1990 R100G/S "Built from scratch"
Last updated Nov 15, 2009
'90 R100G/S |
Left cylinder:
It looked like a material problem to me (Excel), so I contacted the guys at Woody's Wheelworks who put the wheel together for me about 7700mls and 11 months ago. Remember, it was a design featuring a 1/2in offset to the left to allow 130 tires (Airhead GS sizes) in a monolever swingarm. Zach at Woody's was very helpful: his first assessement came down to an excessive stress of the particular area due to two facts: the rim design (non-dimpled, about 5mm rim thickness at that point) and the stresses induced by offcenter cross lacing. He had never had this problem before, but then, this is the first time he tried this kind of application. We are still communicating the best course of action but it might be necessary for me to go back to a configuration similar the 1981-1987 stock design, but using a 2.50 x 18 rim, either x-laced BMW OEM (oilhead GS) or centerlaced Excel. There is a certain advantage to it in another area: to compensate for the smaller rear wheel and tire aspect ratio, I had the (1988 GS) front forks height-reduced by moving them about 1in further through the triple tree, thus reducing its travel as well. So, going back to an 18in wheel would eliminate that restriction too.
So first, I figured out the availibilty of 18in rear dual sports tires. The results were encouraging:
Another possibility is the use of a dimpled rim that is reinforced in the area of concern. I am waiting for Woody's confirmation.
I don't.
I also looked again very carefully at the hub design which really supports X-lacing best, due to the directional spoke holes as mentioned before.
Based on the above, I have decided that I will have the rear wheel repaired using a (front R100R) X-lace 18 x 2.50 rim that will be laced slightly offcenter, something like 1/4in or thereabouts, just to get some additional clearance for knobbies. That'll put my worrying mind to rest: BMW must know something and the X-lacing has some merrits.
On a positive note: using 120/90-18 tires I will result in more than 1in additional clearance in the rear, so I will be able to raise the front as well by 1in (the amount the forks are currently extended through the top triple tree to account for the smaller 17" wheel).
The parts finally came back and as usual, the workmanship was excellent and the hours of preparation and measurements paid off:
The Kenda 270 that is currently mounted is a 4.50 x 18 with 121mm (4.76in) width and 27in diameter on the 2.50 x 18 rim @ 32PSI tire pressure. Clearances are as follows:
I have another rear drive, a 33:11 (3.0) in the works that should reduce rpm by another 7%. That is in pieces with Bruno, who will refurbish it to as-new condition. Try-out -> probably next year.
Meanwhile I installed the new alternator stator and rotor (both parts from Rick Jones) to run that combination this season. I have decided to swap over the entire charging system once a year and run them alternatively and keep the other one as a backup.
I have bought the (ridiculously) hi-viz roadcrafter tank panniers (8l each side) to shift weight (especially spare parts) from the rear to the front and for better accessibility. They are really yellow!
I discussed my Ohlins shock with a local guy, especially the fact that I needed 34mm pre-load without luggage and nearly maxed-out the pre-load at 45mm with load. We established that Kyle USA (although they had all the data) did not set it up for me, can you believe that? It has a 70kg/mm spring installed (which is stock at delivery) whereas I should have had a 95kg/mm. John Sharrard from Accelerated Technologies in GTA swapped the spring (charged me only $50 for the spring and took mine as a trade-in) and then lengthened the shock by 3mm. He noticed that the oil was filthy and dirty! WTF? Did that Kyle guy do anything? NOPE! So I spent another $150 on setting up the Ohlins. Am a happy camper now.
Nuts 'n bolts: I thought I'd use high strength plain finish (black) bolts and stainless where it doesn't count, but they all rust badly on the surface. Even the stainless type A2. Only the A4 stainless is holding up. Doesn't look good, hurts my eyes. So, I put another set of zinc/yellow zinc plated screws, washer and lockwashers together and will install that at rear subframe, the entire front end and the covers.
The fork gaitors were shot when I put them on, they still are. I have original replacements and will put them on before the season.
Will also put the marine type ignition switch in that I bought. Three positions: OFF, IGNITION ON, LIGHT ON
I have bought a new stainless steel brakeline locally, C$43 shipped. It has two banjos (45deg at the caliper, 90deg at the m/c) and goes straight from the caliper to the master cylinder (37.5"), nothing
inbetween. See how that works.
The 1in rise and 1in back handlebar riser I had was not really nice, so I had my machinist play around with his machines:
It was necessary to extend the shift lever because getting the boot between the sidestand and the shiftlever was too tight. The springs are stock size, but from an aftermarket supplier.
It wasn't cheaper than buying, but I enjoyed being part of the making.
Link to Mid-Ohio2009 pictures
Not a Christmas tree yet, but not far from it, eh!
Much better!
Next up: doing something about the increasing oil consumption! I made it to about 17k (2 full seasons) when the oil consumption passed 0.7ltr and it was time to re-assess. I have the original barrels of the Nov 1980 built R100CS engine. Only problem is, it has some imperfections in the Nikasil liner. I re-assessed the barrels and decided to use them this time around. What can happen!
Checked prices for piston ring sets at BMW (they are Federal Mogul/Goetze) and wasn't impressed. There are alternatives however: Hastings and Grant. Didn't know about Grant when I started, so I approached Hastings. Their sets were inexpensive but, the oil ring was chromolly which isn't recommend for use with Nikasil barrels, both are hard materials, so chromolly would scratch the Nikasil barrels. So I searched the Hastings catalogs for suitable cast iron rings and this is what I selected for my "C" barrels:
Material: Material: Material:
All six indivdual rings together were less than $50 delivered CONUS. All of them were slightly oversized and I set the end gap to the minimum as per BMW specification: 0.4mm for top and middle ring, 0.25mm for the bottom oil ring. Installed them completely dry in a degreased barrel. For the oil ring to fit, the width and depth of the piston grove had to be slightly increased.
