Section : Cooling

Temperature up, oil pressure down

Posted By : Phil Rogers, 30-Jun-2005, 07:45pm

• Temperature up, oil pressure down

  Posted By : Nigel Gibbins, 30-Jun-2005, 11:24pm

  Big question here... can you hear the crank when you start it up?
  
  Low oil pressure (5psi) is a sign of either...
  
  Not enough oil in the sump...
  Worn bearings...
  
  It could be the pump, but the bearings are usually the first to go - they are the most vulnerable to oil starvation. If you need to change the barings, you can check the pump at the same time. Or vice-vesra.
  
  I would guess that it's the bearings... this means it's time for a rebuild.

  • Temperature up, oil pressure down

    Posted By : Phil Rogers, 01-Jul-2005, 04:20pm

    Nigel
    No sound of bearings on startup. I get a slight rattle for 1 or 2 seconds until the oil reaches the tappets then it's as quiet as you like. As I said, it's running well with no rumbles or any of the other usual tell tale signs of bearing failure. As for not enough oil, i have checked and re checked and it's up to the full mark when 7 and a bit pints have been put in. Thanks for your thoughts.

    • Temperature up, oil pressure down

      Posted By : Chris Taylor, 01-Jul-2005, 07:20pm

      Sorry to sound depressing, but that "slight rattle for one or two seconds" is NOT the tappets, whatever it sounds like. The tappets on the cam are not pressure lubricated, but rely on drain from the head via pushrod tubes and spill from camshaft bearings. The rockers get hardly any pressure at all as the metering arrangement on the rear camshaft bearing purposely reduces the oil pressure to the rockers. The oil generally "oozes" from the rockers rather than pumping out in jets which the number of rockers and rocker/shaft clearances would permit should oil at 60psi get pumped into the rocker shaft.
      I'm afraid what you can hear is the crankshaft bearings knocking until full oil pressure is available.
      That is why your oil pressure falls as the oil warms up and viscosity reduces. The pump cannot pump enough oil to maintain pressure at low speeds because of the rate at which it flows out of the worn crankshaft bearings. Any wear in the pump itself will exacerbate the problem.
      That's the bad news! The good news is that you have not ruined the engine, and if driven with some consideration will go on for many miles.
      Also, if you attend to it now, you can probably just replace the bearing shells without having to have the crankshaft reground. My Herald engine (well thrashed) is now on its third or fourth set of standard size shells but the crank is virtually unworn and fit for many more miles.
      While bearing shells can be changed with the engine in the car, it is a much easier job with it out. Unless you check the oil pump clearances and find it all in spec, I'd replace the oil pump while you have the sump off. You could fit a 1500 pump which has a larger capacity and will help to prolong the life of a slightly worn 1300 crank.
      Although you can end up replacing a whole list of things "just in case" and "because it's easy once the sump is off/engine out) but you MUST replace the crank thrust washers as a precaution. (That can also be done with the engine in the car). I'd also change the crank oil seals and the timing chain and tensioner if the engine is out of the car. This would also be a good opportunity to change the clutch but that depends on how long it's been in the car.

      • Temperature up, oil pressure down

        Posted By : Phil Rogers, 01-Jul-2005, 08:23pm

        Thanks very much Chris for a comprehensive diagnosis. I'm now going to the manuals to see how it can be done. I'm fortunate enough to have an inspection pit, so I've got a bit of room to move. Any further advice would be welcome.
        Phil