Author Topic: Missing crankshaft/bearing hole?  (Read 139 times)

0 Members and 1 Guest are viewing this topic.

ahowell

  • Administrator
  • Full Member
  • *****
  • Posts: 249
    • View Profile
    • Email
Missing crankshaft/bearing hole?
« on: May 04, 2017, 06:09:04 AM »
Here's a valid question I received from Richard Piaseki on May 1, 2017:

-----------------------------------------------------------------------------
I just bought the plans for the Farm Boy engine and after reviewing the drwgs., I have a question. Sheet #3 does not show a .500 hole for the crankshaft/bearing. Is there a reason for this or just an omission error?
Regards,
Richard Piasecki
-----------------------------------------------------------------------------

I wasn't sure, and I also noticed a similar issue with the connecting rod end, so I asked "EngineMaker' (builder of Farmboy #3).  Here's his reply:

-----------------------------------------------------------------------------
On page #3 your Dad gave the dimensions for the placement of the holes as 1.820" from the back edge of the frame and 1.280" from the back of the lap joint. Now the size of the hole is the .500" dimension shown on the crankshaft bushings shown on page #9. Half of the hole is in the bearing cap and the other half is in the frame. I drill and ream my 1/2" holes as the bearing should be captured by the bearing cap ( so it doesn't spin) bur not crush the .376" inside bushing dimension.
 
On page #8 if you look at the connecting rod drawing, the bottom of the connecting rod dimension is .400" wide and the cap is also .400" wide. The hole goes at the seam of the 2 parts and in the center ( the .900" divided by 2 = .450") from  the edge. The hole size is the .561" dimension shown on page #8 as the rod end bushing. You could actually make the hole drilled an reamed .562" and the bushing .561" dimension .562". In this case the rod cap bolts going through the bearing keep the bearing from turning. My guess is that your Dad meant to say "Drill and Ream a .562 hole through rod big end" instead of .282" as shown on the rod big end assembly picture shown on page #8.