that the U-shaped limiter spring comes into function. The small pin limits the full advance to 22 degrees camshaft relative to static. So the advance unit advances 2x22=44 degrees crankshaft. Add 9 degrees BTDC for the static timing and the "Früh" spark will be at 53 degrees crankshaft before TDC instead of 39 degrees crankshaft
2. The index pin which locates the advance unit relative to the magneto rotor shaft is slightly off. The result is that the adjustment plate for the breaker points needs to be rotated more and is near the end of it's adjustment range. I could barely set the breaker points within spec.
3. The sheet metal clips with the small bolts that keeps the advance unit assembly together were too high, sporadically touching the (Noris) breaker points during rotation. I didn't notice this during riding but can imagine this can sporadically lead to sparks at the wrong time or sometimes a weaker spark. The original Bosch points were 0.7mm lower than the Noris points and never hit the advance unit.
I wonder if anyone has similar observations.
- malmac
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Re: WATCH OUT: New production ignition advancers
Really good video clip. Most informative. Thank you for bringing it to our attention.jwonder wrote: ↑Sun Jul 19, 2020 10:33 amAll,
I wanted to share a video I made for a supplier that shows the issues with the new production ignition advancers on the market today. I spoke with another supplier and they had reports, like mine, about these and stopped selling them.
Check out the video here: https://youtu.be/29pq6S90jEo
Mal
Toowoomba- Australia