Hard starting after valve adjustment. - PeachParts Mercedes-Benz Forum

Antsrcool · #1 12-11-2017, 09:07 PM

So my car had a bad smoking problem and very rough idle. So I did a compression test and cylinder 4 had 60 psi. No good. So I removed valve cover and the valves were stupid tight. After adjusting number 4 went up to 375 cold. And once it finally starts it idles smooth as silk and the smoke is very much reduced. I think the smoke I get now is unburned fuel in the exhaust. However now it will not start cold. And by cold I mean 45 degrees. Glow plugs all work I checked them. Even once running and got it cranks about 10 seconds before starting. Any ideas? Would a loose intake valve cause this? I may have not adjusted them tight enough because they were so tight I was thinking that they would tighten up rapidly after the valves were slamming into the head and finally seating knocking off carbon. There not crazy loose though. Injectors are all new and bench tested. Prior to valve adjustment it started pretty decent.

leathermang · #2 12-11-2017, 11:25 PM

I would say go back and start over.
Be sure to set the valves with the engine stone cold... so leave it overnight to make sure. It is easy to put the wrong specs on a valve... mark the valves before you start.

How long are you running the glow plugs ?

The Chart in the Factory Shop Manual shows how hot they get for being on up to one minute... use a watch and leave them on .. no ' cycling'... for 45 seconds and see if that fixes it... after you are sure your valves are properly set.... if they are too tight.. they can expand once warm enough that they are not in proper contact with the head...half the cooling for the valves is provided by that contact with the head.. so once that is not sufficient.. even more heat and thus expansion of the valve occurs... and bingo.. you have burned a valve....

vstech · #3 12-12-2017, 07:34 AM

Be SURE you mark which valves are which and which you have adjusted.
It's pretty easy to set intake to exhaust spec and vice versa...

Don't set them loose.
Set them right and go back and reset them again after 500 or so miles...

Antsrcool · #4 12-12-2017, 01:19 PM

so i rechecked the valves and they are perfect. Thinking air intrusion from hand pump? it still has the old plastic type and it leaks when you use it

dkr · #5 12-13-2017, 01:01 AM

I'm not sure if this would apply to a valve adjustment, but I would also check your surrounding vacuum lines and make sure all are connected and not broken off. I have accidentally disconnected these when doing jobs and the results are often strange and unpredictable.

Dkr.

Maxbumpo · #6 12-13-2017, 07:46 AM

Quote:

Originally Posted by Antsrcool

so i rechecked the valves and they are perfect. Thinking air intrusion from hand pump? it still has the old plastic type and it leaks when you use it

Bingo, this is one problem that you need to fix before continuing to diagnose the problem. My first thought after reading your original post was "air leak allowing the fuel system to lose prime".

If this fixes your cold start problem, and you are sure there are no other air leaks into the fuel system, then as already suggested you should drive the car for 500 miles and check/adjust the valves again, pay close attention to #4.

The smoke you see now is probably from un-burned fuel / carbon build up in #4. Italian tune-ups can speed the process of removal, but you will continue to get smoke until all that carbon is removed. Burning it out by hard driving is the easiest and least expensive, but takes time, perhaps thousands of miles.