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Old 12-15-2002, 10:26 AM
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Question Intermittent Engine Tapping


Lately, my 1990 300E has been making what sounds like a taping noise from the middle of the valve cover. I suspect itís a bad lifter.

Iíve searched the archives, but I did not find any threads that address this one.

This started as a tapping noise when starting the engine cold. Two or three seconds and it was gone. Sometimes it will not do it at all.

Now, it comes and goes even when warm. Runs strong but at idle it starts to tap. Once under way, the tone changes and speeds up with engine revs. Sometimes, it disappears when oil pressure rises. Other times, it continues.

Background: Oil level doesnít seem to make a difference. Changed plugs last weekend and they looked fine. Nice tan color and they were very easy to replace. There is no oil in the coolant, nor is there a milky color to the oil. Running 10W40 Dino Oil. Replacing with Castrol 10W40.

That said, if the oil change I am doing this morning does not help, how difficult is it to replace the lifter? A DIY job for a fairly good parts changer? Any special tools other than a torque wrench?

I like a challenge but not at the expense of the motor.


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Old 12-15-2002, 12:06 PM
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I think, before I would consider changing the lifter, I would run a can of engine flush through it or about a half a quart of ATF before you change the oil. My E320 would do the same thing periodically so I put a can of engine flush in it, ran it for about 20 minutes, then drained the oil (hot). I put in a thinner oil (at start-up 0W-40) and it took care of it.

It's probably worth a try before you dig into it, carbon and other deposits that are running around in an engine can sometimes clog the small oil gallery in the lifter.

Good Luck,

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Old 12-15-2002, 12:49 PM
Registered User
Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
my 190 was doing the same thing, but in my case it was the timing chain, replaced it, it was 3cm longer then it should have been and really loose. It almost always tapped on low revs and on a cold start. It's was one heck of a job to replace it, took two days. Now engine runs very quiet, but I gotta get a new thermostat and housing along with a tensioner bearing. Housing cracked causing a huge coolant leak, and bearing started whinning. All will be take care of after my exam tomorrow night he he.

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Old 12-16-2002, 08:40 AM
J.HIDALGO's Avatar
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Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
Check the belt tensioner shock in front of the engine!

It is worth a try before you do anything else. It is a cheap fix.
'86 300E
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Old 12-16-2002, 09:02 AM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,315
It's not a huge deal to replace the lifter, assuming that you can determine which one is bad. They slide into the rockers and you remove the rockers in pairs. There are four bolts per pair.

There is a special tool for measuring the pre-load of the lifters, and different size valve pads are available to adjust it.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 12-16-2002, 10:29 AM
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Thanks for the replies.

I changed my oil (Castrol GTX) and went for a drive. Kept the revs up around 3000 to 4000 and the motor now purrs like a kitten -- so far.

Started this morning without any clatter! Now that's a very good sign.

Keeping my fingers crossed in the Windy City.

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