Timing everything! Cam timing that is... - Page 2 - PeachParts Mercedes-Benz Forum

Thomaspin · #1 08-22-2003, 03:40 PM

Dave -

Point taken on the degree issues.

Interesting on your 617 chain.

I changed mine at 110k - 7 degrees stretched. At 200k (i.e. 90k on the second chain) it's only two degrees stretched. Maintenance regime the same, albeit more start-stop driving in the first 110k miles. Maybe I was an even lousier mechanic when I did the first change and just measured it wrong? Still, I would expect more than 2 degrees after 90k. I check it every time I do the valves (every 15k).

No such need on the sixes, I guess, which makes me ask whether owners of sixes tend to overlook chain stretch checks as they have no other incentive to take off the cam cover.

gsxr · #2 08-22-2003, 03:53 PM

As an interesting anecdote, Marshall Booth (who has a fleet of diesel MB's and has owned dozens over the last 30+ years), says that timing chain wear (elongation) appears to cease completely when using synthetic oil. Remember this is just an anecdote, his exerience may not be the norm, but still it's interesting IMO.

And yes, I think 60x chain stretch can be overlooked as you just don't need to go in there much.

Although I paid a shop to do the first valve adjust on my 617 whenI bought it (with 202k), because I didn't have time to mess with it, the shop DID NOT check the chain stretch. And this was a German repair specialist that dealt mostly with MB's. I wasn't happy, I assumed that was part of the job. It has 225k on the clock now so I'm due to check the valves and the chain myself!

R Leo · #3 08-22-2003, 04:46 PM

Essentially, It's acedemic what happens at the cam because all of the rotational measurements are conducted at the crank. Only linear measurements are made in the valve train (valve lift).

According to the FSM, the offset keys are calibrated (?) for degrees of crankshaft rotation (see graphic). After all, that's where the measuring devices (pointer and degree markers) are.

I don't know about the 6.5°, 8° and 10° keys but the 4° key altered Marlene's intake valve timing (at 2mm lift) EXACTLY 4° from 15° ATDC to 11° ATDC (the spec for 20,000+kM chains).

That is 4° of crankshaft rotation...and, it was the 4° key. Go figure!

My mileage went from 21 to 24+MPG and off-idle performace improved so I think the procedure works exactly like the MBZ FSM says it should.

Oh sure, my IP timing is probably not right on the money but, she is driveable and, much more fun to drive as well. The IP timing will just have to wait until I have another afternoon to piddle with cars.

R Leo · #4 08-22-2003, 04:47 PM

According to the FSM, the offset keys are calibrated (?) for degrees of crankshaft rotation (see graphic).

Thomaspin · #5 08-22-2003, 05:03 PM

Which reminds me that I have been meaning to time the IP on the 617 for a while now, especially after Dave M put me on to the MB thingummybob tool that pops into the side of the IP pump and tells you about start of delivery. Cost me some $30. I got the manual one, not willing to blow the mega$ on the one with the diodes. Never could get comfortable with the 1 drip/second approach.

I'm down to 24-25 mpg at 75-80 mph that is typical on the 280 Fwy in the Bay Area. I used to get 29-30 mpg at 65-70mph in (slower) days past. Now maybe it's a combination of CA's oxygenated poor quality diesel and a/c use in the summer, and I have adjusted the ALDA far enough in for max economy without compromising performance, but that still seems a little low to me.

#6 08-28-2003, 11:35 PM

I just went to the local dealer and bought the offset key. They had only 0*, 1*, 2*, 3*, 4*, and 5* keys. I saw the computer screen and it was the corect 617.952 I asked for. Did mercedes change their order parts from the 4, 61/2, 8, and 10 Or do they have the wrong parts?

It's great the I will be right on rather than worring about being 1* under or 1.5* over. But, I do worry about it not being the right part.

gsxr · #7 08-29-2003, 12:15 AM

That is EXACTLY what I was trying to say in my earlier posts. The EPC ("dealer computer screen") shows 2, 3, 4, and 5 degrees. The service manual, for the same part numbers, refers to the keys as 4, 6.5, 8, and 10. As R Leo said, we only read in crank degrees, so the service manual is more technically correct. The 2 degree "dealer" key will provide a 4 degree adjustment measured at the crank. Read the last few posts on this thread carefully and it should become clear(er).

BTW - That's a great quote about know-it-alls, also one of my faves!

#8 08-29-2003, 01:09 AM

So by ordering the 5* key I got the wrong one. My recipt said 621-991-00-67.
Darn, I'll just have to sell the one I bought on ebay and get the right one.

gsxr, you are right. I should have read a little more closely.

Also, check every once and awhile, I'll change the quotes to suit the general mood.

#9 08-29-2003, 11:56 PM

I just bought the CORRECT key today. If anyone in the forum wants the other key I got (5*/10*) e-mail me. I'm willing to sell it for very cheap.

Is there a reliable way to adjust IP timing without a bench or drip tube? EX. Scribing a mark on the IP/block and slowly adjusting it until it runs well/ is adjusted correctly? Does moving the IP x* similar to cam timing (i.e. 3* cam=6.5* crank)?

#10 09-03-2003, 06:00 PM

I just got the chance to install my 4* key and a valve lash adjustment. The first start was very rough compared to normal, but it settled down very well after a few seconds.

Low end power is somewhat better, midrange is MUCH better, highend is very nice. The time it took me to do 2000RPM-4000RPM in 3rd gear before was 14.57 seconds, now it's 12.19 seconds.

I still can't bark the tires so I'll be adjusting the IP timing tomorrow.

jerryyoung · #11 09-04-2003, 12:00 PM

Thomas,
What is the part number/nomenclature for the IP manual timing tool? Did you get it from MB or a tool supplier?
Thanks

#12 09-04-2003, 04:55 PM

Just advanced the IP timing, and I have very good results. Low end is MUCH better, midranger is also good, and I will wait to test high end until I'm satisfied with these changes. It sounds much more dieselish now, it used to sound like a bad gas engine. #1 still nails very hard.

If you install an offset key in the cam, I reccomend this as well to anyonne.

gsxr · #13 09-04-2003, 05:04 PM

Yeah, that's right. The offset key fixes the CAM timing but leaves the pump retarded. Theoretically, if you rolled in a new chain, that should also cure the pump timing (unless someone already adjusted it, in which case it could end up too advanced). Your MPG (and power) will be best with proper cam AND pump timing, naturally.