'88 300 SE, Stripped Rocker assy bolt locations in head - PeachParts Mercedes-Benz Forum

gschira · #1 06-28-2010, 10:14 AM

1988 300 SE, 240,000 k, Mobil 1

#5 Rocker assy. somehow just pulled loose (as in stripped threads on all 4 mounting bolts) last Tue am when I was arriving at work. Tapping sound and rough running. I thought maybe one or two lifters, or sticking valves, just going by where the sound under the VC was coming from , so when time to leave work drove home (20 miles). Seemed to get up to speed ok, even with the rough running, and was not as loud, so I put off opening up VC until weekend. Put a little Marvel oil in fuel in the meantime and drove the rest of the week. It actually started easier cold or hot than before , which I thought strange. Imagine my surprise to find what I found! Engine has plenty oil, and was not running hot. No extreme accelerations (ever).
What caused the force that stripped those bolts? Would a sticking valve cause this?
Will helicoil work ok in that area?
Does anyone know what size those bolts are or part numbers?
What torque?
Should I change valves? Would they have bent somehow and how do you tell?
So many questions? I have read some of the archived threads, but can't seem to find anything on the CAUSE of this. Is #5 a bad spot in the head? I did read about someone else having same (#5 assy.) problem.
Except for hard starting when hot (normal OT) the engine ran very good with no noises, until this just suddenly happened. Engine VERY clean inside.
Any educated thoughts on this problem? Sorry if I'm not calling parts by proper name. Feel free to correct me as I would like to know..........Thanks

mbdoc · #2 06-28-2010, 11:07 AM

Heli-coil OR Time-sert(s) will work just fine, use the newer longer bolts w/washers made on.

gschira · #3 06-28-2010, 12:58 PM

Thanks for your reply M.B.Doc. Can you get those at auto supply stores. I mean I'm sure I'll probably have to get bolts from Mercedes, but where do I get Time-serts for this project? Woul the newer longer bolt be the 73 mm one, and where do I find part #'s?
Any idea on why this happened?

mbdoc · #4 06-28-2010, 04:38 PM

MB part number is 914007-008043 & they are 10.9 hardness & torque to 18Nm.

tinypanzer · #5 06-28-2010, 06:17 PM

Perhaps somebody's worked on those before and forgot the old maxim "After tight comes loose".

I can't see how that would happen to factory torqued bolts.

I notice you say that you never accelerate hard EVER. Really? M103 motors just love to be revved. Unless you've got other bad repairs in there, you have nothing to worry about (other than whiplash). You'll probably blow some soot out of there as a plus.

I would think a compression test would indicate if your valves are buggered or not.

gschira · #6 06-28-2010, 10:54 PM

I appreciate the info guys. And how much MORE damage would I have done by Really getting down on the accelerator? Any thoughts on the WHY? When I tried to remove the slender tin oiler rail (that probably AINT what it's called) atop the rocker assys, I had to put 30 foot pounds on that center rocker assy bolt to break it loose. That seems excessive to me for that size bolt. Can anyone direct me to a conversion chart so I can figure out the Nm values? Also what size heli-coil do I ask for to repair this? Where's best place for time-serts? Which is better? Thanks for everything y'all......

Ivanerrol · #7 06-28-2010, 11:48 PM

If you don't like installing the helicoils your self there are mobile guy's who do this.

Last time I had this done in a M103 it cost $ 65.00+tax.

gschira · #8 07-11-2010, 10:51 AM

Well people,
After some time and upon further inspection, I shall pull the head to replace at least the 2 #5 valves. The int. valve stem was buggered quite a bit. Car has approx. 133k miles on it. Any thoughts on replacing just the two valves as opposed to all valves. Should I do a valve job as opposed to replacement? Car was running great before this happened. You should see how clean the exhaust manifolds are. Should I Heli-coil ALL rocker arm mounting bolt locations? Best place for parts? As always, I appreciate this site and all the great info. Surely someday maybe I will be able to help someone out of a bad situation, with MY Mercedes experience..........

samiam44 · #9 07-13-2010, 10:02 PM

M103's are hard on valve guides. You should if replacing valves- do a valve job with new guides.
For the heilcoils- only the stripped bolts. You should use the factory replacement 73mm bolts or use 75 mm from the hardware store(grade 8.8 or 10.9). I'd buy a bottoming tap and even grind a thread or so off the end.. clean each thread one by one. Removing 1 bolt at a time. I did mine that way... you'll have to get a long tap to make it easier from a machinist supply place.
Timeserts, helicoils are both good products.
Buggering ... are you just going to replace 2 of the valve seals? I'd replace them all.
M

junqueyardjim · #10 07-14-2010, 02:44 PM

I had the same situation on my 86 300E. However, I bought it that way and the PO put about 200 miles on it and then I put about 300 miles on it in that broken condition and it really beat the cam shaft up. But I would really look at that cam critically because any running after those blocks break loose is likely to do some cam shaft damage. I thought that Mercedes had resolved that problem of the head by their changes to that engine in mid 87, but evidently it still does happen.

gschira · #11 07-17-2010, 12:30 PM

Thanks for the replies, guys. I will check that cam really close. I didn't know the m 103 had the guide problems, so I rekin I'll go ahead and replace those too. In the head removal process, should I completely remove intake from engine bay, or is there room to maybe tie or secure it to the side out of the way? Also, I'm having trouble breaking the two allen head bolts at rear of head that appear to secure the heater hose connecting tube. Can that tube stay in place till I remove head? (pic attached) It seems as though it is blocking access to the int man. mounting bolt, at least with the limited tools I have....Any special tools for this head job I should purchase? Thanks again for replies........

gschira · #12 07-19-2010, 03:48 PM

I'm mighty worried about those two allen bolts holding the coolant tube to rear of head. They are super tight. Do they ever strip out too? Any tricks to loosen them? Thanks............................

junqueyardjim · #13 07-19-2010, 04:18 PM

Make sure they are very clean inside. You can't get a good bite on them if there is dirt in there, but being on top of the head they should be clean. I would recommend that you use a good grade hex socket, not an allen wrench. The socket heads I have are mounted in 3/8 drive socket and I would recommend using an adapter to go to 1/2 drive. Get that hex head into that screw real good and give it a good pull with a half inch ratchet or breaker bar and it will move and it will not break or strip.

gschira · #14 07-19-2010, 04:42 PM

Junqueyardjim,
Thanks for that quick reply. I have tried the hex head socket (3/8' drive) to no avail. Haven't tried hooking up to 1/2" drive yet. Just hate to strip anymore bolts from this dang aluminum head. Do you know if the head can be removed without first removing the tube in question. If that's possible I would have a better angle of attack on those 2 pesky bolts.

lorainfurniture · #15 07-19-2010, 04:49 PM

I agree with the "allen sockets". They are the only way to go.

When you have a questionable allen bolt, try tapping it in with a hammer a bit.

If it strips, dont worry. I had multiple stripped allen bolts when I rebuilt my m103. You will have to buy a torx bit set anyways to remove the head bolts.

When you strip the allen bolt, find the next size up in the torx size, and hammer it in. It will get so stuck in there the bolt will come out easily, but you will have a hell of a time getting that allen bolt out of the bit.