[Roadsters] Valves leaking while cc'ing

[Steve Ehlers]

   Hi,
      If  you  have  Brass  intake  seats  ,which are sock , They MUST be
   replaced .They will be pounded-out and a stock valve will be "sunk" in
   the head and will fall out of the head eventually .
      If  you  have steel ,or a derivative ,you  may be  ok . That said ,
   Nissan  does  not publish actual valve heights/ Stem lengths  ,so they
   could  not  duplicate the dimension . They may have had spring heights
   dimension  ,that  is  controlled  by this number ,however their method
   would  have  involved  using valve shims under the valve springs .This
   doesn't  change the relationship with the actual stem length ,or valve
   position  relative  to  the  seat  . Since you had them install bigger
   valves  ??  ,  that  would have raised the valve and made stem lengths
   shorter
   than  spec  ,possibly . Anyways , Seat material used in the 1960's was
   designed for Leaded Gas ,how would they know  ,unless the seats
   had bean changed ?
    Steve Ehlers
   www.risingsunperformance.com
   Daryl Smith wrote:

     Thanks for the note Steve, and others as well.
     I  provided  the machine shop with the list of spring specs/heights
     and stock valve dimensions with the work order.
     Seats?  This  is  the  SECOND  shop that has told me that the stock
     seats  in  the aluminum head were in good shape, would be fine with
     the  unleaded  fuel,  and there was enough material there to modify
     for my oversize 1.70" intake valves, and 1.35" exhaust valves.....
     I  had suggested that they should change the exhaust seat since the
     new  valve  was  almost 2.3mm larger, but they were adamant that it
     was fine and they didn't need to be changed.????
     Is this a case of "we just don't want the work"???
     Here's   hoping   this   discussion   saves   someone   else   some
     time/money.......
     Daryl
     -----    Original    Message    -----    From:    "Steve    Ehlers"
     <stevenehlers at charter.net>

     Hi,
     This  is typical of  poor quality  machine work .Even with a slight
     interference angle made on seats and valves ,there should be NO
     leakage . If the head wasn't assembled you can seal the valves with
     a  thin grease coating ,as we do when building a combustion chamber
     matched high Performance head set up .If the valves had been lapped
     in  during the valve work a problem would have been seen in contact
     or  possible  run  out  on  the seat .Quality machine work can't be
     assumed by the end user if  you don't know the details of a quality
     job .
     For example , did you have new steel intake seats installed ,and at
     the right valve height ? Can the Machine shop even provide you with
     the correct stem height dimension . I doubt it !
     Good Luck ,
     Steve Ehlers
     www.risingsunperformance.com