RE: [MV] M 151 A2 Engine -testing before buying

From: Farley, Denver D (denver.farley@monroe.army.mil)
Date: Fri Jan 26 2001 - 08:54:58 PST


Anith,

A cylinder compression test is done on each of the 4 engine cylinders.
Since we are talking about a 4 cylinder engine, ALL FOUR spark plugs are
removed first, and A simple pressure gage, that holds the highest pressure
reading, is inserted, or held, in each cylinder while the engine is rotated
(with the starter) through 5 or six revolutions. If the engine is not
installed in the vehicle, the mechanic can either connect a battery to the
starter or spin the engine with a large impact wrench (air or electric). I
have done it literally hundreds of times both ways. Since both valves
(intake and exhaust) should be closed at maximum compression, the reading
will be acceptable assuming that the piston rings are good, that the valves
are not leaking or burned and that some other mechanical problem is not
present.

This is a great way to tell if the engine is mechanically capable of
running. Of course, it says nothing about the engine fuel and electrical
systems.

If the readings are not acceptable (I could analyze them for you), there are
other tests that can be run to determine precisely what is wrong (piston
rings, intake valves or exhaust valves). Lower than normal reading are not
necessarily bad. The difference between the cylinders is important. For
the engine to run smoothly, the cylinders should be somewhat the same.

I am not sure what the readings should be, perhaps we could pose this
question to the List as follows:

Does anyone know what the engine cylinder compression readings should be for
an M151A2 engine?

Hope I have helped.

Denver Farley
Southeast Virginia, USA

-----Original Message-----
From: Anith@wfp.org [mailto:Anith@wfp.org]
Sent: Friday, January 26, 2001 10:54 AM
To: mil-veh@mil-veh.org
Subject: [MV] M 151 A2 Engine -testing before buying

Thanks Denver,

I am with the U.N., based in Sudan (North-eastern Africa near the Red Sea
Coast). Thanks for the advice. But what is a cylender Compression test and
how is it done? (Here the language is Arabic and since I do not speak it, I
need to know what exactly to expect from my mechanic).

Thanks in advance.

Anith

Sudan

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