[Top] [All Lists]

Re: Damaged MGA Engine?

To: Robert Guinness <>, MG List <>
Subject: Re: Damaged MGA Engine?
From: Barney Gaylord <>
Date: Mon, 14 Aug 2006 00:35:27 -0500
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.

Barney Gaylord
1958 MGA with an attitude

<Prev in Thread] Current Thread [Next in Thread>