1983 R100RT Bean can timing

[richr208]

I was hoping that a BMW mechanic could help me with a difficult problem I went for a short ride about two weeks ago and noticed that alternator light was flickering at lower RPM. a quick check with a voltmeter when I got home found it was not charging at all , removed the front cover and a diode fell out on the ground , one of the rubber mounting studs broke and melted the ground wire and also a resistor on the diode board , replaced the mounting studs . diode board , alternator brushes and new style voltage regulator, and it charges great 13-14 volts and light is out even at an idle , THIS IS WHERE THE REAL PROBLEM STARTS , being and licensed A&P ( aircraft) mechanic for the past 48 years I decided to check the timing (it was running great something to be said for the old mantra IF it works don't F-with it ) hooked up my snap on timing light and no timing marks could be found in the window , moved the "bean can " stop to stop and still no timing marks , pulled the plugs and turned the engine over using the 6mm alternator allen bolt got to the ot_ s mark and painted it white advanced to the Z mark and did the same , hooked everything up and got the wife to be my throttle master , and went looking for the marks again turning the bean can stop to stop and nothing no timing marks at 1200 to 3500 rpm's , never took the bean can off , that was yesterday,, this morning I pulled the plugs again and noticed that the engine was not on TDC when the OT|s mark was lined up with the line in the timing hole , I got it as close as I could to TDC compression stroke using a small rounded wood stick , maybe 2-3 flywheel teeth off and made another paint mark on a flywheel tooth , when it was as close to TDC as I could get it, I turned the engine about 75 degrees BACK to the OT mark , By now my head was spinning and I had to put a new blade belt on the mower and Forest Gump on the lawn for a while , and think about this some more , I bought the bike about five years ago and it had around 20K miles on it it has 34k now and I have rebuilt the carbs , steering head bearings and a few other things , I called a friend (Tod ) and he suggested that someone put the flywheel on one bolt hole off , five bolt holes is 360 divided by 5 = 72 degrees . Does this even sound right ,he thought someone might have removed the flywheel to replace the rear main seal , ? with 20,000 something miles on it ? , could the factory have got the flywheel miss installed ? I really don't want to pull the flywheel off just to find out , is there some kind of TDC tool like they use for two strokes , I have one I made for aircraft engines but it wont even come close , got out a one inch travel dial indicator and it wont work either, Does anyone make a TDC tool so I could find the true TDC and remark the flywheel ? I counted the flywheel teeth and it's ten teeth between the OT mark and the Z mark so if I could find the true TDC I could remark the flywheel , I was thinking of removing the left cylinder head and using a dial indicator directly on the piston and cutting a 4" disc out of brass shim stock and mounting it to the front of the alternator rotor and marking by using a pointer ? ANYONE having any ideas on this please let me know what your thoughts are , I have my Great Falls ticket and need to get it fixed ! Rich Rabe Middleton , Idaho or prabe50@ msn.com or text @ 1-208-880-9650

 

[20774]

Welcome to the forum! It sure does sound like the flywheel (for your model, it's called a clutch carrier/flywheel combo) might be off. Note that TDC is TDC regardless of compression stroke. Certainly when checking valve clearances, you need to find TDC on the compression stroke for that cylinder. But to get the right mark on the flywheel, TDC is just that...the piston has come to top dead center...both will be at TDC at the same time.

They make top dead center measuring devices. Various speed shops, even Harbor Freight sells one. Find one that will screw into your spark plug hole. Basically, you will use the device to find the point in the crank movement between when the piston falls away from the maximum throw. There will be a small range of degrees where the piston won't move. The measuring device will show that to you. The point in the middle is then TDC...that's where the mark should be. I believe that the S-mark should be 6 degrees BTDC. On my /7, the tooth spacing is right at 2 degrees per tooth...likely the same for your '83. That's the minimum you need in order to get the bike timed and valves set. I'm not certain at this point where the F-mark (or Z-mark) should be for your model...probably something like 39 to 43 degrees BTDC.

Lots to read about here...Snowbum has a section here on how to determine TDC:

https://bmwmotorcycletech.info/F,OT,S,Z.htm

 

[stevenrankin]

Idle and mark

OKAY while I am not a professional mechanic, I have dealt with a similar problem when my friend bought a 84 R80RT the previous owner had replaced the oil pump o-ring on and mis installed the flywheel.

1200 RPM is a tad high for idle, perhaps this is the reason the OT mark is not showing up? At 3000 RPM the Z mark should be showing up in the window. Now if neither of them are showing there is a possibility the previous owner did install the flywheel wrong. I can say for certain BMW didn't. Never underestimate what a previous owner will or can do.

