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

Exactamundo.

Didn't I hear this once before...........oh yes........I did:

;)

You posted that at 08:10PM, 1minute before I made my post. :rolleyes:

The bigger problem here is that you have no idea where the tooth (if something was improperly installed) was skipped. Either the cam or the crank.

the cam, being on the chain before the IP will cause a different change in timing than a tooth skipped at the crank.

If you are crafty and a few machinist tools, you could simply drop your lower oil pan and determine TDC for yourself (for sure). Then follow the FSM for whatever timing method you feel most comfortable with.

I have yet to do the drip method, sorry.

Once you have determined when your IP is set in relation ti TDC, all your adjustments can probably be made at the cam.

^^assuming that someone previous made a bimbo mistake and the major order of the timing is in good setting.

Nope, a tooth is a tooth and it will make an 18* error at the crank no matter which sprocket it skips on.

Is it not possible for the crankshaft gear to slip a tooth, rather than the camshaft gear slipping a tooth?

That might result in those 9 degrees vs the 18 degrees when you slip a tooth at the camshaft.

Ken300D

As said above, a tooth is a tooth. Skipping any tooth on any of the three sprockets results in an error of 18* at the crank.

If you skip a tooth at the crank, its 18*.
If you skip a tooth at the IP, its 18*.
If you skip a tooth at the cam, its 18*.

Actually, I posted it at 6:11 PM in post #2..........but, who's arguing.........;)

agreed. I dont mean a different amount of change.

I didnt read the previous posts either, FI and BC were basically saying this already.

...just a little cryptic for some to pick up on.

for clarity and reference

from top, clockwise: cam, IP timing gear, crank

That's not correct. There's 40 teeth on the cam gear, 360*/40 = 9.
Or by your logic 18*X 40 teeth = 720*.

No, shifting the location of the chain results in an error of 18* as measured at the crankshaft. If you measure at the cam or IP it is a 9* error. Since the crankshaft operates them at exactly a 2:1 ratio, any timing change made to the cam or IP is double at the crank. Likewise in reverse, any change made at the crank is half at the cam and IP.

You're still wrong. If the cam timing is off 9*, it can be made perfect by moving the cam sprocket one link (tooth) of the chain.

If the cam timing is off 9° at the cam, it can be corrected perfectly by shifting the cam sprocket by one tooth.

However, we reference all our angles off the crankshaft, which provides twice the camshaft readings. So, 9° at the camshaft will be 18° at the crankshaft.

Since we only have a difference of 9° at the crankshaft, if we shift the cam sprocket by one tooth, the change at the crankshaft will be 18° and we'll be blown out the opposite side.

It's a bit difficult to grasp, but think of the crankshaft as doubling everything that happens at the camshaft.

Alright, I see what you and FI mean.

My high school geometry teacher would get literally red in the face and then he'd kick his stool over when the students frustrated him... which was often :P. The stool was about four feet tall and only a foot in diameter, so you can imagine our amazement when one day he kicked the thing all the way across the room and it didn't so much as wobble - it landed on all four feet and came to a perfect, upright stop. There was some geometric precision for you :D.

Anyway, I just realized... How do I identify a woodruff key versus the stock "single edge key" that should be under the cam gear?

Thanks. Couldn't it just be whatever is causing my -9 degree offset that's thrown the pump out of range, though? I guess we'll find out soon enough since I'm definitely going to fix the timing chain issue first.

Thanks for your help, guys!

the woodruff key is a type of key - a generic term for the keys being used on camshaft.

the profile of the offset keys are S-shaped

the profile of the original key is simply a rectangle.

first drawing is the original

second is the offset

you are looking a the camshaft with the cam gear removed at the front of the engine

Thanks. I'll check it in the morning!

Okay... This is what I found.

I pulled the gear forward about half a centimeter. The camshaft appears to be smooth except where the alignment marks are; there is a raised square knob there (see pics).

Is that where the woodruff key would be? If so, is it the 'stock' key or an adjustment key? Based on jt20's description I'm guessing it's the stock one.

Thanks...

That first one looks like there is a shoulder on the key which means its an offset one.

http://img.eautopartscatalog.com/hir...9021382OES.JPG

Aha
 

I looked at those pictures from Fastlane and I was having a hell of a time figuring out how they worked. Now that I get it, it seems so obvious! The part they label "bottom" is what I would consider the top, though. That really threw me off!

Unfortunately, it looks upon closer inspection (and with better understanding!) like the one I've got is the stock key, not an offset key. So now the question is, what could be causing this and how do I fix it? :confused:

I suppose I can install a 10 degree key in reverse, right? That should put it back to spec. But that doesn't solve whatever caused this to begin with... :(

you are going to have to pull the key out to verify it's stock or not.

Wouldn't the best thing to do at this point be, align the crank and cam then pull the IP, set it to its marks (at the compression stroke :)) and then roll in a new chain if need be??

the point is, there is no way to align the cam to the crank if it's off by 10° ... you have to get a offset key.

I don't think we have all the data. I do not see how it's possible to be off by 9° with a brand new chain...........something is amiss.

is it possible that the chain was installed on a severely worn set of gears?

...........like virtually no teeth??

...........I still don't see a possibility of 9°.

Humm, interesting puzzle, time to interrogate the PO :D, thanks vstech, new I was missing something.:)

When do the valves meet the pistons?
 

Doe anyone know how far before and after TDC the camshaft timing can go?

18° at the crankshaft is the generally accepted limit (one tooth).

I will just throw this in. I own an 81 SD. When I bought it 10 years ago I knew a lot less about MD diesels than I know now. (A common occurance I am told)
The engine ran like crap. After reading and running tests, I took it to a well know MB tech. He noted the engine idled rough and would not smooth out when revved up. Had a lot of strange noises going on,even for an old diesel. His conclusion was a timing issue, probably timing chain off by a tooth. I had checked the chain for stretch, and got some wierd results. He checked it and got a BTD result, but not 18*.
Shorten the story here, and I have forgotten most of the info, but I loosed the chain tensioner and carefully rolled the chain over a tooth. Never cut into it, just carefully rolled it tooth to tooth.
Timing fell right into place, after that it show about 4* of stretch, not the BTD as it did before. The wierd noises stopped and it ran better.
of course by then it had bent a valve, but that is a different story.

A friend has a 240D that was off by one tooth for years. The only problem the car had was, hard starting, so the owner rigged up a 24v starting system. Other than that it ran fine:confused:

That's good to know. I've always wanted to play around with different valve timing using offset keys to see what the torque curve, mileage does. Never knew how far I could safely.