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Valve seat issues after rebuild?

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  • #16
    You MUST do a static valve to piston clearance check before you do any more work on the car. Who knows how many times the head has been cut or the block decked. The only way to find out what's going on is to measure everything before you put it together. Not doing this is a sign of poor workmanship, no matter how much you think of the shop. Two things will cause bent valves, not enough PTV clearance (and you cannot tell if you have enough clearance by turning the motor over), and/or improper cam timing.

    For someone to have bent valves and then just reinstall everything without checking PTV is unbelievable.
    Several E30 M3's.

    More than I need but not as many as I want....

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    • #17
      Thanks for all the advice and info! This is extremely useful.

      I believe they did a static PTV clearance every time EXCEPT the first time they assembled the motor. The engine builder even created a special jig to measure piston/valve clearance while the cams are in the car (not sure how this works, haven't seen it myself). I'll verify exactly what they checked every time.


      '89 E30 M3
      (Diamondschwarz) | '01 E39 M5 (Silbermetallic)

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      • #18
        Measuring ptv clearance is really a simple process. Replace the springs with soft springs and measure gap between each valve and piston at min clearance. I can't understand how a machine shop would get this wrong. Its something that garage mechanics on this site have been doing for years without problems.

        Have you seen the ptv clearance data that they supposedly measured? I would be real interested to see those numbers. I hate to say it but they are definitely not qualified to do this job if they didn't do ptv clearance the FIRST time. I mean that is the ONLY way to accurately install schricks. It can be done with a dial indicator or clay bar. Absolutely has to be done though.

        Really sorry your going through this man. I've been there done that in one way or another, its no fun.

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        • #19
          When my engine was rebuilt (Schrick 284/284) I also had strange leakdown figures but they disappeared once it was fully run in - rebore with new piston rings were suspected (you could hear hissing through the oil breather). It then went on to record excellent Dyno figures, so in my case driving the car for a while did fix the compression.

          Re Oil pressure, I have a new oil pump and fully rebuilt engine and a combined digital SPA Oil/Fuel pressure gauge. At hot idle I get 2.2 bar from Castrol Magnatec 10/40 so unless your oil pressure switch is faulty (possible), I too would suggest you have an issue.

          Cheers and good luck.

          Dave.

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