Logbooks of '72 R75/5, '79 R100T, '82 R80G/S Paris-Dakar, '93 R100GS PD, '71 CB750 and others, a.k.a.
1990 R100G/S Franken Project
Last updated July 2008
Where it all started ...
Second thoughts on the project
Timing Chain
Cylinder and Pistons
Clutch
Cylinder and Pistons (again)
Gearbox
Fitting a monolever swingarm to a GS frame
Monolever swingarm extension
Second round on sourcing
Digital Cockpit
Connection Rods
Wheels
Triple Trees
Electrics and Wiring Loom
Exhaust System
Assembly starts ...
May 2006:
I was always dreaming of building a Frankenbike with the "Best Of" 33 years Airheads, 1969-1996. Here is what I have acquired so far:
GS frame and subframe
complete GS Front End
a 1983 R80RT frankenbike
miscellaneous parts to make a complete bike
Here is a description of all parts so far:
July 30, 2006:
I am not exactly sure where this project is heading as it has not really started yet. But it already looks like something.
August 20, 2006: Toughts on the project
Where is it heading? I am starting to get the general idea: a R100ST is what I am trying to build here. The GS frame gives me the opportunity to go offroad with a different set of wheels/tires. I will be having a monoshock swingarm with a 37:11 final drive, don't need speed here in Northamerica, I am more of a "torque" person anyways. I will use a GS rear hub with an 18' Akront/Sun or Excel, the front will be a 19' rim on a GS hub. Tires: I guess I will go for slightly wider tires, 100/90-19 in the front and 130/80-18 in the back. GT501's are a preferred choice, something that sticks. 2.15' wide rim for the front, up to 3.50x18 for the back, laced to the GS hubs by the folks at Woody's Wheel Works should do just fine. That, together with a Wilbers/Oehlins supported monolever swingarm and the GS front end with progressive springs (or better a RaceTech 'Gold Valve' cartridge emulator should guarantee a very nice and solid chassis. The subframe will (or may) be a modified /7 subframe to get the hinged seat pan working. Might as well be a GS sunframe. A Corbin gunfighter will be my choice (just because I have one!).
December 2006:
Things are moving along and the fact that I acquired a blue-white windshield, white headlight housing and fender (featuring the 1988-1990 Alpine White/Blue Scheme Code 642) had a lot to do with the decision to build the bike as a G/S with a blue-white colour scheme:
Mind you, a 1991 R100GS never had a monolever rear end, so I am going to dubb this newest project of mine in good ol' BMW tradition:
R100G/S
When it is finished, it should very much look like this 1990 Alpine White Color Scheme (Code 642), except for the exhaust (which is planned to be a stock BMW 2-in-2) and the rear suspension which is based on a monolever, the color scheme is the 1990 Alpine White Scheme Code (642).
Spring 2007: Second thoughts on the project
- I acquired a couple of parts during the winter, amongst them a very nice complete R100R exhaust. Polishes up very nicely and most inmportantly, fits a GS and allows the use of equal size bags! That and my recent runs on the G/S made me think: maybe I should make this baby my long distance tourer instead of eyeing a Flying Brick or an Oilhead.
- Maybe I should acquire the 33/11 monolever final drive, as it makes long distance travelling bearable, from a RPM point of view. I had the same setup on my R100T and it was the perfect tourer. But I might also look into the possibility of adding a long 5th gear to the tranny.
- The monolever rear shock idea does not work with the GS frame, the design of the upper mounting point is different: where on the G/S the shock (360mm) runs from the center of the right downtube to the center of the swingarm, the monolever shock (410mm) runs sort of offcenter from the outside of the rear right main frame downtube to the finaldrive shock mounting bolt, I have therefore modified a monolever rear shock, shortened by 50mm and will see how that goes.
- I am also contemplating to go for a thumper as my local dirt ride: an XT500/600 comes to mind. The G/S is just to heavy for that. That and this new R100G/S would make my R80G/S surplus to requirements, sort of. So it will be sold.
August 2007: The fun begins ...
I am tackling the engine first: after a quick rework of the carbs, back last year, I had the engine running. It wasn't running too bad, a little rough but I did expect that because it wasn't properly tuned.
