Valve adjustment technique ??? - PeachParts Mercedes-Benz Forum

Angel · #1 08-05-2003, 03:27 AM

Hello All,
I really hate to throw up ANOTHER thread about valve adjustment, but I am totally lost....what am I doing wrong ?

short version- I loosen the nuts, tighten them, check clearance w/ feelers, remove feeler, turn engine over using 27mm, then recheck clearance... its WAYYY off from where I just had it.

Long version- I have a .302mm and a .33-somethingmm feelerguage (616 motor, exh valve for example), I've been adjusting them so the .302 goes in but the .33 doesnt- is this too stringent a test ? The book says .3mm gap, but there has to a a few .0Xmm tolerance thats satisfactory. For intake I have a .10something and a .12something. I searched and saw someone talk about "make sure the .3 fits through and the next size up (.4mm) does not- thats a pretty wide tolerance.

When I have the nut tightened, and I run the guages, I pull them out, and then bend back down so I can crank the engine around- to double check myself. I crank the engine around 1 or 2 times (doing this by hand after every valve gets annoying, it might be starter switch time). almost every time I do this, I come back and the clearnace is way off from before (if the .33 didnt fit before, it does now -type thing). I have been trying to get the cam back in the same exact position it was when I first adjusted the valve (having the cam positions more than 20deg off appears to REALLY affect valve clearance... are my feeler guages growing or shrinking on me ? I have no tension on wrenches or valves when checking or re-checking them. I try to wiggle the rocker and valve, to be sure they are seated, but this changes little.

I dont know, and there are lots of old school wrenches here that can adjust valves in their sleep. I just know that tomorrow night I'm gonna go back to that 616, and run the feelers through and NONE of the valves will be where I set them before. I just bought the car, 100k miles (origional says PO...we'll see.....) and some of the back intakes were a bit off...and all but 1 exh didnt like my "between .30 and .33 test" method. I think I have them good now... My last MB diesel ('82 300D) had its motor seize, so I want to be darn sure that its not me mis adjusting anything.

Any comments/ideas on the best valve adjusting technique ?

-John

dabenz · #2 08-05-2003, 05:53 AM

John, you're thinking too hard. Dollars to donuts you're adjusting and checking a valve on different strokes (compression vs. power, or some other combination) on your "new" engine that has a bit of carbon build-up. And very few people set the valve where they think they set it because they move the middle wrench a bit when tightening the top nut. I'm assuming here you're using the bottom wrench to push down on the spring keeper. 0.302 to 0.33mm is 0.0011in - you've got to be really good to get that every time while holding three wrenches with two hands and a big toe. Remember: a shade loose is better than a shade tight with this engine as the valves tighten over time, so set 'em, do the Italian tune-up, and check 'em. And write the numbers down each time you check or set 'em.

P.E.Haiges · #3 08-05-2003, 11:46 AM

Angel,

Where are the cam lobes when you are adjusting the valves? Each one should be pointing straight up when adjusting the respective valve. Maybe the clearance changes when your engine BTW, its an engine, not a motor, is upside down (you said you "turned it over") LOL.

There is no need to rotate the engine and check the valve clearances again. One they are set correctly, they stay that way. I checked the clearances on my '79 300SD 116 engine after 25,000 miles and they were all within spec . So in 2 1/2 years they don't change much. Somehow somehow your adjusting procedures are wrong or your cam is not mounted properly. Make sure you are not confusing the intake and exhaust valves. You can tell by looking at the exhaust or intake manifolds.

I use .003", .005", .013" and .015" thick feeler gages as go/nogo gages for intake and exhaust valves respectively. That way my clearances will always be nominal + or - .001 and I alway set the valves on the loose side because the clearance becomes less with use.

P E H

Maxwell · #4 08-05-2003, 01:40 PM

Wait a sec, PEH, shouldn't the lobes be pointing away from the rockers toward the oil pipe?

Thomaspin · #5 08-05-2003, 02:10 PM

The lobes should be perpendicular to the rockers when you adjust. That's how the Maintenance Manual illustrates it. However, given that the cam profile is fairly level around much of the camshaft on the side opposite the lobe, you can be quite a bit out and still have no rocker movement from the perpendicular setting.

