The Haynes manual lists the torque on the engine mount centre bolt as 96 ft-lbs. The bolt is an 8 mm hex. I just swapped out the engine mount and am going to torque it. After what my arm perceives as approx. 50 ft lbs, I noticed that the bolt didn't seem to be getting much tighter, though it still turned. I didn't turn it much further because I did not want to strip the threading. Is the torque really 96 ft-lbs, or is there a typo in the Haynes manual? What do you guys typically tighten this bolt to?

With the other, original, motor mount still in place, I take the torque wrench up to it and turn. The torque wrench is still set at 96 ft-lbs. After some effort, I am able to tighten that other bolt without the torque wrench clicking. Again, it makes me wonder if the Haynes manual is off.

96 ft-lbs is WAY too much. That's more than your wheel lugs, and your caliper bolts, for the sake of comparison. For future reference I'd suggest that you should be using the online factory service manual. It's available for free.

http://www.startekinfo.com/StarTek/doclist.jsp

Here is a link to the section from the FSM that talks about changing engine mounts on a 240D.

http://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/615/00-211.pdf

Assuming your 240D is a W123 you'll have to identify which bolt type you have - but since it's an 8mm hex it's probably the M12x40 - if my memory serves me that's what is on all the later turbo diesels too.

Assuming (again) that is the case then your tightening torque would be 70 newton-meters (nm). That equates to just a touch over 50 lb-ft.

My concern at this point is the fact that the bolt on the mount you were working on is still turning, but not tightening. The arms on the engine that the mount bolts to are aluminium, I think. It's possible that the threads have stripped.

Personally, I'd start over - back the bolt out, and see about running the appropriately sized tap through it to see if the threads are OK. Then try again and set your torque wrench to 50 lb-ft.

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I suspect that Haynes did the Nm to ft-lb conversion backwards. As in, they divided 70 Nm by .73 instead of multiplying.

As a result, Haynes is probably responsible for countless ruined engine mount arms.

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Don't leave that there - I'll take it to bits!

Yikes....I usually just "snug tight" those bolts...probably well under 55ft/lb, have never had one come loose....

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I hope I did not over tightened the engine mount bolt. I knew I was going into a metal that did not look like steel, so I was naturally very cautious when I saw such a large number for the torque. I turned about 1/10th of a turn beyond what I was comfortable with.

I unbolted the bolt today and did not see stripping on the bolt. I shined light into the engine mount arm and didn't see any obvious stripping, although it is tough to determine from that vantage point. I retightened the bolt to 40 ft-lbs and will periodically check the bolt for loosening up.

Thanks for the information on the FSM. The first startek link returned a null pointer error. How do I view and download each page of the factory service manual? To subscribe to that website costs $3100/year.

Sorry about the bad link.

STAR TekInfo

Click on MB Workshop Resources

Then click on Service Manual Library CD/DVD

Then click on W123 Service Manual Library

Click on Disc 1 and then click on your year under the 240D section. If it say to switch do disc 2, just go back and select that instead.

Then just navigate to the section you want.

Sounds like you'll be OK on the mount. If it threaded back in and tightened up then it's not likely stripped.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

uberwasser, thank you for this link with instructions. Is there a place to download and print a concise single PDF for a particular model year? If not, what about a place to order the printed copy?

To lighten the mood, here are some torque specs I have seen:

Old shop I worked in: Tighten until you strip the threads, then back it off 1/4 turn

British biker oil change guy: Tight enough to not fall out, loose enough to not strip the threads

Every place that has put on tires for me: Torque until the 1/2" extension breaks, fetch a new exention, and repeat. Average torque 200lbs per lug.

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