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Pretty specific question about valve clearances

Discussion in '308/328' started by Kingswood, Jan 21, 2023.

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  1. Kingswood

    Kingswood Karting

    May 16, 2022
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    Stew
    #1 Kingswood, Jan 21, 2023
    Hello all,

    I have a 1975 308GT4. This is a project car that had the motor rebuilt many years ago. I have recently taken ownership and am working through getting it on the road.
    I have the cam covers off and have measured all of the valve clearances. Results below -

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    I have some adjustments to make, but it looks like whoever put the motor together was pretty deliberate about having a .40 clearance on the exhaust sides. Manual states it should be .3 to .35

    Could there be a reason for this? or should they all be changed back to .3 to .35?
    I am not sure what details about the car can have an effect on valve clearance, but this is a US car, with all the air pump parts taken off, stock bore, new JE pistons.

    I also have another question, if someone could help. I have the distributors off, and I need to change the timing belts anyway. I don't have the special tools to hold the valve bucket down and change shims over. So I thought I would just set the car to TBC, and take the cam shafts out. Then measure all the shims, order what I need, and then re-install everything with all of the timing marks lined up. Then install my new belts and tensioners. I assume all the cam caps need to go back the same way they came out, but is there anything I need to keep in mind with that approach? Is that a sensible way to do things?

    Thank you.
     
  2. fatbillybob

    fatbillybob Two Time F1 World Champ
    Consultant Owner

    Aug 10, 2002
    29,070
    socal
    #2 fatbillybob, Jan 21, 2023
    Go with stock clearances. Pull cams is the only way I have ever done it. Your method is sound. Gt4 runs fine on assembly marks but cam time if you want accurate.
     
    Nuvolari likes this.
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    #3 Steve Magnusson, Jan 21, 2023
    Last edited: Jan 21, 2023
    The non-air-injected 308 are specified at .30 to .35 for the exhaust.
    The air-injected 308 are specified at .35 to .40 for the exhaust.
    The exhaust valve runs hotter, so expands more, with air injection.

    The cam caps and the cylinder heads should have stamped numbers on them that should always be matched together in the same orientation. Nothing too technically wrong with removing the cams (and doing the math/measurements/shim replacements) then reinstalling the cams (but if it doesn't go perfect you'd be reusing the new cam seals or getting another set of new cam seals). Do you have any punch "dimples" added into the bores where the cam seals go? It was a typical "fix" to try to not have the cam seals squirt out (and later models added some grooves to do the same function).
     
  4. Kingswood

    Kingswood Karting

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    Stew
    #4 Kingswood, Jan 21, 2023
    Thanks FatBillyBob. Legend.
     
  5. Kingswood

    Kingswood Karting

    May 16, 2022
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    #5 Kingswood, Jan 21, 2023
    Thanks so much for the response.
    At the risk of sounding like a complete amateur, what is air injection? Is that part of the US air pump/smog stuff?
    My exhaust headers are just regular headers, with nothing attached. Normal carby'd 308 with regular air filter and intakes.

    And no dimples that I can see.

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  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #6 Steve Magnusson, Jan 21, 2023
    Yes (generally). You don't have it.

    IMO, it's a useful refinement. Here's an example of the later design (that has a separate part to hold the cam seal) where they added 2 small grooves that the flexible material on the OD of the seal expands into to better retain the cam seal:
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  7. Kingswood

    Kingswood Karting

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    #7 Kingswood, Jan 22, 2023
    Thank you, thank you, thank you.
    I will get to work on restoring the clearances to .3 to .35 on the exhaust valves. I'm really glad I popped the covers off to check these, and always very appreciative when people help me out like this.
     
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  8. GordonC

    GordonC F1 Rookie
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    Aug 28, 2005
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    #8 GordonC, Jan 22, 2023
    Your rear exhaust cam seal is protruding a few mm from the seat currently. As Steve mentioned, you should plan to install new cam seals when you have the cams out.
     
  9. Kingswood

    Kingswood Karting

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    #9 Kingswood, Jan 22, 2023
    Yeah it's the best time to do it isn't it. I had been moving them around a bit once I had the cam covers off. They are brand new, but maybe 10 years old, so I think I will change them. The pulleys have a fair bit of surface rust in the teeth, so probably best to pull those off and treat them.
    There was no sealant around the outside, do you put sealant on yours when you install them?
     
  10. FiatRN

    FiatRN Formula Junior

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    Jonathan Drout
    #10 FiatRN, Jan 22, 2023
    https://autoricambi.us/search-results-page?q=valve%20tool

    The tool works great, and if you don't get it perfect the first time removing the cams, it is a lot easier to swap out just one shim. I found my Fiat cam tool was a little frustrating in one bore, and I ended up using a Fiat SOHC cam tool there instead. A tiny pick to help get the shims out of the top of the buckets makes things easier.
     
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  11. Miklas

    Miklas Karting

    Dec 10, 2018
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    #11 Miklas, Jan 23, 2023
    When you remove the bolts holding the cam caps be very careful that you don't drop them or the washers down the oil galleries because it can be a pain to get it out (ask me how I know). Some of them are under tension due to the valve spring so they can "fly" off when they are removed.
     
  12. Kingswood

    Kingswood Karting

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    #12 Kingswood, Jan 23, 2023
    That's good advice, thank you.
     
  13. Kingswood

    Kingswood Karting

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    #13 Kingswood, Jan 23, 2023
    Looking at the torque specs, the cam shaft cap nuts are meant to be 6.5 lbft
    That doesn't seem like much, how do they not rattle loose?
     
  14. yelcab

    yelcab F1 World Champ
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    #14 yelcab, Jan 23, 2023
    The cam oil seals are installed DRY.
    The cam cap nuts are just M6 x 1 and they do not need much torque. No they don't rattle off.
     
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  15. kiwiokie

    kiwiokie Formula 3

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    #15 kiwiokie, Jan 23, 2023
    They also require Belleville conical washers not standard flat washers like I used and will now have to replace at some point.


    Sent from my iPhone using FerrariChat
     
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  16. yelcab

    yelcab F1 World Champ
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    #16 yelcab, Jan 23, 2023
    I have never seen conical washers on any of the Ferrari I have opened up. It may be a good idea, but I have never seen it.
     
  17. kiwiokie

    kiwiokie Formula 3

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    #17 kiwiokie, Jan 23, 2023
    Interesting. I will have to search for where it came up in a prior thread.


    Sent from my iPhone using FerrariChat
     
  18. kiwiokie

    kiwiokie Formula 3

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    #18 kiwiokie, Jan 23, 2023
    I don’t know how to link a thread on the app but it was from 2019 and is called “Cam cap washer”


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  19. smg2

    smg2 F1 World Champ
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    #19 smg2, Jan 23, 2023
    They're on every single one I've touched. If the cam cap washer is black, then it's most likely the original Belleville one. They have a very slight conical curve.
     
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  20. Kingswood

    Kingswood Karting

    May 16, 2022
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    #20 Kingswood, Jan 23, 2023
    I just checked my cam cap washers, and yes they are shaped. The inside edge sits slightly offset to the outside edge.
    They were installed randomly though, doesn't seem to be "domed upwards facing the nut" kind of install, they are mixed.

    More awesome knowledge thank you guys.
     

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