Announcement

Collapse
No announcement yet.

Degreeing Cams and Checking P-V Clearance

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

  • Degreeing Cams and Checking P-V Clearance

    I'm not swapping cams at the moment, but I do have the engine out of the car and want to do some looking around and educating myself while it's nice, easy, and accessible. I may do a valve adjustment, and take some measurements while I'm in there to get the hang of this...

    First, does anyone have a good set of instructions on how to degree cams on our motor? There are a lot of threads discussing this, but I haven't found one that I would qualify as a good writeup. For example, if you have a cam to be set at 106 degrees, exactly what does that mean? Does this mean that you are setting the point of maximum lift (is this the cam lobe centerline?) to be 106 degrees ATDC? How would you do this on our motors? Put the dial indicator probe on the #1 cylinder shim / bucket for the cam you are measuring at TDC, then rotate the engine by hand measuring the point of maximum travel downwards as the cam rotates? Then rotating the cam on the timing chain, or using adjustable sprockets (if necessary) to set the cam such that maximum valve lift is exactly at 106 degrees ATDC? If I have the theory right, are there any tips or tricks to be aware of?

    For Piston - Valve Clearance. I know you degree your cams, and rotate the engine carefully by hand to make sure there's no p-v contact. Then you pull the head, put clay in the valve reliefs, put the head back on and re-torque, and rotate the engine through a full cycle again. Do you then just pull the head, and look at the valve reliefs to see how deep the impressions in the clay are? How do you measure P-V clearance? Just screwing around with feeler gauges trying to estimate the thickness of the clay where the valve left an impression? It seems like there should be a method more precise?

    Thanks in advance, learning about cam timing is a little more interesting than going up on the roof to fix the leak I discovered this week :o
    sigpic
    Track Car Build | COM Sports Car Club

  • #3
    Brendan, no one has an S14 specific write up because it is a pretty involved process and frankly it would take a lot of writing. To really do it right would involve lots of pictures also, because some of the steps are hard to explain. The write up the late Jefrem did on the Iigomotive website was pretty comprehensive, but the site is now down. Maybe someone saved it?

    The various links you posted should give you a good head start. Maybe the best plan is to ask specific questions about specific parts when/if you get stuck?

    Also, are you doing it with the engine in the car or removed?

    Comment


    • #4
      If someone still has Jefrem's writeup saved, I'd love to see it.

      I'm actually not doing a cam swap right now, I just have the engine out of the car and figured this was a good opportunity to learn a little more about the process.

      First question: When a cam is spec'd to be timed to 106 degrees (like some of the Schrick's I think) does that mean that max valve lift for cylinder #1 should occur at 106 degrees ATDC? Am I understanding that right?

      I think I could figure out a good way to measure based on the links I've seen, using a dial indicator, magnetic base, etc - But want to make sure exactly what timing or degreeing the cam actually means first - what it's really looking for given manufacturer specs.
      sigpic
      Track Car Build | COM Sports Car Club

      Comment


      • #5
        Part of the problem is, that various cam manufacturers post cam data in different ways. The good ones will tell you that you should have a certain valve lift measurement at certain crank degree measurements. I don't remember how Schrick does it.

        Regarding your question, my best advice is to install the cams directly to stock specs. CAREFULLY rotate the engine by hand to make sure there is no interference. Then, the cams will be very close to Schrick specs if not dead on. If at this point, you install your degree wheel and hardware to measure valve lift, you should be able to make sense of the specs given by Schrick.

        IIRC, I wound up noting the opening degrees at a certain valve lift, say .020", then noted the degrees as the valve closed when it again reached .020". Then I did the math and figured the point in degrees midway between these two events, and took that point as max lift (the lobes on Schrick 284/276 cams are symetrical). This worked best because as I recall (I did this several years ago) the cam tending to "linger" a bit at max lift and it was hard to figure precisely where the max point was.

        Another interesting point of trivia.... While doing this, I noted by my measurements that the 284 cam had shorter measured duration than the 276 cam. I took multiple measurements and noted I had the correct cam in the correct place to confirm this. I cannot explain why that is so. I emailed Schrick and asked them, only to get, somewhat predictably, no response.

        HTH
        Last edited by Ironhead; 12-14-2008, 08:12 AM.

        Comment


        • #6
          Makes sense. I suppose this is one of those things I'd need to revisit when I actually have the manufacturer's specs in hand. If anyone has Schrick 284/276 cam cards lying around, I'd love to see a copy just to satisfy my curiosity.

          What about P-V clearance? Time and degree cams, remove head, install strip of clay across valve pockets, re-install head with an already compressed head gasket, rotate engine 2x, remove head, carefully remove clay, measure clay with calipers, feeler gauges, or fine ruler?

          Thanks for the help.
          sigpic
          Track Car Build | COM Sports Car Club

          Comment


          • #7
            Checking cam timing is not that difficult. All 4 stroke engines are checked the same way. However, unless you have the manufactures cam card, and a set of adjustable pulleys, their is no need to check it.

