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mercedes 300sel
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Discussion Starter #1
so i changed the valve cover gasket the other day on my 300sd and i check the valve clerence, intake shoudl be .10mm exaust .35mm. when i put the .10 feeler gauge its tight on all the valves even the exaust. one thing i dotn understand is, when the valves need adjustments dont they loosen? not tighten? ive had the car for 4 months now, i notice no problems witht he engine or the valves (that i knwo of) i just ckecked them while i was workign on the car. so my question for you guys is. if its running fine shoud i keep it liek that? whats the dangers or symptoms you will notice with un adjusted valves? what do you guys recomend. thanks alot for your help
 

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1991 300 SE
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Although counter-intuitive, yes, the valves become misadjusted when they tighten. Even with the engines being indestructible, a proper balance of the engine components is needed to ensure long-term engine health. Please adjust your valves every 15,000 miles per spec.
 

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1980 LWB 280GE
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Not counter-intuitive if you think about what really wears to cause a need for valve adjustment. Wear between the cam lobe and the rocker (where you stick the feeler gauge) is not normally significant. Especially with the chilled iron cam and carbide faced rockers in the .951 and .952 motors, and not even in the older .950 motors with softer cams and plain iron (steel?) rockers. Anyway....

The real wear that's happening is the valve wears into it's seat a little bit over time, and as it does, the spring is always pulling the valve farther and farther toward the cam as the valve face receeds into the seat. As the valve stem tip moves toward the cam, so does the rocker pad. That's why valve clearances close up over time.

One more element coming into play has to do with the reason why exhaust valves have greater clearance than intakes. The reason for this lies in a few things. One - you set clearances when the valves are relatively cool (compared to the temp of those valves after you've been strafing the autobahn for four hours at 150kph). Two - the valve stems get longer as they heat up. And Three - exhaust valves get hotter than intakes do since they're always surrounded by hot gasses where the intakes get a continual cool intake air bath. So as a result, in order for clearances to be optimal under normal running conditions, you have to set the exhausts to a wider clearance when cold, allowing them to come into about the same clearance as the intakes when everything's up to temp.

IF the valve clearances opened up with wear, the only risk would be a little loss of power. But since they close up, the potential problem is far more insideous. Eventually, the valve receeds so far (and don't forget that the valve gets longer and the clearance gets even LESS than you measure cold, when the engine is hot) into the seat that when conditions are hottest, the rocker pad will actually ride the cam FULL TIME - with no clearance at all. This is where the real trouble begins.

The only way the exhaust valves can be cooled is by contact with the seat in the head. The water running through the head cools the seats and the seats cool the valves. If the rocker isn't clearing the cam, then the valve is never gaining full intimate contact with the seat and never getting properly cooled. SO the hotter valve grows longer, eventually lifting off the seat at some small point, getting no cooling at all, and in a VERY short time, burned valves, eroded seats, loss of compression, and very expensive repairs come into the picture.

Long story short, maintaining proper valve clearance is VERY important. UNderstanding just what's going on in there is maybe the most powerful motivator to keep after those clearances at proper intervals.[;)]

All the best,

-Dave
 

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mercedes 300sel
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Discussion Starter #4
wow. thanks alot for the great detailed info. so i guess il be doign this job, so i got one other question. i just changed my oil. shoudl i adjust the valves next oil change, becasue ive heard that you should flush the oil after you adjust valves incase something fell into the engine it would be flushed out. so do i have tiem to wait another 4000miles? if not are the special valve wrenches reccomended, theres not alot of space to work around there but are there any recomendations for the special tool for this job?
 

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1980 LWB 280GE
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Sooner than later

If your exhaust valves are already closed up to less than the intake spec, let me tell you, I'd be doing them TODAY. Change the oil after the valve lash if it makes you feel better. I never have. Just be careful as you do the valve lash not to jam the wrenches around in there nicking things up.

From that point of view, yes, it's better to have the factory tools, if only because you'll be in generally better spirits as you tackle the job, not cursing the thing all the way through.

A "remote starter switch" makes the job a ton nicer too since you have the button right there with you under the hood and can just blip the motor over to where it's ready for the next valve.

I don't mean to alarm you with that "...TODAY..." comment, but it is a really important thing for avoiding expensive repairs.

-Dave
 

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Discussion Starter #7
thanks hipin, yes i think il do it asap probably tomoro, cause it probably needed adjustment since i bought the car 4 months ago. howeever if you dont have an electric starter how will i turn the camshaft? i heard somewhere that u can use a wrench and turn it manualy? is that possible? and when i complete the job what woudl i notice about the car? better fuel ecomony? smoother? more power? becasue it honetly rides in my opinion perfect. so im lookign forward to see the improvements after the adjustment.

and one more thing. theres a clearence for cold and warm engines.. can u define a cold engine because its -10 celcius up here and adjusting this engine cold in florida is very diferent than cold in canada. thansk for the help
 

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ladybee - 2/27/2005 6:58 PM
....if you dont have an electric starter how will i turn the camshaft? i heard somewhere that u can use a wrench and turn it manualy? is that possible?...
If you need to turn it by hand, you should only do it using the bolt on the end of the CRANK shaft. That is the 27mm bolt at the center of the lower belt drive pulley on the front of the engine. NEVER try to turn the engine using the bolt on the front of the CAM shaft, you stand a good chance of damaging the cam chain or tensioners. Also only turn the engine in the CLOCKWISE direction, never the other way, you'll damage the cam chain tensioners for sure like that.

The remote starter really is the best way. If you don't already have a 27mm socket, buying one will cost you darned near as much as buying a remote starter trigger switch. On your car you should find two screw terminals on a terminal block below the battery tray. Just clip the two leads of the remote starter to the two scews you find there. Pushing the button will turn the engine over.

....and when i complete the job what woudl i notice about the car? better fuel ecomony? smoother? more power? becasue it honetly rides in my opinion perfect. so im lookign forward to see the improvements after the adjustment....
Probably marginally better power. Right now the exhaust valves are staying open too long as a result of the decreased clearance. That results in some of the intake charge being lost out the exhaust valves, and slightly lower ultimate cylinder pressure. You should also notice it's easier to start on cold mornings when the valves are properly set.

....theres a clearence for cold and warm engines.. can u define a cold engine because its -10 celcius up here and adjusting this engine cold in florida is very diferent than cold in canada. thansk for the help
The workshop manual defines "warm" as 60 celsius, +/- 15 degrees, and defines "cold" as approximately 20 degrees celsius. Personally I think it's just plain no fun at all to work on a 60C engine. I always do this work on a "cold" engine if I can help it.

One more tip. The whole thing will be a lot easier if you remove the glow plugs before you start. That'll allow compression in the cylinders an easy way to escape and make it much easier to put the cam position exactly where you want it (pointing directly away from the rocker pad - about 40 degrees from vertical, not straight up from the head), and if you have to turn the engine by hand, it'll make that job a lot easier too. If you're fighting compression the engine tries to "jump" forward as you pass top dead center on the compression stroke of any cylinder. Can be frustrating.

Good luck!

-Dave
 

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Thanks for the kind words.

Just trying to be a good citizen. My first post to the forum was asking for help. Glad I could help someone in return.

-Dave
 
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