[alfa] 105/115/116 starter interchange

["John Hertzman" <johnhertzman@xxxxxxxxxxxxx>]

Responding to a question from Dana Loomis on starter interchangeability 
(re use of the post-1975 1.1hp starter in place of the pre-1975 .7hp 2000 
starter) Brian Shorey wrote If it's got the same number of teeth (9 vs 8), then 
it will work fine. Jason Hagen, responding to Brian, wrote on the basis of his 
bad experience fitting a 1975-1979 starter to a 1973 engine, do NOT put the 
wrong starter in this car. You will chew up your gear gear, regardless of 
whether the starter has the same number of teeth (because the pitch is 
different).
I disavow any special knowledge or experience, but the questions had been 
addressed by the late Herb Bridge in an article in Velocissima, November 1995, 
partly on the basis of experiments which Dr. Bridge (a Professor Emeritus at 
M.I.T.) had conducted along with his brother Jim (a precision machinist at Los 
Alamos), both alfisti whose opinions were highly respected by the late Fred Di 
Matteo. It had also been the subject of an ARI Service Bulletin Group 05 #02, 
October 1975. The problem was evidently not the pinion teeth, but the diameter 
of the ring gear; the 1.1 hp starter is about one cm larger in diameter than the 
.7 hp starter, placing its axis about .5 cm farther out while requiring the use 
of a larger ring gear, some relief-grinding of the motor mount, usually a little 
grinding of the block to relieve interference with the starter, and the use of 
one special eccentric bolt. These small changes are necessary to avoid the 
tooth-mesh problem Jason Hagen had, but with them the Bridges, Fred, and 
ARI say there is no problem. The later geared starter (which is lighter) may be 
a still better solution, but they are probably less easy to find on the 
used-spares market.
A transcription of the Herb Bridge article is included in a 
post by me to the digest,13 
March 1998, AD6-046 which should be in the digest archives; the ARI Service 
Bulletin Group 05 #02, October 1975, should be be vailable in various 
compilations of Service Bulletins.
A minor curiosity sidebar is that the .7 hp starters of the early 105/115 
2000 cars had a 116 part number, while the later 1.1 hp starters of the 116 cars 
and late 115 2000 Spiders had 105 part numbers, contrary to the usual part 
number logic, but an occasional anomaly is probably to be expected when dealing 
with Alfas, if not with Italian things more generally.
Cheers
John H. 
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