350 Chevy

Discussion in 'Gas Engines' started by mikealston2428, Aug 13, 2013.

  1. mikealston2428
    Joined: Jul 2011
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    Location: aussie

    mikealston2428 Senior Member

    Hi All,

    I am currently rebuilding a 350 Chevy SB.

    I have purchased new hydraulic lifters, the next step is value adjustment, I have studied up on this.

    The engine has roller rockers.

    Browsing to internet I came across the below comment ?

    What does this mean ?

    However, if the engine is equipped with a mechanical tappet cam, then the procedure varies a bit.
    :confused:
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    There are now several version of the Chevy small block, which do you have (yep, it matters)?

    Roller rockers can be put on every generation of small block and is a good idea, if you plan on winding this puppy up a lot. Roller rockers are free HP, typically about 15 - 20 HP on the marine variants.

    Yes, valve adjustment differs from hydraulic to mechanical tappet. Mechanical lifters (tappets) are literal a hunk of steel, riding the cam lobes. Hydraulic lifters are like mini shock absorbers, filled with oil that cushion the impact from the cam lobes and more importantly, don't require constant adjustment as mechanical lifters do.

    There are thee types of lifters, mechanical, hydraulic and roller. Each has their advantages and disadvantages. Mechanical are usually reserved for full up race engines, where tear downs are common and your working on the engine frequently enough to tolerate the constant valve adjustment these lifters bring to the table. Hydraulic lifters are the install them and forget them assembly. Most engines have plain Jane hydraulic lifters. Roller lifters reduce friction a little bit and let the engine rev up quicker as a result, so these are also free HP. Unfortunately, rollers require a roller style cam, which can use more aggressive ramp profiles so they get more out of the engine, then hydraulics.

    Roller rockers and lifters are good choices for engines, with the power gains you can get, using a stock cam profile, though there's some costs associated with these choices, compared to a set of stamped steel rockers and hydraulic lifters.
     
  3. thudpucker
    Joined: Jul 2007
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    Location: Al.

    thudpucker Senior Member

    I have heard the Cam and Pistons are different for Marine Engines.
    Do you have someone down there to ask about that?
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It depends on the application. The cam is usually different, though on most "manufactured" assemblies (Mercruiser, Crusader, etc.) the pistons are automotive. This is because the output of these engines aren't all that much (350 @ 250 HP), which is about the same as the truck variants of these engines. The cam profile is understandably different, as the engine works in a much smaller, less flexible RPM range, though lope heights and durations may be similar, ramp profiles and lope separation will be different, to accommodate the marine application.
     

  5. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    follow the procedure for roller rockers from a mercruiser manual
    I have always used that and it works well
    make sure the grub screw that locks the adjusting nut has a sharp smooth protruding end and not serrated and make sure the rocker studs have flat ends on them

    Merc HP donks ( with hydraulic lifters) ask for;
    "turn adjuster to zero lash, tighten grub screw 20ftlbs then turn adjuster nut to 30ftlbs"
    which takes some lash out and jams the grub screw into the stud
     
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