camshaft bearing torque HELP!
 

hello folks

i have a problem. i'm replacing the cam in my 88 420sel. i just can't get the socket head 10mm bolts to break free. this is what i have done so far.

1. after making the 8mm socket tool i tried using a long handle 1/2" drive rachet but could not break the bolt loose.

2. then i tried a 150 lb standard torque wrench. had it to 100 ft lbs and nothing.

3. then i tried a 3/8" drive impact gun. not an air drive rachet but a small 3/8 drive gun and nothing

4. then i tried a 1/2" drive impact gun (250 ft lbs rated) nothing

5. then i got my craftsman clicker torque wrench set at 150 ft lbs and i finally broke the 8mm allen wrench shaft. twisted it right off.

other things i've done.

checked the torque in the book. cylinder head bolts are 60 nm (60 x .738 = 44.3 ft lbs)

camshaft bearing towers call for 50 nm (50 x .738 = 36.9 ft lbs)

checked for a left hand thread in the book and nothing mentioned so i assume std right hand threads meaning ccw to remove.

in prep to tear this engine apart to do the rails i discovered it had already been done. car has 143k. so that means it has been worked on in it's past. what i am afraid of is that who ever worked on this car might have had to take the heads off and in assembling it did not use an anti-seize compound on the bolts and may have galled the block and the threads.

i tried several bolts and they all seem to be stuck the same. has anybody got a suggestion on what i'm doing wrong. i'm no rookie when it comes to motors and such. but i've never encountered a bolt i could not undo:(

I just removed the camshaft from my '84 380SE yesterday and although I don't have any advice for you, I can tell you that the short intake side bearing tower bolts felt "funny" when I unscrewed them. I used an 8mm X 3/8" hex tip socket with an 18" long wrench. When I put the wrench to them, I would pull hard and they would just break loose with a pop. No gradual give. I thought I had sheared the first on off inside the block but they all came out fine but the threads were dry. The longer exhaust side bolts felt normal with the gradual give as they were unscrewed. I think in your case the impact wrench is the way to go although if the bolts are torqued to high to start with, there is that chance of galled threads.

Now I just have to figure out how to get the rear bearing tower out as there doesn't seem to be enough room to slide out the long bolt, it hits the firewall before I can remove it.

On the worst of mine, I slipped a 3' piece of pipe over my half-inch ratchet handle to get some more leverage. But most came out with just the ratchet, which has a 24" handle.

Take exquisite care not to round the hex socket in the bolt. Clean it out with carb cleaner to make sure you get the hex bit all the way in.

bolt torque
 

thanks gentlemen for your replies.

I've been thinking about this today and I guess even if a MBZ mechanic was working on this they'd run into the same problem as i have now.

I know one thing i'll do when i get to work in the morning i'm going to make another tool except i will shorten the hex arm to be just long enough to fit correctly in the socket head bolt. the shorter that arm is the less twisting of the shaft there will be thus exerting more of the torque i am applying with a gun or wrench. this twisting would have dampened the blows from the air impact guns i used.

rato: the book mentioned regarding the rear tower that the tower must have the bolt in it already when "introduced" to the engine. this sounds like your description. you've probably already tried that. but the book was on my 420/560 type and i could see what they meant. also perhaps pulling the cam out of the journal before removing the rear tower might be another way.

ctaylor : I think your experience with the pipe will probably be the solution. I was reluctant to do this saturday nite until i had time to think it over and hear from the forum.

the tool i will build tomorrow will have bar stock for the body length rather than hex key. i will make it as thick as possible allowing just enough space for the body to slip down the side of the cam bearing towers. then i'll bring out the big guns 3/4" inch drive tools.

thanks guys for your input. i'm going to watch this post till tomorrow aftn. then i'm going with the "brute force and ignorance" let it snap approach. I'm sure my problem was probably with the tool i was using. i made it like the one in the book.

any more replies with be greatly appreciated.
tks much
craig

success!
 

well they finally came loose. all it took was a 3 ft extension on my 3/4" drive breaker bar.:D