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From: gmp@hjuxa.UUCP (PLEWA)
Newsgroups: net.auto
Subject: Re: Help with a lawnmower engine
Message-ID: <142@hjuxa.UUCP>
Date: Tue, 5-Jun-84 21:04:04 EDT
Article-I.D.: hjuxa.142
Posted: Tue Jun  5 21:04:04 1984
Date-Received: Wed, 6-Jun-84 07:24:04 EDT
References: <2091@ihnss.UUCP>
Organization: Digital Equipment Corp., Holmdel, NJ
Lines: 33


     The problem you appear to be having is a generic problem
with old "El Cheepo" Briggs & Stratton engines.  There is either
a large amount of carbon buildup around the intake valve, which
tends to restrict the flow of carburated air from entering the
cylinder.  This in its extreme, will even prevent the valve from
closing completely.  The other cause way be just excessive wear
of the aluminum cylinder wall.
     The determination of which is relatively simple.  First
remove the spark plug and squirt a small amount of 30w motor
oil into the cylinder.  Reinstall the spark plug (don't connect
the plug wire) and pull the starter cord.  If the compression
(effort to pull the starter) has increased, than the problem
is excessive cylinder/piston ring wear.  If the compression
remains the same then the problem is due to poor valve sealing.
(The oil only tends to increase ring to cylinder seal)
     Excessive ring wear on this engine is cost in-effective
to repair.  Valve seal or restriction on the other hand can be
repaired with out too much cost if you are willing to spend some
time.
     The process consists of removing the head and valve tappet
cover.  Removing the valves and scrapping off all carbon build-up.
The valve seats can be restored by "lapping" with lapping
compound, which is an abrasive powder in an oily paste.  The paste
is applied to the seatting surface of the valve, and the valve is
inserted into the port from which is was removed.  The valve is then
rotated back and forth 1/4 turn.  This causes the mating surfaces to
be polished to a positive fit or seal.  When this has been done to
both valves ALL traces of lapping compound should be cleaned from
both the valves and the block.  Alot of damage will occur to the
remainder of the engine if this is not done.  Reinstall the valves,
reinstall the head and tappet cover, and your problem should be
solved.