Pressure testing newly rebuilt engine

[billrabe]

I just finished a top and bottom rebuild of a 657x for my 95 Sportster and pressure tested it using a Mityvac through the pulse line and blocking off the intake and exhaust manifolds with round rubber welch plug sealers and blocking off the oil ports on the crankcase and oil pump. Plugs are in and torqued and previous compression testing was 150 and 150. I pumped it up to 10 psi and the pressure drops about 2.5 psi every 10 minutes, dropping to 7.5 psi after 10 minutes, 5 psi after 20 minutes, 2.5 psi after 30 minutes. I can’t find any obvious leaks with soapy water or WD40 sprayed around the gaskets. Is this good enough or do I need to keep trying to find the slow leak?

 

[billrabe]

OK, I found the leak. It was at the o ring of the oil pump. I removed the gear and cleaned it up and reinstalled the gear and retorqued the intake manifold bolts and oil pump bolts and now it is holding 10 psi for 10 minutes.

 

[billrabe]

In case anyone is interested, the block off plates for the 657x are Dorman 02606 1 7/8 inch for the exhaust manifold and 02603 1 1/2 inch x 2 for the intake manifold. The Pressure source is a Mityvac MV4560. I initially didn’t block off the oil nipples on the pump and crankcase. I ended up just attaching a 3/4 inch tube between the two nipples on the crankcase and zip tying them. I had tried spraying WD40 previously but spraying Dawn dish soap mixed with water in a spray bottle worked much better. Now I can finish assembling my engine!