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Re: valve noise

To: "DenverD" <>, "mgs" <>
Subject: Re: valve noise
From: Barney Gaylord <>
Date: Sun, 24 Jun 2001 18:16:16 -0500
At 11:31 AM 6/24/2001 +0200, DenverD wrote:
>.... adjusted the valves (cold engine, .015)--imagine my disappointment
when it sounded just about the same when it was started.
>my friend theorizes that the noise is coming from a worn cam lobe.  he
said he thought the area just after the valve full open peak has been worn
down and is allowing the lifter to "slam" down onto the cam, rather than
"ride" in contact with the cam..
>so, we've made plans to pull the engine and replace the cam ....

Changing a cam can be a particularly expensive and aggrevating chore,
especially if you still have the noise afterwards.  Do some diagnostic work
to try to isolate the true problem before getting into expensive surgury.
But go ahead and check the cam first, because it's fairly easy to do.

You may be planning a lot of work for nothing.  When a cam lobe wears down
it generally wears down the peak of the apex, and maybe a bit more on the
leading side of the peak.  I have never heard of one wearing on the far
side of the apex without first wearing down the top.  You can tell without
major disassembly if the cam is worn.  Just remove the valve cover and
mount a long travel dial indicator to measure the travel of the valves,
each in turn.  First screw all the valve adjusters down to zero clearance
(tight) to remove all clearance, then turn the engine through one or two
turns and observe the reading on the indicator to get the valve travel.
Repeat for each valve.  The lift for each valve should be the same within a
few thousandths of an inch.  If it is, stop worrying about the cam.  If you
find a lift variation of more than .005", then you need a new cam.

There are other possible sources of tapping noises.  A worn connecting rod
bearing can sound about the same.  A rod knock will generally be more
prevalent under light load and accelleration at about 2500 rpm (just blip
the throttle when running and parked), and may tap only slightly at idle.
Remove one spark plug wire at a time and run the engine.  If the noise
subsides considerably when one wire is removed, it's a good probability
that it's a loose rod bearing.  Slightly worn rod bearings can be changed
by removing the oil pan without pulling the engine.  Worn bearing journals
on the crankshaft can only be repaired by removing and disassembling the
engine to remove the crankshaft for regrinding.

I have also had a freshly rebuilt engine tap in about the same manner,
tapping consistently at idle, sounding like a loose valve adjuster, and not
getting noticeably louder with variation of engine speed.  This is usually
cam related, but not necessarily a bad cam.  It could just be a tappet
sticking in its bore and dropping late to tap on the cam.  This might be
cured with a little solvent around the tappets.

The end float of the cam is controlled by the front retaining plate which
is screwed to the face of the block and is trapped between the front face
of the front male journal and the back of the cam sprocket.  This is a
steel plate with a soft bearing surface on the back.  With much use the
front cam journal wears slightly into the soft back surface of the plate,
thinning it out slightly and allowing a little excess end float for the
cam.  Many engine rebuilds are done with reusing the original cam retainer
plate, with the end result of an audible tapping noise at idle as the cam
and sprocket oscellate endwise and slap at the front retaining plate.  This
tapping noise is nothing to worry about, just annoying.

Occasionally a cam can warp slightly, more often if the car has been stored
for a few years or more without running.  A cam that is not perfectly
straight can slap audibly in one of the journal bearings, especially if the
engine has a lot of miles on it.  This tapping noise is generally not
anything to worry about unless it is particularly LOUD.

Check the end float in the distributor shaft.  If the dizzy shaft has
excessive end float it can oscellate by floating endwise and tap audibly
when running.

Use a stroboscopic timing light on the crankshaft pulley to observe the
timing mark when running.  If the timing mark appears to jump around more
than one or two degrees while running it could be caused by end float of
the dizzy shaft, or by a worn shaft bearing in the distributor, or by a
loose timing chain, or by end float in the camshaft, any of which can cause
a tapping noise.  The loose timing chain can often be cured by replacing
the tensioner.  The sloppy dizzy can be repaired by replacing the shaft
bearing or adjusting a shim just above the drive gear.

For an engine with a lot of miles (maybe 150,000+) on the original block
the cylinder bores can be worn to the extent that the piston will slap
against the side of the bore causing a rapping noise that sounds a lot like
a bearing knock.  Also don't over look some obvious little external thing,
like a vibrating radiator shroud or exhaust pipe, or fan blade, or worn
water pump bearing.

I recently acquired a nearly perfect engine for a very small price.
Internally it was in almost new condition, and the only obvious problem was
that the water pump pulley hub was loose on the shaft where it should be a
tight press fit.  This would probably cause a nasty knocking noise and may
have been the reason this engine was taken out of service (and ultimatley
sold cheap).

Food for thought, and things to check.

Barney Gaylord
1958 MGA with an attitude

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