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Torque setting for 250GT

Discussion in 'Technical Q&A' started by Glassman, Jul 27, 2004.

  1. Glassman

    Glassman F1 World Champ
    Silver Subscribed

    Apr 23, 2002
    13,115
    Can anyone suggest the proper torque setting for the four nuts that hold down the Cam Roller assemblie on a 250Gt. I don't know what this part is called but it holds the cam roller and the screws that in turn actuate the valves.
     
  2. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    26,949
    Austin TX
    Full Name:
    Brian Crall
    My 275 shop man. states 28 ft. lbs. 250's and 275's use the same design pieces as well as the same fastener sizes. In practice however the aluminum has on many cars become softer thru an annealing process that takes place over the life of the car. Also the studs get weak by many reinstallations of the rocker assy's and almost certain over tightening on several of those occasions. Check the studs carefully for "Hourglassing" or streching of the upper threaded end, near the base of those threads. A better solution would be to order a new set from ARP (American Racing Products). I dont have a number for them here but you should be able to find them on the web. They usually stock them, I'm not sure they know what they are for but so many Ferrari shops buy from them that they usually run off a large lot. You may have to send them one or a good drawing of it to match. In any event I, for the previously stated reasons, never torque them past 18 ft. lbs. to keep them from tearing the threads out of the head and have never had one come loose.
     
  3. davehelms

    davehelms F1 Rookie

    Jan 3, 2004
    4,629
    Full Name:
    Dave Helms
    Ditto what Brian say's. I made a note in my 275 manual many years back and changed it to 18'#'s. Never had any problem on any of the race cars either.
    Dave
     
  4. Fiat Dino 206

    Fiat Dino 206 Karting

    Apr 19, 2004
    144
    Mississippi
    Full Name:
    David
    I checked two references:

    1. Ferrari 250/GTE, Coupe Pininfarina 2+2, USO E MANUTENZIONE
    2. Ferrari Tuning Tips and Maintenance Techniques, FAF Motorcars, Inc. 3rd Edition

    250GT Torque Specifications

    Models 250GT, 250GTE
    Engine type: 128, 168 variations (b, c, d, e, f)
    Years: 1956 - 1964

    Rocker Assembly/Cam Bearing Nuts 20 lb. ft.

    There is a note which may apply:

    "Note: Torques indicated are for clean, lubricated threads in good condition, with air and thread temperatures between 60 degrees F and 80 degrees F. Flat washers must be free of knick and burrs to insure proper torque."

    Further, the 168 engine is from the 250 Lusso series and the (b,c,d,e,f) refers to style variations of the 128 type engine.

    The 18 ft. lb. number would seem reasonable as it is only 10% below the suggested torque.

    (I am not sure that the 28 ft. lb. number mentioned in one post would have applied to the 250 GT series and; if the 28 ft. lb. number were correct, a reduction from 28 ft. lbs. to 18 ft. lbs. would likely be too great to ensure that the fixing nut stay secured as the reduction in toqure is approximately 36%? comments?)

    Best wishes
     
  5. davehelms

    davehelms F1 Rookie

    Jan 3, 2004
    4,629
    Full Name:
    Dave Helms
    The nuts in question are 1.0 thread pitch if I remember correctly. Plenty of clamping force with this fine thread. An 8mm stud with a fine thread and 28#'s applied will pull the stud out of the aluminum. Been there! Even with a helicoil it barely holds in the head. We raced (7) 250 series cars (inside and outside plug engines), that came apart most every winter and never had one loosen at 18#'s. That aluminum is getting pretty punky at this age.
     
  6. Fiat Dino 206

    Fiat Dino 206 Karting

    Apr 19, 2004
    144
    Mississippi
    Full Name:
    David
    Thank you for comments.

    Best wishes
     
  7. Glassman

    Glassman F1 World Champ
    Silver Subscribed

    Apr 23, 2002
    13,115
    Thanks for the comments guy's. 18# it is!
    Bill
     

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