Sunday, May 08, 2011

BMW M3 Valve Adjustment, S54 Engine

My M3 is way overdue for a valve adjustment. The maintenance schedule calls for doing it at every inpection interval which is roughly every 30,000 miles. I've had this car for 19,000 miles but I have no record of it ever being done. It probably was done at least once, but I'm betting it's way overdue. When I measured the clearances, every valve was out of spec, and all were on the "loose" side of the spec, which is actually better than them being on the "tight" side. They weren't really TOO far out of spec, considering. Just a few hundredths of a millimeter, on average. The worst one was 0.08mm out of spec. The car has 102,000 miles on it now so I want to get it in spec and give everything a good going-over so it will be ready for the next 100,000 miles. As usual with this blog, this is not a "how-to" but rather a "you can". On my difficulty scale of 1 to 10, with 1 being putting air in the tires, and 10 being an engine rebuild, this is about a 3. Seriously, it's not hard. All you need is your basic hand tools, the BMW shim removal tool, and a digital micrometer. I paid about $30 for a cheap-ish micrometer specifically for this job. I paid $30 plus a crazy $20 for shipping for the shim removal tool, and I'm spending about $50 on shims. If you need to get this done in one day you'll need to buy the full shim kit which is about $375 but that includes the removal tool and when you're done you can easily sell it online for most of what you paid. I didn't do that so my car will be down for about a week while I wait for the shims to come from Pelican Parts. So I'm into this for about $130 and maybe 4 hours of labor, probably 5 by the time I'm done. A shop quoted me close to $1000 for this service, so it's a good DIY project. I referred to an excellent video on YouTube that covers the project in good detail. I definitely recommend you watch a couple of those before you start.

Valve cover is off and I'm ready to start measuring clearances and removing shims. It takes about 30 minutes to get to this point.

Here's my spreadsheet where I recorded all the clearances, the thickness of each shim, and do a little math to find out what size shim would give me the exact clearance I want. I calculated the Theoretical Best Shim (TBS), and compared that to the shims I actually have (24 of them) to identify which shim should go in each location. Doing this, I was able to reuse 14 of the 24 shims. I have to buy the remaining 10 because none of the 10 I have left are the right thickness. No way I could have kept all this straight without a spreadsheet. It took me a couple hours working slowly to measure and record all the data.

Here's where I laid out my shims to keep them straight until I did all the math. A few have already been put back in the engine in this photo. Now that I have the exhaust side all done, and none of the remaining shims can be used except two on the intake side, I no longer have need of these shims or this sheet of paper.

Here's the official BMW shim removal tool. I say removal tool because it was far harder to put the shims back than it was to get them out. This little plastic tool was almost $50 with shipping and everything, but it's a necessary evil. I finally got the hang of using it to put shims back in, but not before dropping a few shims. It is IMPERATIVE to block all the little oil passages in the head so that errant shims can't disappear into the engine.  That would be BAD. A magnetic pickup tool helps fish them out from where they fall. God help you if you lose one in the engine.

This is the micrometer I bought for this job. It was in the $30 range at Harbor Freight. It may not be extremely accurate, or it could be that I just had to learn to use it. That thousandth's decimal place should definitely be taken with a grain of salt.

UPDATE: 5/14/2011

The shims I ordered from Pelican Parts on Sunday arrived via USPS on Friday. Perfect timing. So this morning I finished the job. Unfortunately, when I put the new shims in place, most of the clearances turned out tighter than I had calculated them to be with my spreadsheet. A couple were just under the minimum and I wasn't comfortable with that. Upon re-measuring things today, everything was measuring bigger. Checking my technique with the micrometer with the new shims of known thickness, I think I was cranking down too hard on the micrometer last week. You can definitely influence the measurement by how hard you turn down the dial. Once I standardized my technique and got consistent results, I ended up re-measuring all the clearances and moved several shims around to get closer to the clearances I wanted. My main concern was to not leave any valves too tight as that can lead to problems. In the end, I got all the clearances on the lower end of the tolerances. The minimums are 0.18mm on the intake cam, and 0.28 on the exhaust cam, while the maximums are 0.23mm and 0.33mm for the intake and exhaust, respectively.

Most interestingly, and to my surprise, the engine really does feel smoother and a little bit quieter after the adjustment. I swear I can feel and hear the difference. I didn't expect to. The S54 really likes proper maintenance. I also took this job as an opportunity to inspect the bolts on the VANOS system as there have been internet reports of them backing out and causing catastrophic failure of the timing gears and chain. Everything looked absolutely perfect so I didn't touch a thing there. I feel better having had a look at them, though.


  1. Hello.
    I have a quick question; why not replace ALL shims with new even if they are not out-of-spec? Do you replace only the out of spec shims or each one? It seems like the carbonization layer of the steel shim would wear over time and even if the shim is not currently out of spec it would be softer and wear faster. So it would make sense to replace them all.

    Very very cool blog I will continue to follow glad I stumbled onto this website. Cheers!
    Dan from Raleigh

  2. Hi Dan, thanks for commenting! I think the major reason is cost. Five or ten shims is a lot cheaper than 24. From the reading I've done though, and from what I saw first hand, there's really no wear on the shims themselves. The wear is at the valve seats in the head.