Oil circulation/pressure problem

Discussion in 'Mech Tech' started by Pumpkin jack, Mar 24, 2019.

  1. I’ve just re-read your first post and notice you’ve fitted a new pressure relief spring and piston. It’s definitely worth checking the piston diameter and spring length, was there anything wrong with the ones you took out?

    There’s always this: http://www.tangerineracing.com/oilpressurerelief.htm

    Incidentally, did you find the engine number?
  2. The Spring I took out was shorter but seemed stiffer compared to the new one piston was the same
    haven't checked engine number yet
  3. Another possibility is the pressure relief piston is getting stuck slightly open because of wear in the piston bore.
    A too short spring ( losing tension with age or swapped with an EMPI spring) could also cause the piston to drop.

    Its not the length of the spring but the force it applies when you do up the big screw thats important.

    When I rebuilt my previous engine ( now departed ) I had a right game actually getting the oil cooler bypass piston to move or come out of the engine as it was stuck.

    30 psi cold start is low. Should be more like 50 psi.

    Take the top plate off the oil pump and see if the plate has wear on it.

    An initial low pressure situation gets worse when the engine then wears faster because of the pressure.

    Slightly OT..
    Also it depends on the location of the sensor on the CHT reading.
    Old engine Autolinea heads got up to 130C sensor in CHT boss on head. Oil at 100 to 110 C. If the sensor is at the spark plug then it reads higher. Scarily somewhere around 160-180C the cylinder head starts to weaken.

    New engine EMPI heads sensor in same place same carb jetting : heads up to 110C oil 90 to 100C at motorway speed. And still about 15 psi oil pressure at idle, 45 at 4000 rpm.
  4. The springs tend to relax over time (free length of a new spring is about 62mm) but it’s the loaded tension that is important. Anyway, even a soft spring would not cause a total loss of pressure and if the piston is the correct size…

    Time to split the case to investigate I’m afraid.
  5. I think that whatever the cause that engine needs a rebuild now.
  6. Engine number cb209340 differs to engine shroud number cb079216
    If the engine originally had hydraulic lifters they were changed for solid before I had it. I assumed they were correct and bought the cam to suit.
    Would this have an influence on oil pressure?
    I will find a Vw mechanic to take a look
  7. That’s odd, a CB209340 engine is/was a 1700. It’s newer than the shroud but still years before hydraulic lifters – they were only fitted to late 2.0l engines. A 1700 should be dual relief; are you sure there isn’t a tri-square socket screw between the pushrod tubes on the right side of the engine?

    Hydraulic lifters won’t make any difference to oil pressure.
    Majorhangover likes this.
  8. image.png Just looked between #1 push rod tubes and see this hole.
    It looks like it's been sleeved, no threads and is about 33mm deep. I'm guessing that's where the other piston went....is this a common modification. In which case the pressure relief Spring was too short, as dual relief springs are longer?
  9. That’s exactly like my single relief CJ engine, it looks factory to me but I can’t understand how a 1700 case is not dual relief.

    Has that engine ever run with good oil pressure?
  10. Couldn't say about oil pressure
    It got delivered off a low loader. It started up sounded like a bag of spanners ( it had a rotten exhaust) so I turned it off and stripped it down.

    I just started it again today after changing Venturi sizes on carbs. The pressure rose to about 60psi and steadily dropped to about 35psi after 2 minutes of running.
    It is a much colder day today so oil temp probably a lot colder to begin with. Not sure if that means anything.
  11. That is not so bad.
    And compared with a T1 the T4 engines sound like they have a lot more spanners in the bag.
  12. With cold oil and the engine idling 35psi after 2 minutes running is okay. But you haven’t found the problem and if the pressure keeps dropping…
    Last edited: Apr 3, 2019
  13. When you start driving the bus those head temps will increase to circa 135/150C and more on a long climb, and some of that heat will go into the oil. Oil temperature can easily be above 100C.

    I hope the Tangerine Racing pressure relief valve cures the problem, please let us know if it does.
    Gooders and snotty like this.
  14. Have you received the Tangerine Racing pressure relief valve?
  15. Pressure relief valve arrived and fitted.
    It increased start up pressure to 70psi +
    Unfortunately the pressure still drops to near enough 0 by the time head temps reach 68-70degrees and the temp doesn't seem to rise any further.
    I've removed the oil cooler and checked it flows...all okay. If a gallery was blocked surely pressure would increase and bypass the cooler?
    Oil pump spindle not engaging camshaft once warm maybe??
  16. Start up pressure of 70psi +means the pump must be working and well engaged, if it was only just in the cam it would pop out making that pressure. It’s easy to check how much engagement there is by taking the pump cover off, pull the pump drive gear out and turn it 90deg and push it back in again – the distance the gear sticks out is the engagement. Incidentally, how much cam thrust clearance did you have building the engine?

    If a gallery was blocked the pressure would indeed increase and the oil system would act as if the oil was cold and thick and by-pass the cooler – as you thought. The cooler would also be by-passed with very high oil pressure, 70psi at start-up for instance. With a single relief case the by-pass oil is returned to pump suction, unlike a double relief where the oil goes back to the sump, but I don’t think that is significant.

    Unfortunately I think you’ve run out of options of what can be done externally.
  17. Cam thrust clearance was 0.05 using a feeler gauge
    I may tap the block and full flow to an external cooler
  18. But you haven’t got a temperature problem, with head temperature so low the engine is only idling or very lightly loaded; the oil is probably barely warm.
  19. I was thinking more that it would bypass that circuit and go straight from the oil pump (after blocking the output and fitting a take off plate) into the main gallery...
    Unless the oil isn't circulating of course, but first I shall check the pump engages properly
    77 Westy likes this.

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