Timing 22 deg at TDC - PeachParts Mercedes-Benz Forum

tomm9298 · #1 10-31-2004, 10:45 AM

I checked my chain stretch today. When at TDC my timing is around 20 - 22 degrees. Is this acceptable? I have seen threads speaking of it being later, but never before 24 deg. All suggestions will be appreciated. Thanx!!!

psfred · #2 10-31-2004, 01:51 PM

Can't be, the valves would hit the pistons if the cam was that fast.

Some notes here, just in case:

You MUSt turn the engine in normal direction (clockwise from the front), else you pull all the slack onto the wrong side of the chain.

The notch on the cam thrust washer must be CENTERED on the bump on the cam tower -- from experience, I can tell you this isn't as easy at it looks.

24 BTDC is correct for INJECTION timing, surely you don't have IP timing confused with cam timing? (22 BTDC would be fine, by the way, although a bit late).

Double check this way:
Rotate engine around by hand in normal direction a couple times, watching the thrust washer on the cam tower. On the 61x engines, the timing mark is at about 2:00 o'clock on the front tower. Ease the engine around until the notch is exactly centered on the "bump" -- use a flashlight and look from directly above the mark, it's actually harder to see than it sounds sometimes.

When you get the mark exactly centered (go all the way round again if you overshoot, DO NOT "back up" and try again), without moving anything, immediately check the timing marks on the crankshaft balancer. You must be after TDC (0|0), between 2 and 8 degrees. More than 8, time for a new chain.

If, in fact, you are BEFORE TDC, the cam is off a tooth OR the balancer has moved on the hub. The only way to check the latter is to pull the #1 pre-chamber and use a probe to tell when the #1 piston is at TDC manually, not something I would do just for the hell of it!

If you are in fact 22 degrees "fast", I'm not sure the engine would run -- 20 degrees late, the exhaust valves are are hitting the pistons and I'm fairly sure the cam towers would break!

Peter

tomm9298 · #3 10-31-2004, 03:15 PM

I removed the valve cover and turned the engine CW twice and then stopped when the cam mark was centered on the mark on the thick spacer. I looked at the timing marks and the pointer was at about 21 deg. You are correct, positioning the two marks was a pain. They were dead lined up though. I thought I was checking the timing to check for chain stretch. My understanding was that when you line up the marks the timing pointer should read 24 deg. Then you can determine your chain stretch. Example: if you lined up the cam marks and the timing pointer said 30 deg, then you would have 6 deg of chain stretch. Please correct me if I am wrong. I am not trying to set the IP timing, just check for timing chain stretch. Thanx....

psfred · #4 10-31-2004, 07:39 PM

With all in good shape and a new chain, TDC marks should align exactly -- with the cam washer notch centered on the cam tower mark, the degree pointer should be exactly on TDC on the crank.

24 degrees BTDC is the correct injection timing using the drip method (which actually measures when the piston in the IP rises enough to close the fuel inlet, not the actual point of injection!).

22 degrees is WAY fast, about 2 teeth on the cam sproket (12 degrees each, more or less). I don't believe the engine will rotate that far off due to valve to piston interference.

Recheck, and if you can, verify that the #1 piston is at the top of it's travel when the pointer is on TDC (the 0|0 mark). It's possible that the balancer has been incorrectly installed and you are off one bolt. Easiest way is probably to pull the #1 glow plug and crank engine around by hand. Will stop pushing air past your thumb over the hole near TDC on the compression stroke, close enough for you to tell if the balancer is off a hole or not. Otherwise, the ring on the balancer may be loose on the rubber and slipping, so that the scale now has no fixed relationship to the crank!

Peter

tomm9298 · #5 10-31-2004, 09:14 PM

The engine runs great. So either I am way off, 180 deg, or something. I was hoping I was doing something wrong. I hope I am checking everythiing according to procedure.

psfred · #6 10-31-2004, 09:57 PM

Something is goofy, for sure -- 22 degrees fast I'm sure a valve would hit, and you'd know that!

If it runs fine, it almost has to be the balancer. I'm not sure if the balancer is bolted to the hub on that car, since it's not in my engine manual, but if it is, you could be one bolt off. Not 22 degrees, though! Cam cannot be off as the washer won't fit on any other way (notched for the Woodruff key) and the cam wouldn't turn without the key in it.

I'd pull the #1 glowplug and see where the crank is when air stops puffing out on the compression stroke - I'll bet the balancer is off somehow.

You can check valve timing by valve lift, but it won't tell you anything if the crank pointer is wacky.

I'd also clean the balancer off, it's not all that easy to read when it's all rusty, and you may in fact be about right.

By the way, before TDC is to the right of TDC, After TDC is to the left. I think there is a pin at TDC, but I'm not sure.

Peter

tomm9298 · #7 11-01-2004, 06:29 AM

Thanx, I will recheck this on Wednesday. Is this the proper procedure for checking chain stretch though?

psfred · #8 11-01-2004, 08:04 PM

This is the easy way, the "book" way is to measure cam rotation in degrees when the intake lifts 2 mm. Much easier to just check the degrees late on the balance.

Neither method will work properly if the degree wheel on the crank is not correct!

Peter

tomm9298 · #9 11-01-2004, 09:14 PM

I have a Haynes manual and I checked DIY and skinnerbox. No referrance to checking stretch.

d.delano · #10 11-01-2004, 10:19 PM

Quote:

Originally Posted by psfred

You must be after TDC (0|0), between 2 and 8 degrees.

Peter

What if you are at 0 deg? Or 1 deg? I'm at just a hair past 2 deg, and I have about 150k on the clock I estimate. Just wonderin'. I read about people 'having zero stretch' and was just curious. I thought MB recommends a new chain at 5 deg.

psfred · #11 11-02-2004, 12:35 AM

I believe it's one of those "secret" things -- I'd never heard of it till Hans told me to do it (wish I'd listened then!). Easy enough, but the only procedure in the manual is for correcting valve timing with offset Woodruff keys. I guess you could assume that if it's too much to correct, you replace the chain, but it's not directly stated anywhere that I've found.

Peter