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Flathead cam

Discussion in 'The Hokey Ass Message Board' started by ford6man27, Jul 24, 2013.

  1. ford6man27
    Joined: Aug 7, 2005
    Posts: 67


    I have a 1950 pickup with an 8RT V8 engine. How much lift on a cam can be used without having the heads machined for valve clearance. I would like to use an L100 cam which has .375 lift. Will it work without machine work?

  2. ronnieroadster
    Joined: Sep 9, 2004
    Posts: 894


    Andy to determine if the L-100 will clear theres a few things you need to figure out first. Do you know if the block has ever been decked. Have the valve seats and valves been ground or are the valves new replacements. Next head gaskets what type material is it made of and how thick is the gasket.
    Going from the stock lift Ford cam to the L-100 will add around an addtional .060 thou valve lift. Each area mentioned above will reduce the stock clearance to the point where the valve is now to close to the head or possibly even touching. To determine the clearance you must always check. Try laying the heads on the block with no head gasket after installing the cam if you find the head raises as you turn the motor over by hand then you can be sure YOU DO NOT HAVE ENOUGH CLEARANCE.
    Hope this helps.
  3. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907


    All good points, Ronnie .... He didn't mention if his heads are new, or used

    Happy Roddin' 4TTRUK
  4. ford6man27
    Joined: Aug 7, 2005
    Posts: 67


    The motor has been rebuilt, bored .040 over and the valves have been ground but I don't think it has been decked. If the heads have been milled I think it would be minimal. I just have no idea as to how much room the stock 8RT heads have for valve clearance. Thanks.


  5. I would suggest you go over to our sister site, the FordBarn. Check out the earlyV8 forum. Do an intro and then ask over there. There is a guru there called Ol Ron (Ron Halloran) who will chime in, and he is the expert on the L100 cam. In fact there's several flathead cam experts there.
  6. dan c
    Joined: Jan 30, 2012
    Posts: 2,243

    dan c

    my 2 cents--the 8rt heads most likely are like the 8ba heads, having valve clearance of .375. measure at the top of the valve pocket. merc heads (8cm) have .425, but will drop the compression a lot on a 239. back in the old days most aftermarket cams had small lifts and more duration so they could be used with stock heads.
  7. rotorwrench
    Joined: Apr 21, 2006
    Posts: 633


    You can put little balls of clay on the tops of the valve & piston and bolt the heads on with a gasket then turn the engine through to see what kind of clearance there will be. 8RT heads were a replacement head for 8BA when they started making EAB heads in 1952. The 8RT should clear but you might have too much clearance. Ron likes .050" to .060" over the piston for clearance. He would likely recommend the EAB heads for better compression. You can go in the Fordbarn & ask. He like the L-100 grind for sure.

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