A curious noise coming from an overhauled engine

[watson2]

I would concur with Cees. They seemed to have removed way too much metal form the head. If I see correctly, the exhaust valve is out of the combustion chamber.

I see the exhaust valve on the left in the photo near the plug. So the valve out of combustion chamber is the inlet one, on the right. But the side is not relevant. The real problem is that the chamber is too little.

Do you think a thicker head gasket could work? Which are the problems of this type of gasket?
I calculated that we could increase the volume of 5,3 cubic centimeters (= 0,325 cubic inches) for each mm. of thickness.

@tel76 : could you kindly tell me if the calculations about the volume of the combustion chamber were right?

[ja17]

Did anybody ever record the head thickness in various places?Are you below minimum thickness? Also certain areas of the combustion chamber can be "carved-out" to provide more volume. It is a common procedure when "blue-printing" engines. The volume of the combustion chambers can be adjusted, measured and matched exactly. Two head gaskets would be very risky on these engines since the space between cylinders is so minimal. I don't think they would hold up. 

[ctaylor738]

These are not the quietest engines ever made.

When you say "noisy," on normal acceleration, what do you mean?  Is it "pinging" aka pre-detonation, which is sort of a sharp rattle like rocks in a tin can?  Or some other kind of noise?   

[Benz Dr.]

These are not the quietest engines ever made.

When you say "noisy," on normal acceleration, what do you mean?  Is it "pinging" aka pre-detonation, which is sort of a sharp rattle like rocks in a tin can?  Or some other kind of noise?  

I knew a guy once who was about as sharp as '' rocks in a tin can. '' Does that count?

Measuring a cylinder head seems simple enough but we often cut the top of the head to make it straight and level with the bottom of the head. This would leave the impression that the head is under the minimum 84.00 mm spec and yet it isn't. Most cylinder heads are also warped on the top surface as well as the bottom. You can straighten a cylinder head by heating it in an oven and pulling it straight. Done properly, only a minimal cut is required to make it level again. The top of the head should be checked and planed as well if needed.
I use .015'' cam bearing shims to compensate for removed material because the valve stems will sit higher after any material is removed from the top of the head. Since you need a minimum of .050mm intake valve recession, the valve seat sometimes needs to be cut deeper to adjust this measurement. This will also cause the intake valve stem to rise which can lead to rocker geometry problems. By raising the cam shaft with shims under the cam bearings, you can compensate for deeper valve seats and any removed material from the top of the cylinder head. A standard lash cap is 4.5mm and if you run out of ball stud adjustment using this part you can get ones that are only 2.5mm.  I generally never use more than two cam shims per cam bearing (.030'' ) and if I still have adjustment problems then I use a thinner lash cap.  

[ja17]

Head thickness measurement is still a good gauge since material cut from the bottom of a head is  cut at each end and most material cut from the top is central. So theoretically a head warped .020" will get .020" cut at the ends on the bottom. On the top it will get cut .020" in the center and you still end up with a flat head cut .020" overall.  The bad thing is you get very high compression on the end cylinders. Dan, are those camtower shims something you can order or do you make your own? I've always had to make them, but would rather buy them.

[tel76]

Joe,
Metric Motors sell them in different thicknesses, you do have to modify the rear one to allow the oil to drain back into the sump.

[ja17]

Thanks Eric.

[Benz Dr.]

Joe,
Metric Motors sell them in different thicknesses, you do have to modify the rear one to allow the oil to drain back into the sump.

This is news to me. Mike never mentioned it, which I expect he would have if it was important, and I've never done it myself. Odd that nothing has blown up yet.    These shims are made in the same shape and dimension as the bottom of the bearing so I'm not sure how they could close off the drain hole for the oil return. Am I missing something here?

Shims come in different thicknesses up to .015'' which is what I use.  They are stainless steel and well made.  Less than 10 bucks each. 

[Benz Dr.]

I checked out the cam shims on the last bearing and yes, on some engines the valley below the bearing isn't that deep and it may cause a restriction of sorts. Any extra return oil would run down the chain case so I don't think it's a really big issue.

[tel76]

It would be a very big problem, the front of the engine is higher than the rear so if the oil cannot get down the rear oil return hole a large pool will develop in the rear of the rocker cover, this could/would compromise the rocker cover seal resulting in an oil leak. The rocker cover seal is not intended to hold back a large quantity of oil.
I should also have mentioned that if the oil cannot drain at the rear of the engine and the pooling accurse then the rear cylinder valves springs and oil seal are fully immersed in oil, the seals cannot cope and oil will enter the cylinder or exhaust tract resulting in smoke.
MB were aware of this problem ( caused by the block drain hole being too small) and during this engines production run the rear oil drain in the block was enlarged.
At the time it was not unknown for some engines to be stripped down only to find that there was nothing wrong.
Perhaps Achim will have information on when this change happened.

[Benz Dr.]

Maybe. I've never done this small mod and none of my rebuilds leak at the back of the engine. A lot has to do with the cylinder head casting and if this is such a big problem why have I never seen it before? And believe me, I check everything very closely before it leaves. If anything, not adding shims when you need them is a far bigger issue.
I will however, check this out in the future.

[watson2]

These are not the quietest engines ever made.

When you say "noisy," on normal acceleration, what do you mean?  Is it "pinging" aka pre-detonation, which is sort of a sharp rattle like rocks in a tin can?  Or some other kind of noise?   

It's difficult for me the description of this noise , expecially in a technical language that I don't know with richness of terms . So I will provide an audio record to allow you to listen the noise.
I asked to two engine experts an opinion about the noise. Both told that the noise is coming from the rocker arms ; in relation to the frequency of the noise they told that  both have ventured that could come from one or two tappets, and the noise is anyway coming from the high part of the engine.   

