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Roll-on / roll-off bucking

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Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

I have 170,000 miles my 1979 R65, ridden myself and maintenance done myself. She did not originally do this. The problem developed slowly. For twenty years I’ve been wondering!

 

If I am coasting in gear with the throttle closed, in any gear at any RPM, then I crack the throttle open any amount, the bike surges forward with uncomfortable abruptness. When I close it again it decelerates with similar discomfort. It happens 100% of the time. There is no clunk or noise. It is severe enough that when rounding a corner at low speed it disturbs my centrifugal balance.

 

I have completely rebuilt the carburetors, replaced the throttle cables, and verified that the idle circuit is clear of obstruction. None of this helped. On the centerstand, in first gear, the rear wheel freely rotates two inches measured at the tread. In fifth gear it rotates four inches. I am unclear whether this is excessive drivetrain lash, or whether it could cause the roll-on / roll-off bucking, or what to do if it is the cause. Any ideas?

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 09/27/2023 13:20
Richard Whatley
(@wobbly)
Posts: 2498
Member
 

Some ideas....

• Replace the centrifugal ignition advance mechanism return springs and service (thoroughly lubricate) the advance unit.

• Have you set the ignition timing at high RPM using an ignition strobe lamp ?? Time the ignition at ~4500+ RPM to insure the ignition is at "full advance". Forget anything about timing the ignition at idle speeds, as some older manuals suggest.

• Are you running "high test" gasoline ? Are you running "Top Tier" fuel ? LINK

• Is the air filter, and engine air passage, clear of obstructions ?

 

This post was modified 5 months ago by Richard Whatley

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

 
Posted : 09/28/2023 06:46
Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

@wobbly

Thanks for responding! I will replace the ignition advance return springs and lubricate that mechanism.

I will also try a higher octane from a station on that Top Tier list. I have been using 87 Octane from cheaper gas stations.

I do the timing with a strobe lamp. At idle I verify that the S mark is by the viewing notch. At 3500 RPM I verify that the Z mark (which has a bright ball bearing by it) is at the notch. 3500 is what my “BMW Repair US Model R65” says. You say I should take it up to 4500 RPM?

The airways are clear.

Steve

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 09/29/2023 14:48
Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

Richard,

About the ignition advance mechanism, I don't see how any springs can be replaced. My bike has a can-shaped "spark trigger" or "ignition trigger." You rotate it to change the timing. You take the cap off it to access the points. The Repair Manual says, "Never disassemble the spark trigger, always replace entire unit." Part number 12 11 1 244 088. However, in 1988 I had to have it replaced due to pinging, and my mechanic installed a "rebuilt, better than new" one. Implying that somebody DID disassemble it and do something inside. Can you shed any light?

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 09/29/2023 15:51
Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

Richard,

MAXBMW calls it an ignition sensor and says the part has been superseded by 12112413906, which costs $620. Related to that same unit, they also sell a "Hall sender unit" for $325 and a "repair kit for ignition sensor" for $330. No springs are visible in the photo.

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 09/29/2023 16:07
Steven Rankin
(@14724)
Posts: 143
Estimable Member
 

You have a 79 bike correct?  in this case you do not have a Hall effect unit, unless someone replaced your points with one or as this is a R65 and they can be a bit of an oddball.  If you have a black module under the gas tank, you have electronic ignition.

Prior to BMW fitting airheads with electronic ignition which do have a Hall effect unit, they decided to put points into the next generation "bean can" they would move to with electronic systems.   

Unlike the older point equipped bikes where the advance system and points were out in the open visible and relatively easy to work on, your stuff is in the can.

So, if I am wrong and you have electronic ignition sorry, if not, you should be able to remove the can from the front of the engine take the cover off and work with the internals at your bench.

Even if you do have electronic ignition, the cover of the can should come off and the advance system springs should be accessible just not easy to get to.  St.

This post was modified 5 months ago by Steven Rankin

Beware! I do not suffer fools gladly! St.

 
Posted : 09/30/2023 05:10
Richard Whatley
(@wobbly)
Posts: 2498
Member
 

Hi Stephen -

My 1979 R100 also had the "can" and it had a mechanical advance mechanism inside which was controlled by springs. When the mechanism pivots AND springs wear out, the advance mechanism (which should change the timing slowly accord to strict RPM requirements) is able to make sudden and drastic changes to the ignition timing. This is what I think is happening to your engine.