While the mileage is low, the age is not so perhaps the PO, did replace the main seal at one time and was off when reinstalling the flywheel.

Luckily, airheads are pretty easy to get to the OT mark using an Allen wrench as you mentioned. It is easy to see into the spark plug holes to see when the pistons are at OT. Both will be at OT the same time but only one will be at compression. You can clearly see when the pistons have reached OT and start to withdraw after OT. One side or the other will have both valves closed at compression at OT. Since the bike is running, the cam and crank are timed correctly. I mean the pistons are at OT and one side is in compression. Does this make sense?

The only time to worry about which of the pistons is on compression at OT is when a valve adjustment is being done, timing for ignition doesn't matter as both plugs fire at the same time, a lost spark system.

If you have a trip planned and don't want to mess with tearing the bike down, I think you will find it will run just fine as long as it is not pinging or performance is off or dodgy. The bean can should be just about centered for a starting setting.

Two major problems with ignition timing being off would be loss of performance if two far retarded but far worse would be pinging under acceleration or load.

The only other concern I would have if the flywheel is off a hole is if the PO when he put the clutch pack back together improperly distributed the weight of the parts. There are three white marks for the three heavy spots on the flywheel and clutch assembly which have to be lined up properly. I have seen people line the marks up and re install which is not the way to do it.

If the bike is running fine, not pinging, wait to tear it apart during the off season or if something else comes up. That is what we did with my friend's bike once we figured out why the timing marks didn't line up. We set the timing by ear and feel, riding it until winter then we tore it down and replaced the main seal which needed replaced and should have been replaced when the oil pump seal was replaced. St.

 

[beemeruss]

it had around 20K miles on it it has 34k now. I really don't want to pull the flywheel off just to find out ,

Welcome rich. I believe that you are on the right track in surmising that the flywheel is off by one bolt hole. There are good reasons to open it to daylight to confirm. It is often suggested to lubricate the transmission input splines around 5 years anyway and your clutch, rear main seal, and oil pump O-ring should be inspected at the same time. Any time spent on a workaround may be better spent doing the above so that you may establish a benchmark for future. Given your background you probably already have a maintenance log established. You would really be doing yourself and future owners a favour. It is not too challenging of a task. Your profile does not say where you live but if there are airhead owners living close by one may offer to guide you and perhaps lend you the few specialised tools required. You would only need to get TDC in the ballpark before disassembly and if it is indeed out of phase by by 72 degrees then you could nail the correct TDC, once and for all. As steven has mentioned, it is also important for correctly setting valve adjustments. Just my $0.02

Russ

 

[RPGR90s]

Timing

I was hoping hat a BMW mechanic could help me with a difficult problem I went for a short ride about two weeks ago and noticed that alternator light was flickering at lower RPM. a quick check with a voltmeter when I got home found it was not charging at all , removed the front cover and a diode fell out on the ground , one of the rubber mounting studs broke and melted the ground wire and also a resistor on the diode board , replaced the mounting studs . diode board , alternator brushes and new style voltage regulator, and it charges great 13-14 volts and light is out even at an idle , THIS IS WHERE THE REAL PROBLEM STARTS , being and licensed A&P ( aircraft) mechanic for the past 48 years I decided to check the timing (it was running great something to be said for the old mantra IF it works don't F-with it ) hooked up my snap on timing light and no timing marks could be found in the window , moved the "bean can " stop to stop and still no timing marks , pulled the plugs and turned the engine over using the 6mm alternator allen bolt got to the ot_ s mark and painted it white advanced to the Z mark and did the same , hooked everything up and got the wife to be my throttle master , and went looking for the marks again turning the bean can stop to stop and nothing no timing marks at 1200 to 3500 rpm's , never took the bean can off , that was yesterday,, this morning I pulled the plugs again and noticed that the engine was not on TDC when the OT|s mark was lined up with the line in the timing hole , I got it as close as I could to TDC compression stroke using a small rounded wood stick , maybe 2-3 flywheel teeth off and made another paint mark on a flywheel tooth , when it was as close to TDC as I could get it, I turned the engine about 75 degrees BACK to the OT mark , By now my head was spinning and I had to put a new blade belt on the mower and Forest Gump on the lawn for a while , and think about this some more , I bought the bike about five years ago and it had around 20K miles on it it has 34k now and I have rebuilt the carbs , steering head bearings and a few other things , I called a friend (Tod ) and he suggested that someone put the flywheel on one bolt hole off , five bolt holes is 360 divided by 5 = 72 degrees . Does this even sound right ,he thought someone might have removed the flywheel to replace the rear main seal , ? with 20,000 something miles on it ? , could the factory have got the flywheel miss installed ? I really don't want to pull the flywheel off just to find out , is there some kind of TDC tool like they use for two strokes , I have one I made for aircraft engines but it wont even come close , got out a one inch travel dial indicator and it wont work either, Does anyone make a TDC tool so I could find the true TDC and remark the flywheel ? I counted the flywheel teeth and it's ten teeth between the OT mark and the Z mark so if I could find the true TDC I could remark the flywheel , I was thinking of removing the left cylinder head and using a dial indicator directly on the piston and cutting a 4" disc out of brass shim stock and mounting it to the front of the alternator rotor and marking by using a pointer ? ANYONE having any ideas on this please let me know what your thoughts are , I have my Great Falls ticket and need to get it fixed ! Rich Rabe Middleton , Idaho or prabe50@ msn.com or text @ 1-208-880-9650

