1st non SBC rebuild - Oil Pump question

[nbn]

49 Plymouth

I pulled and sent engine to machine shop. Once work was completed, machine shop pointed out part of the oil pump housing was broke and missing (covering shaft). I ordered a new pump and am getting things lined up to put this engine back together. Playing with both pumps, I noticed the original pump had a little "catch", as if it was creating a vacuum. The new pump spun with no "catch", essentially spinning freely. 

Why the difference? Does my rambling make sense?

Probably a simple answer, I just want to do this right the first time so that I'm not having to do it a second time.

[Dave72dt]

I'd guess there was some damage internally in the old pump, possibly the cause of the break.  it's not supposed to "catch".

[allbizz49]

Pack it with petroleum jelly and bolt it on. The new one that is. The old one was shot. 

[greg g]

The oil pump drives the distributor.  It should be installed indexed on the cam gear so that the rotor points to seven o'clock with number 1 cylinder at TDC on compression.  This was the factory setting. Takes a bit of filling sometimes.

[DJK]

Been some concerns with replacement oil pumps. Check out Freewheeling Tony Smith for proper oil pump prep.

[FarmerJon]

 

Here is the pdf of how to prep a new oil pump. Sounds like the new manufactured ones need a little love, but nothing you can't do on a kitchen table in an hour or two.

 

[JBNeal]

additional information - flathead oil pump conditioning

[9 foot box]

   I would only use a Melling M-37 pump. I would prime it in a can of oil you are going to use on start up and index the pump as indicated in the service manual. Most recently Marcel had an oil pump gear failure. The gist of it is, a few aftermarket repops of these oil pumps are inferior.