OM617 Stripped Bolt Head @ Flexplate!
 

Background:

1983 300TD (Touring - as in the proper use of 'T' )

OM617.952

134k original miles

The wagon has been out of service for years. Once it returned to the road...the rear main seal failed.

During disassembly to access the rear main seal I (the genius) stripped a
bolt head that mounts the flexplate to the crank shaft (standing ovation...thank you, thank you and now for my next trick...)

How did he do it?! they all gasped... I used my 18v Dewalt impact with a twelve point impact socket with short bursts on bolts in a star pattern around the array of bolt heads. When I got to this one I was lazy about holding the impact so the socket was not fully engaged on the bolt head. (there I admit it...but don't feel any better)

I am mostly "thinking out loud" here but also hoping that the Peach community will chime in with the collective voice of reason.

Options I feel are realistic solutions:

1) use left handed drill bit, tap in an easy out, hope it doesn't break off in the bolt...

2) drill an appropriate size hole in the end of a mild steel flat bar then tack weld said bar to the damaged bolt head to create a leverage on the bolt in hopes of breaking the torque (not the bolt) and loosening the bolt

3) uh... I got nothin'

Ideas, comments, doubts, concerns, criticisms...Gentlemen, the floor is open

See the pic in post #52.

Some Sockets have too large of a tapered radius and they don't grip much of the bolt head. Grinding most of the tapered radius off allows the socket a better bite on the bolt.

If the bolt is a 6 sided hex sometimes a 6 point socket is better. Note that I have never scene my flex plate.

Pretty sure the go to remedy for the flywheel stretch bolts is to grind the head off and they come right out with vice grips once the FW is off

Can you remove the yoke in the transmission. Will a socket fit through the center of the flexdisk?

What I would probably automatically do as well in your situation. We who live in rustbelts get all too familiar with fastener problems unfortunately.

I agree with cut or drill off the head, then remove the flexplate. You will need another bolt, and they are quite special. I recall you can still buy them, albeit >$10 each. Check if they are 1-use only (torque to yield, why they are necked-down?).

Re changing the rear seal, search for Rollguy's post w/ photos where he did so. He left the crankshaft in but loosened the main bearing caps enough to drop it to get the rope seal out. M-B (thoughfully?) put a locking pin in the seal groove so you can't just pull a new graphite rope thru like people would do in a 1960's Chevy V-8. Rollguy's photos will show if he left the flexplate attached.

What I did when flexplate bolt rounded off during my 4 speed conversion:

Took one of the bolts that came out, went to lowes/ace/homedepot/yourfavoriteboltstore, found a giant nut that fit snug over the head, plainest steel I could find, not galvanized or anything.

bought 4 or 5 of em (cost a few bucks)

Stick the nut on the rounded off bolt, weld it onto the bolt, start with some gentle tacks and try an impact on it, then work up to filling the inside of the nut with a nice solid bead if it doesn't come out before the nut snaps the weld off (thats why you bought more than one nut.)

Believe it took me 1 or 2 tries with a little 110v flux core welder before it spun right out.

The nut protects the flexplate from getting hit with a grinder or weld spatter or anything.

Used the same technique to remove the manifold studs from my f150. the nuts are normally 13mm, I could fit a 10mm on them. they all rounded off. In this case i was replacing the manifold so I cut the nuts off, then welded new nuts onto the studs and removed nearly all of them by hand. two or three needed a ratchet and socket, and one needed an impact.

He's talking about the flywheel flex plate. Not the driveshaft guibo joint.


To the OP, I just drill in the center of the bolt head and pop the head off. The tension should be released and you can easily get the rest of the bolt off.


.

1) "I agree with cut or drill off the head"

2) "Check if they are 1-use only (torque to yield, why they are necked-down?)"

3) "Re changing the rear seal, search for Rollguy's post w/ photos..."


1) Drilling the head off seems to be the popular vote.

2) Yes these are torque-to-yield, non-reusable bolts. I bought a new set in
preparation for the job.

3) Thank you for the good information. As always, wish I had read the directions first...

Thanks to everyone that has replied so far.

I'll post an update when I get through the issue

I agree with All posted.

1st thing I would try is grinding the socket flush for the best bite possible.

Next, just grind off the bolt head. If ya wanna be super special, grind only the outer edge of the bolt off... but that requires some skill.

With flywheel out of the way, should be no issue to remove the rest of the bolt.

Good approach in many cases. You get a massive assist if rust or corrosion is involved as the reason for the bolt being so tight it stripped the head as well.

The heat from welding a nut on really shakes up the thread corrosion . So the bolt usually is much easier to extract. Than it would have been otherwise. I would not do this on a bolt going into aluminium though. You could melt the threads.

Also I use my 180 amp mig with gas to secure the best weld properly. Over the years I never used a flux wire in a mig unit until not long ago. It worked okay but the welds I felt had some slag in them. With a flux core you either should deslag after every stop if you are going to increase the weld mass. Otherwise weld strength is less than optimum. Anyways the heat used to weld the nut on is really your friend as well usually.


Putting the nut right over the old bolt head is yet another thing I have not tried. Although it reduces the pit depth you are welding into. It may make this application more usable on smaller bolts. Where I just have placed an undersized nut over the stripped bolt head before and welded in the deeper pit.

I also thought about an approach I have never had occasion to use. On smaller bolt heads one might weld a suitable thickness of washer on first. Then weld a nut on the washer after grinding the first welding job flat. Or at least suitable to take the nut.

Everyone should be aware that once a fastening starts to back out. If it tightens up. Stop and get some penetrating oil in there. Then work it back in and out. Applying more penetrating oil.

Otherwise the bolt just continues to seize or tightens up and all too often the head just snaps off. Just because people thought that it is loose now. so I will just keep cranking through the new tightness.

Another approach I use and was mentioned on this thread. Is drilling the center out of the remains of the bolt head. I usually start with a smaller bit. Especially if I cannot get a good hit with a center punch. Otherwise drill bits seem to love wandering around leaving you off center.

Myself and some of my friends have discussed the low quality of far too many locally available drill bits today. At least around here. It seems only price sells and the vast majority out there today are almost worthless compared to good bits. Little sense using garbage drill bits to do things.

You even get the speed right and reasonable pressure and they just polish the surface without more pressure applied than they should need. Then after the one use they are even duller. Perhaps they think today that good high carbon steel bits will break too easily in the wrong hands. Many of the bolt heads you will be drilling into are harder than lower grade bolts as well. You want good bits.

When I cannot even get a new drill bit to perform well in my drill press. There is little to no hope for that bit in a hand held power unit. Starting with a small bit and sizing up until you get to the bolts shank size is about all you can manage sometimes with them. When you get close just taking a cold chisel and giving the remaining portion of the head a whack. It seems to break off cleanly enough usually.

As for dealing with nuts that are rounded off etc. Nut splitters are cheap enough.

This has been a wealth of information so far.

I appreciate everyone's input to date.

I have welded nuts onto rounded heads in the past with good success.

I will update this thread with a success story once I get back to this repair.

This weekend I have a W116 450SEL on the lift to solve some exhaust issues.

Another trick that has not been mentioned is take the next oversize 12 point bit (a good quality one) and hammer it in before using an impact gun or breaker bar (impact it with your palm). If there's room to swing a hammer, it has worked for me every time I've tried it.