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piston to valve clearance specs and some other help needed

Discussion in 'Engine Building' started by GSRCRXsi, May 19, 2006.

  1. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    ok im trying to check my piston to valve clearance on my build. i know i can do it without taking the head off by using dial indicators on the retainer, setting the cams to the overlap position, and setting the piston to TDC. then loosen the cam gear bolts and turn the cam til the valves touch the piston, zero the guage, then turn the cam back til im at my minimum allowable clearance. and that will tell me how far i can safely go for cam gear tuning purposes.

    now i just need an easy way to lock vtec. i really dont want to disassemble the head. ive never pulled the rockers out and im a tad scared to. head is already installed on the block and toqued down, dont want to take it off as ill have to get another HG.

    i checked how far it would go til it hit the piston on the non vtec lobes (pointless i know) but it tops out the cam gear (full advance intake, and full retard exhaust) and the skunk2 gears do something like +/- 12 degrees. so its looking promising.

    the head/block has been milled but i dont know how much. i calculated the degrees that the crank was off when the cams were at TDC, not the other way around. and the crank moves twice the amount the cams do right? so the 3.4 degrees i got the crank being off by would then mean my cams would only be off by 1.7 degrees correct?

    also need piston to valve specs for skunk2 stage 2 cams... or is it general to use the specs mentioned in another thread .050 intake .080 exhaust ?

    and a little OT, i know the exhaust clearance it going to be bigger anyway since the exhaust lobes (generally) have less lift and duration but why would you not want it tighter? like what would be the big deal if you had .050 on the exhaust side?

    ive pretty much figured all the cam stuff out now and how to do this without taking the head off, but im looking for easier ways to lock vtec, without taking the rockers apart, and if possible without using air. the main reason i want to avoid the air thing is because people have been saying that you loose pressure very fast since it just leaks out. but someone from h-t said something about being able to keep it in vtec without having a ginormous compressor, something about moving the cam back so that the pins stay still.. any ideas?
     
  2. brian11to1

    brian11to1 Senior Member

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    You could probably use compressed air to activate VTEC...
     
  3. MikeBergy

    MikeBergy Blah blah blah....

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    You should only have to do one cylinder, so I'd opt to just the pull the rockers from the number 1 cylinder, lock em up, reassemble, and then do your tests. It's not hard or intimidating to pull the top end apart. You don't even have to touch the valvesprings, which I'd say is the hardest and most aggravating part. other than that, air is gonna be your only way, so you choose. You might find some info on degreeing cams and such on the m24x forums.

    yes to your question about the crank being off. If your crank is off 3.4 degrees when the cams are at tdc, then the cams will be 1.7 degrees off when the crank is at tdc. why would it be off though? Timing belt irregularities?

    The fact that the exhaust clearance is larger is for the exact reason you stated. Maybe having a tighter clearance would be to some negative pumping effect...i dunno, at this point, I'm talking out of my ass trying to visualize the air flow around this clearance while the exhaust port is closing. It's possible you could have a more complete exhaust stroke if the clearance was tighter, due to the slightly smaller volume of air allowed in the chamber after the exhaust ports close. Maybe the larger pocket on the exhaust side creates a more swirly motion of the air on the intake stroke. I am just speculating.

    If you already have oil in your system the air might not as easily escape, Maybe try priming the vtec system with oil and then using air, it could hurt.
     
  4. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    yea, i think im gonna just pull the rocker.

    and the gears are off from milling. i just dint know how much. so i measured. and i corrected it by advancing both gears
     
  5. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    so i need to remove those oil control orafices. how to i get them out? needle nose pliers?
     
  6. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    ok i got the orafices out, needle nose worked great. got the vtec engaged, i just put a small piece of plastic in the rocker to push the pin out. this way its engaged on both valves and not just one like when you switch the pins...

    checking clearance now.
     
