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Thread: New Member Question and Intro 1975 R90/6

  1. #1
    Registered User bandersnatch's Avatar
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    New Member Question and Intro 1975 R90/6

    Hi everyone,

    Larry here from Hillsboro, Oregon. Over the Fourth of July I drove to the Seattle area and brought home an orphaned and neglected 1975 BMW R90/6. Since its arrival in my garage I have overhauled the carbs, cleaned and flushed the gas tank, replaced the fuel petcocks and lines and replaced the battery, points, choke cables and spark plugs. I also disassembled and cleaned/greased the throttle hand grip and the choke assembly.

    The last plates are from 1995 and the bike was last registered in 1992, so it appears to not have been on the road for almost 25 years. After the above work and setting the timing, the bike now starts easily although I'm still working on getting it to run without the choke.

    My question is this. As several others have experienced, the mechanical advance retaining nut was broken off leaving me with the choice of replacing the camshaft or drilling it for a retaining screw. As I'm just trying to get the bike running for a bit before a complete teardown and restoration, my preference was to try modifying the existing camshaft. To my amazement I found a previous owner had already drilled a hole down the center of the camshaft.

    I filed the remnants of the retaining threads off smooth with the face of the advance plate and per some instructions I found on this site, proceeded to drill it out in one drill size increments up to 11/64" then tapped the hole for a 5x.8mm thread. When i inserted a bolt with a lock washer, I found it very successfully locked the advance mechanism in place.

    Now to the issue I'm having. While the advance appears to be holding really well, I'm concerned that it may slip as the remaining nose (round with a locating flat) was pretty buggered up as if someone ran the bike with the advance loose on the shaft. I can rotate the advance mechanism counter-clockwise about 30 degrees from the original location.

    My thought was that since the advance mechanism has two apparently identical lobes to open the points, would it be feasible to file another flat opposite the original flat in order to lock the advance firmly into one position? Based on the amount of adjustment in the points plate it seems like it wouldn't have to be perfect, just close.

    Any thoughts or recommendations would be very much appreciated.

    Regards,
    Larry from Hillsboro, OR
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    Last edited by bandersnatch; 10-02-2019 at 06:39 PM.
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  2. #2
    Liaison 20774's Avatar
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    Larry -

    Welcome to the forum! You definitely have a survivor there!

    I don't recall there being a "flat" on the nose of the camshaft. On my /7, there is a semi circle cutout on the nose and then on the inside of the advance unit, there's a matching peg which fits into that circle. But maybe in your case, since the end was modified, maybe the circle turned into a flat...or maybe they did it differently on the /6. But as to your question, I can't think of anything right off to say you couldn't relocate the flat to the other side given that the ignition is a wasted spark, both cylinders firing at the same time, one on compression the other on exhaust. I think that the advance unit is symmetrical in that sense.

    An option that you might want to consider is a Boyer Microdigital ignition system...it doesn't use the old advance system and the stripped nut on the nose doesn't come into play. I believe there are other ignition systems which also dispense with the old ATU...some even use a new sensor that is driven by the crankshaft which results in more precise firing control and smoother operation.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User bandersnatch's Avatar
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    Thanks for the quick response Kurt.

    I'm probably not using the correct terminology, but I think you described the situation perfectly. In the advance plate there is a "D"-shaped hole that fits over the end of the shaft which prevents the plate from rotating. In my case, the shaft is buggered up, allowing the plate to rotate quite a bit.

    When setting the points, it appeared that both lobes on the advance mechanism raised the points arm the same amount, leading me to think it would be possible to file the opposite side of the camshaft allowing me to install the advance mechanism 180 degrees from the original position.

    I have read about electronic ignitions but was hoping to keep the bike as original as possible. Call me silly, but I like the experience (a few years ago, I restored a 1957 MGA roadster completely stock. It rides rough, it's slow and it corners worse than a Honda Civic, but I love it!).

    I do appreciate the suggestions and may consider the Boyer down the road.

    Again, my thanks.
    Larry
    Last edited by bandersnatch; 10-01-2019 at 06:15 PM.
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  4. #4
    Liaison 20774's Avatar
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    Larry -

    Even in the stock setup, there is some slop. We're "trained" to hold the advance unit against one side of the slop and then tighten the nut. IIRC, hold the advance unit as far CCW as you can and tighten the nut/bolt CW. I believe the camshaft rotates CW so just from inertia it pushes the advance unit CCW but since it's against the stop it doesn't go anywhere. If I have the rotation directions, reverse everything I said!!
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    Rally Rat 1074's Avatar
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    Quote Originally Posted by 20774 View Post
    Larry -

    Even in the stock setup, there is some slop. We're "trained" to hold the advance unit against one side of the slop and then tighten the nut. IIRC, hold the advance unit as far CCW as you can and tighten the nut/bolt CW. I believe the camshaft rotates CW so just from inertia it pushes the advance unit CCW but since it's against the stop it doesn't go anywhere. If I have the rotation directions, reverse everything I said!!
    Agree.
    Boxerbruce

  6. #6
    Registered User Bob_M's Avatar
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    Welcome to the forum. I have nothing in the way of advice, but I do hope to see you in area.
    Bob

  7. #7
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    Larry good luck with your project. Not sure I can help but I have not ridden in an MG A since Heckter was a pup. So sweet.

