Tractor Repair: 8N Knocking noise - followup, ford 8n tractor, pin bush

Question
Eric, my 49 Ford 8N tractor starting knocking loudly all of a sudden.  Danny told me to drop the oil sump since he thought that it may be a big end bearing or pin bush.  I did as he said but everything looks tight from below while turning it over, nothing is obviously wrong. Is there a trick to checking these? (Not really sure what the pin bush is). Compression is good on all cylinders.  I checked the value springs from the side and all seems to be working fine. I'm not sure what to do next. Is there anything else I can try myself or is it time for an expert? Thanks...

Answer
By pin bushing I am assuming that he was refering to the wrist pin -- this holds the piston to the rod --- You can check the rod bearings by giving each rod a wiggle when the unit is not running --- you will be looking for a rod the any up and down movement or excessive side to side movement -- you will know what I mean by excessive if you come across it.  

Checking a wrist pin will be very difficult -- piston/rod assembly removal is necessary -- a loud knock is most likely is from the lower end -- main bearing - rod bearing - or a spun bearing ---

When all else fails pull the lower end down and inspect the crank roads and pistons for wear ---