Undertray bolts... a suggestion - LotusTalk - The Lotus Cars Community
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post #1 of 26 (permalink) Old 09-30-2007, 10:46 AM Thread Starter
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Undertray bolts... a suggestion

Take this for what it's worth.

Executive Summary: Replace the large undertray and rear diffuser bolts as part of a regular maintenance program.

Long Version:
I had the supreme misfortune of shearing one of the two bolts that hold the undertray in place. I'm speaking of the large center bolts, measuring M8 X 1.25 X 25 , with the hex head. There is a matching pair holding the rear diffuser in place.

If you suspect that someone may have ever used a big-torque pneumatic tool to tighten these bolts before, then you want to replace them. PROACTIVELY.

I don't know for certain why I was so fortunate as to face this challenge, but I will say that it only took about approx 20nm of torque to take the bolt's head right off. The bolt broke inside the threaded receiver on the rear "lower wishbone to chassis bracket" requiring a very careful extraction. A replacement bracket costs $78.63, but it is not a simple swap. There are a number of bolts holding it in place and this bracket serves three purposes: securing the undertray, one of the hard points for the lower wishbone and also a stay for the parking brake cable.

I suspect two causes: the first is the aforementioned weakening of the bolt due to overtorquing and the second (to a lesser extent) is the fact that the threaded receiver is open on the top end, thereby allowing grit and dirt to accumulate in the threads. If a thread locker has ever been used in there, then the threads are going to get really nasty when you repeatedly R&R these bolts. If you feel an unusual amount of resistance when installing the bolt, STOP and clean the threads.

I ended up using a bolt extraction kit from Sears. It appeared to be a new, well thought out design. Pricey at $39.99, but the alternative was to have a shop attempt an extraction. The three with whom I spoke, were not very anxious to put a Lotus on lift and sweat this little job. Two actually refused and one just didn't appear very confident.

The kit was similar to this:
http://www.sears.com/shc/s/p_10153_12605_00952156000P

I used a very low RPM, very high torque 1/2" right angle drill from Milwaukee. The Sears kit warns against using this size drill, but I wasn't interest in fiddling with one of my 3/8" variable-speed drils.

The extraction tool uses a left-twist drill bit with a tapping collar on it. You drill the center of the bolt and once you have a decent hole, you bring the tapping collar down and manually run it into the bolt. Then you use the power drill to extract the bolt. Of course my drill promptly broke the extraction tool off in the chuck, but wasn't not a problem, as the collar is designed to operated by using a regular box wrench on it.

Bolt came out with no problems, and the stress on the bracket should have been minimal.

Lowe's usually has a pretty decent bolt selection, and they came through yet again. I bought every bag that they had. M8 X 1.25 X 25 . Two per bag at $1.17. Bolts were graded properly at 8.8.

For comparison at lotusgaragedotcom, the bolts are currently $1.05 per.

In searching this website, I have been unable to locate a proper torque value for these bolts. I think my strategy is to tighten the bolt until it feels "right" and then use a torque wrench to measure that value.



extract extracting bolt bolts broken sheared shear undertray under tray belly pan rear diffuser screw screws torque.
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post #2 of 26 (permalink) Old 09-30-2007, 10:55 AM
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I used this for my undertray:
http://www.elisetalk.com/forums/showthread.php?t=46219

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post #3 of 26 (permalink) Old 09-30-2007, 10:57 AM
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This was covered a while back over on Monkey:
http://www.monkeytuner.com/forum/viewtopic.php?t=754
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post #4 of 26 (permalink) Old 09-30-2007, 10:58 AM Thread Starter
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Quote:
Originally Posted by 25psi_Elise_Killer View Post
that was a nice thread. unfortunately, the bolts to which i'm referring aren't sheet metal to sheet metal though. they're going into suspension brackets which probably eliminates the ability to use another method.
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post #5 of 26 (permalink) Old 09-30-2007, 11:00 AM Thread Starter
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Quote:
Originally Posted by Dave View Post
This was covered a while back over on Monkey:
http://www.monkeytuner.com/forum/viewtopic.php?t=754
well i guess now it's covered here... i don't frequent that other place.
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post #6 of 26 (permalink) Old 09-30-2007, 11:04 AM
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this site has a ton of fasteners:
http://www.southco.com/
http://www.southco.com/landingpages/dzus/

OLD CAR '06 Evo IX Stage 1E Tuned by Road Race Engineering(Stock:turbo,intake,internals,ECU) Walbro 255lph fuel pump,RC Engineering1000cc Injectors, AVO exhaust,RRE dyno tune flash, Dejon Tool boost controller (325whp @ 22PSI Costco 91 octane, 353whp @ 25psi on 100 octane, 383whp @30psi on E85)Graphic/Interior Design,Brand Identities,Invitations www.nomadic-nomads.com NEW CAR: '10 Evo X MR-Touring with flappy paddle gearbox. Stock with just RRE Ecu Tune: 290whp, 313 torque
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post #7 of 26 (permalink) Old 09-30-2007, 11:21 AM Thread Starter
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Quote:
Originally Posted by 25psi_Elise_Killer View Post
it's not a question of the fastener (ie bolt, screw, etc). the receiver for the fastener in this application is absolute... it's a hard point on the car and you don't have access to the backside of the bracket once the trays are installed.

