Adjusting valve clearance

Adjusting valve clearance is dreaded by all first-timers. The task seems daunting - unhooking all of the linked parts on top of the engine (throttle linkage), tearing into the engine itself, then putting it all together ... It's not a piece of cake like an oil change, for instance, but I can tell you up front - it's not that hard. Before we go any further, let me make one thing clear to you: I cannot be held responsible if you follow this entry and somehow your dumb ass destroys the engine. I described what I did on my 1984 Mercedes-Benz 300SD, and if you spill your Coke on the valves, or leave a wrench inside, or turn something clockwise when it has to be counter clockwise on your particular car and in accordance with your car's manufacturer's manual, it's your own fault. You must adjust valves every 15,000 miles, some say every 12,000. You basically have to accommodate for natural wear of valves/cam lobes by loosening one nut and tightening the other on top of the valves. You have to be methodical and patient. When you're done, you will feel the sense of pride and accomplishment like you've never had. Here's what I used to do this job for the very first time:
  1. Wrenches. Can't do this job without them. Don't listen to people who tell you that you can use regular straight wrenches. You'll have enough on your plate when you do it for the first time, so screwing around with straight wrenches is very uncalled for. Buy your wrenches from www.performanceproducts4benz.com, or www.mercedessource.com. The guy from Mercedes Source makes wrenches himself - they work really well. This is the best investment for your Benz.
  2. Feeler Gauges. I erroneously thought this was some kind of a hi-tech tool I had to buy off the Internet or the dealership. Turns out it's a stupid set of metal blades of various thickness with some numbers on them. Don't buy them off the Internet! Hit up your local dollar stores and save yourself ten bucks.
  3. Cam box gasket. It's that rubber thing on the bottom of the cam box. My mechanic was really surprised when I told him I replace the gasket every time I adjust the valves. He said every other time (every 20-25k) is fine. What does he know, he's only been in MB fixing business since 1957 ... I didn't listen and I get a brand new gasket every time.
Theoretically, you're all set to adjust your valve clearances. However, I found it to be a more satisfying job when I picked up a few extra things.
  1. Absorbing shop towels. Those are thick smooth grey towels that look like they are stitched through diagonally (but they're not). They are five bucks at WalMart and they work miracles when it comes to wiping oil or grease off anything. You'll be doing some cleaning and laying out of the parts on them, so pick them up.
  2. Deep 27 mm socket. You'll turn the nut on the power steering pump clockwise. It's either that or constantly running in and out of your car and jerking the starter because you will need to turn the engine. Also, people tell me you can rig up a starter button by hooking up a couple of wires to starter solenoid ... never tried that one.
  3. Mother's Aluminum Polish. The engine compartment was brutally dirty, so I decided to pick this up to hit all metal parts. It worked ok, but if you know of a really good metal cleaner, tell me.
  4. Steel wool. I took the grime right off with some steel wool and rubbing. It was good to see my parts get their shine back. Be careful when cleaning the cam box (valve cover) - don't get any of the steel wool shavings inside the cam box!
  5. Gloves. I used double latex gloves, but now I wish I used those cheap plastic one-size-fits-all gloves that don't form-fit the hand. I went through about 15 pairs of latex gloves because they broke all the time.
  6. Masking tape. I taped a little piece on the fender, indicated valves and clearances, and checked off each valve as I adjusted it. It is important to keep track of valves you've hit, regardless how you do it.
  7. Digital camera. It was highly annoying to drop everything and take a picture every step of the way (and get the camera dirty), but it helped a lot when the time came to put everything back together. I felt like taking pics because of this blog and, more importantly, because if I fucked something up, I'd have no car.
  8. Large flat-headed screwdriver. Used for many things in this job.
Ready? First off, here's how everything looks like before you unhook anything. A word of caution - vacuum lines can be very brittle and need to be handled with care. You will feel incredibly stupid while adjusting the valves knowing that you still need to get some vacuum lines for your vehicle to run properly. Start unhooking throttle linkage. Don't just go crazy and unhook every socket, unhook in a few strategic spots. You do it by prying the round sockets with the large flat-headed screwdriver off the round pins they are sitting on. If you use a screwdriver with a small head, you'll cut into the surprisingly soft metal and leave some gashes. Here's where I unhooked the linkage: I then proceeded to take off the air filter housing to facilitate easier access to the valves. I unscrewed the top nut in the middle of the air filter lid, took off the lid, removed and inspected the air filter, and unscrewed three nuts inside the air filter housing. Then I lifted the air filter housing off the pins and moved it aside towards the passenger side. You can't go too far because bent plastic hoses are still on, so be careful. While you are unhooking everything, be alert and try to memorize what you're doing. Don't tear into stuff and disconnect everything just because it comes apart. Germans did everything with a sense of purpose, so the absence of every little nut will be known by your trusty diesel. After you unhooked the linkage, organize it inside the engine compartment so it's out of the way of you removing the cam box. Also, organize all nuts and wrenches on towels. Keep everything clean, you'll feel better. Last second note: If you choose to disconnect the "STOP" assembly, my mechanic suggested putting an alligator clamp or some other clamp with handles onto the piece of linkage attached to it. He said engines with better compression tend to start when you bump them, and that creates a mess. With a clamp, you'd be able to stop the engine easily. There are four bolts that hold the cam box on top of the engine. Two are easily accessible from the left. You can get to the other two after you unhook the linkage. No, you won't need pictures to unscrew four bolts. But I'm giving them to you anyway. The cam box comes right off. It feels very light. It is very dirty. My first impulse was to steel-wool it, then polish it, but then I realized I got my engine compartment all torn up and it might rain. Naturally, I postponed the cleaning in favor of actually adjusting the clearances. A-a-a-ah, here she is. When I saw this for the first time, I immediately knew where everything was because of reading the newsgroups religiously for months. During that time I realized how friendly, intelligent, and helpful the newsgroup people are ... and how lazy. No soul would take one lousy picture! I'm making it up for it all. Here's a 1024x768 of the 617 engine without the cam box. Here's a close-up. You will get to adjust and check the distance between all 10 lobes and the valves. Some clearances you won't have to adjust. Your next big step is to affix a piece of masking tape to the fender and indicate each of the 10 valves with either an "I" or an "E", for "intake" or "exhaust" with their respective clearances. You will check valves off as you go. This is my tape in the middle of this job (disregard writing in pencil): By now, everything should come halfway together in your head. Time to adjust. Remember this for the rest of your days: INTAKE valve clearance is 0.004 in, EXHAUST valve clearance is 0.014 in. Refer to my sticker for valve identification. From back (Mercedes star) to front (OEL cap) valves go as follows: I E E I I E E I I E Here's where my hands got too dirty to take pics. Bump or turn the engine until one of the cam lobes is pointing at 1 o'clock. I used a 27 mm wrench to turn this nut (and the whole engine) clockwise. When one of the cam lobes is pointing at 1 o'clock, stick the appropriate feeler gauge behind the lobe. If you can move the feeler gauge in and out with a little tug, you're good, move on to the next valve. If you feel it's too loose, too tight, or you can't stick the gauge at all, time to use those wrenches. I normally place both wrenches on both of the nuts when I adjust the clearance. The bottom nut is the locking nut. The top nut is the adjusting nut. Righty - tighty, leftie - loosie. If you turn the nuts counter clockwise, you are "unscrewing" them, and the distance between the valve and the cam lobe becomes SMALLER because the adjusting nut gets HIGHER. If you are turning the nuts clockwise, you are "tightening" the nuts, and the distance becomes GREATER as the tightening nut gets LOWER. Sounds simple, but if you don't understand this, you'll spend two hours on a single valve. Also, remember that you never have to turn the nuts more than half a turn. Don't get excited, some of the clearances don't even have to be adjusted. The lobe in next image is positioned INCORRECTLY. Your lobe should be at 1 o'clock. The lobe in next image is positioned INCORRECTLY. Your lobe should be at 1 o'clock. Clearance is adjusted between the indicated parts: That's it. Move from valve to valve, adjust, check off valves on masking tape. Remember: it's better to leave the clearance a little loose that too tight! When I was done with adjusting, I steel-wooled and polished all disconnected linkage parts and the cam box. I made sure no particles got inside the cam box. Then I put the new gasket on the cam box, carefully moved all vacuum lines out of the way, and slid the cam box on the four bolts. The gasket came off a couple times, I admit that was a little frustrating. When I finally got it to slide on, I realized how clean everything was: Start putting everything back together - the air filter housing, the linkage, the vacuum lines. Don't forget that if you followed my directions, you have a piece of linkage that goes on these holes before the bolts: One last thing: if the valves are turning on you as you are trying to adjust, some suggest jamming a large screwdriver next to the valve to press against the hex valve collar. That prevents the valve from spinning, but I don't feel good jamming screwdrivers into my engine ... Be honest, now that you're done, wasn't that a piece of cake?


