I purchased my '81 300TD with a boat load of receipts 2 years ago. However, I could not find where a valve adjustment had been done so I made an appointment with my mechanic for it finally this past week.

After starting on the job, he called me and stated that he was concerned: 3 of the first 5 valves he started on were nailed down so tight he couldn't get a feeler gauge in there at all. He broke a wrench on one and had to make a replacement.

He also stated that turning the engine over manually for the valve adjustment should usually be quite difficult but he was able to do it relatively easily, which he thought may be due to poor compression.

This car starts and runs well, it seems to have plenty of power, although I know that I am leaking some oil and there is oil appearing in the air cleaner. Mechanic says that this is evidence of blow-by and may be a harbinger of problems in the future. However, he states, there is no reason to push the panic button- it may go for a long, long time yet.

On the telephone he stated that he has personal experience with dropped valves after adjusting valves which were nailed down this tight all the way back to factory specs. He said his concern is that the metal becomes weak with age and cannot adjust to the new tolerances. He said that his suggestion would be to back them off about 1/2 way to the factory specs, to run it for a few months and then bring it back in to see how they are and possibly restore them back to factory specs at that time. He charged me $90.00 for the work, not including the gasket which I purchased myself.

This is my only car and we use it for business and pleasure. The thought of dropping a valve was not attractive to me, especially since we're heading out of town this weekend. Knowing that the car was starting and running well prior to the adjustment, I decided to take him up on his suggestion.

After posting for my buddies on the Diesel forum, there was a deluge of e-mails questioning my mechanic, his knowledge, and his motives. I trust my mechanic but I also trust the forum and the expertise and experience from its members.

Still, I thought that I would post here and see what feedback I get.

Thanks very much!

anyone out there have any input?

More likely that the valves will go tight pretty fast rather than one breaking -- I've never heard of an MB engine "dropping" a valve (ie the tulip snapping off the stem).

What will probably happen is that there is quite a bit of crud on the stem of the valves that were too tight, and it is holding them open. It will wear off pretty fast, and the clearance will vanish again.

I'd do another valve adjust in about 5000 miles. If any of them are tight again, have him leave them with more gap than specified, then repeat the adjustment in a couple thousand miles. This should take care of it.

The real problem with letting the valves go that long is that the exhaust valves tend to erode very badly when they don't close properly, and they then refuse to seal when the clearance is correct. The only way to fi that is to do a valve job, and you almost always have to replace the exhaust valves then, since they will be too worn to grind.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

That sound reasonable to me.
FYI I my mechanic charged me $90.00. The dealer was going to charge me $400.00!
-shawnster