At 10:16 PM 8/13/2006 -0500, Robert Guinness wrote:
>.... at highway speed in my MGA 1600, the oil gauge hose blew out
>.... racket under the bonnet and .... 4 quarts of oil. I put three
>of them into the engine .... and started the engine. It purred at
>idle, so I tried to limp it home. It would not provide power above
>2000 RPM and became overheated after two miles, .... oil gauge ....
>used to register pressure of 60 lbs at speed. Now if reads 20 to 40lbs. ....
>What is going on?
When the ngine runs out of oil the pressure and flow both go to
zero. Oil in the crankshaft bearing journals immeduiately overheats
and breaks down, you then have metal to metal contact causing
excessive friction and heat. The white metal on the working face of
the bearing shells promptly melts and flows like solder.
If you are unlucky and shut it off when it is that hot, the bearing
material can cool and solder itself to the crankshaft, resulting in a
siezed engine. Apparently you are not quite that unlucky, but the
crankshaft bearings are damaged all the same, especially the
connecting rod bearings. Excess running clearance in the worn
bearings allows oil to escape easier resulting in the low oil pressure.
If the knocking noises did actually go away when you put oil in the
engine, then there is a chance you may not have toasted the
crankshaft. The only way to know is to pull the oil pan and remove
bearing caps to have a look at the bearing journals. You are going
to have to do that to replace bearings anyway, as a bare minimum. If
the crankshaft journals are not scored, you may get lucky and fix it
with a new set of bearings and some gaskets (and a new oil pressure hose).
Rod bearings are the first to fail when you lose oil flow. Pull the
rod caps first (don't mix them up), and carefully inspect and measure
the crankshaft journals. The journals should be mirror smooth and
perfectly round. If any one journal has any imperfection you can see
or can feel with your finger tip, the crankshaft will need a
regrind. If any one journal is undersize or out of round by 0.001"
or more, it needs a regrind. For that you have to pull the engine,
remove everything on front and back to remove the end plates, and
remove all bearing caps to remove the crankshaft. You do not have to
remove the cylinder head or pistons or camshaft if you are only after
fixing the crankshaft.
>.... Also, any hints on how to prevent the oil gauge hose from
>becoming disengaged in the future will be appreciated.
Install a new oil pressure hose and hope for good fortune. I replace
my pressure hose about as often as I give the car a new
engine. Meanwhile, try not to hit it with a heavy wrench.
1958 MGA with an attitude