Announcement

Collapse
No announcement yet.

Timing chain tensioner

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Timing chain tensioner

    Topic originally created by Bryan on May 6, 2006 3:32 AM and viewed 1913 times in the old forum.

  • #2
    Originally posted by Bryan on May 6, 2006 3:32 AM
    An individual on Fchat is looking at a C4 and asked the following. Any input?? The early 365 GTC/4's had automatic timing chain tensioners but the later ones were switched back to a manual system. Does anybody know if there were problems with these early systems? Should one avoid an early car for this reason? Thanks in advance for your opinions Stacy O'Blenes

    Comment


    • #3
      Originally posted by Michael Bayer on May 6, 2006 4:02 AM
      Bryan: I read it as well, my C/4 has one of these, it works fine, Tom Shaughnessy did the PPI on my car and he was comfortable with it, the car has also been in one of the best shops in this part of the world, Grand Touring where there is significant experience working with C/4s and they saw no issues. To be complete, my car has only 14,500 miles, 1,500 of those since I bought it last year. I have E Mailed that gentlemen and asked if he would send me a copy of what ever he based his note on, will let you know his reply. Michael Bayer

      Comment


      • #4
        Originally posted by Trachsel on September 30, 2007 7:31 PM
        When I bought my car, I was told that I never should turn or have turned the enginge backwards, because of the automatic timing chain tensioner (Renold) the timing chain could jump over the sprocket and what then happens , everybody can imagin. I think, that's why they switched back to a manual system. Now I know and I am happy, that on my car (s/n 16'273) is a manual tensioner, but even though I never will turn the engine backwards... Jacques.

        Comment


        • #5
          Originally posted by Aaron on October 1, 2007 9:27 AM
          Regarding turning the engine backwards – Thanks for posting info about the automatic timing chain adjustor and reverse engine rotation. I too have read or was told to never turn the engine backwards – I have blindly followed this advice and gone so far as to repeat it, never really understanding why. I have the manual chain adjustment (15777) and it made no sense to me why I could not turn the engine backwards. Regardless – when recently dialing the cams in, I always went around twice forward if I over shot a cam timing point. I though it might be due to the automatic chain adjustor on the pump chain – but there is so little force on that chain at manual rotation RPMs that it did not make sense either. The issue with the auto adjuster is the first thing that made since Aaron.

          Comment


          • #6
            Originally posted by Ian Levy on October 2, 2007 7:32 AM
            Aaron May I suggest that fear is the key. If turnig the engine back might be a dangerous & therefore very expensive mistake it made sense not to even take the chance I too went round again if I overshot a mark without clearly understanding the reason for so doing. Regards Ian

            Comment


            • #7
              Originally posted by Michael Bayer on October 3, 2007 9:16 AM
              I replaced my "self adjuster" with a factory upgrade it was a couple of hundred dollrs, frankly can not see much difference with a full manual version.

              Comment


              • #8
                Originally posted by jackdwitt on October 4, 2007 2:33 PM
                Let me explain why turning the engine backward is a dangerous practice regarding the chain tensioner. It is not a matter of a "wives tale" with no technical justification. When the engine is running in forward direction, the crankshaft is pulling the chain in the "forward" direction (in our case, counterclockwaise) against the resistance of the cams opening the valves. This is considerable resistance. The "tensioner" (slack remover) is always located on the back side, where there is no work being done by the chain. Therefore, the slack remover does not have to overcome any tension created by mechanical resistance to push against the chain to keep it tight. The slack remover pushes the chain into a vee path. When you turn the engine backward, the previous back side becomes the "forward" side. When going backward, there is resistance that did not exist before because the chain is opening the valves on the back side. Very few, if any, slack removers are strong enough to overcome this resistance, they are not able to maintain the vee path of the chain. Instead, they collapse against the resistance, allowing the chain to take a straight path. The resistance of opening the valves causes the chain to take a straight path. This CHANGES THE TIMING, the relationship between the crankshaft and the camshafts. This timing is established by the length of the chain AND ITS PATH. When you go from a vee line to a straight line, even though there is a constant number of links in the chain, the timing has been changed. This is why many engines have "eyebrows" cut in the pistons. The eyebrows give clearance between the piston and valves regardless of the valve timing. In normal timing, the valve(s) is NEVER wide open at TDC. There is no possibility the valve will contact the piston. However, without eyebrows, if the valve timing is way, way off, when the valve is wide open it may contact the piston at TDC, with disasterous results. This is more likely in a high performance engine because that engine will have high lift cams and high compression created by the piston dome projecting further into the combustion chamber. This engine will likely have long duration valve timing, so that the possibility of valve/piston collision is closer to "normal" timing. All of this is relevant to our engines. DO NOT turn your engine backward. Also, if you do your own work and have the heads off, when reassembling the engine, put the cams at the timing mark (this is described in the manual) and insure the crakshaft is at TDC for #1 when placing the heads on the block. Do not rotate the crank until the cam drive is complete. This will insure correct timing and prevent damage. By the way, I can speak from experience, although I did not learn this on a Ferrari engine. When turning a engine by hand, piston/valve contact will cause a bent valve. You can consider yourself lucky if you only bend one. I've never been that lucky. Regards, JackW

                Comment

                Working...
                X