valve gaps - PeachParts Mercedes-Benz Forum

twinockchef · #1 11-01-2010, 08:06 PM

The valve gaps keep moving on my engine. Why is this happening?

GaryF · #2 11-02-2010, 08:16 AM

Are the adjustment bolts stiff, they should be hard to turn.

t walgamuth · #3 11-02-2010, 08:32 AM

Right...there is a torque spec for those adjustment bolts. If too weak they are to be replaced.

meltedpanda · #4 11-02-2010, 10:09 AM

how many miles between gapping??

twinockchef · #5 11-03-2010, 06:56 PM

Everyone of the valves, except one, is tight. I plan one replacing the valve seals this weekend. At this time I will check each torque setting.
As to the miles traveled between each adjustment. It was only a couple of hundred miles.

daidnik · #6 11-04-2010, 01:36 AM

Was this on intakes and exhausts or just exhausts?

It's not a good sign to have the valves getting tighter. I had this happen on an early W114 head that I got and it turned out to be that it didn't have 'hard' seats (stellite seats). I had to take the head back off the new short block and do a valve job again to fix it. New exhaust seats the second time.

Wearing away the seats can also happen even with stellite seats if the guides get too worn and the valves start to jiggle around.

These problems are almost always seen only on the exhaust valves.

meltedpanda · #7 11-04-2010, 09:47 AM

I have to agree < I think you have a sleeve issue and not seals

230/8 · #8 11-04-2010, 01:40 PM

You need to ensure you are making adjustments and then re-checking them in full accord with the recommended procedures. Measuring clearance must be done with the cam on its heel of the base circle. This is the point directly opposite the tip of the cam lobe. If you fail to get the cam lobe positioned correctly, then you may be checking clearance when the cam profile is beginning its rise to open the valve. Cam lobes are ground with a "clearance ramp" which is a name given to the portion of the cam lobe that gradually changes to slowly reduce the clearance so there is no sudden shocking force on the cam/valve during its open/close cycle.

Once you are sure you have properly set the valve clearance, IAW proper procedures, you can then look for any other problem area that seems to be giving you the trouble you describe. There is a torque specification for the ball pin. There is also the remote possibility that valve seat erosion may be allowing the valve tip to move toward the camshaft; this is called valve recession and usually is due to use of unleaded gas in engines with soft valve seats. Lead compounds were formerly used to lubricate valve seats on soft cast iron cylinder heads. Other additives are used today to achieve this same lubrication. Mercedes has always used hard steel seat inserts under the valve so valve recession is seldom a problem.

Finally, remember that with an aluminum head, clearance naturally increases as the engine heats up, so unless you have zero clearance when you are checking it, it is unlikely that you are doing any permanent damage during normal operation.

twinockchef · #9 11-18-2010, 10:36 PM

Well the problem is the rocker arms. It looks like the previous engine rebuild was a half ass job. I pulled the head and discovered that all of the rocker arms are heavily grooved which should explain the gap problems. Also, two valves are bent and coolant port holes were not properly cleaned out from the welding work. To be on the safe side I replaced the cam shaft and the head bolts.
I was lucky that I had an extra cam shaft and a set of rocker arms.

meltedpanda · #10 11-19-2010, 08:03 PM

still , even with the rocker issues, if you set gaps with bad rockers why would they change so rapidly?