Anonymous Michael Sova said...

Wow max, you've become quite the little mechanic.


11/08/2005 09:49:00 AM  
Blogger Em said...

You goddamn right I have.

11/08/2005 09:56:00 AM  
Anonymous Adam said...

Hey, I was just poking around your site because i'm interested in picking one of these cars up. If I do, I'll be sure to refer to this page. You did a heck of a job...I'm very impressed with the time you took into showing how it's done. Good work!

1/16/2006 07:43:00 PM  
Anonymous Anonymous said...

Very nice.

8/22/2012 12:08:00 AM  
Anonymous brad said...

still running? I'm an hour east of you with an '84 SD running strong with 354,000 on the clock.

9/25/2013 10:34:00 PM  
Blogger Sonny Batzle said...

What happens if you don't do a value adjustment after 15000 what damages could happen to engine.

4/13/2017 04:03:00 PM  
Blogger inCaffeine said...

@Sonny many mechanics will tell you that this is an often overlooked maintenance item. The OM617 engine is very forgiving but will let you know its valve adjustments are being neglected by not starting easily and running rough. Eventually the clearances could reach zero mm in which case they will not completely close, and your engine would be very hard to start. Maybe a mechanic has seen them get burned out in some worst cases?

9/17/2017 09:53:00 AM  
Blogger Unknown said...

Mine is making a loud knocking noise. Does this model have lifters everyone I talk to said it sounds like a lifter. Please help I'm trying to get this running for my husband who has Cerebral palsy

8/13/2018 06:22:00 PM  

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