Engine Mount Bolt Torques - LotusTalk - The Lotus Cars Community
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 35 (permalink) Old 03-29-2009, 10:35 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
Engine Mount Bolt Torques

I recently upgraded my lower engine mounts with inserts, and discovered that some of the torque settings in the instructions were incorrect (discovered the hard way - stretched bolts, but fortunately on the ones easiest to replace and that used nuts) . The big concern is that overtightened bolts can break under load. The torque settings are not listed in the service manual. So, I tried to examine the bolts to determine their size and class, and looked up the proper torque value for the bolt. Of course, this says nothing about what the female threads in the engine, transmission or the frame can handle, but the bolt specification is a start.

First, here are the two best references I could find on recommended torque for metric bolts. I liked the first one better, but the second does give some lubricated values. Unfortunately, there is a lot of variation in recommended torque settings out on the web, but these two sources seemed consistent with most, had more information, and in general appeared to be more reputable. You might want to save them to your computer in case the web sites vanish.

http://www.imperialsupplies.com/pdf/...rqueCharts.pdf
Metric Bolt Torque Table - CNCexpo.com
(By-the-way, Bolt Depot's recommendations seemed consistently higher than other references, so I didn't use them. Nor were they as complete in their specifications as compared to the others.)

I was upgrading the lower engine mounts. Here are the bolts I examined:
1) Rear lower mount:
1a) mount to frame, rearmost pair (with nuts)
Class: 8.8 (says so on the bolt head)
Diameter: M10 (10 mm)
Pitch: 1.5 mm (thread spacing, which is how metric bolts are specified)
Plated (looks like zinc)
Recommended torque for this specification: 38.25 foot-lbs

1b) mount to frame, forward pair (bolts into frame)
Class: 8.8 I think (not listed on the bolt)
Diameter: M8 (8 mm) I think. I forgot to measure it before installing, but it was definitly a size smaller than the other pair of bolts (1a).
Pitch: 1.25 I think (again, forgot to measure, but the threads didn't seem as fine as a 1.00 pitch)
Plated (looks like zinc)
Recommended torque for this specification: 18.75 foot-lbs
(of course, you can't fit a torque wrench in the space, so you just have to estimate your strength)

1c) big center bolt through mount
Class: 8.8 I think. (The only marking on the bolt head was a lower case b with a dot over it. I don't know what that means, but Lotus generally doesn't use the higher class bolts.)
Diameter: M12 (12 mm)
Pitch: 1.5 I think (measured it, but lost my note. This my best recollection.)
Plated (not sure with what)
Recommended torque for this specification: 69 foot-lbs


2) Forward lower mount
2a) mount to transmission housing
Class: 8.8 I think. (The only marking on the bolt head was 11. I don't know what that means, but Lotus generally doesn't use the higher class bolts.)
Diameter: M10 (10 mm)
Pitch: 1.25
Plated (looks like zinc)
Recommended torque for this specification: 40.5 foot-lbs
(of course, you can't fit a torque wrench in the space, so you just have to estimate your strength)

2b) big center bolt through mount
Class: 8.8 I think. (The only marking on the bolt head was 11. I don't know what that means, but Lotus generally doesn't use the higher class bolts.)
Diameter: M10 (10 mm)
Pitch: 1.25 I think (measured it, but lost my note. This my best recollection.)
Plated (not sure with what)
Recommended torque for this specification: 40.5 foot-lbs

It would be good if others could check the bolt measurements and classes, and add in the bolts I didn't list, such as the upper side engine mount bolts.

The bolts I damaged were listed in 1a above. I ended up replacing them with higher class bolts (10.9), and torqued them to the appropriate specification for that class in the Imperial Supplies chart above.

Last edited by ChrisH; 09-13-2009 at 02:13 PM.
ChrisH is offline  
Sponsored Links
Advertisement
 
post #2 of 35 (permalink) Old 03-30-2009, 02:43 AM
Registered User
 
EliseAtLeast's Avatar
 
Join Date: May 2005
Location: Basking Ridge, NJ
Posts: 1,788
Thanks for taking time to post this info.

