1964 BMW R69S
Every aspect of the power train of this matching number '64 R69S proved to be
challenging. A cursory inspection revealed incorrect size & year Bing carburetors;
24 mm 151 & 152 left and right respectively.
Engine: Disassembly exhibited dome less pistons (with broken rings), scored
cylinders, R60 cams, a badly worn crankshaft and impacted oil slingers.
Fortunately the timing and oil pump drive gears were serviceable.
Two studs in the front main bearing carrier were broken. The Bowman flywheel
fell off when the large retaining bolt was removed; indicating that it was tightened
against the rear main bearing rather than the crankshaft taper. While the floating
bearing was unsound, it had not spun in its rear carrier.
Uli's Motarradladen supplied a rebuilt crankshaft, the remaining corrected parts and
stainless steel hardware were purchased from Bench Mark Works. Bore Tech Racing
performed the second overbore with carbide hardening process. With the exception of
the flywheel, reassembly was straight forward. Careful measurements indicated
that 0.032" had to be removed from the Bowman's mounting boss to obtain a safe
0.060" clearance from the rear main bearing when the flywheel was fully tightened
to 175 lbf-ft. Due to the new crankshaft's taper the Bowman was lapped to mate. Only
by slowly "walking-on" the Bowman with a special tool could I achieve an acceptable
0.004"run out. The the drain-plug hole of the deep, aluminum oil pan (a period
accessory) had been stripped. The problem was solved by fitting a spark-plug-hole
repair insert and machining a magnetic 14 mm x 1.25 plug with a shoulder that would
accept a crush washer.
Transmission: The splines of the input shaft, normally square in profile were worn to
sharp points; likewise the mating clutch splines. Furthermore, disassebly revealed
that the input shaft front bearing had spun in its carrier & its seal bushing was grooved.
All spur gears were serviceable but their respective phosphor-bronze bushings needed
replacement. The input shaft rear bearing also spun in its cover carrier. Suggestions
from fellow restores ran from welding and reboring the carriers, to purchasing a new
transmission case, to bearing retainer. I decided on the latter and consulted a Loctite
technician who recommended Loctite 640 sleeve & bearing retainer; good to 400 F
continuous temperature--breaking down at 650 F. Furthermore, it would hold a sleeve
or bearing that had up to 0.005" loose clearance. Both carriers had their diameters
enlarged by 0.0025" & 0.003" front and rear respectively. And neither were egged.
The input shaft with its new bearings was installed in the case and the cover secured to
ensure proper alignment & allowed to cure for at least 24 hours. The output & intermediate
shafts were installed and all three were shimmed to an end float of 0.0035" to 0.0039".
Disassembly of the shifting mechanism evidenced worn parts which were replaced. All seals
were renewed with Viton items. New segment and idler gears were renewed. Whoever
installed the output shaft seal had done so with its sealing lip reversed, i.e., the lip was facing
inward. Moreover, to gain clearance for upgraded socket-head clutch retaining screws (which stand slightly proud) a ballpene hammer was used to flatten the case-strengthening gussets.
Very careful examination showed that the case was not cracked.
In retrospect, the case may have been distorted from this heavy-pounding. In short, I am not
satisfied with the manner in which it shifts and will revisit the transmission this winter.
Final Drive: No one had ever opened this case. Other than the thrust ring, there were no shims
present. Based on the tooth wear, the alignment of the pinon and ring gear where correct. Upon
reassembly; a 0.2 mm shim was inserted on the pinion shaft. The splines of the ring gear where
worn to the point that a rebuild was needed.
It should be noted that owner was and still remains dediacted to this project.