Remember that on an Airhead, just removing the spark plugs gives you a decent view of the top of the piston when searching for TDC. As others have said, it sure sounds like the flywheel was removed (rear main seal, oil pump seal replacement) and then installed 72 degrees off. Not a big deal. Just establish TDC with paint as you've alluded to and then rotate the engine about 8 degrees and make a new "S" Timing mark.

If you like, I can tell you how many flywheel teeth separate TDC and OT when I get home from vacation on Saturday. I have a spare flywheel in my cabinet. Otherwise, you should be able to buy an indicator from Harbor Freight that you could attach to the front of the crankshaft (alternator side) and do some degreeing from there.

 

[richr208]

Thank you very much for all of the good information , I have overhauled several airheads both mine and others and had never run into this type of problem
before . I have a lathe , souix valve grinder , both TIG and MIG welders and have overhauled about every type of engine from steam , V16 Cummings tug
boat engines , large V12 cat. industrial NG engines and on and on , I cant remember one where the timing marks were this far off , most dampeners or flywheels
are clearly marked , or indexed with a keyway or dowel pins . Last night after reading some of the excellent information in the links ( Snowden) I am 100% certain that the
flywheel was installed 72 degrees off . I ordered a 14mm TDC indicator and a nice 6" dia. degree wheel last night and will get the flywheel remarked . There
also may be a balance issue as many flywheels and crankshafts are balanced as an assembly , This didn't seem to be an issue as the bike didn't vibrate any more
than others I have ridden . Thanks again for all the positive help , Next fall or winter I just might tear it down and re-index the flywheel correctly but have
too many things going on now . Stay safe and believe in science !


Rich Rabe Middleton , Idaho

 

[stevenrankin]

Yep ride it

Yep, wise choice ride it and do the work later. Just out of curiosity why would you invest in tools you won't or don't need now? I mean it is pretty easy to determine if the pistons are at OT when doing a valve adjustment, no fancy tool is required. As for timing, same thing goes, if it runs fine, once it is set unlike points, it won't need to be changed.

I guess I work from my late uncle's advice on timing a car from back in the day when I had to change points all the time. "set the timing to just about where it starts to ping then back off a bit". Yes, it is far from scientific and not a taught method but, for a long time it worked on my chevy. When I finally consigned that car to the scrap heap due to major body and frame rust, the new car had electronic ignition. Set once, I never had to mess with it again.

Anyway, just my two cents, at my age. I am starting to give away tools rather than accrue them.

While the miss aligned flywheel and clutch carrier system may not cause problems now, I myself would when I got time to do so, would correct it. Same goes for the flywheel position. I am picky and believe things should be done right and correct however sometime over thinking something just costs more and adds more work. Winter is the time to make things right or, a week of rain. You CAN remove the flywheel and make things right in a day's worth of labor. Brook Reams has some very good videos pertaining to the work involved. Be thankful you have an airhead and not an oil head or newer. St.

 

[PoorUB]

I find it ironic that a techie company like BMW would not stagger the bolts in the flywheel,, or a dowel pin to make sure it goes on only one way.

 

[stevenrankin]

Directions

Seems the first thing the BMW repair manuals spell out is to make sure the pistons are at TDC and line up the OT mark before installing the flywheel. Adding a dowel or pin or some such thing would have cost BMW extra money out of their pocket to fix a problem that is easily solved by first, a mechanic having some skill and knowledge as well as following the repair directions available in either the original BMW literature or in Clymer or other publications.

