valve adjustment question - PeachParts Mercedes-Benz Forum

#1 12-09-2002, 02:58 PM

I've adjusted my valve's on my new 1979 300d. I noticed that the springs were turning while I worked the adjustment nuts. Could this create a problem? Also my motor seems to idle a bit rougher and smoke a little more. And there's a slight hesitation when I step on the accelerator. Any thought's? Thank's CJ.

#2 12-09-2002, 06:40 PM

If the valve spring was turning, then the valve itself was turning. Did you verify that the lash was correct after tightening up the locknut? If you're turning the valve, you are likely not adjusting anything. I had to fuss with a few of mine to insure that the proper adjustment was still there after getting the locknut tightened down.

I would go back in and check the gaps to insure that they are indeed in spec. If all is, then you may be looking at a valve job, as the valves may not be sealing correctly. I would also recommend running some diesel purge to help insure that all of the carbon is out.

The initial drive with my 240D after I finished my adjustments felt like all of the power was gone. This very quickly progressed to back to normal response within about 30 minutes of driving. I'm sure that I'll need to recheck and readjust my valves again, considering how badly out of spec they were on the initial job.

Aaron · #3 12-09-2002, 09:16 PM

If you don't already have the MB valve adjustment wrench set, you need to get it. It includes a wrench to hold the valve spring while you undo the locknut and adjust the capnut.

#4 12-09-2002, 10:32 PM

Thank you both for your feedback. I'll look for the spring tool. Also I had four out of five bad glow plugs, which I replaced. It's still a bear to start unless I plug it in for a couple of hours. I'm wondering if I bought a summer only car?

rwthomas1 · #5 12-10-2002, 01:08 PM

There is a couple of big IF's here. You may or may not have got the clearances right, did you check them when you were done? Provided they were okay I would say you might have a loose timing chain, and/or retarded timing. Provided the compression is good and the new glowplugs function correctly it has been my experience that retarded timing will make starting a bear. I would check it all again. RT

samiam4 · #6 12-10-2002, 08:01 PM

Let me say first: No the valve moving should not damage the seat/valve. Infact, they rotate naturally during operation. Hey- that's what the third wrench prevents=0)

It should start better with a valve adjustment-not worse. Double check your adjustments. You engine must be dead cold(over night), spec calls for measurement at 18 C (shop temperature). Don't get overly hung up on temp- 50-100 seems to work. I've never met someone that got a good adjustment with the "hot values".
Measure your glowplugs with a DVM. They should be around 0.6 ohms if they are pencil parrallel glowplugs. If they are series-you'll have to lookup the specs. Series means the condition of each plug effects the starting condition.
Checking timing is not a bad idea-if there is a reason. But, hesitation, valve noise , and hard starting to me suggest you need to double check your adjustments.
Are you loosening the locknut all the way and then adjusting the top?? Describe how you did your adjustment... I can give you some pointers to make things easier.

Michael

#7 12-10-2002, 10:53 PM

To Samiam: Thanks for the feedback. On the adjustment, I bought two 14 mm. wrenches from the hardware store and put the torch to them. They came out pretty nice, but I think a little more angle would help. Anyway I loosened the bottom nut maybe a quarter turn, then made the adjustment turning the top nut. I had to do this a few times per valve until I felt some drag. Should the drag be tight or loose? It's difficult to tighten the lock nut very tight without changing things. How tight should the lock nut be? I rechecked my clearences and all seemed well,but maybe something got loose. I went up to .005 on the intake and .013 on the exhaust and they would'nt go in so, so I thought things were ok. If you know some tricks that would be way cool. Thanks for the help. CJ.

samiam4 · #8 12-10-2002, 11:33 PM

I believe the correct adjustment is 0.1mm and 0.3 mm which is approx 0.0038 and 0.0118 inches.

Sounds like you have them close. I like to adjust them right on the money. YOu can use a standard feeler gauge or a no-go feeler gauge. No-go's you would use a 0.011/0.013. It should have zero drag on the small side and not go on the large.

As far as adjusting a valve. I make the decision on which way it needs to go- tight or loosen. Then I "work the adjuster around". Let me explain. Say you need to go tighter. That's ccw. So, holding the bottom wrench very firm, move the adjuster a hair(15 degree?????) and then tighten the locknut by holding the adjuster still. Then repeat as nessary. IF you hold preload on the locknut, you will not be as random. This is the "secret mechanics handshake" if I ever found one=0)
The feeler gauge should have some drag when pulled through the gap. Distictive. Yes, make the locknuts tight-but not brutal force.
You could grind down one of the wrenchs to be a little thinner for the locking nut.

Hope it all helps. When adjusted correctly, there shouldn't be ticking valve noises. It will sound like a sewing maching with the diesel ignition causing a distinctive clank of the piston to cylinderwall.

Michael

#9 12-11-2002, 12:16 PM

Samiam, when you say preload, do you mean hold the locknut fast, or tighten it up instead of tightening the adjustment nut down? Thanks CJ.

samiam4 · #10 12-11-2002, 12:27 PM

I mean you are never making the adjuster/locknut combination loose. You are moving the adjustment and keeping things tight-but varying the tightness. If you loose all the binding between the locknut/adjuster, then your in the trial and error valve adjustment method.

Makes a huge difference if you are doing a 911/930 valve adjust.

Michael

#11 12-11-2002, 11:02 PM

If I only had a porsche. Thanks for the tip Samiam. I'll give it a try. Probably will only need one of these cool wrenches I made though. Thank's again CJ.

samiam4 · #12 12-11-2002, 11:50 PM

I use three wrenchs but have done it with two=)

I think you'll figure it out..... Good luck and write me if you have problems. I'll be traveling accross Siberia, so don't expect a reply till late Jan. Really-

Michael