[Zmagnette] Engine Clatter & pressure drop

[jenntoo at shaw.ca]

Easy to tell if it is a broken crank.  Take off or loosen the fan belt and see if you can easily move the crankshaft pulley a few degrees in either direction.  If you can the crank is almost certainly broken.  The "T" series cranks break whether the engine has been recently rebuilt or not and breakage appears independant of the engine overall condition.  The thought is that a harmonic vibration sets up in the crank at about 4100 rpm and finally fatigues the crank and it breaks.  With the stump pulling 5.125 rear ratio 4100 rpm is around 60mph.  Do yourself a favour and change the ratio to 4.3:1.
    I broke one in the late 60's.  Picked up a used crank for $25 from a Worseley 4/44, had it ground, picked up a complete set of bearings, pulled the motor, took off the pan and installed the 4/44 crank.  Nothing else was done.  After I had the parts this was done in less than one day and I drove the car for 10 years without any problem-mostly in the city of Sydney OZ.
             Hugh Pite
  ----- Original Message ----- 
  From: Allen Bachelder 
  To: List for the Z Magnette Group - North America 
  Sent: Monday, November 11, 2013 6:12 PM
  Subject: Re: [Zmagnette] Engine Clatter & pressure drop


  OK, 5# oil pressure tells you it's hemorrhaging some place.  If it's a bearing, why should just one bearing catastrophically fail?  I rather like the broken crankshaft theory.  A friend of mine had that happen recently with his TF. As to repair, you can always get by for some time with a minimalist approach if you don't drive it too hard or too much.  If all you do is take it out on 40 mph club tours - about 500 miles per year, then that might be OK. If you want it right, do what it takes to make it right.  You may have to pull and disassemble quite a bit before you have your answer - and by that time, it will not make economic sense to put it back together with a minimal repair.  Most of us don't want to go this way more than once...


  OTOH, a friend had to shut his TD down in Kansas on the Rallye to Reno due to a horrible clatter that, after a tow back to Michigan, turned out to be valve gear banging on an ill-centered valve cover! Of course that was not associated with a loss of oil pressure...


  FWIW,
  Allen

  ****************************************************************
  Allen & Florrie Bachelder       =iii=<
  Spring Creek Home for Wayward MGs
  '57 ZB, '65 B, '69 C/GT, '73 B/GT
  North Street, MI 48049, USA
  http://www.mgexperience.net/member/bachldrs
  ****************************************************************


  On Nov 11, 2013, at 7:36 PM, Richard Greenberg wrote:


    Still plenty of oil.  After I stopped, I restarted the engine to drive it slowly a few hundred feet to a safe spot off the highway.  The engine has never been rebuilt to my knowledge, but who knows its history? I have owned it about 15 years. It has always run fine, although not super peppy.  

    If it proves to be a bearing, does one just fix the offending bearing, or is it a sign that everything is about to need redoing?

    I haven't had time to look at the rockers or the bearings.

    --Rick


    On Nov 11, 2013, at 5:25 PM, Steven Trovato wrote:


      Rick,



      I think you have to investigate the problem before you can decide on a course of action.  Sorry for stating the obvious, but there is still  plenty of oil in there, right?  If something failed causing all the oil to pour out on that hill, you would have a sudden drop in oil pressure and a whole lot of clatter.  What is the state of this engine?  Recent rebuild or old and tired?



      -Steve T.



      At 06:40 PM 11/11/2013, Richard Greenberg wrote:

        Hi all,

            This is about my TD, but I bet you folks can help.

            I decided to drive the TD, instead of my Magnette, to our British car club's annual BBQ.  About 25 miles out, running at about 50 mph uphill but not too hot, the engine started clattering and the oil pressure suddenly dropped to about 5 psi.  I had the poor car carried home.

            Any ideas about what happened? Rod bearing wiped out? Broken rocker arm?

            If it is one of those things, should I just make the repair, or is it time to have the whole engine rejuvenated?

        Thanks,

        Rick



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