Richard

'13 Scion FR-S (Whiteout)
'07 Lotus Exige S (Aspen White) Touring, Traction, Starshield
'95 Miata (Montego Blue)
EliseAtLeast is offline  
post #3 of 35 (permalink) Old 03-30-2009, 10:04 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
One caution for anyone trying to determine a bolt torque: DON'T estimate the torque of an installed bolt by seeing how much torque is required to turn it some more.

It will generally take much more torque to start the bolt moving (breaking the static friction) than it took to tighten it to that point. This is because the static coefficient of friction is much higher than the kinetic (moving) coefficient of friction. (The bolt was moving when it was originally tightened.) And, if the bolt had seized a bit (fairly common due to corrosion or other slow chemical bonding), then that would lead to an even greater overestimation. If you used that method to estimate the proper bolt torque, you will overtighten the bolts and damage them, with potentially catastrophic results.
ChrisH is offline  
 
post #4 of 35 (permalink) Old 04-29-2009, 05:02 AM
Registered User
 
tvacc's Avatar
 
Join Date: Apr 2004
Location: Buffalo, NY
Posts: 2,990
I agree completely. I put mine on this past weekend and nearly stripped one of the rear bolts trying to tighten it up to the specs in the install instructions. I figured something was amiss and did not tighten mine up so much.

Tony Vaccaro
2005 Elise Ardent Red, www.lotusowners.com LOONY (Lotus Owners of New York) and the Church of the HolyLotus, Drive Fast Take Chances, 93 Caterham 7, 71 Elan, 70 Elan GTS, 1991 M100, 1999 Sport 190 Elise, 1974 Europa TC, 1973 Europa JPS #15 TwinCam.
tvacc is offline  
post #5 of 35 (permalink) Old 04-29-2009, 10:37 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
Quote:
Originally Posted by tvacc View Post
I agree completely. I put mine on this past weekend and nearly stripped one of the rear bolts trying to tighten it up to the specs in the install instructions. I figured something was amiss and did not tighten mine up so much.
You should replace the bolt(s) that you nearly stripped or that you overtightened. They are damaged and could break under hard acceleration, fast releasing of the clutch (if your rev matching isn't so good), etc. Your local autoparts store should have them. I upgraded my rear lower frame bolts (the ones with the nuts) to class 10.9 after stretching the original bolts.

Last edited by ChrisH; 09-13-2009 at 02:14 PM.
ChrisH is offline  
post #6 of 35 (permalink) Old 04-29-2009, 10:43 PM
Registered User
 
Join Date: Jul 2007
Location: Orange County, CA
Posts: 974
I just finished installing my inserts yesterday. I was able to torque the large bolts but couldn't get my torque wrench on the smaller ones. Those numbers you have are WAY lower than in the installation instructions. Yikes!

07 Phantom Black Exige S - TP/TP/TC/SS
Happiness is adding modifications!!!
300hpMR2 is offline  
post #7 of 35 (permalink) Old 06-05-2009, 07:33 AM
Registered User
 
PECivil's Avatar
 
Join Date: Nov 2008
Location: SandyEggo
Posts: 419
yes mucho gracias to Chris for this info, I am installing mine tomorrow!!

10 Porsche Cayman
PECivil is offline  
post #8 of 35 (permalink) Old 06-05-2009, 12:09 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
If you have any concerns about the torque being so much lower (and I think the lower values are correct), then put some thread locker on for insurance. I didn't bother, but it may be worth the peace of mind.
ChrisH is offline  
post #9 of 35 (permalink) Old 08-07-2009, 08:10 AM
Registered User
 
glacialmoraine's Avatar
 
Join Date: Apr 2009
Posts: 319
Re threadlocker. The linked table lists dry and lubed torques, use the lubed torque if threadlocker is applied.

gm

2007 Exige S, LSD - Sold
glacialmoraine is offline  
post #10 of 35 (permalink) Old 08-19-2009, 12:59 PM
Registered User
 
caboydman's Avatar
 
Join Date: May 2009
Posts: 79
torque values

So other then this thread is there a place where I can get the exact torque specs for all the engine mount bolts.
I paid the $25 for the online lotus catalog but it didn't have any information I needed.
I also called a dealer and couldn't get an answer.