You do NOT want to spend a fortune renewing the old BMW ignition design. At this point that would be silly because: 1) that is 50 year old ignition technology, and 2) the fuel it is trying to ignite has been radically altered by the EPA. If you change anything having to do with ignition, then it should be designed and manufactured in THIS century !! And is compatible with the fuel now available.

On my 1979 model, I chose the Boyer system. It consists of a plate that replaces the "points plate" inside the can, a magnetic rotor, and a digital pack about the size of a pack of cigarettes. There are no springs, because there is NO advance mechanism. All the changes are done in software that resides in the digital pack. The new advance curve is so long that the unit must be timed at 5000 RPM. At 5K RPM the ignition and engine have both reached "full advance". Once installed the software administers the spark control for perfect idle, acceleration and highway speed riding according to what the engine is actually doing. The Boyer is designed to work with the stock BMW coils.

I'm not pushing the Boyer. There are several systems that are similar. What I'm telling you about is an ignition triggering system from this century that does not rely upon anything mechanical to achieve it's advance curve. Another advantage of the Boyer is that it is designed to work with your existing BMW coils. Many systems will require you additionally purchase their coils, which besides being an cost adder, may/may not mount correctly. My Boyer was also about $300, so about half the cost of the OEM replacements.

Additional Information

1. You should start by changing out your 50 year old spark plug wires (which MUST be the older metal core) and new 5,000 Ohm spark plug caps. (Most people are using the NGK 5K Ohm.) These parts are simply worn out and leaky after 50 years. 

2. When you convert to a digital ignition, additional work is required. If your harness looks like a rat's nest with patches, iffy connections, twisted copper wires wrapped in shoddy electrical tape, mis-matched types of wire.... in short if it doesn't look like what's under the hood of a showroom Toyota then you'll have nothing but trouble. The problem is that analog ignitions will work "fine" with intermittent harness connections that make/break with every bump in the road and/or low voltage supply (down to 8V). But digital systems, which are making decisions 5000+ times every second, need 100% connections, AND due to the presence of transistors demand a steady voltage supply well above 12V. So crusty battery terminations, shoddy wiring, 50 year old mechanical voltage regulators, nearly dead or poorly maintained batteries, etc will no longer "cut the mustard". 

Most of the people having issues with newer digital ignitions do not understand the above paragraph. Simply put: it's not the new ignition's fault; it's their trashy, poorly maintained motorcycle. 

 

Hope these ideas help.

This post was modified 5 months ago by Richard Whatley

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

 
Posted : 09/30/2023 06:02
Richard Whatley
(@wobbly)
Posts: 2498
Member
 

Posted by: @18678

I will also try a higher octane from a station on that Top Tier list. I have been using 87 Octane from cheaper gas stations.

I do the timing with a strobe lamp. At idle I verify that the S mark is by the viewing notch. At 3500 RPM I verify that the Z mark (which has a bright ball bearing by it) is at the notch. 3500 is what my “BMW Repair US Model R65” says. You say I should take it up to 4500 RPM?

1. In computer speak, the term is GIGO. Garbage in; garbage out. Expecting good things from bottom tier fuels is pure folly. You can get it in a water-cooled car engine, but cars made since ~1990 have an internal computer that changes the ignition timing and varies the amount of fuel entering the engine to optimize the burning of fuel. Last time I checked, 1979 air-cooled motorcycles did not have any such capability. 

It appears that you are subconsciously drawing parallels between your late model car and your vintage motorcycle that absolutely do not apply. Apples and oranges, my friend. And it's very dangerous for the orange.

2. Most poor performance AND ALL ENGINE DAMAGE happens at full ignition advance. No one ever burned a hole in their piston or dropped a valve seat at idle. Therefore, we only really care what the ignition is doing at high RPM. Ignition requirements at idle are so lax that checking the timing there (especially when there is a worn out ignition advance unit) is just a waste of good riding time.

 

Hope this helps.

