I took off the rocker shafts and it seems that there's a lot of wear
on both rocker arm and pushrod. I heard some guesses that this kind of
noise probably comes from lifters but could it be enough to just
replace the rocker arms and pushrods ?
(I also found the story below from a website)
The pushrods and rockers on the 4.0L tend to show a lot of wear, even
on engines with low miles. We suspect that there are two reasons for
this problem: (1) The material in the rockers appears to be too soft,
so they wear on the tip, and; (2) there's not enough oil getting to
the pushrod socket, so it gets worn out, too.
There's pressurized oil at the rocker shaft to lubricate the rockers,
but there's no direct way for that oil to get to the pushrod sockets.
There's a passage in each rocker that allows oil from around the
rocker shaft to migrate out to the small hole in the top of the
pushrod socket, but it's wide open on the outer end so there is no
pressure there to feed the oil down into the socket.
Apparently the small hole in the pushrod socket that intersects this
passage is supposed to meter oil down into the socket somehow, in
spite of all the motion that's trying to sling the oil out from the
open end of the passage in the rocker. It's hard to believe that any
oil can actually get into the sockets, so it's no wonder they wear out
prematurely. Rebuilders should expect to rebuild or replace most of
the rockers. The tips can be ground if they're not worn too badly and
the sockets can be repaired by installing a special insert that's
available along with the tooling needed from Silver Seal
(800-521-2936) or Goodson (800-533-8010). Or, if you prefer to have
someone do them for you, rebuilt rockers are available from Delta
Camshaft at 253-383-4152.
You may want to consider flame-hardening the tips, too. Ed Davis at
Waterhouse Motors in Tacoma, WA, has been doing this for awhile to
eliminate wear on the tips. He found that the wear on the tips was
loading the valves so hard to one side that they were wearing out the
guides and causing other problems in the process.
Plan on buying a lot of new pushrods, too. Most of them are scuffed
and worn on the tip due to the lack of oil in the socket.
That's the story on the 4.0L. It's pretty straightforward if you keep
the castings straight and pay attention to the details. This has been
a common engine in some of Ford's most popular vehicles including the
Ranger, Explorer and Aerostar, so there are over 3 million of them on
the road and plenty of business waiting for the shops who know how to
rebuild them and make them live.
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