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  • cam question?

    I going to put Schrick 284/276 cams in my 2.5, currently I run evo 3 272 intake and 248 exhaust cams . Does anybody know what the lift specs are on the evo 3 cams ? The schricks are somewhere in the 11's mm range right? The question I have is my head has been shaved 5 thousandents, I know bmw does not reccomend this but will I have enough valve clearance with the schricks? How much clearance would you say there is between the piston and the valve when running schricks? If its any help I have the weisco pistons that come with the Turner kit, they seem to have deep valve pockets.

  • #2
    Unfortunately this is very hard to predict without direct measurements. I hate to say it but I don't think there is any way to be for sure otherwise.

    Regards,
    Jake Larsen

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    • #3
      Hey Jake thanks for the reply, I bought the cams already and the heads on. If I had my mechanic drop in the schricks check all clearences and then turn motor by hand and nothing binded up would you say everything is all right?

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      • #4
        I have the same setup, Schricks and Wiseco pistons. My head has not been shaved. My advice, is do not assume ANYTHING. Things are very tight. You need to do, or have your mechanic do, a piston/valve clearance chart where you measure valve clearance at 20 degrees BTDC, 10 degrees BTDC, 10 degrees ATDC, and 20 degrees ATDC.

        On mine the tightest clearance was .065" on the intake side at 10 degrees ATDC. This is pretty tight by most standards, the often stated rule being that you want at least .100" minimum. Jefrem and some others advised me I should be OK, since the only clearances below .100" occurred ATDC, where the valve is "chasing" the piston and is not dependent on the spring closing it as the piston approaches.

        I very carefully set up the Schricks to their specs with adjustable sprockets. If you fail to do this, particularly on a shaved head, you can also affect piston/valve clearance.

        The fact that the engine turns over by hand without binding means very little, as you could have .001" clearance and it would probably turn over fine by hand.

        Doing this clearance chart is a bit of a pain, it took me most of a day before I was confident in what I was doing. But Jake is right you have to do it. If your mechanic does it I am sure it will go faster (assuming he knows what he is doing).

        Many people have assembled S14s with Schricks and Wiseco pistons. If you just put the thing together and run it chances are you would be OK. But these engines and parts are so expensive, in my opinion you cannot chance it. Too much is at stake.

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        • #5
          The fact that the engine turns over by hand without binding means very little, as you could have .001" clearance and it would probably turn over fine by hand.
          Exactly.

          Stroker2.5, Ironhead's statement above is right on. The deal is static state clearances (engine not running) and dynamic clearances (engine running) are not the same. If you crank it over by hand and you can't feel any contact, this doesn't mean you're ok.

          HTH,
          Jake Larsen

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          • #6
            Jake why does the piston to valve clearance change from one to the other ? Like with Ironhead said one of his intake clearances was .065, do they vary because of wear on the seats, valves, and springs? In most cases with people doing 2.5 and throwing in schricks do you think they all checked there piston to valve clearance ? Where would you say the average range your going to find? In my case with the head being milled .005 , I lost .005 of my safe margin right.

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            • #7
              Originally posted by stroker2.5
              Jake why does the piston to valve clearance change from one to the other ? Like with Ironhead said one of his intake clearances was .065, do they vary because of wear on the seats, valves, and springs?
              I'm pretty sure he's just referring to the crank degree at which clearances were the least, not comparing between cylinders. Although I'd suspect they will vary. Spring wear doesn't affect clearances really but valve and valve seat wear sure does.

              Say you've got an engine that sat around for a while and the valves that were open that whole time developed some heavy corrosion. So you pull the head and take it down to you're local machine shop. They look at everything and decide all they need to do is remachine those few valves but the rest could get away with just some lapping compound.

              For those that get remachined, material will be removed from the valve and the valve seat to restore the mating surfaces. Those valve assemblies will now have a higher stack height and thus greater clearance from the piston compared to those that were only lapped in. With that logic it may be a good idea to check them all. I don't know if it's typical to check them all but I would, at least until I got a feel for how much they can vary.


              Originally posted by stroker2.5
              In most cases with people doing 2.5 and throwing in schricks do you think they all checked there piston to valve clearance?
              Judging from conversations here, on the SIG, and E30 M3 OG lists, I don't think most check them, but I really don't know. I've done a lot of studying and ton of listening when it comes to S14 building but I haven't actually built one up yet. I've torn a few down and I'm always tinkering with it, but the fact is I've never built one.

