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348 valve clearance?

Discussion in 'Technical Q&A' started by ernie, Dec 29, 2003.

  1. ernie

    ernie Two Time F1 World Champ
    Owner Lifetime Rossa

    Nov 19, 2001
    21,821
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    Okay, I FINALLY got some time to work on my engine. I am at the last part of the major. I just finished putting the cams back on banks 5-8, and set the timing marks to TDC. But before I went any further, I figured it would be a good idea to recheck my clearances before the belt goes on. I'm in California so I have the stupid smog crap to deal with. Anyway. My inlet clearances weren't too bad. My tollerances are .20 - .25mm for the inlet, and .30 - .35mm for the exhaust. Most of the inlets clearances are .20mm, but I have a couple that are a bit tight at .178mm. The same for the exhaust. Most of them are right at .30mm but I have a couple that are off a bit, at .279mm. My question is can I get away with a few of the valves being tight? They are only one off. Cause I really don't wanna take the freekin cams off again. This is so frustrating. I haven't mess with the cam timing at all. I left it as is. So I'm hoping that a few valves being tight will be okay. If they won't, I'm gonna have to remove the stinking cams all over again, and I just torqued them down.
     
  2. Dale

    Dale F1 Veteran

    Oct 7, 2003
    5,211
    uk
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    Dale Juan
    Hi Ernie,if it were an inlet and depending on how hard you drive it i may leave it on the tight side,exhaust its a hot valve and you need to cool it slack off the clearances,your in there and its not that hard a job,
    have a good new year,
    cheers
    Dale.
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    ernie -- Why MUST you remove the cams? Can't you use the prybar+spacer tools to R&R individual valve shims?
     
  4. fatbillybob

    fatbillybob F1 World Champ
    Owner Consultant

    Aug 10, 2002
    16,633
    socal
    ERNIE.....DO IT RIGHT!!! This is your concious talking. Do it right!!!

    Actually, You are better off ant the most open end of the valve lash range. You make more power this way with these cars.
     
  5. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,334
    Can you get away with a few that are tight--yes, however, the cam timing will not be right, and teh tune of the motor will not be as good as it can be. If you already have the motor this far apart, do it right and change the thin shims. A tight intake will have more duration, a tight exhaust may burn.
     
  6. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
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    Thank guys.

    LOL billybob, "this is your concience talk". In the back of my head I knew I was gonna have to change them out. I just didn't wanna face the facts.

    What has me puzzled is I shot for the middle, and ended at the tight end of the specs. For example on one of the exhuast valves the clearance was .381mm. The far end of the spec is .35mm, The old shim measured 4.089mm. So I calculated that I needed a shim with a thickness of 4.14mm to put the valve right in the middle of the specs at .33mm. But when I checked the valve after I put the thicker shim in, and the cams back on, I got a measurement of .305mm for the valve now. That is were I just don't get it. My math is right, so what gives?

    91tr, the reasons I don't use the valve tool are, 1) I don't have one, 2) I had to pull the cams off anyway to change the cam seals and o-rings, 3) Ferrari is out of it's mind what they want for it.
     
  7. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
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    socal
    What has me puzzled is I shot for the middle, and ended at the tight end of the specs. For example on one of the exhuast valves the clearance was .381mm. The far end of the spec is .35mm, The old shim measured 4.089mm. So I calculated that I needed a shim with a thickness of 4.14mm to put the valve right in the middle of the specs at .33mm. But when I checked the valve after I put the thicker shim in, and the cams back on, I got a measurement of .305mm for the valve now. That is were I just don't get it. My math is right, so what gives?


    Well a couple of possilbe things. 1) if you or the PO is smart you put the numbered side of the tablet away from the cam so you can read it. 2) you have to look at the shim number AND measure the shim. 3) make sure you measure clearance at the base circle which is perpendicular to the head deck not with the lobe point straight up perpendicular with the ground. 4) If you are using a digital caliper you have to zero it before use every time for accurate measurments. 5) if you are using a caliper you really need a caliper with comparator points because the center of the shim could wear more than the edge. 6) when you measure with a caliper you have to pinch the shim and let go of it with the other hand. If you hold the shim and measure you can "cock it" and that will through you off a tenth easy. 7) make a drawing of your head on a piece of paper and wirte down the measurements as you go. Keep the paper orientation drawing the same as the orientation of the motor. This way you don't make mistakes in transfering the data. 8) There is stiction and clearance slop upon reassembly. You have to turn the motor a few rpms to make sure everything seats home then measure.
     
  8. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
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    Yeah I did make a chart of the motor on paper when I first measured the valves, and the shims. When I checked the valve clearance I did it with the cam lobe facing away from the top of the shim. As for the mircrometer I used one that is not digital. I didn't like the digital ones because of what you said that they have to be reset every time. I just don't trust them. When checking the shim thickness I didn't hold on to the shim. I held the shim till the mic. started to grab it then I let go. Also when I was measuring I used the clicker to turn the mic. piston. This way the same pressure was used every time. I checked the middle, and four different points on the outside rim of the shim. Hey that rymed, LOL. Anyway, there was different wear on some of the shim. But for the most part they were wearing pretty even. If there was a difference in the wear is was a few thousands of an inch differance, and some times a hundred of an inch. But that was on the outside edge of the shim, not in the middle were the cam lobe is at full contact. So I went with what the middle of the shim measured. I just checked banks 1 - 4 yesterday and the intake valves are good to go. Same thing for the exhaust. I think what I'm gonna do is put the cams on, then the old belt. Turn the engine over a few times, so that things can get settled in, then recheck everything as you suggested. It isn't as bad as I thought when I first checked them. I have two or three valves that I have to change, maybe four but thats it.
     
  9. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
    16,633
    socal
    GREAT! Lets get that thing on the track. You are halfway to button willow raceway.
     

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