Checking the timing chain is my next task. I expected it to needing replacement, the condition I found it in certainly supports that:
Here is my opinion and way forward based on the findings:
- the (upper) crankshaft gear doesn't look too good, so time to buy that Kuko puller I always wanted and replace bearing and crankshaft timing gear in situ
- the (lower) camshaft gear looks fine, hardly any wear, I will leave it as is (I know it is a controverse decision whether to replace all gears or not, but I think the wear is so little that it will not reduce the lifetime of the chain considerably)
- the timing chain (see video) - definitely a gonner ... to be replaced
- the timing chain tensioner and guide - always replace with new chain
The engine was stripped down anyways, so let's prepare for the operation and get the patient on the bench, strap him down and get the Dremel ready:
I got a 3-jaw 4in Bearing puller and removed first bearing and the crankshaft gear:
The crankshaft gear isn't completely toast yet, but is being replaced. The chain is knackered, as you could see on the above video. Got myself a drift, a 1 1/2 x 3 in steel pipe, availabIe in Home Depot's plumbing section. Heat up bearing and crankshaft gear, a bag of ice to cool the crankshaft and the job's half done. I did not support the flywheel center, so I might have buggered bearing and thurst sleeve completely ... but I do'nt think so.
The whole procedure didn't take longer than 30min. The below is my way of dealing with the masterlink: connect both ends from above with the old masterlink, install the new masterlink from the rear (watch those openings, that is where these things disappear in the engine cavities!) and assemble coverplate and C-clips:
Done.
Next thing was loking at heads, cylinders and pistons:
- the heads came off easily, valve heads and rocker arms show no pitting, exhaust threads are fine, will get a valve spring compressor and examine the valves, guides and seats later
- the pistons are the low 8.2 compression type, but I found some nasty surprises on the cylinder walls, "holes" in the Nikasil coating:
So, those holes don't appear to be rust pits, they appear to be material flaking off. There have been reports that the first engine using the Nikasil coating had problems withj material flaking off. Given the fact. that this is one of the firstR100CS engine (#6188056, Nov 1980) and probably even one of the first after the introduction of Nikasil coated cylinder walls, I might have that problem. I will look for a used pair of jugs with high comp 9.5 pistons to replace those. If I can't find them in time, I will probably run the engine with those "flaky" jugs, they may run forever, you never know.
Next on the list is the clutch: it was very difficult to remove. t first it wopuld not budge, even soaking and a mallet would not help. In the end, I had to pry it off:
- The parts are very rusted, so this engine was sitting for a long time. However, first assessment of backing and pressure plate shows very little if no wear, apart from the pitting. So I will attempt a very good non-abraisive cleaning with nylon pads, measure them and decide then, whether they are still usable. Even if pitted, I will attempt to use them, and only replace the friction plate.
The flywheel teeth look hardly worn as well, which points to a low mileage engine.
- It seems by the oil-soaked dirt that either the rear engine seal or the oil-pump o-ring was or is still leaking. So, that has to be taken care off befopre re-assembly.
I cleaned the clutch parts up to see whether they can be reused:
I looked a bit more closely at the pistons and wrist pin bores:
I guess, that is for the barrels and pistons!
End of September, I got lucky on eBay Germany with a set of barrels off a 1979 R100S with 80.000km (50.000mls) and a set of matching 9.5 pistons. The seller was willing to ship to Canada, so they are here:
Very good condition of both pistons and barrels, no scoring inside, very smooth, could turn out to be a very good deal.
December 2007:
I am looking at the tranny from my 1982 G/S that got busted during my 2006 Transamerica Trail Trip: completely scrap, said Bruno. The gearbox has a kickstarter which can be of help in emergency situations. I decided to give it a complete makeover (I leave that to the experts: Bruno's Machine and Repair) and have it modified to the latest design plus add one significant improvement:
- new helical gears with the new and improved 17.5deg mesh angle have been used
- long 5th gear (HPN) installed
- all new seals and bearings
This new gearbox should be quieter with easier shifting and subsequently reduced wear. We will see about that!