            Comment


            • #8
              Originally posted by Brendan View Post
              What about P-V clearance? Time and degree cams, remove head, install strip of clay across valve pockets, re-install head with an already compressed head gasket, rotate engine 2x, remove head, carefully remove clay, measure clay with calipers, feeler gauges, or fine ruler?

              No easy answer here....

              I don't really like the clay method, because it gives you the bare minimum clearance, but you are not sure where it is occurring...

              A better way, IMHO, is you remove the outer valve springs on the valve(s) for which you want to check clearance. I would probably just do the forward #1 intake and #1 exhaust. Unless something MAJOR is wrong somewhere, the reading you get on any intake valve will be the same as the other intake valves at the same relative cam position, likewise for the exhaust.

              With compressed air through the sparkplug hole or other methods, you should be able to get the outer valve spring off without pulling the head.....hopefully.

              At any rate, you get the two valves so they only have the inner spring, then reassemble everything and time the cams where you want them. The idea here, is that with only the inner valve spring on, you can depress the valves by hand. Rig up a dial indicator with a long probe, so that it rests on the valve bucket/shim you want to test. The best way to do this is to bolt a flat piece of steel to the cam cover studs, attach a magnetic base to that, then position the indicator as perpendicular as possible to the surface of the valve shim. Then position the probe from the dial indicator on the shim. When all this is done, you can zero the dial indicator, then push on the valve shim (easiest with a long tool with rubber on the end) to depress the valve until it contacts the piston. The distance it travels before contact, as shown on the dial indicator, is the piston-valve clearance you have at that crank position.

              I would do this with the crank at 20 degrees BTDC to 20 degrees ATDC for both the intake and exhaust valves, in 5 degree increments.

              You will find the exhaust valve clearance is the smallest at around 10 degrees BTDC, whereas the intake valve will be closest to the piston at roughly TDC or 5 degrees ATDC.

              FWIW, my closest clearances worked out to .068" on the intake side, and .075" on the exhaust. That is pretty tight, right at the minimum recommended by most S14 experts (way less than the minimum recommended by the domestic V-8 crowd). I have run the engine for years now though, without a problem. I had the head off a few months ago, and there were no signs of of valve/piston contact, so I think those clearances are OK. I run a 7600 redline. If I reved to 8K or more, who knows? It would be pointless anyway with the 284/276 cams because they lose power past around 7400.

              Comment


              • #9
                good post, well written.

                Comment


                • #10
                  Bumping my own thread to add some more links for future reference...


                  Cams: advance/retard basics
                  - Jake

                  Best way to find #1 cylinder TDC? - Brendan

                  Cam Installation - Sector7G

                  I screwed up, but how bad? - Sector7G

                  Schrick 284/276 Valve clearances - ShepsEVO3

                  Valve seat issues after rebuild?
                  - rsnodgrass

                  Specifications - babarabus

                  Schrick titanium retainers - rewilfert
                  sigpic
                  Track Car Build | COM Sports Car Club

                  Comment


                  • #11
                    good move Brendan putting all the links in one post, will save alot of people a lot of searching in the future!

                    Whens yours finished?i am a fan of your project and enjoy your updates, i am just finishing the complete custom loom off in mine.... then fuel lines and ill be firing it up for the first time.......fingers crossed!

                    Comment


                    • #12
                      Originally posted by babarabus View Post
                      good move Brendan putting all the links in one post, will save alot of people a lot of searching in the future!

                      Whens yours finished?i am a fan of your project and enjoy your updates, i am just finishing the complete custom loom off in mine.... then fuel lines and ill be firing it up for the first time.......fingers crossed!
                      Well, I'm not sure it'll ever be finished - Brendan's Track Car Build

                      I'm finishing the final details on the dash and wiring now, and then it's just some housekeeping before I switch gears to figuring out the MegaSquirt and getting it tuned. On track in April if everything goes to plan.
                      sigpic
                      Track Car Build | COM Sports Car Club

                      Comment


                      • #13
                        Bump for good reference

                        How's the MS3 plans coming Brendan? I think I'm sticking with my 3.57 until I switch to ViPEC V88.
                        Rich!

                        Comment


                        • #14
                          FWIW, I hope to post a complete "how to" on adjusting cams come January. Pictures, text, downloadable too.

                          Jake

                          Comment


                          • #15
                            FYI, here is Jefrem's write-up. Sometime after I originally posted this thread I snagged a copy and cleaned it up - Jake, this may be a good starting point if you're doing revisions...

                            https://docs.google.com/Doc?docid=0A...thkey=CPD7jc0M

                            Rich, Just took the car off the road for the winter and am ordering parts now. Remember, the 3.57 is the Mainboard - You can have a MS2 3.57 or a MS3 3.57. If you have a "standard" MS2 3.57, you can upgrade to MS3 simply by removing the daughtercard, and replacing with the upgraded MS3 version then updating firmware and settings. I'm getting a little more involved because I'm switching to COP, Sequential, and installing a J&S interceptor for knock control so will be doing some re-wiring.
                            sigpic
                            Track Car Build | COM Sports Car Club

                            Comment

                            Working...
                            X