I also mounted my new DIY oilsump extension (with integrated oil temperature sensor) ansd sump guard. Both sump/engine and tranny guard are home made.
I always wanted an oil sight glass on the tranny. Bought a standard J.C. Winko fluid sight glass in stainless (part #160FREA/B) and had my machinist change the thread to a M18 x 1.5:
"The Making of the R100G/S"
Where it all started ...
Then I looked at the effect of bike geometry when changing the rear wheel. I found this website (U.S And Metric Tire Size Information Calculator) and compared a 130/80-17 with a 120/90-18 (TKC80, D606):
Update on cracked rim:
The crack is indeed a result of stresses induced to the rim by offcenter lacing which puts additional loads on the rim as the hub is originally designed for X-lacing (BMW OEM) so the spoke holes are directional. There would a dimpled rim available but Zach @ Woody's was more or less suggesting not to do it again unless I NEED the additional clearance to the swing arm.
Last year, I bought a BMW stock R100R 18" front rim. Admitted, it was an impulse buy then. Now, that 18in R100R front rim is laced to my rear GS hub, thanks to Woody's Wheelworks. It raises the rear nicely so that the front can follow (which is still 2in lowered). That 18in rear wheel requires a 1" dent, yes a huge dent in the R100R collector so that it can be mounted. My machinist is taking care of that.
You also know that I am still not happy with my rear brake setup: deep bumps still activate the rear brake. Hwere are the three design that didn't work to my satisfaction:
This season (2009) I will be running a 32:10 (3.2) rear drive as opposed to the shorter 37:11 (3.36) that I ran 2008. I hope will improve gas mileage and reduce highway rpm.
For this season i will try an ignition setting that supports the theory of faster combustion on dual-plugged engines better: 3deg BTDC for static and the full
advance at 28deg @ 3200rpm (setting #1 of the OMEGA ignition). See what that does to the gas mileage and carbon build-up.
The sidestand of both, the G/S and the GS is a laugh: skinny and not very comforting. I have asked a fellow Airhead for a loaner of his 1993 R100R sidestand to see whether that can be made to fit a G(/)S. It attaches to the front mounting bolt:
I opted however to have the stand itself custom machined (to make it fit with a crashbar mounted) and made of thickwall stainless. My trusty machinist was doing his magic and a couple of weeks later, this was born and assembled:
This is the bike after the "re-design" phase in the spring of its second year (and yes, the heavily dented tank was replaced by a less dented tank):
Now featuring
985cc rebuilt engine with '77 R100S pistons+barrels (A-bore), 1980 R100CS big valve dual-plugged heads, 1983 R80RT bottom end (approx CR 9.7 and 70hp)
Edited 09-Nov-2009: 11/80 R100CS engine, US specs, unknown mileage, refurb'ed big valve heads (km 0), dual-plugged with 10mm second plug (km 0), new rings (at km 16864)
Edited 10-Nov-2009: oilsump extension (1l DIY) with integrated oil temperature sensor, oilcooler (without thermostat, installation instructions here: http://www.airheads.org/content/view/218/98
Added Nov 2009: two 20W ATV driving lights for better visibility
Added Nov 2009: Run-n-Lites Lite Buddies (TM) running lights
Adding real horns to the bike:
I found some leftovers in my garage: non-matching design, but matching Hi-Low tones, great sound, they make incredible noise - pointing forward!
Mid-Ohio 2009:
Did a long weekend run to Mid-Ohio as I had never been there before: 
Iron Butt SaddleSore 1000
It's called a SaddleSore 1600 for us Canucks (1610km = 1000mls), link to ride report
Winter 2009/2010:
Time to do something about lighting: found a very reasonably priced ($25 + shipping) pair of running lights that have HomeDepot-type halogen bulbs installed, a cheap and cheerful measure to increase visibility, have a better chance to be noticed. Secondly, Klaus Hueneckes Lite Buddies are the ultimate: a cluster of 2 x 4 red LEDs for integration into the indicator housing, shiningg red through the amber indicator glas:
Before I put the engine together in early 2008, I measured the 1977 R100S pistons and barrels: they were barely in spec for both, taper and ovality, even after honing: "The taper on the barrels is more than 0.1mm with only a maximum 0.08mm allowed. Ovality is most certainly more than allowed. The ring end gaps will be just about in spec.". I expected to get no more than 25,000km out of that set.
Ring No. BMW stock shape Hastings equivalent Notes
#1 
Type 032
Barrel Face
3.71" dia.
0.675" width
0.168" wall
part #35896
#1116 cast iron
#2 
Type 126
Rev Torsional Taper Face
3.71" dia.
0.775" width
0.169" wall
part #29900
#1116 cast iron
#3 
Type 507
Cast Iron Oil
3.7175" dia.
1.86" width
0.157" wall
part #31635
#1116 cast iron
Run-in started with 1min @ 3000rpm and then cool down, followed by 50km hard riding on the road, constantly opening and closing the throttle full in all gears, but mainly first to third gear. Later that day, I went for a leasurely 3hr ride (Nov 8, 18degC). Bike was feeling great, no blue smoke as far as I could tell. I guess that is as far as it goes before the winter.
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
Maidentrip and finishing up