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  • #16
    Originally posted by TommyP View Post

    There’s no such thing as a stupid question. Unless you’re a VW owner but in this case it’s not a stupid question.

    I’m not sure I completely follow you with your question on leak down. Compression tests are done when cranking which has oil flowing about and yes the oil helps seal the cylinders for blow to some extent. What do you mean why you say leak down test?

    Low compression can also be a sign of poor valve seating / blow by too.

    Valve stem oil seals are important in any engine. Especially at idle as a turbo engine isn’t making any real boost in the intake and an N/A is making vacuum. Deceleration too. The crankcase is pressurised and during the above conditions that pushes oil past the knackered stem seals and into the intake tract and it then burns it. My Volvo T5 is doing just this at the moment and has extremely high oil consumption. It also fucking stinks.


    Sent from my iPhone using Just T4s
    I'm not so much a VW owner Tommy - more of a short-term funder of the German engineering industry.

    Leak-down Test - where you turn the piston to TDC by hand (so valves closed, and with the diesel cut-off valve blocking the supply), and then pressurise the combustion chamber with air to a set figure, then observe the rate at which the pressure drops. The avoidance of engine cranking at speed means that a LDT should be a more reliable test than a CT as you are not introducing so much extra oil?

    Increasingly I'm beginning to appreciate how clever some (not all!) aspects of the design of these OHC heads really are - there's no cockling of the valve stems in their guides because the lifters are taking the brunt of the sideways swiping of the cam lobes, and they are a much larger diameter than the valve stems for distributing wear, plus directly oil fed too, so the guides have a relatively easy life. But not the valve oil seals. (Mind, I remain highly sceptical of the use of rubber timing belts though, and that vacuum pump on the 5 -Pot is a design blunder, pure and simple).

    It will be interesting to see what condition Lee's injectors are in, and whether they have ever been rebuilt since leaving the factory.

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    • #17
      Originally posted by Activ8 View Post
      Are the stem seals coloured for intake and exhaust?
      No, they’re all the same colour and I’m pretty sure they’re all the same size stems. It’s just the valve heads that are different but I’m happy to be corrected on the stem sizes. They are the same colour stem seals though for sure and all in the same bag from elring.

      Interestingly, There are varying types though as they went from a thicker stem at some point to a thinner one on the ABL’s for either cost saving or flow but don’t know which. Knowing VW it’ll be cost saving on raw materials.

      I think it was 7mm to 6mm but it could be 8-7. I can’t remember but it bit me in the arse on old my ABL engine in the camper years ago. I had to change for the smaller guides and regrind the seats.


      Sent from my iPhone using Just T4s
      Last edited by TommyP; 19 April 2024, 10:30 PM.
      #vanlife

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      • #18
        Originally posted by Jim24 View Post

        I'm not so much a VW owner Tommy - more of a short-term funder of the German engineering industry.

        Leak-down Test - where you turn the piston to TDC by hand (so valves closed, and with the diesel cut-off valve blocking the supply), and then pressurise the combustion chamber with air to a set figure, then observe the rate at which the pressure drops. The avoidance of engine cranking at speed means that a LDT should be a more reliable test than a CT as you are not introducing so much extra oil?

        Increasingly I'm beginning to appreciate how clever some (not all!) aspects of the design of these OHC heads really are - there's no cockling of the valve stems in their guides because the lifters are taking the brunt of the sideways swiping of the cam lobes, and they are a much larger diameter than the valve stems for distributing wear, plus directly oil fed too, so the guides have a relatively easy life. But not the valve oil seals. (Mind, I remain highly sceptical of the use of rubber timing belts though, and that vacuum pump on the 5 -Pot is a design blunder, pure and simple).

        It will be interesting to see what condition Lee's injectors are in, and whether they have ever been rebuilt since leaving the factory.
        I’m not clued up on a cylinder leak down test, I haven’t even heard of testing compression that way. Logically though, what harm does the oil do to any test as that would be the conditions that the engines will run under? I suppose it’s still a like for like test doing an LD but I’ve never heard of it before myself whereas compression tests seem to be the standard.

        When I get 5 minutes, I’ll take a look into it. I’ve put it in the dairy for the 17th of July 2032. I’ll ask my engine machinist on his take and see what he says too.

        Genuinely interesting though. It’s got me thinking.


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        #vanlife

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        • #19
          Originally posted by Jim24 View Post

          Increasingly I'm beginning to appreciate how clever some (not all!) aspects of the design of these OHC heads really are - there's no cockling of the valve stems in their guides because the lifters are taking the brunt of the sideways swiping of the cam lobes, and they are a much larger diameter than the valve stems for distributing wear, plus directly oil fed too, so the guides have a relatively easy life. But not the valve oil seals. (Mind, I remain highly sceptical of the use of rubber timing belts though, and that vacuum pump on the 5 -Pot is a design blunder, pure and simple).
          Wait, what? You think there are any merits to pushrod or side valve engines? Fair enough if you like old stuff they’ll be stuck with that ancient tech but fuck me things have moved on considerably since then.

          The 5 pots have a few flaws in my opinion and from my own experience and knowing the engines pretty well I’d say. The poorly supported camshaft being one of them and as you said the vac pump which I suspect takes out more than the odd camshaft and top end but it’s far from the worst engine VW have ever made. That would be the T5 2.5tdi lol.

          Timing chains are an excellent invention but the nylon faced guides? Not so much and that along with the tripled cost of parts, labour and specialist kit to change them make me think the polar opposite to you on this one. Fuck chains, rubber belt for the win. When they not ran in oil that is……. I’m looking at you PSA….

          Fun fact and further evidence of how shite VW are, the 1.9PD has an oil pump driven by the crank via a chain, the later 2.0tdi has a virtually identical setup but it uses a rubber v belt like alternators were 40 years ago but this is in oil. VW garbage.


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          #vanlife

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          • #20
            I'm not a lover of side valves, or two strokes, but yes there are some very capable OHV engine designs, (and many crap ones). The better ones have camshafts set high so that the pushrods are short and stiffer. They are so easy to work on.

            For OHC I'd prefer to see a series of pinions, or even better a vertical bevel drive to the camshaft, but they would both require skilled setting up and precise machining to tight tolerances, so not really viable for mass production. On the other hand rubber timing belts are cheap & hopefully cheerful?

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