excessive valve tappet noise

[johnk]

Gentlemen
My 1968 280sl seems to have excessive tappet noise despite a recent valve job. It was noticeable to me before the valve job as well. I just purchased it in April of this year. We replaced the valve guides, ball studs and rocker arms, but did not replace the springs and the lash caps/washers. Buds sent me the wrong valve springs and I did not want to have to wait any longer. I passed on the thrush washers as the only ones I could find were almost $500 for the set.
I have readjusted the valves a few times, and while it sounds better it is still very noticeable. Any ideas what the issue could be? I can install new springs and lash caps if that could be the problem.  The car has 74,000 miles on it.

Thanks
John K

[ja17]

Hello John,

There are several unusual problems which can cause "tappet-like" noises that are not related to valve adjustment. First of all check to make sure that the valve cover hold-down straps have not distorted inwards. You must have approx. a minimum of 1/4" between the three straps and the camshaft. If not when the valve cover is tightened down, the straps pull in-ward and against the camshaft causing a "tapping noise" as the camshaft rubs against them. Simply bend the straps out and away from the camshaft to cure the problem.

Another item to watch out for after head work............The rocker arms "arch" over the top spring retainers to reach  the  contact pads (lash caps). After head work the rocker arm  geometry may change enough to cause the
rocker arm to contact the upper spring retainer rim where it crosses onto the contact pad. In this case when the camshaft contacts the rocker arm, the rocker arm contacts the upper spring retainer rim BEFORE it presses on the contact pad. You get a "double hit" which also creates a tappet noise. Inspect each rocker arm where it arches over the upper spring retainer. Remove the ones which look close and inspect the arch on the bottom of the rocker, you will see a noticeable "wear mark" if this is happening. To fix, grind the arch a little higher so it clears the rim. Re-adjust the valves on any that you work on.

Keep us up to date. Let us know if you need more information on these fixes.

[johnk]

Thanks Joe,

I will give the rocker arm issue a look and see if that could be the problem. The valve cover brackets did clear the camshaft, but I will recheck to make sure the clearance is at least 1/4 inch.

John

[garymand]

A few other points to consider:

1) The clearance is very tight, tighter than what I was used to on American solid lifters: 0.004 and 0.008
2) I like them tight.  It is a stug pull on the feeler gauges.
3) I don't like to adjust hot because it takes me a while and the motor cools off.  I prefer to do it cold.  
4) I always go around twice.  Once to adjust and once to verify.  Sometimes I find one too tight or too loose.
5) Always look for wear on the lobes AND on the back of the cam lobes.  I ran across a picture someone here submitted and you could clearly see that more than one cam lobe had seen constant contact all the way around the lobe.  That means the valve never closed fully, and the gap was 0.00000, zero, zilch, nadda.
I'd rather hear them a little than not at all! (Its better to be too loose than too tight!)
6) It is tricky too, because with age and infrequent adjustment, the balls wear into the lifter sockets with a ridge an valley.  When you rotate the ball, that orientation changes and will have a tendency to wear rapidly resulting in a loose gap sooner than more round shapes.  I've seen little posts left at the tops of the balls as the balls wore down around the hole in the lifter, but still, they held clearance pretty well because the car wasn't drive much.

http://www.authenticclassics.com/Valve-Cover-Label-Decal-for-Mercedes-280SL-p/auth-003776.htm
http://www.sl113.org/wiki/Restricted/ValveAdjustmentTour

The 'tour' is not out of the manual, but a good tutorial of 'how' you do it.  notice the head should be retorqued hot and with the motor hot you can adjust the valves hot to 6 and 10 rather than 4 and 8. 

[johnk]

thanks Gary. I am hoping that its just that my definition of snug was a little too loose. I should find out in a day or so as an experienced friend of mine will be rechecking them. We will be checking the items Joe suggested as well.

John

[wwheeler]

3) I don't like to adjust hot because it takes me a while and the motor cools off.  I prefer to do it cold. 

Please correct me if I am wrong, but I believe the specs are when the engine is COLD. The BBB seems to be definite about that and that is the way I have always done it. 

[garymand]

Please be corrected.

[Cees Klumper]

Yes, valve clearances are set on the engine cold.

[garymand]

Hmm, where is it in the BBB?   I'll take a look tonight.  I don't remember hot numbers in the BBB actually.
 
 Why is it on this: http://www.authenticclassics.com/Valve-Cover-Label-Decal-for-Mercedes-280SL-p/auth-003776.htm

I've never seen this as an original decal on a valve cover, so I have never seen one in person, but why would they reproduce a false or incorrect decal?  Aside from the motor cooling off, due to the head retorqueing and then valves adjusted, I thought it resonable to have a hot setting because my 58 Chevy required setting the solid lifters with the motor running.  That was great fun.  I still rem,ember they were 8 and 10 hot.

[Garry]

I actually have a few of the original ones of that decal. I understood that it applied to the 280SL only?

Someone else here who is an expert on labels can chime in anytime.

[66andBlue]

Hmm, where is it in the BBB?  .....  

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Why would anyone put absolute faith in a reprinted label??