 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

 
Posted : 09/30/2023 06:39
Steven Rankin
(@14724)
Posts: 143
Estimable Member
 

Well, not sure about if you need to change your ignition system or not.  I will admit I hate points and have in the past replaced them with two different systems.  The first was a Dyna unit, that was replaced by the new Wedgetail system.   On the whole, I found the Wedgetail system to be very easy to install with the only exception being where to place the supplied ignition module and that was not terribly difficult.   I can't give you any long term information on reliability because I only got 5000 miles on it and I totaled the bike in an accident.

This system is well laid out and designed and very closely follows the later year BMW stock electronic ignition system.  No wiring is needed if your stock wiring is in good shape.

I assume a lot considering the age and mileage on the bike, as Richard mentions there are other things to consider in troubleshooting.

The plan of attack on tuning up an airhead is first, valves, are they in good condition and set right?  Set right is easy, condition may require a leak down test performed or disassembly.  Honestly, you are long in the tooth and perhaps need a valve job.  I can't say for sure.

Second, ignition has to be right and working.  Points, have to be gapped properly and timing has to be set properly.  As written, the advance mechanism has to work properly.  All components must be in good order.

Last thing is carbs.  As mentioned cables have to be adjusted and they have to be synchronized to work together at pull off and let off.

 

I will address the drive train as you asked.  When was the last time you had the input splines of the transmission lubricated?  I am clutching at straws but perhaps a sticking clutch plate could contribute.

All said, you have a bit to work with, where are you located at, you never know I could ride over and give a hand or have you come here.  I have tools and a shop, I also know a dedicated airhead shop nearby.  Good luck. St.

 

 

Beware! I do not suffer fools gladly! St.

 
Posted : 09/30/2023 06:47
Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

@14724

My 1979 R65 has the “bean can” with points and condenser. Sounds like I can take it apart and that I will find springs in there. But how to replace them when they are not a replacement part?

Richard says I should install electronic ignition. I see your point with respect to modern fuels. But if electronic ignition requires perfect wiring to operate correctly shouldn’t I replace the wiring harness too? My wiring isn’t a rat’s nest. Everything seems to work fine. But the harness is old. It probably has brittle insulation, fatigued copper, and iffy connectors here and there. I want to replace the wiring harness some day, but not right now. Maybe until then I should stick with points and condenser if they are more forgiving.

As for octane, I was under the impression that if an engine doesn’t ping then the octane you’re using is okay. No biggy, I’ll try better fuels and see if it eliminates the bucking.

By the way, I’m a leisurely rider. Owners of bigger models pooh pooh the piddly R65, but it has plenty of power as far as I’m concerned. Increased performance would not be a reason for me to get electronic ignition.

I’m wedded to this bike. I love it and I am sentimental about it. I’ve always done right by her to the best of my ability. I like working on her now that I'm retired. My challenge is lack of knowledge. I’ve never had an automotive class or a mentor of any sort. However, over the years I have accumulated BMWMOA tech articles and have kept notes and receipts. I understand her more all the time. I don’t want to have to start over again with a different bike (or wife)!

I changed my spark plug leads in 1988. Probably the caps too, not sure. I suppose 1988 is too long ago and I should do it again.

I’ve always kept my valves adjusted. The heads have never come apart. Should I get a leak down test? A valve job?

I recently put in a new clutch and had the transmission input splines lubricated, so that’s not causing the bucking.

I live in Bremerton, WA. I appreciate Steven’s offer of help but I believe you live in New York. Here in the Seattle area these days I do not have a mechanic I like. I take her to one of the dealers whenever I have to.

Thanks again, Richard and Steven!

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 09/30/2023 14:04
Richard Whatley
(@wobbly)
Posts: 2498
Member
 

Posted by: @18678

Richard says I should install electronic ignition. But if electronic ignition requires perfect wiring to operate correctly shouldn’t I replace the wiring harness too? My wiring isn’t a rat’s nest. Everything seems to work fine. But the harness is old. It probably has brittle insulation, fatigued copper, and iffy connectors here and there. I want to replace the wiring harness some day, but not right now. Maybe until then I should stick with points and condenser if they are more forgiving.