In all honesty, how many people have come across this problem out of all the thousands of bikes BMW built and how many mechanics have removed and re installed the flywheels improperly? Not enough to justify I bet, in BMW's account the extra money to machine a dowel or some sort of failsafe to assure the flywheel is properly installed. It was not cost effective at the time for BMW to make such a change.

Also, BMW really doesn't like non BMW trained mechanics working on their products.

Sorry, I have had my flywheels off of my bikes a dozen or more times over the past 40 or so years and have never had a problem determining how to properly position the flywheel in my 77, 78 and 84 bike. I am not a trained BMW mechanic but I do have common sense and don't get in a rush. To be honest even if I did find I had mistakenly installed it improperly, it does not take a whole lot of work to take things back apart again and correct the problem.

As I said thank god it is not an oil head. I watched a friend do a clutch replacement on one of them and to be honest, I will never own one after seeing the absolute nonsense and trouble involved with the job.

Previous owners can be the bane of BMW owners. Like my friend, who bought a bike from someone who had no business changing the oil pump seal while neglecting to change the rear leaking main topped off by reinstalling the flywheel improperly, frankly, he should not have been allowed to pick up a wrench. Granted sometimes generic repair manuals are fuzzy and perhaps difficult to read but someone with common sense should have no problem using them IF they have a fair amount of mechanical ability.

Sadly there are people out there who despite having dowels or pins or something else to ensure the flywheel is installed correctly will still screw things up. St.

 

[PoorUB]

It wouldn't cost them anything to stagger the bolt pattern.

I wonder how often this happens. I haven't been on the forum very long, 2-3 years and this is probably the third time I can think of where it happened.

 

[jhall]

Bolts Not Staggered - Unbelievable

It wouldn't cost them anything to stagger the bolt pattern.

I wonder how often this happens. I haven't been on the forum very long, 2-3 years and this is probably the third time I can think of where it happened.

I too, find it hard to believe the bolt holes are not staggered. Even my 1956 Studebaker has staggered flywheel bolts. No excuse for such poor engineering.

 

[52184]

And yet there are countless shop and shade tree mechanics who have correctly installed the flywheel/clutch carrier on BMW motorcycles. Translating a poor assembly job that was likely performed with little or no prior research into an engineering failure is a pretty long stretch, I’d think. Don’t get me wrong—I have my own list of engineering changes I’ve wished for, but this isn’t one of them.

Best,
DeVern

 

[pglaves]

A non-symetrical hole and bolt pattern creates a balance issue.

 

[PoorUB]

Moving one bolt hole over .040" won't create much of an imbalance with the small diameter of the bolt flange, and it can be easily accounted for in production. It can be dealt with when the crank is balanced during machining and not add one cent to production costs.

An asymmetrical bolt pattern on flywheels has been used often over the years on various engines.

 

[stevenrankin]

So why

So why is it BMW's responsibility to correct somebody's mistake which could easily be avoided?

To be honest, this thread is drifting off the original subject. I will admit my role in the shift, I am not afraid to say, "Some people should NOT be allowed to work on any kind of mechanical device". Despite factory safeguards, someone will always find a way to mess something up and pass the problem onto the next owner.

Looking at the answers to the post there are good suggestions and a course of action the original poster is taking to correct his problem.

A while back, I was accused of stirring up trouble and being mean. Maybe I am, I just remember the adage "you can't fix stupid".

Of the thousands of airheads out there, a tiny percentage have had the flywheel installed improperly after having them removed. While I HAVE never done this, nor personally am friends with anyone who has, I have seen it done, and knowing the mechanical skills of the person who did it only reenforces my belief some people should NEVER work on things. Just because someone thinks they are a mechanic doesn't mean they are or should be.

There are a lot of reasons why BMW didn't arrange the bolt holes differently or put in some kind of one way set up, it makes sense and yes OM companies did. Bottom line, BMW never wants or expects the small minority of hacks to be working on their products.

I have seen people weld things together because they could not properly align gears or pulley and were too lazy or stupid to do things right.

I hope the original fellow posting this question and concern has enough information now to fix his problem. He unlike a tiny minority is a professional mechanic. I bet when he gets done with fixing his problem, it will never happen again. St.

 

[PoorUB]

Pretty sure the OP will get it figured out once his degree wheel shows up. One reason I don't feel badly about the thread drift. With his experience he should be able to find TDC, mark it, and add a second set of timing marks if that is what he decides.