[ja17]

Hello watson,

Sometimes after cylinder head repairs you can get a very hard-to-find, elusive noise from the valve train. During cylinder head repairs, the valves and their seats are ground and as a result, they sit higher in the cylinder head. As a consequence, the rocker arm may be contacting the upper spring retainer before actually hitting the valve shim. This happens at the arch of the rocker arm where it passes over the upper valve retainer.  The contact causes a "tappet type noise".  Look closely for any rocker arms which are suspicious and examine the "arch". You will see sings of contact if this is the case. Grind the arch slightly and your noise will disappear. Also any place where a thinner than standard "pressure piece"  was used, is more likely to be the culprit.

There is a danger if this is the case and it is left un-fixed. The early contact to the upper spring retainer slightly loosens the valve keepers for an instance on every revolution. Eventually a valve, in the cylinder head, could be released and be sucked into the engine, causing catastrophic failure.

[ctaylor738]

Second what Joe said.  I fixed a 230SL where the valve dropped into the cylinder because of this.  It was a complete mess.

[Benz Dr.]

Second what Joe said.  I fixed a 230SL where the valve dropped into the cylinder because of this.  It was a complete mess.

Me too. And it was a 230SL.............

[watson2]

Hello watson,

Sometimes after cylinder head repairs you can get a very hard-to-find, elusive noise from the valve train. During cylinder head repairs, the valves and their seats are ground and as a result, they sit higher in the cylinder head. As a consequence, the rocker arm may be contacting the upper spring retainer before actually hitting the valve shim. This happens at the arch of the rocker arm where it passes over the upper valve retainer.  The contact causes a "tappet type noise".  Look closely for any rocker arms which are suspicious and examine the "arch". You will see sings of contact if this is the case. Grind the arch slightly and your noise will disappear. Also any place where a thinner than standard "pressure piece"  was used, is more likely to be the culprit.

There is a danger if this is the case and it is left un-fixed. The early contact to the upper spring retainer slightly loosens the valve keepers for an instance on every revolution. Eventually a valve, in the cylinder head, could be released and be sucked into the engine, causing catastrophic failure.

When we changed the pins and the rocker arms this problem was detected 'on the table' and, I'm not sure, but they installed a piece that could be the nr.85 in the following picture. It was a little thicker to avoid the contact, it seems to me.

[ja17]

Looks like your onto something.  Go back and check the rest.

[Benz Dr.]

If the rocker geometry is right it won't hit anywhere. How much thread do you have showing on the ball stud pin?

[watson2]

If the rocker geometry is right it won't hit anywhere. How much thread do you have showing on the ball stud pin?

I have only this image showing the detail that you want to know  (if I have understood your question).
No thread is visible, but the the right pin is a little taller.

[Benz Dr.]

Those are very low - probably within less than a turn before they bottom out. I prefer to see a couple of threads on the ball stud showing above the base portion so that the rocker arm is sitting in the right plane. One or two cam shims would cure this problem and that's only if the valve guides aren't already damaged.

   

[watson2]

Here it is the file that I prepared.  No sophisticated devices, only an Iphone.
I captured this video with both side windows open and the phone near the left window.  Walls around the car  and a small climb to overcome to make a bit of effort to the engine  are all expedients to increase the audibility of the noise .
When the engine is warm the noise doesn't  change.


I inserted a detail of another problem I have on my 230 with automatic gearbox.. The video shows the taco increasing and decreasing the rpm for 500 units. When I push the brake  the rpm increase , when I release the pedal the rpm return to normal.  An information : the servo is not working properly. is it possible that the engine take air through a broken membrane ?

Excuse the quality.
The video will take some seconds to be loaded.

https://www.dropbox.com/s/8gn8wlrw3t7ef69/IMG_3252%20%281%29.mp4?dl=0

[watson2]

Those are very low - probably within less than a turn before they bottom out. I prefer to see a couple of threads on the ball stud showing above the base portion so that the rocker arm is sitting in the right plane. One or two cam shims would cure this problem and that's only if the valve guides aren't already damaged.

  

This is due to the fact that the valves sit higher?
And also the thicker piece nr 85  I think has played the same role.
Tell me , please, where I could buy the 0,015" shims.

[Benz Dr.]

This is due to the fact that the valves sit higher?
And also the thicker piece nr 85  I think has played the same role.
Tell me , please, where I could buy the 0,015" shims.

Yes. As the height of the valve stem increases the height of the rocker arm must decrease in order for you to obtain the desired clearances of .003 and .007''  Once you get the ball end of the rocker that low, it will deflect the valve stem sideways and take out the valve guide/s. The exhaust guides tend to wear at a faster and higher rate possibly due to the larger and thus heavier diameter of the stem. In other words, the valve stem won't bend and all that force has to go somewhere. Once I figured this out many years ago my rebuilds became much better. By raising the cam shaft you have to raise the valve adjuster with it and the ball end of the rocker arm moves up. This isn't a one to one ratio but it's likely more like a two to one figure. The rocker is actually a lever and it will do a proper job once it's set up properly.

I should have a few cam shims here or you can get them from Metrics.
   

[watson2]

Thank you Benz Dr for the clear explanation, thank you indeed.
Two remarks: the difference between brake pedal Up and pedal down is so remarkable with cold engine. With warm engine the difference is of 100 rpm. A phone headset could  be usefull to emphasize high frequency sounds

[Benz Dr.]

Your brake booster could be starting to fail. I've changed a lot of them over the years.