  7. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    set cyl 1 to TDC with cams in overlap ("up" pointers on gears pointing down, TDC mark lined up dead nuts on)
    setup dial indicator
    loosen cam gear bolts
    turn cam til it hits piston (advancing for intake, retarding for exhaust)
    zero indicator
    back off the cam til you are at your min allowable setting

    and viola you have your max allowed settings for cam gear adjustment.

    i did clearance check. this is what i came up with.

    note, because of milling my "zero" is +2,+2

    using .050 on the intake i got my max to be +7 (+5 from zero)
    using .080 on the exhaust i got max to be +1 (-1 from zero)

    sound right? i think im gonna redo the exhaust to double check it, maybe i saw -1 instead of +1 (which would be -3 from zero)
     
  8. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    ok so i double checked everything and come up with this

    .050 intake : +6 on gear (+4 from zero)
    .080 exhaust : -1 on gear (-3 from zero)

    i rotated the crank and had valve-valve contact (weird since dan said this wouldnt happen with stock pistons and stock valves, but oh well i guess)

    changed the gear settings to +4in, 0ex (+2, -2 from zero) and its smooth sailing now. this is what im gonna use for my max settings when i dyno tune. but for now im back to +2, +2 (0,0)
     
  9. MikeBergy

    MikeBergy Blah blah blah....

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    Doesn't sound like you have much play room on the exhaust side if I understand you right.

    Maybe I should check my cam gears...never really thought they could be off. They are not a mass mfr'd gearset though, so maybe the specs are okay. How did you go about checking that? timing belt off or on? When you stuck the dowels in the cams to align them to TDC, did your markings all line up?
     
  10. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    read the newest post. :p i rechecked stuff. im safe +/- 2 degrees on both.

    about the dowels in the cams. (didnt use dowels, just drill bits. and i broke one, lol) anyway i only did that for torquing down to cam gears. they are "close to TDC at that spot, but not dead on. they shouldnt be used for the TDC marks. i just lined up the marks from, the gears. then noticed it wasnt perfect so i adjusted them accoring to how much i measured them to be off

    i checked the TDC of the gears by settuing the gears dead nuts on TDC for cyl #1. then i measured how much the crank was off (only did it this way because the crank TDC markings are further from the center of the crank, hence more accurate) so i measured how much the crank TDC mark was off, then measured the distance from the center of the crank to the timing mark. basic trig tan^-1(opp/adj) and viola you have your degrees the crank is off. and since the crank turns 2 times for every revolution of the cam gear, the cam is then off by half that much. done with the timing belt on and tensioned.

    i checked the p-v clearance by using the method i just described. set everything to overlap, cyl 1 at TDC (make sure its dead nuts on). remove the cam gear bolts (adjustment bolts, not the bolts the hold the gear to the cam) adjust the cam (advance for intake, retard for exhaust. since these both bring the valve closer to the piston) until the valve touches the piston. set up your dial indicator and make sure it cant move. then back off the cam til you are at your min allowable clearance. then note what your cam gear settings are at. since this is the maximum you can adjust and still retain your min clearance.

    also when checking your p-v clearance make sure you have some way of engaging VTEC. i did this by taking a small piece of plastic (a bb works too) and putting it behind the vtec pin (not the one with the spring, the other one) so this pushes the pin out and locks the rockers together. then check your clearance in the fashion i just said.

    and all this was done without taking the head off the block.

    it will also be good to check the valve to valve clearance. you cant really measure it, but on mine, at my maximum settings i had some valve to valve contact. i had the intake mani off and the header off so i could look in the ports and see that they were touching. i could also feel it. when turing the engine over to check dont go crazy. turn slowly and pay close attention to the valves. you will be able to feel and kinda hear when they touch. just back off and go back degrees til they dont touch. i went a little more back just so i knew i wouldnt have a problem. and my settings ended up so that i have +/- 2 degrees of room on both gears for tuning.

    damn that was long but i hope it helps understand.
     
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