[Supras] MHG's (now cam oiling)

[berniek at technicaldevelop.com]

Jeff:

    My JDM did not have that many miles on it either.  The cylinders were not worn more than 1/2 thou or so, and the main and rod bearings were in like new condition.

    However, the camshaft journal caps were worn, especially on the exhaust side, where the rearmost ones plastigaged at .006".  The problem is the lack of oil feed to the head, and the fact that all of the journals are cross-drilled.  As I'm sure you know, oil is fed into the hollow cams at only the front journal.  As a little wear occurs, there is less and less oil for the rear journals.  That is especially true at high speed because the oil tends to be thrown out of the journals increasing as the square of speed.  So less and less oil is available for the rearmost journals.  Moreover, the oil passages in the block and head which feed the cams are small.  

    As my rebuild wears, I'll probably refinish the caps every 20K miles or so.  But the thought did occur to me to drill into the 7th exhaust journal support in the head, intersecting with another drilled passage on the exhaust side, and run an external oil line to feed at least the exhaust cam from both ends (with a groove machined in its rearmost journal).  But one problem with doing that is the reduction in head saddle journal support width.  It reduces down directly under the cam journals, so putting an oil feed hole in the rearmost one and grooving the cam journal itself for oil feed might be self-defeating.

    Strange that the bottom end is built like the proverbial outhouse (with proper oil pan pickup provisions), but the top end oiling provisions are far from the best.   

            Bernie
  ----- Original Message ----- 
  From: Jeff Mohler 
  To: berniek at technicaldevelop.com 
  Cc: t72pwrd ; Bigmacz28 at aol.com ; SPOOLED91T at aol.com ; Supras at supras.com ; supr91tt at yahoo.com 
  Sent: Tuesday, February 13, 2007 11:58 PM
  Subject: Re: [Supras] MHG's


  Ya..but were talking a JDM import motor, with about 30k miles on it..and it's sat on the floor for 12yrs.

  It aint worn..its just a _mess_.


  On 2/13/07, berniek at technicaldevelop.com <berniek at technicaldevelop.com> wrote:
    Higher than normal compression pressures can also be due to increased valve
    clearance.  The cam opening and closing ramps are very gentle, but at
    cranking speed, a few thousandths less clearance can mean quite a bit. 

    As stated in the past, the cam journal caps wear and cause excessive valve
    lash before the shims wear.  The caps can be refinished.

            Bernie


    ----- Original Message -----
    From: "t72pwrd" < nholden1 at woh.rr.com>
    To: <Bigmacz28 at aol.com>; <berniek at technicaldevelop.com>; 
    <SPOOLED91T at aol.com>; <Supras at supras.com>; <supr91tt at yahoo.com>
    Sent: Tuesday, February 13, 2007 8:08 PM 
    Subject: Re: [Supras] MHG's


    > Carbon build up.
    >
    > -Nick
    >
    > ----- Original Message -----
    > From: <Bigmacz28 at aol.com>
    > To: < berniek at technicaldevelop.com>; <SPOOLED91T at aol.com>;
    > <Supras at supras.com>; < supr91tt at yahoo.com>
    > Sent: Tuesday, February 13, 2007 7:21 PM
    > Subject: Re: [Supras] MHG's
    >
    >
    > > BernieK, are you using the 2.0mm also or some other side? 
    > >
    > > Question Group: I got a JDM 7MGE and checked the compression with two
    > > different gauges.
    > >
    > > Both are reading 198 to 200PSI on every cylinder. What could be causing 
    > > this?
    > > The spec is around 150PSI.
    > >
    > > Any idea's?
    > >
    > > Joe Mac
    > > 89N/A
    > > _______________________________________________
    > > Supras mailing list 
    > > Supras at supras.com
    > > http://supras.com/mailman/listinfo/supras_supras.com
    >
    >
    >



    _______________________________________________
    Supras mailing list
    Supras at supras.com
    http://supras.com/mailman/listinfo/supras_supras.com