[DeTomaso] Need a machinist lifeline

David Fisher fisher95020 at gmail.com
Thu Mar 21 22:30:42 EDT 2013


Disclaimer first - this thread is about an Alfa 2L motor, but this
forum seems to have the best collection of brainpower and experience
so I'm posting here

http://www.poca.com/index.php/gallery/?g2_itemId=39123

Summary.   I'm trying to figure out how to re-align, bore out and
replace the centering dowels that have ovalled and fallen out of the
aluminum block where it mates to the bell housing (without stripping
down the block and sending to a machine shop)

http://www.poca.com/index.php/gallery/?g2_itemId=39128

http://www.poca.com/index.php/gallery/?g2_itemId=39126

How did this happen?

Just a theory at this point.  I bought the car a few years back and
took it to Concorso Italiano 2011.  The car had a pretty noticeable
vibration in the shift knob, which i figured was the drive shaft. I
balanced the shaft, but it didn't help and it was time to go to the
show so we drove (from San Jose).  After the event, the starter spun
but wouldn't engage.  Turns out the vibration had loosened one of the
starter bolts and the weight of the starter cracked off part of the
bell housing on the trip.  We push started it (thanks to the Alfa
attendees), drove home and parked it and there it sat while I bought
the Pantera and proceeded to work on all its issues.   Now my Pantera
is running and its back to the Alfa.

Upon separating the bell housing from the block I discover one sheared
off bolt, both dowels are gone ( were they ever there?) the dowel
holes are ovaled.  The crankshaft bushing is pretty thrashed implying
the trans input shaft has been wandering around.

My theory on the vibration is that the trans input shaft got a few mil
off center in the crankshaft, putting the clutch plate into a slight
eccentric and creating all the vibration.

I just finished rebuilding the trans and now I am staring at the block
and trying to figure out how to fix the alignment from bell housing to
block. The threads in the block are all loose from abuse (8mm) but it
appears I have enough good metal left on both the bell housing and
block to go up to 10mm on all the bolts and (rethread) the block.  I
am quite sure the original manufacturing tolerances on these bolt
holes did not anticipate them being the primary alignment mechanism
for getting the trans aligned with the block, hence my desire to
replace the dowels.

the trick - how to figure out where the dowels are supposed to be
(exactly) and how to drill a larger hole over the oval hole that is
there.

Tools at my disposal - small milling machine (bell housing will fit
under, but block wont ( even if i could lift it). Hand drills, mig
welder, torch, full taps dies,  indicators,etc.  The engine and trans
are outside the car on a test jig

I'd rather not take the motor apart just to fix this if I can avoid it.

My best ideas so far



1) put bell housing on mill and bore out bolt holes for a snug 10mm
bolt to try and use the bell housing bolts for partial alignment.
Replace crankshaft bushing for partial alignment.  assemble and test
for vibration. Reassemble slightly offset if vibration found.  Repeat
until happy

http://www.poca.com/index.php/gallery/?g2_itemId=39130

 2) try and make a template off a good block or bell housing and use
that to find dowel centers... But how to bore out with some kind of
hand drill.  How tight of tolerance do you suppose those dowels align
to? .001?     Machine an alignment tool that bolts on to block and
centers a drill where the center of the dowel should be?


Ideas?

Many thanks

David



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