PeachParts Mercedes-Benz Forum - 87 300 sdl 603 eng timing

#1. go Here: (Courtesy of GSXR) http://www.w124performance.com/images/OM603_head_replacement/

A reprint courtesy of GSXR (Photo courtesy GSXR)

Well, I tackled the timing chain in my 1987 300D this past weekend. I slowly accumulated the proper tools over the last ~2 years (long story, see separate post) which ended up paying off, sort of. Some background info first. I bought the car with 186kmi on the odo, and assume it was fed dino most of its life. I switched to Mobil-1 pronto with no ill effects, consumption is about 7kmi per quart. While replacing the cylinder head in spring 2002, I adjusted the TDC pointer with a micrometer on the piston crown (it was off one degree). Then I checked chain stretch with the eyeball method numerous times, and compared to the dial gauge method on the valve lifter. The numbers matched - 4 degrees stretch, the limit at which MB dictates a new chain is in order. Way back in '02 when I got the chain it was a measly $55, the price has gone up significantly since then. It was an Iwis (OEM) chain. It sat in my shop, rather lonely and ignored, for the past 18 months or so. Now let's fast forward to last weekend.

First I double-checked the chain stretch, yep, still at 4 degrees. Checked IP timing and it was 13.5-14.0, where I had set it previously. After covering up the chain cavity & cam, I took my now-huge-looking 5-inch angle grinder to a link on the old chain. Yeeesh, I wish I had something smaller, it was like swatting mosquitoes with a sledgehammer. Anyway I finally ground enough off the ends and discovered those plates are really STUCK on there! Pliers coaxed it off. I had installed the chain loader (retainer), but as you are about to learn, I did not have it tight enough against the sprockets. I used a clip-type master link to attach the new chain to the old, and started slowly cranking away. Then disaster struck. About 10 links in, I noticed the crank (which I was turning by hand), was moving forward while the chain was not! Oh SH...OOOT! Not good. It was already 90 degrees but my sweat output about tripled at that point. I saw the retainer was allowing the chain to pull off the sprockets on the feed side! Aaaagh! I hoped it would let me still turn the engine, but I could tell with one more partial turn that pistons were kissing valves - very positive stop.

So, I sat down in my pool of perspiration and felt faint for a while. Now what? I tried turning just the cam forward, no go - wouldn't budge (odd). By a total fluke, the crank happened to be right on TDC - I had made one full turn so far. I decided to pull the cam, set it on TDC, so at least the cam & crank would be in time. A little more thinking and I decided hey, while I was at it, I could turn the crank 1 turn with the cam out, and get it back in time pretty close. I knew the IP was likely out and would require an R&R to remedy, but that was to be a later headache. Problem now is, the factory manual specifies how to pull the cam when it's at TDC- not 180 degrees out! Different lobes are under tension, and following the factory sequence could mean a snapped cam. More perspiration (d'oh!). Oh well, worst case I get a new cam out of the deal. I did every other cam tower bolt, one turn, in a Z-shaped pattern back & forth, slowly letting the cam up. Thankfully it survived. I turned the crank one more turn, keeping TIGHT rein on the feed side of the chain... The IP piston tension likes to periodically YANK the chain in and you really have to pull hard to keep it out, otherwise the IP will get out of time (BT, DT on the head job last year - wasn't fun).

OK, turned the crank back to TDC again, re-installed the cam at TDC, then re-installed the now modified chain loader. (I beat on it to bend the edges in so it was TIGHT on the sprocket this time.) I slowly rolled the chain the rest of the way in, and when it was done, I had one extra link! Greeaat. I figured that was the slack side for the tensioner and "dropped" the extra link down, ignoring that little quirk for now. I installed the clip link on the new chain and turned 2 more turns to make sure nothing bad happened, and that the marks lined up. To my surprise, they lined up, and the cam showed zero stretch - just as it should have! Woo-hoo! Half way there. Ok, now to see how far out the IP is. I just about fainted, then danced a jig, when I discovered the IP had NOT lost time with the crank & cam! YESSS! It was now at 11.5-12.0 degrees, as expected due to the new chain. I set it to 14.0 (actually a tiny hair advanced from 14, but close enough) and triple checked everything again.

OK, now to swap out the clip link for a rivet link. I found the OEM link that came with the chain was different from a Genuine Mercedes link (which I bought "just in case"). I'll go into details in my next post about the tools. I pressed the new (Genuine MB) link in, riveted it up, and looked around to see if I could spot the guardian angel that must have bailed me out. What should have been a simple job took waaaaay longer than expected, but at least it's done. Buttoned up the engine & cleaned up.

Results: Seems to be a smidge more power - not much, but perhaps a slight bit snappier off the line? Could be the infamous Placebo Effect. Too soon to tell on MPG. Interesting note is considerably more "diesel klatta" at cold idle. I mean you really notice it. My other 603 had a new chain and was always like that, but I didn't know that was the REASON! Hmmm. When cold, if you raise the RPM a bit, say to 1200rpm, the klatta vanishes (thanks to the IP timing advance device) and it's nearly silent. Back to idle, and KLATTA! The noise goes away when warm though (on both cars). Interesting phenomenon.

Anyway, sorry for the LONG post, but I thought I'd instill some real fear into you DIY's out there contemplating a timing chain job. It's not THAT bad but just be REALLY careful! I'd plan on 2 hours minimum, more like 3+ if you go slow & meticulous. YMMV, etc.