Howdy,
Quick question here.
Is it ok to re-use my old oil pump shaft on a rebuild, or do I need a new hardened one?
Will be using an MP solid flat tappet cam.
cheers.

look at the shaft and the tip to see if it is twisted ..

I am assuming you are using the hardned shaft intermediate shaft???

and would you be using a HV oil pump?

I will use them over again if they check out fine

If you are going to run a high volume oil pump you need the hardened one.

I put together a new stroker small block with the high volume pump and just did a visual on the shaft not a magnaflux (was a stock shaft), it looked fine so in it went. Put about 500 miles on the new engine and one day I started it to move it in the yard (was about 38 deg outside) and within minutes of running the oil pressure went to zero.
Pulled it out and torn it down and found a twisted broken shaft. Guess the oil was to thick (15/40 rotella) and the shaft couldn't hold the pressure.
Showed the signs of twisting where the "U" grove is cut into the shaft.
I would say for the price of a new one ($35 or so) I would change it with a hardened one, if nothing more than just a piece of mind.

cheers,
thanks for the replies.