Hi Ron and Gordy,
This question takes me back to my old 1935 Austin 7 days.
Main bearings and rod (big end) bearings make quite different noises when
they have spun or have been "run" as it was in my youth.
As I recall a rod bearing makes a real clatter when the engine is under
power, which dies down a little when you lift the throttle. You occasionally
hear one of these on the street. To determine which cylinder has the
problem, as if it makes much difference, you run the engine at a fast idle
and short out one of the plugs, these days I guess you would pull off the
plug wire. The bad cylinder will produce a very distinct change in sound.
Main bearings tend to rumble more than clatter and as I recall make more
noise in cruise i.e. constant speed but less during acceleration and
deceleration. They are little affected by removing a plug lead.
If you suspect a bearing is getting loose but are not sure start the engine
with no oil in it for a second. Boundary lubrication will prevent any
serious damage but the noise will be considerably amplified with no oil
pressure.
As mentioned by others there will be little flakes of silver metal in the
pan and, with these modern engines with them, the oil filter if you choose
to cut it apart.
In my experience once a bearing has got that bad you will find that the
crankshaft will be worn as well and will probably need a regrind.
Michael Salter
100S (1955)
3000 Mk111(1965)
100 (1953)
AHX12 (1953)
Bugeye (1961)
http://www.netbug.net/blogmichael/
-----Original Message-----
From: Ron Fine [mailto:RonFineEsq@earthlink.net]
Sent: May 15, 2007 12:25 PM
To: Michael Salter; 'Alan Seigrist Blue 100'; 'Healey'
Subject: Re: Broken Engine - 100 - tips
Just so I can learn more about these engines (and have something to worry
about) what would the symptoms be of a spun rod or main bearing?
Ron Fine
61BN7
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