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View Full Version : Spitfire '72 Spitfire Oil Pressure Up-date



dklawson
09-13-2008, 04:15 PM
I started a thread last Saturday about our project Spitfire's maiden voyage. It did not go as well as I'd hoped. Oil pressure was one issue, the gearbox was another.

This week I checked the calibration of a Smiths oil pressure gauge I will be installing in the dash. Today my son and I installed the gauge and took the car around the block to determine a baseline oil pressure. It was about 15 PSI with a hot idle (180oF water temp, 800-900 RPM).

Then we changed the oil to fresh 20W50 and took another lap around the block (after letting the car idle for a while). The oil pressure was only slightly better... perhaps around 20 PSI (with wishful thinking).

This car is not a restoration project. It is to be a moderately reliable daily driver for around town, not for long highway trips. As such, I'm not thrilled about pulling the engine and/or doing a complete rebuild. I can see dropping the pan and putting in new bearings and a new oil pump (assuming the crank isn't toast).

As a stopgap measure during our work, I may (God forbid) simply add STP or similar to the sump to bring up the viscosity. Apart from the bearings and oil pump are there other short term things I can do that don't involve pulling the engine?

BTW, for those who read the previous thread and want more info on the gearbox, I'm convinced it's the synchros on 1st and 2nd. Careful shifts with the pedal all the way down still ground. Double-clutching completely eliminated the problem. If my friend Jamie does have a later 1500 gearbox, that will be our fix. While the box is out we will have our opportunity to work on the oil pump and other bottom end oil related issues.

Andrew Mace
09-13-2008, 06:58 PM
After you changed the oil, what was the "running" oil pressure? I grant you, 20 psi @ warm idle still seems a bit low, but I'll wager new big-end bearings would cure the problem (probably no need to touch the oil pump).

dklawson
09-13-2008, 07:32 PM
The oil pressure was up and down depending on RPM. Going around the block we didn't maintain a constant speed. However, the peak cold temperature with fresh 20W50 was a bit over 50 PSI. Once you got the engine off idle the pressure would quickly climb over 30.

Years ago I slipped new bearings into the GT6 so I know it can be done with the engine in place. Being "in there" I replaced the pump at the same time. Would it not be smart to take the same approach with the 4-cylinder?

Andrew Mace
09-13-2008, 10:05 PM
Maybe replacing the pump would help. But I'm wondering if the big problem is in the bearings, which have a great influence on pressure readings. I still suspect that the volume of oil pumped is probably ok, but the pressure readings you give are definitely a bit below "acceptable" range.

I concede that dropping the pan is a bit tedious, but it's not all that horrible or lengthy a job on the four-cylinder cars. Being the naturally cheap person that I am, I'd probably risk doing just the bearings. :smile:

tdskip
09-13-2008, 10:07 PM
Doug - bearings sound like they are worth a shot to me as well. I bet that would get you a long way before you need to do anything else...

dklawson
09-14-2008, 09:21 AM
I'll be giving this serious thought during the week.

From memory, when I did this on the GT6 (a LONG time ago) I pulled the gearbox to have easier access to the bottom end (and so I could replace the rear main seal). Since I may be pulling the gearbox for other reasons I assume this would be a good time to tackle the rear main on the Spit. I also remember getting a rough idea of the big end journal size using calipers and then checking the actual clearance with PlastiGauge. I assume this would still be the normal method for DIY at home but suggestions are welcome.

I've been postponing my parts orders anyway. Once I know if the crank has been reground I'll add the "right" bearing size to my list of parts. Is one of the usual suppliers better than any of the others for parts like a set of standard or oversized big end bearings?