TheOldHokie
Well-known Member
- Location
- Myersville, MD
I just received an oil pump from a customer who reported that after he rebuilt it himself it still would not hold prime. Here is what I found. Based on the earlier discussion started by WeldingMan on the width of (some???) aftermarket gears I immediately checked the width of the gears he had installed. This is the 8N-6614 I removed from his pump:
I posted full specifications for the OEM gears in WeldingMan's thread and the correct face width is .724/.725. Here is one of about a dozen 8N-6614 gears I have removed from other pumps - they are all dead nutz on.
The difference in width is in excess of .010 and I am quite sure that is the cause of the losing prime problem. The pump has something in excess of .015 end clearance and after sitting a short while cannot produce enough vacuum to prime itself with the small amount of residual oil that remains in the pump. Next step is to see if I can find a supplier of replacement gears that are the proper width. If not this pump may go back to the customer with a set of the old gears I have here. My bet is that would fix the priming problem AND boost the pressure he was seeing.
TOH
PS> His pump also had pronounced scoring on the inside of the cover plate which only makes things worse. That will have to be ground out as well.
I posted full specifications for the OEM gears in WeldingMan's thread and the correct face width is .724/.725. Here is one of about a dozen 8N-6614 gears I have removed from other pumps - they are all dead nutz on.
The difference in width is in excess of .010 and I am quite sure that is the cause of the losing prime problem. The pump has something in excess of .015 end clearance and after sitting a short while cannot produce enough vacuum to prime itself with the small amount of residual oil that remains in the pump. Next step is to see if I can find a supplier of replacement gears that are the proper width. If not this pump may go back to the customer with a set of the old gears I have here. My bet is that would fix the priming problem AND boost the pressure he was seeing.
TOH
PS> His pump also had pronounced scoring on the inside of the cover plate which only makes things worse. That will have to be ground out as well.