 

[richr208]

Fixed the bean can timing problem

Thanks to all for your input , except to the one that suggested that I was entering dementia for buying more tools , I got a small degree wheel
and a real cool spring loaded 14mm TDC indicator , Several made comments about looking at the pistons to determine TDC , TDC and adjusting
valves etc. . Marking the flywheel for timing requires a whole different game plan and I can briefly explain why , If you have ever looked at a camshaft
automotive or otherwise about half of the cam lobe circumference doesn't cause any lift , on any GM V8 engine to set the valves you put the engine
on TDC #1 cylinder and adjust half of the valves , turn the engine over 180 degrees and adjust the other half of the valves , only two cylinders are
at TDC ...on a airhead it doesn't really mater if the cylinder is on TDC when adjusting the valves < it's just easier , for example if the cylinder was
in the middle of the exhaust stroke I could adjust the intake for that cylinder , if that cylinder was on the compression or power stroke I could adjust
both valves almost any where before or after TDC . A lot of people get hung up on what is says in the book without really knowing why . When a piston
is coming up to TDC and just after going down there is a slight dwell time , with a hardwood dowel in the spark plug hole it's just
not close enough to mark the flywheel . I have done this on P&W 985 radials ,for magneto timing and the procedure is the same for any four stroke engine
in marking the flywheel or finding true TDC , We had an 18mm device we made and it had a 1/2' diameter rounded end that contacted the top of the piston , a pointer
ran along a scale that we covered with masking tape someone would rock the prop back and forth, the first mark on the tape was when the piston was
coming up to TDC and the pointer stopped moving ( mark the tape ) the second mark with a real steady prop rocker was just when the piston started down
and we usually checked our marks several times moving the piston up and down , measure the distance between your marks, in the middle is the true
TDC , and that's what what I did with the degree wheel ,put painters tape on a part of it , put pointer on it from a magnetic base , marked the tape found
the middle of the two lines and marked the flywheel (TDC) , my little owners manual says 28 degrees full advance and it was easy to set the pointer to zero degrees
advance the flywheel to 28 degrees and mark it again & I set the timing at full advance , I could care less what it is at idle. It runs good again and I
know the timing is where it is supposed to be .
Thank you again for all the good ideas and I marked the good references as favorites , I am sure I'll be back. After working in the trades for over 45 years
I might know 10% of the knowledge involving mechanical repairs , as a mechanic , machinist, certified welder , hoist and crane inspector. it takes
time and money to keep up with the electronics and computerized engine controls (ie. scan tools) MY next project is building a stroker motor for my Jeep .
See you in Great Falls .
Rich R, Idaho

 

[stevenrankin]

Dementia

Ah, I never implied an entering of dementia regarding buying more tools. I was trying to make a point there was and is no reason to over think this problem, and to spend money on more tools when they are not needed to solve the problem.

Chevy V8 engines and aircraft radial engines are a lot more complex than a airhead twin. So, yes, they are going to require different methods of doing routine maintenance and yes, I can see buying a degree wheel/ special tools, marking the flywheel, and doing all sorts of things to make working on them easier. I would do the same and if I were still working on more complex engines.

Now I am sure you mean well when you wrote the discourse on adjusting valves. I agree with it 100% it really is not necessary to have the engine on the compression stroke to adjust airhead valves.

Please understand, one of the things I was trying to convey is BMW writes repair manuals, teaches it's mechanics and cooperates with aftermarket repair manuals in order to get repairs done right.

In YOUR case, the previous owner was either careless, inattentive or just plain stupid to put the flywheel back onto the bike in the wrong position. He didn't follow the rules and took a shot cut or just didn't pay attention.

Yes, I follow the instructions most people do and yes a large number of us don't understand why, we just do it because BMW wrote it up as procedure and the procedure works.

I am happy you have solved your problem in the way you did and you are happy with the results.

I don't have 45 years in the trades, I myself, have a very mixed career. Oddly enough, at one point, I did consider a career in aircraft power plant repair, (not military, I am 4F) it was a coin toss moment AP on one hand, on the other a career with a local film firm. The film firm won the toss and I ended up in R&D for the majority of my work life. For a long time, I worked on bringing some of the finest B&W photography films, papers and chemicals to the world. A far cry from turning wrenches, lol. St.

 

[Omega Man]

Successful repairs are most easily accomplished when attempted repair procedure makes “sense” to the person attempting the procedure. As one works their way through a problem, lessons are learned and a knowledge base is built.
Great you figured it out
Thanks for letting us know how you made out.
OM

 

[PoorUB]

To find TDC, I always put in a steel piston stop, rolled the engine over until it made contact with the stop, and record the degrees. Then roll the engine over the opposite direction until the piston contacts the stop and record the degrees. In the mid point on these two measurements is TDC.