Quote:
Originally Posted by puppster
My concern is the oil pressure at idle. Once warm the pressure gauge (electrical) drops down to around 20psi possibly lower (hard to remember. It's been a long cold MI winter, and I remember being uncomfortable with the gauge reading.). Previously it would hold higher pressure at idle. I have in the last 10 years replaced the pump with a Mellings hi volume unit.
So my question is, do I need to consider a freshening, and what can I expect to save on a second rebuild? I think it still has the original flat top pistons, and the main journals are 10 thou under sized. |
A few things come to mind:
1. Replace your
oil pressure sending unit before you go any further. You'd be surprised how often this part is responsible for incorrect/irregular pressure readings.
2. 20 PSI is
probably OK at idle....general rule of thumb is that you "need" 10 PSI of
oil pressure for each 1,000 RPM. The old 1960 Cadillacs with the big block motors had the oil pressure "idiot light" switch set at 7 PSI.....it idled all day long with only 10 PSI pressure at 700 RPM.
3. Good choice on the oil pump....volume is more important than pressure (in fact, TOO MUCH pressure can be a real problem, blowing out seals--like the rear and front oil seals). If you'd like more pressure, though, you could remove your present pump and shim the pressure relief spring with a washer. That effectively increases the pressure the pump will provide before the bypass dumps the excess oil back into the pan.
4. I sincerely doubt you'd need a rebuild after 20K miles as long as you put decent stuff into the engine when you did the rebuild. My first question is how much oil does the engine "consume".....NOT counting leaks if there are any. In the 60's it was not considered at all unusual for an older engine to "consume" a quart of oil every 1,000 miles, and new engines were generally expected to use a quart between oil changes (which, IIRC, were set at 6K intervals).
One warning, though.....don't increase oil viscosity in search of greater pressure...it works when the oil is cold, but often works too well. I had a Cleveland that put would out 60PSI at a cold 750 RPM idle, but here in TX that amounts to a 40* morning. At the cold temps you still see in the AM, a heavy viscosity oil could put too much pressure on the pump, resulting is issues such as a stripped distributor gear or a snapped oil pump drive.
I always make sure my engine is at operating temperature before I start driving my replica--making my oil pressure at idle a moot point and switching the importance to the oil pressure at driving RPMs. I know, the "efficiency experts" say it's OK to start driving soon as the engine is lubed, but those recommendations are usually made with standard "sloppy" clearances in mind.....our engines are usually built to much closer tolerances and can be starved by anything other than gentle operation with cold oil circulating in them at startup.
Bottom line....it might not be as bad as you believe.....and unless those 20K miles have been incredibly HARD miles without regular maintenance, the "fix" you're looking for might be much easier than a rebuild.
Cheers from Dugly