              Originally posted by stroker2.5
              Where would you say the average range your going to find?
              I really don't know. I've got some info back home but I don't have much as far as statistics go for this. I hope somebody speaks up because I need some more reference for this too.

              Originally posted by stroker2.5
              In my case with the head being milled .005 , I lost .005 of my safe margin right.
              Yep. It may not end up to exactly .005 across the board but generally yes.

              Hope this helps somewhat,
              Jake Larsen

              Comment


              • #8
                Jake My mechanic is the one who's going to check all the clearances, but I never asked him how he does it. I have heard of people doing the check with clay between the pistons and the valves but that seems like alot of work because you have to set the head put in the cams, adjust valves, and then take it apart to check the clearance. Is there away to check the piston to valve clearance with out pulling the head back off? My mechanic knows s14's pretty good and he may know but I never asked him, I was just curious for my own knowledge. Thanks Jake you always have very helpful info.

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                • #9
                  Jake, Stroke,

                  Don't know if this will help you but I did check all mine, at 20 BTDC, 10 BTDC, 10 ATDC, and 20 ATDC. This was very tedious and I am not sure it was totally necessary, but I figured my time is free. Basically you wind up repositioning the dial indicator 16 times.

                  The max variation was around .008" for the same type valve at the same crank degree position. The number I quoted you (.065") was the absolute minimum clearance I obtained at any point. So in other words, the valve clearance from all my intake valves at 10 ATDC ranged from .065" to .073". This might (probably does) have more to do with technique than variation in the engine. It is very difficult to align the pointer on the dial indicator exactly parallel with the valve movement. Variations in positioning here could easily cause several thousanths difference.

                  It is probably important to say that all my tightest clearances were on the intake side at 10 ATDC. Jefrem told me this is typical with the Schrick 284/276 cam setup. At all the other degree points I was over .100" clearance.

                  This is important because at the point of tightest clearance, the piston is going down and the valve is "chasing" it. Tight clearance in this scenario is of a bit less concern than if the piston is approaching the valve.

                  Hope that helps somewhat, or at least makes sense.

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                  • #10
                    Ironhead thanks for the response, how did you check your piston to valve clearance? Did you read my post just before your last? Is there any certain way to check it with out taking the head back off.

                    thanks John

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                    • #11
                      John,

                      There is no way that I know of to do it without removing the head.

                      Basically you have to remove all the valve springs, and reassemble the head with just the small inner valvespring in place. This is so you can push the valve down by hand.

                      Then you put the cam box on, put in the cams and time them, and set the valve/cam clearance to spec.

                      You put a degree wheel on the crank, and find TDC with a long probe on a dial indicator in the #1 spark plug hole.

                      Then you mount the dial indicator (you will need a fairly long probe on it) so that the probe is resting on the valve shim of the valve you want to measure, as parallel as you can get it to the direction of valve movement.

                      Turn the crank by hand to each of the 4 measure points BTDC and ATDC. Zero the dial indicator. Then, you push on the valve shim/bucket until the valve contacts the piston. You can measure how far that is from the zero on the indicator. For each valve you take the 4 measurements. So you wind up with 64 total measurements if you do all the valves.

                      That is the jist of it. It is not really hard, just a pain in the butt, and time consuming.

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                      • #12
                        Excellent post Ironhead.

                        Thanks!
                        Jake Larsen

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                        • #13
                          Ironhead my head is back on the car already, but it seems the way you explained it the head doesn't have to come off again. You would do all the things you mentioned and when your done checking all the clearances you would then have to take everything back off to get the outside valve springs back in there, does the head have to be off to remove the outer springs?

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                          • #14
                            Well, it is possible to remove the vavle springs with the head on the car. There are fittings where you can introduce compressed air through the spark plug hole to hold the valves up while you remove the springs. You can also feed nylon cord through the spark plug hole to hold the valve up, although on engines like the S14 that would not be easy.

                            In my opinion, once you have the cam box off, there is not much left to removing the head. I would just do that

                            Comment


                            • #15
                              Ironhead you do make a good point ,it would be dificult to keep the valve up and try to get the keeper and retainer back on once you removed the outer spring. I was just looking at schrick cam spec sheet and it say lift is 3.5 mm on the intake and 3.2 mm on the exhaust cams at TDC, does the lift # increase at 10 and 20 degrees in opposite directions of TDC? Doesn't the 11.5 mm lift mean how much lift off the seat , and at what degree of crank rotation is it reaching this max lift? Thanks Ironhead and Jake , you have both been very helpful.

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