• BMW harnesses are very well made. If you have not spliced into the harness to add the kinds of accessories and "upgrades" that were popular in the 1980's, then your present harness will do fine. Of course, you'll want to start treating your harness connections, relays, and terminals with an electrical contact anti-oxidation compound (such as No-Ox-Id), but even if you replaced the harness tomorrow I would still tell you to apply the anti-oxidation compound as well. That's simply due to 50 years of water intrusion from riding in the rain and washing the bike. 

• If you're having trouble choosing between the $600 parts that will haul you back to the 1979 standard vs. $300 system to bring you into the 21st Century, then I can't help you.  🤣 

 

Posted by: @18678

As for octane, I was under the impression that if an engine doesn’t ping then the octane you’re using is okay. No biggy, I’ll try better fuels and see if it eliminates the bucking.

By the way, I’m a leisurely rider. Owners of bigger models pooh pooh the piddly R65, but it has plenty of power as far as I’m concerned. Increased performance would not be a reason for me to get electronic ignition.

• That's good. I have a friend with an R65 and it accelerates and corners much faster than my R100. They truly are nice bikes. 

• "Performance" is different things to different people. A modern electronic ignition will make your bike start easier, idle better and run smoother. You'll also proabably get better fuel mileage. 

• Your engine is proabably pinging on low octane fuel, even if you don't hear it. 

 

Posted by: @18678

I changed my spark plug leads in 1988. Probably the caps too, not sure. I suppose 1988 is too long ago and I should do it again.

I’ve always kept my valves adjusted. The heads have never come apart. Should I get a leak down test? A valve job?

I recently put in a new clutch and had the transmission input splines lubricated, so that’s not causing the bucking.

I live in Bremerton, WA. I appreciate Steven’s offer of help but I believe you live in New York. Here in the Seattle area these days I do not have a mechanic I like. I take her to one of the dealers whenever I have to.

• Next time you have the carbs off, you should do a compression test. Both cylinders should be within 10% of each other. That's all. No rush.

• The reason valve adjustment is critical on an Airhead is exactly because of the newer fuels. Leaded gas cushioned the valve as it seated, no-lead does not provide that. Thus valve seat wear can be faster. "Valve recession" is why Airhead valves always tighten up over time. Other than regular checks and adjustments, nothing else need be done to the valves or heads until you totally loose compression on one side. 

• I live in NE Georgia.

 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

 
Posted : 09/30/2023 16:35
Steven Rankin
(@14724)
Posts: 143
Estimable Member
 

Stephan, I did look on Max BMW's microfiche and I do see the advance springs are not listed.  That does not necessarily mean you can't buy them.  Things got a bit strange for the couple of years BMW put the points into the cans.   Personally I would open the can and see what you have.  A spot of grease is a whole lot cheaper than a new igniting system.  EME sells the parts for your points in a can, sorry I tried to paste the link but it would not on this forum?

If you are not having pinging, run what gas you have been.  LOL, the reason I hate points so much is my first BMW was a R75/7.  As the points wore, the bike would start to ping.  Of course it only started to ping while on a trip meaning I wound up a few times on my hands and knees adjusting damned points in a hotel parking lot.  So as soon as I could get rid of them, I did.  That does not mean you have to.  Properly adjusted, points work pretty well.

As for claims of "better" anything regarding electronic ignition, that depends on the ignition system.  The BMW stock ignition system doesn't work any better than well adjusted points in my long time experience.  MANY of the new replacement systems promise a whole lot of performance improvements but my experience shows otherwise.  They perform roughly the same as well adjusted points.  LOL, however, the problem with points is they go out of adjustment.  

The only electronic replacement system I have experience with that did show a tiny bit of performance improvement was as I mentioned the new Wedgetail system.  I installed one on my 78RS and did notice a tiny bit of starting improvement.  As for other improvement such as acceleration, I could not "feel" or notice it.  To be honest, it was a bit of money to change over from the Dyna point replacement system I had on the bike before.  The Dyna system offered no improvement in performance other than NOT having to adjust points, or changing point gap.

LOL, long winded write up.   bottom line, points are bad if you don't like adjusting them from time to time, don't believe all the hype the aftermarket companies post.  And seriously if you really need to change to electronic, go with the system you feel the most comfortable installing.  I can say in all honesty, the Wedgetail system so far is the top of that list.