    I think if you can snug that threaded bolt down on the advance mechanism it should be fine. You are between a rock and a hard place. Why not use red locktite on the bolt and give it a try. Should it come loose one time then that would put you back where you are now.

    Or am I not understanding the problem?
    1980 R100T
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  8. #8
    I have two thoughts, neither of them very good I'm afraid. The first comes from getting my BSA going again and discovering after much anguish that the front axle has a reverse thread. I don't know which way the cam turns but if does so in such a way that it would tend to tighten the bolt, I think you're ok. Second, I would use blue loctite and then, once installed, the tiniest dab of epoxy to lock in place. Put it where you can easily remove it. I'd even consider silicone seal -- you don't need much extra holding those thread in place.

    That said, I'd get the e-ignition. You can't see it once everything is together.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  9. #9
    Registered User jad01's Avatar
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    I put a Boyer on my /7 and like it a lot. I had stuck with points for a long time on that bike, but don't miss them. In any event, it could be a good solution to your problem as Kurt suggests (at least temporarily if you are set on points ). I've also read good things here about similar products from other well-known vendors like Mottorad Elektrik, etc that you could also look into.

    Also, Portland has a very active Airhead Beemer Club chapter. Someone in the club might have good advice, local part sources, etc. You might reach out to the chapter Airmarshal, Garry Newby to see if they have a tech day coming up.
    Jim (MOA 83200)
    '78 R80/7 (Anastasia) and '84 R100RS (The Millennium Falcon), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  10. #10
    Registered User bandersnatch's Avatar
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    Thanks for all the replies! I am actually leaning toward the Boyer ignition down the road but it's running with the points now after its 25-year sleep, so I'm planning on running it this way while I put my money towards things like brakes and tires.

    I did attend the last Portland Airheads Barley Therapy and met several great folks there. I'm hoping to get to the next one on October 9th, hope to see you there, Bob.

    As far as the advance goes, I worked on it a bit more last night. I found with the advance rotated all the way counter-clockwise (which I did think was good advice, BTW), I wasn't able to set the points to open anywhere near the 'S' mark. I also tried all the way clockwise which should have been the original location but had the same issue - not enough rotation on the points plate to get it timed properly. Setting the advance mechanism near the middle of the range gave me the best result and I was able to set the timing almost perfectly. I still need to fine tune it with a timing light but the bike starts after three or four cranks each time, which I'm thrilled about - although my wife is less so . . .

    Daz, I believe you have nailed it exactly, I cranked down the bolt with a locknut and it does seem to be holding for now. Once I get it on the road I'll need to periodically check the timing to see if it's slipping on me, but it's working for now.

    Although the bike now starts and runs, I can only take the choke about halfway off before it stumbles and dies, even with the bike well warmed up. And I can only give it some throttle with the choke fully on, so something's not right about my setup. I'm not too worried about it yet as I still have to check the timing and set the valves, but I would definitely appreciate suggestions where else to look. I did have to wind in the idle adjustment quite a bit from initial to get as far as I have (set so 3x5" card stock just dragged between the screw and the adjustment arm).

    Much appreciated guys!

    Safe travels,
    Larry
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  11. #11
    Registered User bandersnatch's Avatar
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    Just in case anyone is interested, here are a couple of before and after pictures of my MGA, "Rosie". She's named after our furbaby Rosie, (a Dachshund/Terrier mix) because both of them were short with a long nose and big butt!IMG_0008.JPGIMG_0036.JPG
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  12. #12
    Liaison 20774's Avatar
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    Larry -

    When working with the advance to try and get the timing...were you changing the points gap? The spec calls for 0.016" but it can be set narrower and bigger if needed. On a two cylinder ignition system, the dwell is not really that critical...within reason. And a small points change makes a big difference in where the points open up. When the points open, the coils fire. As long as the points are closed enough during the rest of the rotation, the coils will get enough current to charge up again for the next firing.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  13. #13
    Registered User bandersnatch's Avatar
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    Hi Kurt,

    Thanks for the advice. At either side of the range I can locate the advance mechanism (either full clockwise or full counter-clockwise) no adjustment of the points gap helped and I was unable to get the points to open at the correct position. As a compromise, I rotated the camshaft to the largest point of the lobe, set the points to 0.015", rotated the points backing plate to where it was approximately centered then rotated the advance until the points just opened as evidenced by a test light and tightened down the new locking bolt/screw.

    That seems to work quite well and I was able to start the bike. I haven't checked it with a timing light yet, but when I did the same a week ago before drilling and threading the camshaft, I found it to be dead on with the light.

    I read a thread about propping the advance weights open with toothpicks to verify the points open at the 'F' mark, I thought I might try that in the next couple of days since I'm still working on getting the bike to take some throttle input (see post #10 above).

    By the way, here are some sketches I did of my original thoughts on filing a new locator flat on the end of the camshaft:Camshaft1.jpgCamshaft2.jpgCamshaft3.jpg
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  14. #14
    Quote Originally Posted by bandersnatch View Post
    Just in case anyone is interested, here are a couple of before and after pictures of my MGA, "Rosie". She's named after our furbaby Rosie, (a Dachshund/Terrier mix) because both of them were short with a long nose and big butt!

    Well, that polished out very nicely!

  15. #15
    Registered User bandersnatch's Avatar
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    Quote Originally Posted by khittner View Post
    Well, that polished out very nicely!
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

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