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Dino 246 service

Discussion in '206/246' started by pshoejberg, Jul 1, 2020 at 12:25 AM.

  1. pshoejberg

    pshoejberg Formula 3
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    Peter H
    #1 pshoejberg, Jul 1, 2020 at 12:25 AM
    Last edited: Jul 1, 2020 at 12:39 AM
    It must be time for a little hardware thread. I pulled the engine from my early L series yesterday to perform an extended service. Ever since I completed the car project some 4 years and +-10.000 KM ago I’ve had a few issues that needed attention:

    1. I forgot to use sealing type Loctite on the piston head stud bolts and ended up with a slight cooling fluid leak around two bolts. The problem was solved by applying Loctite to the nut and the spacer washer. Not a permanent solution but it worked very well. I need to address this issue and I will at the same time install new stud bolts and nuts all the way around.

    2. From day one i had slightly lower compression in cylinder #4 and this issue did not improve over time, the opposite actually. I know both the valve seats in this cylinder had been machined more than once and the seats were on the borderline of wear spec. I performed a leak down this morning, and it revealed a clear leak past the exhaust valve. All other cylinders were fine. I will need new seats and valves for cylinder #4.

    3. From first day off I struggled with high cooling fluid temperature in the engine and I never found out why. The radiator is overhauled with a higher capacity core and the water pump and thermostat is also new. I changed to another fabricate of thermostat, but it didn't help. The problem solved itself over a couple of months. Later, I read a thread on FC about the Dino water pump and a small air drain hole above the water pump impeller that has a tendency to be blocked. I have never noticed this drain hole and it struck me that a blocked hole could explain the hot fluid issue. This morning I looked down into the water pump and found a completely plugged air bleed hole. I unplugged the hole in 5 minutes using a piece of wire.

    I cleaned the engine and thoroughly washed out all the stud bolt threads in the block in preparation for new bolts and Loctite.

    Next up is ordering spares and a time slot at my machinist for piston head work.

    Nice summer to all and stay fresh. Best, Peter

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  2. TonyL

    TonyL F1 Rookie
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    Peter, that vent hole comes from the water pump upper chamber above the impeller and stops air locking and possibly pump cavitation. It is vital the hole is open to the thermostat housing so air is bled out. I hadnt noticed this untill comparing my old pump with a new unit i purchased.

    If you have used a new thermostat housing make sure the thermostat actually closes against the inlet port and doesnt leak past. There are some nasty repro therm housings out there.

    Tony
     
  3. pshoejberg

    pshoejberg Formula 3
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    Thanks for the comments Tony. There is no doubt that my cooling problems was caused by an air lock. The air will eventually escape, but in my case that took a long time and there is a potential risk of overheating the engine. All the parts are the original and I've checked the correct thermostat function back then when I changed to an alternative thermostat.

    Best, Peter
     
  4. TonyL

    TonyL F1 Rookie
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    I am sure you have already done this but check the water sender unit, my old one was out of calibration and being non adjustable i eventually bought a new one. There are no accurate resistance reading for the sender so I bench tested a few. The Veglia gauge sender is no longer available and many over here sell "Veglia matched" sender units for silly money. I did a trail of 4 senders on the market and the cheapest one was the best in terms of accuracy to the Veglia gauge.

    If you are still having what you consider as cooling issues (i hope you dont) but put a temperature probe in the flow to the rad, if its reads about 90C then you are good, regardless of what the gauge reads. A small resistor can be used to correct it if needed.

    Airlocking can cause major issues on the dino cooling system as can over dosing the system with corrosion inhibitor. The best way i found was to fill the sytstem via a temporary external elevated tank (the higher the better) connected to the car expansion tank. then vent through the heater matrix with the heater control open.

    Tony
     
  5. pshoejberg

    pshoejberg Formula 3
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    In addition to the gauge readings I could actually feel the raised temperature in the engine room and ended up buying a laser temperature gun and it verified the readings on the car gauges. I’m very optimistic that the issue is sorted now, but will keep you all updated upon completion of my service. I remember reading all your adventures in the gauge issues (and many other very inspirational threads of yours).

    best, Peter
     
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  6. TonyL

    TonyL F1 Rookie
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    Laser guns are good but dont actually read water temp accurately and it depends where you spot test. I tried that as well and the most accurate way was to push a thin probe under the jubilee clip, retighten and read the actual water temp to the rad immediately after the thermostat. It also tells you if you have a lazy thermostat as well, my original was opening to late @ 88c instead of 82C, i changed it for a lower unit and now it opens at 78C.

    I dont like the after market water pumps that are currently for sale, most if not all of them have the impeller set to far from the housing, the spec is 1mm, the ones i have inspected are around 3-6mm which can lead to loss of performance from the pump (short circulating) itself, less flow means poor cooling.

    There are improved impellers on the market and willl try one when i next re-do the water pump.
    kind regards

    Tony
    Ps is that the original veglia sender unit fitted to the head?
     

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