Chain stretch... 10 degrees BTDC?
 

I put in a new (used) engine in my wagon for which I don't have much history - the PO only had it for a little while and didn't know much of the maintenance history before he got it. It runs well but lacks top-end power and knocks, and sometimes smokes a lot (but the price was right ;)). I figured the IP timing was off, but I thought I should check the chain stretch first...

I checked my chain stretch using the cam timing marks method as outlined in the wiki. I know this isn't the most accurate method but until I get a dial indicator it's the best I can do.

The results seem a little strange though. From what I understand, ideally the reading on the crank should be 0 TDC to 2 degrees ATDC, or more if the chain is stretched. I'm getting a little over 9 degrees before TDC :confused:. I did the measurement multiple times, I'm sure I aligned the marks perfectly and I never rotated backwards (counterclockwise). See the pictures...

I'm trying to get my hands on a dial indicator to double check.

What's up with this? What does it mean?? Am I doing this wrong?

Hey Andreas..........good to hear from you again.

My best guess is that some PO got the chain installed on the camshaft incorrectly, If positioned properly, the chain would be 9° late which would signify an elongated chain. That would be an error of one tooth.

The other possibility is that the mark on the damper was removed and reinstalled in a different position. However, the fact that the engine is not running well tends to confirm the advanced timing.

You can try the dial indicator method, but the results are not going to be wildly different. Some PO was clueless, unfortunately.

:eek: Is there anything that can be done about it?

While searching I saw that you said " IP timing is done without relevance to the cam timing" so I just went ahead and tried to see if I could at least get the IP timing right (drip tube method as described in the MercedesShop wiki)... Unfortunately, I get a constant stream of fuel in every position, no drips.

I guess this just confirms something is out of whack. :(

Thanks for your help!

do you have a pic of the cam timing marks you aligned?
it's also possible you have the wrong marks lined up on the cam...

Here's an update...

The PO had the engine out of the car already when he gave it to me. He'd told me he'd "thrown some money at the mechanic" to "get things fixed up" before he decided to just buy a different car instead, but he didn't know exactly what had been done to it ("I just told the mechanic to do his thing" :rolleyes:)... but at least it was running, unlike my old one! :o

I just asked my mechanic, who dropped this engine into the car for me, if I could borrow his dial indicator to check the chain stretch. His response was "What chain stretch? That chain was brand new, there shouldn't be any stretch." I can't tell the difference between a new and used chain, but I trust him to, so I guess the PO wasn't entirely talking out of his butt when he said the engine had some work done!

So, where things stand:
1. The crank indicator reads at ~9-10 degrees BTDC
2. The chain is new and should have no stretch at all
3. 1 tooth = 18 degrees, right?

So it can't just be off by 1 tooth, can it?

Is it possible there was a 10-degree woodruff key installed before the PO's mechanic replaced the old chain, and now that's throwing me off to 10 degrees BTDC? Can I tell if there's a woodruff key without taking things apart?



They are exactly as pictured in the wiki... I'm certain I didn't screw that up.

I don't think you can see the key without removing the cam gear...
STUFF A TOWEL UNDER THE CHAIN BEFORE YOU TAKE THE NUT OFF!@#E@#@@

trust me, it's very annoying to drop a washer down into the pan....

One tooth is 18* at the crank.

Remove the cain tensioner (its on the right side of the block), remove the bolt on the front of the cam gear and slide the gear forward a little bit. If there is an offset key in there you should be able to see part of the lower half of the key.

Thanks, I'll check it this weekend. Can I just remove the key if it's there, or is there a stock "0 degree" key or something that would need to go in its place?

if that is the problem, there is a 'stock' single edge key that should be changed with it

am i missing something here? If 1 tooth is 18 deg at the crank it sounds to me like 1 tooth must be 9 degrees at the cam.Simply moving the chain on the cam gear 1 tooth in the right direction should put you right on. Don

9 at the cam is 18 at the crank. Moving one tooth on the cam changes the crank 18 degrees.

A tooth is a tooth. Since its a 2:1 ratio, everything you change at the cam will be 2x a the crank. Thats why the 2* offset key makes a 4* change, 4* key makes an 8* change, etc.

Start at 9° early. Move one tooth on the cam.

What do you get?

I am not going to apply a lot of thought this evening but you might correct the cam crank timing by a key replacement or reversal. They are cheap enough. Thats if the new chain is sealed. Check for a removable master link just in case one was used. . Also you will want to inspect the quality of the job if the chain is riveted. Any mechanic that would do a chain installation of this quality one should be suspect of everything he touched.

I am slowly coming to the conclusion that a lot of working mechanics should stay away from auto service. It is too bad they are in the field as it pulls the good mechanics down .

The pump not stopping the drip in its adjustment range needs pulled and reset a tooth or so over. I forget the amount of degrees a tooth on the pump drive is. Check the archives.

The pump sounds like it will probably be off a simular amount. Since that is not certain by any means turn the crank with the pump in about the centre of it's adjustment range until the fuel flow just stops. By reading the crank degrees you will know exaclty how much to move that pump. Remember its half the crank degrees you want to correct at the pump I think. Otherwise it probably is open the timing chain up time. Overall not too serious to correct and should really give you a much better running engine when you are through. I am tired this evening so will review this post tomorrow for any errors.

9* late