Okay, on to valves and such.  I have to directly disagree with Richard.  Valve adjustment has NOTHING to do with modern gas.  Valve adjustment has everything to do with regular maintenance.   BMW valves need regular adjustment every 15K miles because that is how they were designed/made.  

Yes, in the past with some BMW heads during the conversion to unleaded gas there were problems with some of the models having valve seat recession and valve problems.  My belief is this is the early 80's bikes such as my 84R80RT.   BMW flubbed up and we owners found ourselves constantly having valves go out of adjustment faster than the normal.   So yes, I did have heads done and unleaded valve seats were installed.  Since then I have 200K on my heads with no problems.   On my 78RS, I never had problems.  I adjust the valves at the recommended interval.

So, if you are having idling issues, you could have a valve out of adjustment.  Or, with your mileage, you could have worn valves.  LOL unless a valve breaks, wear is gradual and may not be immediately noticed.  There is a slow decline in performance and perhaps the valves start needing to be adjusted more frequently than the recommended period.

A compression test is one way to go, a leak down test is better. With a leak down test you can hear the air escaping out of bad valves.

So a compression test that fails does tell a lot, it could fail due to rings or valves or both.  Only at a failure of either compression or leak down would I pull the engine apart.  

Good grief, I have written a novel.  First, pull the bean can apart and give the advance a check and lube.  check the points.  Look to EME for the parts.

 

Oh my, I just thought of something else!  What shape are your throttle cables in?  Sticking or worn cables may cause whacky action.

Yes, WA is just a bit too far for me.  Good luck, St.

 

Beware! I do not suffer fools gladly! St.

 
Posted : 10/01/2023 06:07
Joe Hall
(@joe-hall)
Posts: 70
Trusted Member
 

Just wondering, at 170,000 miles, have you ever changed the timing chain? 

 
Posted : 10/01/2023 07:33
Stephen Ladd
(@18678)
Posts: 23
Eminent Member Customer Registered
Topic starter
 

I put in a new timing chain at 58,000 miles. I replaced the throttle cables just recently. I've always had great luck with my points! They hardly ever go out of adjustment or get worn. The stock ignition system has been excellent (unless it is causing this bucking). My valves never go much out of adjustment either. Power is good and she idles fine.

Now the leading contenders for cause of roll-on/roll-off bucking are:

1. Worn drive shaft spring and coupler

2. Worn output splines in the final drive and rear wheel

3. Ignition advance (rebuild bean can)

(I doubt if these could be the cause but I should also get new spark plug leads and caps and do a valve leak down test.)

As for those three items I can do #3 but 1 and 2 look to be beyond me. Anybody know of a good airhead mechanic in Washington State or Oregon?

 

My first BMW was a 1971 R75. I've had my 1979 R65 since 1982. I've had a BSA Bantam and a Kawasaki 200 along the way too.

 
Posted : 10/01/2023 08:09
Joe Hall reacted
Steven Rankin
(@14724)
Posts: 143
Estimable Member
 

LOL, as time goes on and more information comes to light, other things can pop up in my mind as to possible solutions/areas to check.

First, don't get overwhelmed, start with the simple stuff first.   I am reading you take good care of your bike, that is a big plus.

One thing that just popped into my mind is have you taken a look at the diaphragms in the carbs lately?  To be honest, I have never gotten more than 50K out of them on my bikes.  Bing suggests replacing them every two years.  LOL, sorry Bing I don't agree. 

It is possible one of them may have gone bad, holed or weak.   If they are the originals, you can't go wrong and replace them regardless.    

I personally have never heard of a driveshaft spring going bad as long as fluid has been changed at a regular schedule and the bike has not been hammered in riding.   Not saying it could not happen, I don't recall one ever being changed at my friend's shop.

I just thought of a way to perhaps check the advance system.  I am thinking if the unit is sticking and not retarding upon RPM drop, maybe, with a timing light, you could see this?    If you rev the bike up to the full advance mark and when you let the throttle off, the mark does not drop back to the idle mark, the weights could be sticking or the springs could be shot.  Make sense?

I really don't like tearing things apart unless I have to and I encourage the same thing when I try to help others.  Check the two top items, ignition advance and diaphragms then go from there.   Good luck. St.

Beware! I do not suffer fools gladly! St.

 
Posted : 10/01/2023 09:08
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