Thanks

2008 Exige S240
caboydman is offline  
post #11 of 35 (permalink) Old 08-19-2009, 04:26 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
Quote:
Originally Posted by caboydman View Post
So other then this thread is there a place where I can get the exact torque specs for all the engine mount bolts.
I paid the $25 for the online lotus catalog but it didn't have any information I needed.
I also called a dealer and couldn't get an answer.

Thanks
There is no place that anyone has found (or at least reported). Hence, the reason for this thread.
ChrisH is offline  
post #12 of 35 (permalink) Old 09-20-2009, 12:32 PM
Registered User
 
ads_green's Avatar
 
Join Date: Oct 2008
Posts: 677
I've just been out to have a quick go with the engine mount inserts and failed on the first mount (lower rear).

There's nothing special here with this bolt? I suspect it's just me only having a relatively small wrench (9") so probably need something with a little more length. Just want to check first before I have another go with a longer wrench.

Ta
ads_green is offline  
post #13 of 35 (permalink) Old 09-20-2009, 12:56 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
Quote:
Originally Posted by ads_green View Post
I've just been out to have a quick go with the engine mount inserts and failed on the first mount (lower rear).

There's nothing special here with this bolt? I suspect it's just me only having a relatively small wrench (9") so probably need something with a little more length. Just want to check first before I have another go with a longer wrench.

Ta
Which bolt is causing you trouble? Getting them off or on? On the rear mount, the front bolts for the bracket to the frame are hard to access. If I recall correctly (it has been awhile), I just had to use a box end wrench and use muscle to get them off.
ChrisH is offline  
post #14 of 35 (permalink) Old 09-20-2009, 01:29 PM
Registered User
 
ads_green's Avatar
 
Join Date: Oct 2008
Posts: 677
It's the rear lower mount M12 bolt through the middle of the mount - the one recommended to torque to 69lb/ft - and the damn thing wont' budge. The only wrenches I have to hand are about 9" and I don't thik I'm getting enough leverage. I'm hoping it's just a case of a longer wrench
ads_green is offline  
post #15 of 35 (permalink) Old 09-20-2009, 05:30 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
You need to invest in a breaker bar. I got mine at Harbor Freight.

Or, hit the wrench with a hammer. The shock will often break it loose. You could even try some penetrant, or something to effectively extend the handle on the wrench to get more leverage.
ChrisH is offline  
post #16 of 35 (permalink) Old 09-20-2009, 06:54 PM
Registered User
 
choi0706's Avatar
 
Join Date: Sep 2004
Location: Houston/Austin
Posts: 4,452
Quote:
Originally Posted by ads_green View Post
It's the rear lower mount M12 bolt through the middle of the mount - the one recommended to torque to 69lb/ft - and the damn thing wont' budge. The only wrenches I have to hand are about 9" and I don't thik I'm getting enough leverage. I'm hoping it's just a case of a longer wrench
double up on the wrenches..

Jay-05' ST, HT, Touring Red
choi0706 is offline  
post #17 of 35 (permalink) Old 09-21-2009, 01:05 PM
Registered User
 
ads_green's Avatar
 
Join Date: Oct 2008
Posts: 677
success
Big wrenches sorted.

Thats the rear one done now onto the joys of the front one
ads_green is offline  
post #18 of 35 (permalink) Old 07-23-2010, 01:21 PM
Registered User
 
ekological's Avatar
 
Join Date: Jan 2004
Location: Brooklyn, NY
Posts: 1,581
I have the two bolts in front of me. They are both M10 and same thread pitch. The bolts in 1a (M10x25) are a typical hex bolt, 17mm hex head and require the use of a washer. The bolts in 1b (M10x20) are a flange hex and have a 13mm hex head with a flange diameter of 20mm.

