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Vibration when I put car in gear

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  • #16
    Camshaft - I don't have the spec's on it. It came from the machine shop and I asked for a stock cam. The machine shop supplied the cam, lifters and rods. The machine shop supplied all the parts needed to rebuild the engine.

    I used assembly lube and oil to put the engine together. After I installed the rail rockers I turned the oil pump until oil came out of all the holes on top. Every time a put a part in I rotated the engine to make sure it turned smoothly before I moved on to the next part.

    All the rocker arms were going up and down even on #4.

    I took pictures during the disassembly so I could remember how things went back together. I only took a picture of the timing gears and chain during the assembly.

    The machine shop, had me watch the air test, so I could see the valves holding pressure and were not leaking.

    It sounds like the rings are not my problem. The machine shop felt it was not the rings either.

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    • #17
      In an engine plant, all the parts are the same and clearances have been engineered beforehand. The moment your parts are milled, stock dimensions have changed which also changes the geometry.

      I have questions about your build:
      Are you using the oil baffles under the rocker shaft stands?
      What kind of pistons are used?
      What kind of rings?
      Were the ring gaps 'file to fit' or 'preset'?

      Hypereutectic alloy pistons (the most common pistons used in today's engines) require a much wider gap because they transfer more heat to the rings.

      I always sink the new rings 2" down their bore then MEASURE the gap before assembly. Yes, I've found many that were too tight. Many restorers find this work is too technical so they buy a crate engine or a short block already assembled, but careful-tedious measurements must always be exercised in custom block assembly.

      I asked about lifter preload because you had all your castings milled. Now, they are shorter than stock. New 'unknown' lifters are used as well.
      How much metal was removed from the block and heads?
      What is the thickness of your head gasket?
      You need to determine 'safe' clearances by two methods; lifter preload and piston-to-valve measurements.

      Because the block is shorter (from decking), aftermarket pistons need to be shorter (and they normally are by ~.020"). Your heads are shorter too. So, when you bolt down your heads with the new head gasket, MEASURE lifter preload and MEASURE piston-to-valve clearance. This should have been done as the first pair of pushrod were installed because there is no way to calculate this 'stack' before the heads are bolted down.

      Lifter pre-load comes first. It is done when the lifter is on the cam's base circle. I assume your rocker arms are NOT adjustable.

      If your 'casting stack' exceeds lifter preload spec's, the valves cannot close and you just turned hydraulic lifters into mechanical. In other words, when the lifter plunger is collapsed all the way, there is no more room for the hydraulics to adjust valve lash (and valve(s) may be held open).

      I shoot for .020" preload but never exceed .030" preload. Lifter manufacturers supply this number. To get back in spec's, you need to use correct length pushrods. Adjustable rocker arms will get you there but the rocker arm angle (geometry) needs to be correct, so now we're back to using correct length pushrods..

      Piston-to-valve clearance is done by rotating the crank by hand and carefully measuring the closest distance between the piston and the valves. This measurement can be done between the valve stem and rocker arm. I want to see .040" in my engines. Too close, and the piston can close the valve. That's how valve stems get bent. Sometimes a bent valve will also take out a valve guide. What is your piston-to-valve clearance? This is the reason why they cut piston tops for valve clearance. So important.

      'No compression' can happen if:
      None of the valves open,
      An intake valve stays open,
      An exhaust valve stays open.

      To determine the fault, I use compressed air in the 'bad' cylinder. The piston needs to be down and the valves closed (basically at the end of the 'compression stroke').

      Notice in this picture, the engine is still on its stand and there is an 'air hose spark plug' in #1. I use that for two things; to charge the cylinder and hold the valves up while I remove the valve springs and to check for any leaks.



      If an intake valve is leaking you will hear air escape through the carb.
      If an exhaust valve is leaking, you will hear air escape through the exhaust pipe.
      If rings are leaking, you will hear air escape through the oil filler.

      I'm eager to hear your answers. - Dave
      My latest project:
      CLICK HERE to see my custom hydraulic roller 390 FE build.

      "We've got to pause and ask ourselves: How much clean air do we need?"
      --Lee Iacocca

      Comment


      • #18
        Good questions that I will have to find out the answers to.

        I am using the oil baffles.

        The machine shop fitted the rings on the pistons.

        The rocker arms are not adjustable. The engine is stock as far as I know.

        Comment


        • #19
          Update:

          First of all I want to thank everyone for here for their help, especially Dave. He got me on the right track and I was able to double check things before I started the engine this time. A quote I remember Dave writing is you need to prove that what you are thinking is the problem. This got me off the vacuum leak since I could not find it and I started looking in another direction.

          The machine shop did a great job getting all the parts and machining done correctly. Every time I double checked their work it was perfect. It was me that made the mistakes. They went out their way to help me get this engine together correctly.

          My first build I put a washer between the timing gear and the block which is shown in the manual and on a video I watched. This was caused all kinds of problems. Bent rods, ruin lifters and cam. I had to take engine complete apart and have the engine cleaned again to get rid of the metal shavings. The machine shop rechecked the valves to make sure they were not leaking.

          The second time I built it I thought I had a vacuum leak. The engine ran great in park, but as soon put it in gear it started shaking and making a squealing sound. I thought it could be a vacuum leak, but I could not find the vacuum leak, so I did a compression check and found a dead cylinder. The dead cylinder was caused by the intake valve having a small bend in it which kept it closed.
          After installing the head and getting everything back together the engine started right up. I still had the squeal, which turned out to be a loose alternator belt.

          It runs great and sounds good. Hopefully I will not have any problems for a while.

          Again thank you for your help.

          J.J.

          Comment


          • #20
            Originally posted by JJbird View Post
            ...The dead cylinder was caused by the intake valve having a small bend in it which kept it closed...
            What caused the valve to bend?

            I know your engine is running well but if it were my engine, I would investigate deeper to ensure long and trouble-free engine life.

            Here's the deal... your cam pushes the lifter and nothing will stop it. If your piston bent the intake valve, the valve will hang OPEN. The valve spring is not strong enough to pull the bent valve back up to the seat. That is why we use a rubber mallet to check all the valves, so they return to their seats properly. A bent valve stem will show up immediately.

            The cause of all this is not the machine shop's fault because piston-to-valve clearance should have been checked as the first set of pushrods were installed. As I mentioned, metal was removed from your block and from your heads. Effectively, that makes the pushrods longer. How much longer can we tolerate? It depends on how close the valves come to the pistons AND hydraulic lifter preset.

            A longer pushrod shoves the lifter plunger down farther. If the plunger bottoms out, there is big trouble. We can always buy any length pushrods or adjustable rocker arms, to suit the rebuild tolerances. The most important part of all this is your tolerance measurements because you don't need this to come up again.

            I'm glad I could help and I'm glad your engine is running again. I asked lots of questions but got few answers. It's not important that I know the answers, but it IS important that YOU know because of the cost of your engine overhaul. - Dave
            My latest project:
            CLICK HERE to see my custom hydraulic roller 390 FE build.

            "We've got to pause and ask ourselves: How much clean air do we need?"
            --Lee Iacocca

            Comment

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