From: "Neil Unger 12348ung@gmail.com" <flyrotary@lancaironline.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: no hot start
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Date: Sat, 31 Aug 2019 20:11:57 +1000
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Dave,

                Thinking about your starter problem suddenly brought 
back sad memories from over 20 years ago when I owned 2 Claas 106 
headers (ag machines) which were without doubt the greatest Lemons that 
Claas ever produced , and I had 2 of them. Besides the usual grief these 
monstrosities  gave, the engines always started and ran beautifully up 
until about 2000 - 2500 hours.  The engines were V6 mercedes diesels 
with Bosch starters. Then once these hours were reached they would start 
cold perfectly, but once hot refused to turn over until cold.  The 
starters just did not throw in at all.  To remove the starters required 
the Cab to be tilted forwards which opened up a small gap between the 
cab and the engine bay. By sliding down like a snake, one could then 
remove the side  panel of the engine bay --- all at red hot in the 
middle of summer.  With the engine bay cover removed it exposed the 
starter for removal.  Only trouble was that the exhaust manifold had to 
be removed first to get to the starter!!  Trust me it was such a joy 
that it was sheer desperation to be forced to remove the starter.

Every time the starter would turn over perfectly on the bench. 
Disassembled and resembled many times for no fault whatever, they always 
performed perfectly on the bench, but hot in the machine--- no way.  
Then about the 10th time and many hours later  on the bench it was 
getting dark and when the power was applied to the starter, sparks flew 
from the rear cage of the starter.  In broad daylight it would never 
have been picked up.  The rear cage held the brushes and was solid 
riveted  to the main body and had to carry the current between the two 
parts.  After drilling out the solid rivets it was obvious that black 
corrosion has set in and effectively insulated the Brushes cage from any 
current when hot. Without having seen it I would say it was impossible. 
   All was cleaned up, re -riveted  and soldered for good measure and 
Whacko, all worked as it should hot or cold.

Does it have any relevance to the rotary starter??? I do not know, but a 
change of starter would tell all.  The corrosion in the Bosch starter 
accumulated over 2500 hours and would never had been picked up without 
that chance test in semi darkness.

Suggest all connections to the starter be meticulously cleaned as the 
slightest corrosion may stop current flow when hot, or impede enough 
that it just drags current away for no effect.  A bad connection will 
heat, drag current away and effectively react as if the battery is half 
flat.   Also never buy a Claas 106 header unless you wish to learn to swear.

Neil.