I'm trying to change the motor mounts on my 1991 300d, and on the underside, it appears at first to be a regular bolt, but turns out the outside is round, and it's a hex head on the inside of that bolt, which I hate.

I'm trying to get that out, and unless they put a reverse thread on this for some reason, I can't get the bolt out. I sprayed some liquid wrench on it, in the small hopes it will travel upward. I'll let that sit for a while.

Any recommendations? This isn't a reverse thread by chance is it? I tried the reverse direction, and it doesn't move, either way.

Thanks,

jeff

No, it's not a reverse thread. Do you have a hex head socket set? If not and if there is a Harbor Freight nearby, run out and pick up a cheap set. Might cost you $15 but this isn't the only hex-head bolt you are going to find on a MB. So, first thing is to have the proper size hex-head socket, then slap on an extension to give yourself a little room to work. Then position your socket wrench in such a way as to get some good leverage. You might have to slip a pipe on the end for extra leverage or use breaker bar if there is enough room. I picked up a 24" breaker bar from HF that swivels at the head so you can work at an angle if needed. Once you have the right tools in place just lean on it and it will pop.

Good luck!

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

Yes, I have a complete set of hex heads. Even so, it sort of bobbles around in there, hard to get it to be perfectly still while applying pressure.

Just knowing it's not reverse thread gives me more impetus to push harder, knowing I'm going in the right direction! I'll try it.

Thanks,
jeff

Soak the bolt as you have , for some reason the majority of these bolt are frozen (perhaps the durability of the parts , mostly original ) then get a punch/rod or bolt that fits inside socket head strike it good with a hammer. This will shock the threads.

You can get a cheap set of metric allen sockets , but if you plan on doing a lot of your own repairs you may want to invest in a better set. Craftsman sells a set 30 - 40 dollars and dosent tend to round off as bad as the cheaper sets , plus free replacement if they break . Good luck!

The bolt is secured with blue threadlock heat the end of the bolt with a propane torch for a minute or two and that will heat and soften the threadlock. The Allen head bolt is 8 mm, and of course you recognise that because the bolt is upside down the you'll be putting force to it in the opposite direction from when it right side up. Righty tighty lefty loosy looking at the bolt's head! Make sure the bolt head is clean and you've got the tool completely seated. Keep the force you appy straight and square to the bolt to prevent rounding it out.

X2 - if you have some brake cleaner, make sure you clean the bolt head out good prior to inserting the hex-head.

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

Crap. Now I stripped the inside-hex bolt. I hate those bolts.

I think the only thing I can do now, is to drill it out.

Unless anyone has any other thoughts.

OH Great!

My Indy told me he uses Valve grinding compound on the hex bit. makes it bite a little better.
I have found, instead of steady pressure on the breaker bar, to just give it a quick pull to break it free.

Maybe one of those star shaped bits pounded in will be enough to grip.
I bought a set at kragan for not too much $. the reason I bought these mainly was, the W126 annular axle uses this type bolt instead of the hex head.

Another option is to maybe remove the 2 bolts holding the rubber mount to the body, and then remove the 4 17mm nuts holding the aluminium arm to the engine block. then clamp it to a vice to work on.

I had one like this, so pulled one off a eng at the JY.

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

^^^^Intersting idea - hadn't thought of that one.


Sorry it stripped out . Now I feel partly responsible.

What size socket is this? Why is there that much wiggle room? If it is stripped out already, perhaps you can go the next size up and pound that sucker in there.

Before you manage to get it apart - consider going out and finding a replacement. Can you get the other side out to get the length measurement on it?

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

Sometimes if the wrench isn't all the way in the hole, you can just strip the top end of the hole ... i.e., if you can get the socket deep enough into the hole, it will get a purchase. I had to clean out of a couple of the bolt holes using a screwdriver tip ... once I was able to really jam that allen bit down into the hole, it would turn ... if it's not all the way in, even if the bolt isn't stripped, the bit will slip.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

The 124 chassis has only two bolts, one from above thru the engine mount arm and the other from below! The mount can not be removed with the bottom bolt in place.

If you try any other method of turning the bolt, Torx, larger Allen, internal or external removers you must heat the bolt with a propane torch to soften the threadlock or you'll be screwing yourself again! Last resort is to drill the bolt head off, wear safety glasses to prevent eye damage from the burning steel dropping down on you, use a quality cobalt drill bit and a decent 1/2" drill to push it! Good Luck!

In no way attempting to pick on you or disparage you, this is a perfect example of haste, making waste. A couple minutes getting the right tool, preparing so that you have every advantage, and paying attention to what is actually going on is often the only way to avoid turning a "simple" two minute job into a two hour job needing more tools and more parts!

I will heat that bolt up next time

After the going thru this very same experience once a while ago, so do I, every time!!!!

you can buy bolt remover set for relativly cheap and will save you a lot of tme in the future.buy the type that fits on the outside of head and sinks in as you turn.i have a set and is best tool ever bought,trust me.all you do is pound it on with small hamer and put as much pressure as you want and it will not slip

I was thinking of a 617.952 in a W123 when I was typing .

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works