A picture is worth a thousand words.

Honus · #6 08-05-2003, 05:05 PM

As I read the factory maintenance manual, the cam lobe should be pointed directly away from sliding surface of the rocker arm when checking the clearance.

The exact language from the manual is: "Measuring valve clearance between sliding surface of rocker arm and cam base circle of camshaft, by positioning camshaft so that the tip of cam is vertical relative to the rocker arm."

The picture next to this entry in the manual shows the cam tip pointing up and to the right, directly away from the sliding surface of the rocker arm. I guess that is what they meant when they said "vertical relative to the rocker arm."

Thomaspin · #7 08-05-2003, 05:32 PM

By 'vertical' they mean 'perpendicular'.

Vertical is vertical, bad English translation.

Angel · #8 08-05-2003, 06:30 PM

I appreciate the replys, this isnt an under-discussed subject.

The only othe rtime I've adjusted valves was on my motorcycle (its has 16 btw...) and it is very easy for me to get within +/- .002mm using my set of feeler gauges.
It helps that its a smaller design, and only has 1 8mm nut to tighten. I'm used to turing the bike motor over a revolution (y'know, cranking it w/ a wrench 360 or 720 degrees...2pi or 4pi radians.... =) then re-checking to make sure I didnt shove the wrong feeler in or there wasnt dirt/oil in there or something.

I have been putting the cam lobes pointing perpendicular (at about a 30-40deg angle to vertical) to the followers. got that ok.

I was just frustrated that I could dial these in as easily as I do my bike, I thought I was missing something...I'm beginng to agree w/ dabenz... I was a nuke in the Navy y'know... (ask any submariner what it means to "nuke something out"

thanks for the help
-John

BoostnBenz · #9 08-05-2003, 10:18 PM

I prefer to adjust mine with very little tolerance between gauges, but I still use the same go and nogo tests. It gets pretty annoying while doing it as I always seem to go to far one way or another, buy I don't know how far until I retighten the top nut. Ah well, only have to do it once every 15k miles.

dabenz · #10 08-06-2003, 08:45 AM

Angel, now I understand. I was a destroyerman in a previous life.

P.E.Haiges · #11 08-06-2003, 07:10 PM

BoostnBenz,

Do you check the valve clearance before you do the adjustment? If you do, how many valves need adjustment after 15,000 miles.

The reason I ask is that the last time I checked the valve clearances on my '79300SD at 25,000 miles since previous adjustment, not one of the valves needed adjustment.

P E H

Rick Miley · #12 08-06-2003, 07:17 PM

Quote:

Originally posted by P.E.Haiges
...I alway set the valves on the loose side because the clearance becomes less with use.

Quote:

Originally posted by P.E.Haiges
...the last time I checked the valve clearances on my '79300SD at 25,000 miles since previous adjustment, not one of the valves needed adjustment.

Is there a connection here?

BoostnBenz · #13 08-06-2003, 11:30 PM

I haven't put 15k miles on either of them yet. I suppose I would inadvertently end up checking it before adjusting because I need to go which way to go and how far. Also like you said they probably won't need it, so it'll probably be more like changing the camshaft cover seal every 15k miles.

P.E.Haiges · #14 08-07-2003, 01:30 AM

Boostnbenz,

Replacing the valve cover gasket every time isn't necessary. The gaskets are made out of rubber and are usable until the rubber hardens after years of service.

P E H

BoostnBenz · #15 08-07-2003, 10:48 AM

While I'm sure this is true, I drove my 84 for about 4k miles since the last valve adjustment and decided I would try replacing some head bolts to slow or stop the very minor oil leak it has. It wasn't completely hardened but in the corners the rubber were starting to crack and it wasn't nearly as pliable as the new seal was, so I figured I'd replace it anyway. The new head bolt did help the leak, but it still isn't stopped, I'm debating what to do next. Maybe I'll just give it a little more time, it would sure be nice to not have any leaks.