Added March 2008: Since I will not be using a stock speedo, a little gimmick is needed to first, close the opening and second, provide more generous venting without getting the tranny flooded when submerged:
The 1990 GS frame was intended to be fitted with a monolever shock and swingarm, like the 81-86 G/S. I used a 1987 monolever RT swingarm and had a very sturdy bracket welded to it. Since I had my gearbox back from Bruno's it was time to dry-fit the swingarm to look at various things:
- the lower shock mount bracket location and dimensioning (pictures later)
- clearance of the swingarm if moved to the far left (wider tire)
- clearance of the extended driveshaft inside the swingarm housing with a rear drive fitted (pictures later)
- check clearance of 130/80-17 tire (laced off-center) (tire hasn't arrievd yet)
So I fitted swingarm and a dummy (K100) shock and found that the swingarm is angled a lot more than stock. To the extend that the u-joint grinds in the swingarm! What's going on here?
So, off on ADVRider I went to get dimensions as I sold my own 82 G/S a couple of weeks. Thanks to woodgrain and TEXASYETI, I was able to find the problem. A couple of sketches first.
I did not realise that the top shock mount location of the 88-95 GS was about 30mm (1.25in) lower than the 81-86 mounting point. What did that do to the lower shock mounting location: it needs to be moved by roughly 25mm! I used the good old papermodel to visualise:
What does that mean in plain numbers:
|
| 88-95 RxxxGS | Description | 81-87 R80G/S
|
| 46mm | Upper shock mounting hole to top of bracket "a" | 22.34mm
|
| 55mm | Upper shock mounting hole to frame (rear of tube, measure tangential) "b" | 54.25mm
|
| 76mm | Overall bracket length to the joint with frame "c" | 78.40mm
|
| 302mm | Distance from Bracket (joining the frame) to center pivot bolt "d" | 309mm
|
| 260mm | Distance from upper shock mounting hole to center pivot bolt "e" | 287mm
|
| 312mm | Distance from bracket outer end to center pivot bolt "f" | 314mm
|
|
|
Now, let's use some more sophisticated way of showing the difference:
Learned something new today!
Fitting a monolever swingarm to a 1990 GS frame is one thing, extending the swingarm at the same time another. I deemed the
extension necessary, because the (GS) paralever swingarm is 35mm longer than the monolever of the G/S. That alone, with a
stock GS front end, would lower the rear end. Therefore I decided to extend the swingarm moderately by 30mm. I calculated the
force at the swingarm pivot point to increase by about 30%. Since the Paralever GS uses the same frame, I am taking my
chances and not reinforce that area on the frame. At the same time, the extension also requires a 17% higher spring rate of
the rear shock, because of the change of the levers and dynamics. I found the formulas on the internet.
Now that I knew what needed to be done I started work on extending the swingarm which turned out to be pretty easy: I had
an adapter fabricated (rather than cutting the swingarm and welding a piece of tube inbetween):
I considered the lower shockmount pretty flimsy and had this mount modified with real metal bracket rather than 'folded' sheetmetal:
Next up was the driveshaft, a much more difficult undertaking: my machinist had basically two ideas:
- Shrink-fit, pin and weld an 'outer' sleeve
- Shrink-fit, pin and weld a 'male-to-male' spacer
Unfortunately our first attempt, the outer sleeve was interfering with the diminution of the swingarm and could not be made
to work.
Our second attempt was the male-to-male spacer method and obviously that worked perfectly. So, as per the above drawing, a
shring-press-fit was used as means of interconnect with vent bores for the air trapped inside before the spacer is pressed in. The spacer was then pin'ed and welded. The whole assembly was then smoothed out on the surface so that no sharp corner or edges and weld beads exist.
Looks like it was never touched. Unlike the HPN solution, the cush drive was maintained. Radial runout was measured before
and after, the driveshaft runs true.
It is very likely that this method will work on 2in or 4in extensions just as well. Whether it will hold up in real life remains to be seen but I am very confident that this won't break or shear.
Now, it was time for dry-fitting: first the swingarm with the near rear wheel (laced off-center by 1/2in) and the wide (126mm) wide tire ... perfect, every thing fits as planned. 8mm clearance between tire and swingarm, great!
Next, dry-fitting everything with the swingarm extension ... ouch, the tire rubes the swingarm! Hu? Upon closer inspection I realised I did not take into account the change of shape of the swingarm to accommodate the cush drive. So, the tire was rubbing there. Again, my machinist had the right idea: a piece of the swingarm was cut out and a steel plate welded back in. That fixed the problem.
