I'm not feeling very smart right now. I swapped out the engine mounts in my 300D again, only this time, the big center bolts won't go in all the way. They start normally, but get very hard to turn with probably a half inch left before the washer makes contact with the bottom of the mount. The threads on the bolts look fine, and the threads in the arms look ok as nearly as I can see. I'm wondering if it's some sort of alignment issue getting the engine and the mounts lined up properly. What am I doing wrong here?

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Are you doing one arm at a time, or trying to do both at once? Doing one at a time is a wise idea as the other holds the engine more or less in alignment. I made the mistake of doing both at once the first time on my SDL and took me over an hour of prying, wiggling, and having a helper jiggle stuff to get the engine lined back up. Don't force it, you'll strip the threads on the bolt or the engine mount arm. Leaving the small bolts slightly loose can help get you a tiny bit of extra wiggle room to get things lined up.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

It's probably an alignment issue. Use your jack to raise the engine and try to get a few threads on one and then work to the other side, release the jack and torque both sides.

Dkr.

Something similar happened to me when I cross threaded the bolt. But in my case it was only the first thread that got buggered.

What I had done was jack up one side of the Car and change out one Engine Mount and lower the Car and jack up the other side and changed the mount and that is where I got the alignment off and cross threaded.

So I jacked up both sides if the Car loosened the opposite side and used a tapered punch and a 2x4 lever to shift the engine around till the hole was line up. I don't remember the size of the tap but I was able to get a tape in there and chase the threads an I was able to screw the bolt in and tighten down both bolts.

When I changed the mounts again 5 years later I was careful to make sure the holes were lined up with a tapered punch and I did not tighten both bolts till both bolts were run all the way in OK. I also jacked up both sides of the vehicle so that the Engine would not slide over to one side.

In any event the Aluminum Arm comes off of the Engine. If you don't want to deal with the cross treading issue you could remove it and inspect it and see if it could be reworked by chasing the threads with a tap or a thread insert.

One person solved the issue by taking a drill bit and drilling all of the way through the Arm to the other side and putting a long bolt all the way through it and a self locking nut on the other end.

__________________
84 300D, 82 Volvo 244Gl Diesel

I tried to do both sides at once. The youtuber I watched did it that way and his was apparently easy. He must have gotten lucky. I'll start with dkr's suggestions. If that doesn't work, I'll make a trip to Harbor Freight and try the stuff Diesel911 suggested. Good call on drilling through and using a nut and bolt. I'm less worried about destroying the threads in the aluminum if things go pear shaped.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Anther forum Member thought that up.

Stuff that people post when nothing goes wrong give the allusion that everything will be the same when you do the job. In fact even if you have done the job several times before some un-know problem will show up the next time you do the same thing.

__________________
84 300D, 82 Volvo 244Gl Diesel

I loosened up all the little bolts, used a big Phillips screwdriver to get the holes lined up, and tried again. The bolts still didn't go all the way in. I went to NAPA and got some new bolts, a 10x1.5 tap, and a tap handle. I found the tap didn't reach easily, so I tried the new bolts anyway. They're also 10 mm shorter, since NAPA was out of 10x1.5x40 bolts. The new ones went right in all the way. After a short test drive, things seem pretty good.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.