OM617 timing chain stretch results. - PeachParts Mercedes-Benz Forum

KAdams4458 · #1 10-12-2007, 06:44 PM

I checked my timing chain stretch this morning, and I'm a little perplexed by my findings.

I could not use a dial gauge, since the camshaft is so screwed up, but I wanted some idea as to the condition if the timing chain before I need to place a parts order. I used the marks on the thrust washer and cam instead.

With the marks aligned perfectly, like so...

I end up seeing this at the crank...

I'd call that 1.5 degrees, so I guess there must be an offset key in place already, since this does not look like a new chain at all...

What are your thoughts? I honestly expected it to be all FUBAR. I never expected this, and I can't comprehend why anyone would go to such lengths to correct cam timing, yet leave a scored and flattened camshaft in there.

pawoSD · #2 10-12-2007, 06:46 PM

1.5 deg's is nothing.....MB says that it can be up past 5 degrees before "requiring" a replacement. My car had 7 degrees of stretch on it when the dealer checked it a few months after I got the car.

Promptly had it replaced!! And that was over 52k ago!

KAdams4458 · #3 10-12-2007, 06:51 PM

In case anyone is wondering why I couldn't use a dial gauge, this is why...

That's actually one of the best lobes on the cam. Testing with the gauge, I could watch the reading wonder significantly on the opposite side of the lobe. They're all scored pretty badly.

pawoSD · #4 10-12-2007, 06:56 PM

Ouch! I've never seen one like that before....does it have a history of being run low on oil? How does it run in general??

KAdams4458 · #5 10-12-2007, 07:04 PM

Quote:

Originally Posted by pawoSD

Ouch! I've never seen one like that before....does it have a history of being run low on oil? How does it run in general??

It apparently has a history of having the valves way too tight. Constant pressure from tight valves kept the oil film off of the lobes. A few of them are scored deeply around the entire lobe, #1 intake being one of them.

As for how it runs... Well, it runs fairly well now, but takes holding higher than idle RPM to get a cold start, and never develops much power. I was hoping the power issue would turn out to be chain stretch, but alas, it is not. Now I hope it's just the crappy camshaft, or maybe IP timing. (Lord knows how bad the injectors are, I'm still hunting for a used set to have worked over.)

winmutt · #6 10-12-2007, 07:10 PM

Quote:

Originally Posted by pawoSD

MB says that it can be up past 5 degrees before "requiring" a replacement.

Where does it say this? The keys start at 4 and then it is a key, not replacement. The biggest key is 10degrees. I was at 14 I think. Its on the list of things to do.

junqueyardjim · #7 10-12-2007, 07:21 PM

Bajaman has an excellent non turbo engine for sale in the parts section as of about last Saturday. You ought to talk to him about that one. Compression like new, all over 400 PSI and a cam shaft that can't be told from new. It shines so bright it hurts our eyes.

KAdams4458 · #8 10-12-2007, 07:22 PM

Well, the chain looks serviceable, and is close enough to timed that I'm going to just re-use whatever key it happens to have in it. I do wonder which one is installed, though. I guess it's time to order some valve stem seals and a three-square 12mm bit. At least, I think that's the size of the cam tower bolts... Feel free to chime in if you know for certain.

winmutt · #9 10-12-2007, 07:23 PM

FWIW the turbos and later model NA's had hardened cams....

KAdams4458 · #10 10-12-2007, 07:28 PM

Quote:

Originally Posted by junqueyardjim

Bajaman has an excellent non turbo engine for sale in the parts section as of about last Saturday. You ought to talk to him about that one.

If I change the motor in this puppy, you better believe it will have a turbo attached!

Thanks for looking out for me, though. I actually have a good used hardened camshaft of the "08" flavour, along with the proper hardware to do the upgrade. Compression is pretty decent on this motor, blowby doesn't make the cap dance, and it has just the faintest whisper of smoke at the tailpipe when idling cold. I'm just going to swap the cam and run it. For all I know, the entire power loss issue is just due to reduced valve lift from the camshaft wear.

patbob · #11 10-12-2007, 08:06 PM

Am I missing something? With scores like that, how can you even set the valve clearances? Won't the clearance that the valve sees to the cam always be something greater than the clearance you measure because of the groove depth? Am I safe in assuming that might matter?

KAdams4458 · #12 10-12-2007, 08:31 PM

Quote:

Originally Posted by patbob

Am I missing something? With scores like that, how can you even set the valve clearances? Won't the clearance that the valve sees to the cam always be something greater than the clearance you measure because of the groove depth? Am I safe in assuming that might matter?

Yeah, it makes setting the valves rather difficult. I fudged around with them a while, and eventually gave up and just left them on the loose side, and a serious improvement resulted. Then I spent a couple of months hunting for a good camshaft locally. I finally lucked out one day at a self-service yard, and came up with the updated camshaft, towers, rockers, shafts, and stem nuts from a very nice looking '80 or '81 for about $35.

As for valve adjustment on my old cam in particular... Let me put it this way: If I were to slip a thin feeler gauge between the cam and rocker when the cam was pressing on it, I'd have a v-shaped groove in the gauge. That's how bad this cam is. It's more like a bead roller than a camshaft at this point.

#13 10-13-2007, 05:39 AM

Quote:

Originally Posted by pawoSD

MB says that it can be up past 5 degrees before "requiring" a replacement.

There is no specification or interval for the chain to be replaced.

Stevo · #14 10-13-2007, 11:44 AM

My daughters 240D had a cam in worse shape than yours so we made a visit to the wrecking yard and for $100 got a replacement cam with towers and followers, problem solved.

KAdams4458 · #15 10-13-2007, 12:18 PM

Quote:

Originally Posted by Stevo

My daughters 240D had a cam in worse shape than yours so we made a visit to the wrecking yard and for $100 got a replacement cam with towers and followers, problem solved.

It was actually your post that came up on a search that made me say, "Hey, why don't I look for a used cam?" Prior to that I was really only considering a new cam. The cost was giving me fits, though.

So, it ran much better with a good used cam, didn't it? How big of a difference would you say that you noticed?