Now, here we have the finished result:
Clearances are perfect:
- tire width = 126mm (Kenda 761 Dual Sport)
- clearance tire to Ohlins shock = 6mm
- clearancde tire to swingarm = 8mm
January 2008:
Still sourcing parts:
- new Ohlins rear shock BM317 with custom setup for rider height and extended swingarm (30mm)
- RaceTech Gold Valve for front forks
- new aftermarket headlight, clear cut prismen glas, 8" diameter
- HID H4 -> Xenon light conversion
- a set of LED indicator bulbs and a new relay capable of running either LED or standard bulbs
- LED tail- and brakelight
- a variety of AMP SuperSeal connectors to replace the old Mate 'n Lock on the wiring loom
- a used clutch lever assembly (can't find mine anymore!)
- a used 4-piston Brembo caliper from a 1999 R1100S to replace the old 2-piston version and improve front braking
- a rectifier regulator from John @ Euromotoelectrics to replace BMW stock diode board and voltage regulator (which will however remain installed as a backup), I will stick to the stock 280W stator for now
- brandnew Panasonic Sealed Lead Acid Battery (LC-X1228P) from Digi-Key
- CC Products R100GS fork brace (!)
- Trailtach Vapor Digital speedo with tach, air temp, speed sensor and idiot lights
- custom toolbox (filling the space under the seat completely)
- single seat and rack
- Acerbis Baja front feder with aluminum reinforcement
- BMW Speedster windshield
- Digital blue LED Voltmeter (click here for datasheet)
- an OMEGA ignition ... what else!
- a R80ST bikini fairing that I might extend with the K75C windshield to get the same protection I had on the G/S (click here)
- Hyper-Lite�, flashing LED brake lights
- more to come ... maybe
Worked on a couple designs for the planned digital cockpit (click on image for original size pictures):
Checking the connection rods (conrods):
To get them off you need a special tool: a long XZN socket #10 (I just bought the key, it fits a 10mm socket!), click here for Hazet datasheet, available at good hardware stores, Jeff on ADVRider sells them too: http://www.northwoodsairheads.com/Tools.html.
It is fairly easy to remove the conrods: just loosen the bolts (use new ones for assembly), wiggle out the conrod (two locating dowels!) and mind the end cap (clamp):
The bearing shells can be carefully pried out, no excessive force, just a little help at the locking tab:
When you click the pictures to see details in high resolution, you will see that one pair of bearing sheels has light scoring, the other looks worn, but in a weird way, it almost looks like pitting. I will replace both.
I also measured the big and end and small end and compared it against the spec.
| ConRod Big End I.D. less bearing shell (2 measurements 180� apart) | ConRod Small End bushing I.D. (2 measurements 180� apart) | ConRod Width (6 measurements in 60� increments) |
|---|
Specification | 52.00 - 52.015 | 22.015 - 22.020 (max 22.040) | 21.883 - 21.935 | | |
Specification | 2.0472 - 2.0478 | 0.8667 - 0.8669 | 0.8615 - 0.8636 | | |
| ConRod Left measurements | 52.00, 52.02 | 22.05, 22.05 | .8625,0.8625, .8615, .8625, .862, .8635 | |
| ConRod Right measurements | 52.01, 52.02 | 22.05, 22.05 | .861,0.861, .8611, .8615, .861, .861 | |
| Initial decision | OK to only replace bearing shells | replace both bushings | OK, no actions necessary | |
The new small end bushings were machined to fit the wrist pins, very snug fit at around .006 clearance:
Woody's Wheelworks did an amzing job on the rear wheel (17x2.50in Excel rim laced 1/2in offcenter to stock GS rear hub) and the front wheel (21x1.85in Excel rim laced to stock GS front hub).
The Kenda 761 Dual Sport is 127mm wide which will clear the swingarm just fine (Metzeler Enduro 3 is 113mm) as the rim is laced offcenter a bit less than 1/2in. Dry fit to follow when the front wheel arrives.
Click on pictures for higher resolution ...
Banged up triple trees:
Back in 2006, I bought a (supposedly straight) Airhead GS front end including wheel/brake rotor/caliper/etc from a Bumble-Bee from Germany, which was originally intended to be used on the '82 R80G/S that I refurbished at the time. That never happened, I kept that bike stock.