Quote:
Originally Posted by ChrisH View Post
I was upgrading the lower engine mounts. Here are the bolts I examined:
1) Rear lower mount:
1a) mount to frame, rearmost pair (with nuts)
Class: 8.8 (says so on the bolt head)
Diameter: M10 (10 mm)
Pitch: 1.5 mm (thread spacing, which is how metric bolts are specified)
Plated (looks like zinc)
Recommended torque for this specification: 38.25 foot-lbs

1b) mount to frame, forward pair (bolts into frame)
Class: 8.8 I think (not listed on the bolt)
Diameter: M8 (8 mm) I think. I forgot to measure it before installing, but it was definitly a size smaller than the other pair of bolts (1a).
Pitch: 1.25 I think (again, forgot to measure, but the threads didn't seem as fine as a 1.00 pitch)
Plated (looks like zinc)
Recommended torque for this specification: 18.75 foot-lbs
(of course, you can't fit a torque wrench in the space, so you just have to estimate your strength)

Custom Plug-N-Play Elise HIDs, Arqray SS Double Tip Exhaust, RAC Monolites

Last edited by ekological; 07-23-2010 at 01:32 PM.
ekological is offline  
post #19 of 35 (permalink) Old 02-25-2011, 02:24 PM
Registered User
 
V-RAPTOR's Avatar
 
Join Date: Jan 2008
Location: NOVA (Round Hill)
Posts: 1,338
So I did not see this thread before installing my motor mounts and I stripped one of the holes for the front mount (M10 bolt) by over torquing. Should I just tap the hole and use a M12 bolt or use Heli-coil and reuse a M10 bolt? Please help.

2005 Saffron Yellow Elise // Sport Pack NO touring // Stage 2 Exhaust / bling buttons

SOLD - 05 Starlight Black Biscuit Int // Hard Top // BWR SC // Von Hep Exhaust // Naked rear // Cup Box // Manley Mounts // Rota Wheels W/ Toyo R1R's // ForceFed Carbon Fiber Splitter // Carbon Fiber Engine lid cover // Custom side grills // LidBone // JL Audio VR525-CXi Front and Rear // Micro Mirror // Painted interior bits // Bling Buttons // Darth Holder // STRIPES
V-RAPTOR is offline  
post #20 of 35 (permalink) Old 02-25-2011, 03:34 PM Thread Starter
Registered User
 
ChrisH's Avatar
 
Join Date: Mar 2004
Location: Melbourne, FL
Posts: 2,771
Quote:
Originally Posted by V-RAPTOR View Post
So I did not see this thread before installing my motor mounts and I stripped one of the holes for the front mount (M10 bolt) by over torquing. Should I just tap the hole and use a M12 bolt or use Heli-coil and reuse a M10 bolt? Please help.
The best solution would be to use a Helicoil (or equivalent), and keep the same bolt size. If you increase the bolt size (which generally will mean increasing the hex head size), you will likely have a problem installing the bolt given the cramped space in the mounting bracket.

However, I am guessing that the transmission is still in the car, and I can't see how you are going to be able to drill the hole in order to install a coil. Keep in mind that you have to be very careful to drill that hole straight, otherwise the coil won't work properly. I think you would have to take the transmission out of the car to do so.

I have heard of people using slightly oversized bolts (possibly self-tapping), that used the hole diameter of the stripped hole, rather than going up a full bolt size. The advantage is that there is no drilling involved. A quick Google shearch showed that some folks found them for their brake calipers at NAPA Autoparts.

Another possibility is to use something like the highest-strength version of JB-Weld to glue in a M10 stud, instead of using a bolt. I have heard of people doing that on other cars, with mixed success. I wouldn't do it on my own car, as I would be too afraid it would just pop out one day.

A thread repair compound, such as the one below made by Permatex, would only handle 7 ft.lbs. of torque for a M10 bolt, which is too low for this application.
http://www.permatex.com/documents/td...tive/81668.pdf
ChrisH is offline  
Sponsored Links
Advertisement
 
Reply

  LotusTalk - The Lotus Cars Community > Lotus Discussions > Powertrain (Engine, Transmission, etc)

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the LotusTalk - The Lotus Cars Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome