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  #1  
Old 11-22-2000, 06:55 PM
LarryBible
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After finding the camshaft retarded on my daughters normally aspirated '81 300D, I have checked several things.

Benzmac said that he has indeed seen these engines jump time after a vac pump failure which dropped chunks into the works. I pulled the vac. pump and it's all okay.

The key on the camsprocket is also verified okay.

Has anyone ever seen a crankshaft timing sprocket shear a woodruff key?

How do you time the injection pump. I could find no marks viewable after removing vac pump. Since the pump is splined, do you simply get the cam and crank aligned on number one compression stroke and insert the properly aligned injection pump into place?

It's inevitable that I must pull the harmonic balancer, but I hate to disturb it after all the harmonic balancer problems that I've seen posted here.

Thanks for any help you can offer,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #2  
Old 11-22-2000, 10:20 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
I have seen the key shear, I have seen the crank break right there as well. I know it sounds wierd, but I have seen it.

Yes, you will have to pull the head since the valves are most likely bent, then the harmonic balancer to check the condition of the lower gear. Then line up the TDC with the cam then install the injection pump. You will then have to set the timing on the pump manually.


After thinking about this for a while, I would make sure the engine is putting out proper oil pressure. I have seen the camshaft sieze up in the stand and cause the chain to jump, then when cooled down, it will turn OK.

Check EVERY THING!!

------------------
Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
OWNER OF MB AUTOWERKS .COM
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  #3  
Old 11-23-2000, 12:21 AM
Wm. Lewallen
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Larry, no one has mentioned what a job it is to remove the injection pump. Besides removing all fuel lines going to the pump, the oil filter housing will have to be removed. If you just want to check the injection timing, you don't have to remove the inj. pump.You probably have the manual that describes this procedure. If you don't have it, I can scan it and send it to you.
Keep us posted on how things are going.
Bill Lewallen Lexington,Ky.
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  #4  
Old 11-23-2000, 09:53 AM
LarryBible
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Donnie and William,

Thanks for the responses.

William, are you sure the pump is hard to get off on a five cylinder like it is on a four?

Luckily I have a head ready to go for this engine. I don't have cam and bearing stands, etc. I may pull the cam to see what it looks like before I go further. It may be time to get another engine or car.

This engine was sucking a good bit of oil before all this happened, but she was very good at keeping it full of oil.

I'm under the impression that since the engine WAS making good compression, that the cylinders/rings/pistons would be good enough to bother with the head.

I pushed this car into a short stall in my shop not knowing I was getting into major work. It looks like I need to move some cars around and get it in my work stall where I can use my walking beam and chain hoist.

Thanks again, any more thoughts are welcome. You've given me my "marching orders".

Happy Thanksgiving,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #5  
Old 11-23-2000, 11:31 AM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
Larry -

I can't add anything to the technical debate - Wm. and Donnie have that covered - but I have to commnent that a used or rebuilt engine may be a good alternative to the pain of tearing this one down and putting it back together. Especially considering your comment that "it was sucking a good bit of oil."

Regarding injection timing - I have a 617 engine manual that is doing me no good. I am willing to put it on permanent loan to you if it would help.

Take the day off and enjoy the holiday!

Chuck
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  #6  
Old 11-23-2000, 11:56 AM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Hi Larry,

I haven't replied to this one because I thought you were talking about the chain jumping one or two teeth.

Now that you are talking major engine work, I am confused. Seems to be the morning I guess. If there is only a retarding of a tooth or two, I doubt that anything was damaged. I also think there is a good chance the pump is still in time.

The cam is so easy to retime that I would do it and see what you have. You can't hurt anything more by doing this.

BTW I have racked my brain trying to remember if I have ever seen this and I can't remember ever seeing it on a diesel. I saw it once on a V8 though. Its easy to explain the cause on a V8 (although the failure by only one or two teeth - I consider a miracle of religious proportions).

If you are one to two teeth off because that just happened to be where it stopped after running all the forms of retard and advance that occurs when things aren't attached properly, then you would have broke the cam or bent a bunch of valves. If you still have even but low compression it is because of the timing issue; NOT because of damage.

If putting the timing right fixes the compression and the running, I would pull the sub pan off and look for something that could have rolled through the chain. I also would hand roll the motor over viewing as many gear teeth as possible. Watch the chain tentioner rail while cranking the motor. If there is something on a gear the rail will be shoved back as the chain tightens when it rolls over it.
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  #7  
Old 11-23-2000, 05:12 PM
Wm. Lewallen
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Larry the suspense is killing me!
While I await the arrival of my family for Thanksgiving dinner, I would like to suggest a few things that I might do. With compression as low as you say and the timing mark off as much as you say(one tooth=18 degrees)thats a lot. If it is off one tooth, the pistons will strike the valves at high speed(60mph);At two teeth,something has to give and I think the engine would have jammed and you would not be able to turn the engine over.
I would re-align the marks on the camshaft according to specs. Turn the engine over at the crankshaft to TDC. Make sure the cam sprocket marks line up. With number one piston up take a long screwdriver and pry one of the valves down. Both valves should be closed. I don't know how far the valve should move before it hits the piston, but it should move:maybe a quarter of an inch?
Check the chain tensioner. If it failed to keep tension on the sliding rail, it may have let the chain slip a link over one of gears teeth.
If timing is off' you don't have to replace the timing chain.The Mercedes manual states and I quote"If the timing requires correction, install an offset Woodruff key, or if the chain is excessively elongated,install a new timing chain."They are talking about the key in the camshaft, and keys are available in steps from 4to10 degrees measured at the crankshaft.I believe a lot of chains have been replaced when an inexpensive Woodruff key would have solved the problem, If your tensioner is good,the sliding rail good, and no slack in the chain,there is no need to replace a chain,when a $2.80 key will restore the timing.
Please keep us posted on your daughter's 300D. My daughter,Karen , has had my 1977 300D borrowed for the last week. Since she has no garage the car has had to set outside, and we have had some cold weather for the past few weeks.Fifteen to twenty degrees F. and the old car has started every morning without using the block heater. She doesn't have an extension cord. I'll let her borrow one of mine when she comes over after while. That way she can plug it up and have a warm car to drive to work.
Bill Lewallen Lexington,Ky
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  #8  
Old 11-23-2000, 05:21 PM
Wm. Lewallen
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Larry, I forgot to respond to your question about removal of the injection pump. I'm afraid the oil filter housing will have to go in order to have room to move the pump backwards. Good Luck.
My family is starting to arrive, so we will be eating soon.
HAPPY THANKSGIVING TO YOU AND EVERYBODY
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  #9  
Old 11-23-2000, 10:59 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I hate to disagree, but one tooth, two teeth probably a lot of teeth can be off retarded before things start to hit. The other way (advanced) things are different. Less than one tooth might cause interference.

The natural way for the two shafts to fail is in the retard direction. The motor will die from the bad timing before it can hurt itself. Unfortunately engines don't just stop. Failures usually cause large timing changes with each rotation which eventually puts the relationship in advance which is where the problem arises.
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  #10  
Old 11-23-2000, 10:59 PM
moyukh
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hey larrybible, i was looking through some of the older 123 posts and saw your original post where you decided to get the 300d for your daughter- its great to see that im not thte only teenager in a 123! My 280e is my first car (i had to buy it myself), and so far its been incredible. and hey, with a little work these things can look pretty nice - http://www.dhc.net/~pmhack/mercedes/280801.HTM - mine looks exactly like this, only with 16" rims and the american bumpers.

------------------
81 280e
16" 8-holes
clear indicators, new exhaust/intake

stereo -
jvc head unit
6 infinity kappa coax's
aura mr675h 90x6
2 aura mr475's, 200x2 each
2 audiobahn aw1200s in a ported box
1f cap

not bad for a car older than me, huh
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  #11  
Old 11-24-2000, 03:40 AM
LarryBible
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Thanks to everyone for the thoughtful and obviously time consuming replies.

I suspended work on the car to move toward Thanksgiving. The wife, daughter and I went to my parents and my son met us there. My wifes twin sister and her family joined us there. It was a great Thanksgiving including the special pie that my Mom always makes for me. We just got back home. I'll have to run 10 miles to work it all off.

I'm glad I did not go any further into it. I was just starting to pull the fan and radiator to gain access to the harmonic balancer, which as I said before, I really don't want to pull unless I must, for fear of starting into the failed balancer syndrome.

I will pull the camsprocket and retime it, then turn it over by hand to check for a jerky chain. If it then still looks okay, I will check compression on a hole or two before putting the injectors back in.

If I can experience success to this point, should I pull the lower pan before starting the engine? The thing is crammed in a parking spot in my shop, not a working spot. Working from above is not too bad, but if I can start it and move it before pulling the pan, I can save lots of trouble and frustration. My experience with FOD in the pan, is that it will usually stay there.

I just had a thought. I noticed a small chunk of the plastic guide that is on the drivers side of the engine missing. It is where the bolt goes through it into the head. I have not noticed this chunk gone before. It's right where the bolt goes through, which makes me wonder if it broke by overtightening. I can't imagine it just breaking off while going down the road. Anyway, surely this little piece of plastic couldn't have caused such a problem by traveling through the chain. If it did it will be a stroke of luck because I doubt that the plastic could have caused much damage anywhere else.

Thanks again,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #12  
Old 11-24-2000, 12:44 PM
LarryBible
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Well, I tried moving the chain on the cam sprocket one notch and it didn't line up exactly right, probably still a half tooth off. I checked compression on number one and it was 100. I moved it one more notch and it locked up when hand rotating clockwise to a certain point in probably about and eighth turn. I assume this is valve/piston contact.

I am backing away to think after every step. I think I will now throw in the towel and pull the balancer to check for a sheared key.

Any more suggestions are welcome and thanks to all.



------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #13  
Old 11-24-2000, 04:26 PM
Wm. Lewallen
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Larry, what's all the mystery about the harmonic ballancer? Just mark it so you can put it back the way you took it off and torque the six bolts to 18.35ft.lbs. I have never had any problem with them.
Now about the piece of the plastic chain guide:if the chain tensioner failed or the sliding rail broke,that might let the chain jump a tooth at the cam sprocket and not at the crankshaft.There just isn't enough room down there. That might might explain the piece of plastic broken from the chain guide. I believe that when the chain jumped time, the number one piston has hit one of the valves bending it or both of them. That would explain the low pressure on number one cylinder You can check this by removing the number one glow plug or injector and using an adapter, blow air into it and listen at the exhaust and intakes for any air escaping.
A bent valve(s) could explain the low compression and difficulty in starting.
Do keep us posted on this. The suspense Is greater than a Hitchcock Thriller.
By the way;do you remember when the early Mercedes did not have harmonic balancers? Now they are called balancing discs.
Bll Lewallen
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  #14  
Old 11-24-2000, 06:54 PM
LarryBible
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Posts: n/a
Latest Chapter.

I got the timing right and still have low compression, since the timing was retarded I don't know how it could have bent valves, but the compression has gone somewhere.

I decided to pull the head to see what's up because I have a head with fresh valve job that I bought for a good price some months back. I thought that before I pull the head, I should check the one I got, as I had yet to unpackage it. The problem is that there are no precombustion chambers, no problem, I can put them in. But the head is for the early model with loop type glow plugs. If I put in new chambers and find some bushings for the pin type plugs, which prechambers will I need, early or late.

With the cam timing right, the compression must be lost by the head somehow. I am going to pull the head and take both of them to the machine shop. I will see if he can sort out the prechamber/glow plug problem, or just do the old head. If the valves are bent, it will probably be better to put prechambers in the fresh head and go on about putting it back together. This engine needs at least a valve job, and maybe a short block. I just can't imagine the compression loss being anywhere but the valves, how could rings/pistons cause this much compression loss in all cylinders. I mean, going from 300 across, to 100 to 200 in a few thousand miles?

I suppose I have been using some incorrect terminology. The part of the "harmonic balancer" that bolts with the big bolt to the crankshaft is where I believe that people have been having trouble. I did not know that the balancer is actually in two pieces. I thought I was going to have to pull the big bolt and that part to get to the crankshaft sprocket to check for a sheared key.

BTW, I have good oil pressure. It came up quickly when turning it over to check compression.

Thanks for everyones help and interest,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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  #15  
Old 11-24-2000, 11:58 PM
Wm. Lewallen
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Posts: n/a
Larry, the suspense is beginning to fade.It appears that you have bent valves.Since you will be removing the head from your daughter's 300D, why not take the parts from the head you have stashed away and put them on the head you are removing? That way you can keep your pin type glow plugs and you wont have to worry about swapping the pre-chambers.
While you are doing the job, you might want to install a new camshaft sprocket. I always put a new one on when I rebuild an engine. They do wear and will cause the timing to be off and some people will think the chain has stretched. This is the time to use an offset key.
Keep us posted on how you ars doing.
Bill Lewallen
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