===>>>
Now, they will be used on this project, meanwhile de-Bumble Bee'd and all new plastic parts and bushing in conjunction with a
Race Tech Gold Valve, but that set aside, my first dry fit was a disaster: the fork tubes were running out badly about 1/8in
at the bottom. That triggered me to inspect the lower triple tree very carefully and low and behold, one steering stop was
severly damaged, not yet sheared off, but close. Now what?
Well, time to visit my friendly local machinist Richard and he had the right ideas:
First, he took the steering stem as a reference and created a new plane perpendicular to the stem and machined it
accordingly. With that new reference, the tube bores were rebored and oversized to accept a sleeve.
Overall, a painless exercise, it created a perfect fit for the tubes and ensured their parrallelity (?) in both X- and Y-plane. It remains to be seen what happens when everything is back together. It should be a perfect fit though.
Electrics and wiring loom:
Having had the pleasure to help others (and myself) out on the road, I have thought long about how to equip the bike (especially when it comes to backup) and here's how:
Hardest part is to get all parts mounted in a tidy manner. The Xenon ballast is very small und will fit behind/underneath the headlight, all other parts have to fit underneath the tank:
- 3 relais sockets
- 1 BMW Voltage Regulator
- 2 Dynatek Dualcoils
- 1 Motoelektrik Voltage Regulator / Rectifier
First I thought of a very simple solution:
A bit of a bath tub, don't you think? And don't I need some air to cool there ... not good.
What if I took some aluminum, JB Weld and rivets, fabricate some brackets and see how far I get? The aim is to integrate the three existing brackets that are welded to the backbone, so that a solid platform exists for the parts to be mounted.
I have finally received my coils, added some more bracketry, aluminum rivets and JB Weld and completed the dryfitting:
I accounted for everything and somehow I will find the two spots for the additional AUX relais (horn and aux power). Note that this setup also includes the 14.5V voltage regulator, which (together with the diodeboard) is the backup for John Rayski's recitifier/regulator combo.
This setup is baseline and intended for use with a dual electronic ignition. Should that fail, I use the points as a backup, combined with 2.6Ohm low energy coil in place of the Dyna coil:
Now, the model goes to my favorite machinist to make something more professional ... although, that model would probably be good for a year!
Dry-fit of luggage carrier and bags, just in case I ever wanted to go with cases on a street-only ride ...
Exhaust System:
A lot of interesting things can be done with a R100R exhaust on a G(/)S, such as this ...
... or that!
Underneath the chrome covers, there is a full stainless steel exhaust. The front chrome cover can be easily removed by drilling the 4 rivets out. The brackets come off with a Dremel tool, some polishing and off you go. Can be mounted to the GS canister if you remove the big bracket.
When using with the R100R canister the GS centerstand now clears the exhaust, due to a very convenient design (see the big "chamfer"?):
Now, the rear chrome cover can be removed as well, just like in the second picture above, saves another 4.5lbs.
I am already past stage 1 (removed front cover and polished) and will be utilising this as a low exhaust to run equal size bags (and to experience that low frequency 2-in-1 rumble from what was originally a K1 / K-16V exhaust). I would like to attempt to remove the rear cover as well. I am even contemplating to get a GS canister and run the exhaust high or low, depending on the mood of the day (or whether I need bags or not).
I did not know that the HPN Baja exhaust is based on the R100R muffler, in a different "package".
Assembly starts:
A couple of notes taken during the assembly phase:
- clutch actuation arm: replaced needle bearing, spring, rubber boot and clamp, messed up the first time when I used a vise to hold the arm to drive the old bearing out, oval'ed the bore by more than 4 tho and had to ream it, later had the "axle" fabricated from hardened steel to go with the chrome needle rollers, works fine now
- electrical system: running ground from the battery minus in star configuration to frame, gearbox left lower bolt (will not use tranny vent screw for its fragile thread) and didoeboard (direct) to improve grounding and achieve maximum voltage output from the alternator, will use a voltage rectifier/regulator from Motoelectrics (specification), but the stock system stays on board for backup
A couple of notes with regards to heads, pistons and barrels:
I received my re-conditioned heads back from Bruno: A work of art!
Seats were fine, guides and valves were renewed and the heads dual-plugged, one spark plug thread and both valve cover stud threads needed Helicoil. The guides were actually slightly shortened to support a high lift cam (if I ever wanted to do such a modification). Both heads were skimmed to remove warping, leading to an approximate increase in compression of 0.2.
I also measured barrels and pistons, actually with not so desired results:
The pistons from the 1980 US R100CS (8.2:1, stamped 93.98) measured 93.95mm with no wear/abrasions, the 1977 pistons from the 1977 R100S (9.5:1, stamped 93.96) measured only 93.88, but showed no wear at all. The barrels of the same bike (1977 R100S) measure 94.0308 on average. The taper on the barrels is more than 0.01mm with only a maximum 0.008 allowed. Ovality is most certainly more than allowed. The ring end gaps will be just about in spec. The piston clearance of the high compression piston does not scare me, on the contrary, it will help the heat transfer on the high comp pistons. So, high comp pistons it is, although the measurements and tolerances would certainly favour the low comp pistons!
I will however count on German ingenuity (and design margin) to run the new rings in and get at least 30,000 to 40,000 km out of this combination.
With the heads being back, first thing I did was dry-fitting the R100R exhaust with the all chrome covers removed: looks great. With that being a GO, I fitted rear swingarm, suspension. I bought some 21x36x2.5mm nylon washers to fill the gaps between the swingarm bearings and frame so that they don't get washed out in rain. Finally I set up the relocated brake rod and cleaned up the workplace for the more delicate work on the engine, which requires a bit more cleanliness!
The bike is slowly starting to look like a bike again, especially with that bad-ass 9" headlight that has a XENON HID conversion kit. Let there be light!
My thoughts and resulting activities on engine balancing:
We are looking at 1230g of metal, unevenly distributed amongst connection rod, wrist pin and piston. The big question really is whether a 5g (or 0.4%) mass difference between left and right side makes a big difference? Most people say it does, but who knows whether they synchronized the carbs at the same time or whether other changes came about.
Let's talk about Moment of Inertia first:
Moment of Inertia is a scalar (a number), with dimensions of distance squared times mass. Moment of Inertia is a property of rigid bodies. Being a scalar, it is additive, so that the Moment of Inertia of a composite body is the sum of the Moments of Inertia of its parts (relative to the same axis). That, in my mind applies to the conrod+piston+wristpin assembly. Poses a question: do all elements need to be perfectly balanced or can the whole assembly be?
Furthermore, inertia loads are both compressive (crush) and tensile (stretch). To better understand, lets look at those 2 assemblies without the combustion process. When the rod is pulling the piston down the bore from TDC, the mass of the piston plus any friction caused by ring and skirt drag imparts a tensile load on the rod. Once the piston reaches BDC, the dynamics shift. Suddenly the rod is pushing the mass of the piston as well as the friction load back up the cylinder bore, and a compressive load on the rod results. Then the piston stops and reverses direction to head back down the bore, so the inertia of the piston, once again, tries to pull the rod apart as it changes direction.
Does that not mean, since there's only a "simple" push-pull operation that that the weight distribution doesn't matter, as long as the masses are on the same axis? I am deliberately counting the circular crankshaft motion out, as I don't think it matters much in the scenario.
I believe that since all individual masses are on the same axis, the distribution of masses along that axis in first approximation doesn't matter much in the case of that push-pull operation of a "reciprocating engine", a.k.a. Airhead. Equal reciprocating masses are reducing vibration, reducing the overall mass would increase the overall improve performance. I don't think that balancing each individual component makes a huge difference, the crankshaft pushes against piston ring friction and inertia (which is additive along the same axis).
Subsequently I separately balanced conrod+wristpin+piston assemblies, and bolts+conrod clamps to be of equal weight, within 0.1g. The pistons itself were within 0.9g of each other already.
I removed about 4g of material in total.
Now we're getting somewhere. 2 years and 2 months after the idea was born and the first part bought, I am only one week away from the maiden trip of my 1990 R100G/S. I will have to run the dented GS tank a while to figure out which of the two seats (Solo or Corbin Gunfighter) fits my butt best. Very excited but also worried if everything will work out as planned:
Not much longer ...
To be continued ...
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