nor do i think that i want to physically alter the bracket due to its critical multifunction design. the bolt threads into a suspension bracket... which serves the three purposes i listed in post#1.

i dunno, i don't love the design, but i think with proper care and feeding it's serviceable.
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post #8 of 26 (permalink) Old 09-30-2007, 02:06 PM
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Quote:
Originally Posted by ace10 View Post
I had the supreme misfortune of shearing one of the two bolts that hold the undertray in place. I'm speaking of the large center bolts, measuring M8 X 1.25 X 25 , with the hex head. There is a matching pair holding the rear diffuser in place.
I over-torqued one of the big diffuser bolts. From what I can tell, if you put that spacer/washer on the wrong way the bolt goes fully tight while leaving the diffuser loose. Since the diffuser was clearly loose I figured the threads were just a bit clogged and kept tightening; then suddenly it turned too easily. When I took the bolt out to flip the washer and examine the damage, some little thread-shavings came with it. I'm pretty sure the bracket is what stripped, but as the bolt is still holding I haven't put a lot of effort yet into figuring out which part needs to be re-cut or replaced.
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post #9 of 26 (permalink) Old 09-30-2007, 02:17 PM
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Quote:
Originally Posted by dododge View Post
I over-torqued one of the big diffuser bolts. From what I can tell, if you put that spacer/washer on the wrong way the bolt goes fully tight while leaving the diffuser loose. Since the diffuser was clearly loose I figured the threads were just a bit clogged and kept tightening; then suddenly it turned too easily. When I took the bolt out to flip the washer and examine the damage, some little thread-shavings came with it. I'm pretty sure the bracket is what stripped, but as the bolt is still holding I haven't put a lot of effort yet into figuring out which part needs to be re-cut or replaced.
The first time I went to take off the undertray, one of the 8mm bolts was half loose because one of the 8mm frame nuts was stripped. I helicoiled it, it has been working fine since.

Francis
2006 Chrome Orange Elise: LSD/TC, Nitron SAs with 425/650 springs, BWR 7/8" ("Hardcore") Front Bar, Eliseparts bumpsteer kit, VF Stage 2, 2bular Header + Sport Cat + 8x24 GT3 Muffler, ECU Tune by Jermaine, Smaay's fuel rail, ACT XT clutch, Saikou Michi dual catch can, Moroso pan, Manly's mount inserts & FF Engine Damper
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post #10 of 26 (permalink) Old 09-30-2007, 02:27 PM Thread Starter
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Originally Posted by fpitas View Post
The first time I went to take off the undertray, one of the 8mm bolts was half loose because one of the 8mm frame nuts was stripped. I helicoiled it, it has been working fine since.
i think i've got a problem with one of those too (the bolts on the diffuser threaded into the frame). it's a bit lower on my priority list as the bolt threads in fine, it just won't seat snugly.

i'm not sure if all off this carnage happened at one visit to a service provider or if it isn't the accumulation of repeated abuse. i know that none of it is from me, and i'm gonna go way out of my way to make sure that no one ever has the need to take off these body parts.

I HATE PNEUMATIC TOOLS!
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post #11 of 26 (permalink) Old 09-30-2007, 02:34 PM
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Quote:
Originally Posted by ace10 View Post
i think i've got a problem with one of those too (the bolts on the diffuser threaded into the frame). it's a bit lower on my priority list as the bolt threads in fine, it just won't seat snugly.

i'm not sure if all off this carnage happened at one visit to a service provider or if it isn't the accumulation of repeated abuse. i know that none of it is from me, and i'm gonna go way out of my way to make sure that no one ever has the need to take off these body parts.

I HATE PNEUMATIC TOOLS!
Mine had never been worked on by anyone but the factory and Criswell. Luckily I do my own work on the car, so it shouldn't be a recurring problem.

Francis
2006 Chrome Orange Elise: LSD/TC, Nitron SAs with 425/650 springs, BWR 7/8" ("Hardcore") Front Bar, Eliseparts bumpsteer kit, VF Stage 2, 2bular Header + Sport Cat + 8x24 GT3 Muffler, ECU Tune by Jermaine, Smaay's fuel rail, ACT XT clutch, Saikou Michi dual catch can, Moroso pan, Manly's mount inserts & FF Engine Damper
2000 Black Integra Type R - DD: 231,000 miles!
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post #12 of 26 (permalink) Old 09-30-2007, 04:21 PM
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The mechanic at the dealer told me that it is important to use antiseize on the 8mm difuser bolts because the threaded part of the subframe into which they are fastened is open at the top and can collect moisture. This can cause corrosion and bolt failure.

Jerry

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post #13 of 26 (permalink) Old 09-30-2007, 04:25 PM
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Are you sure you are suppose to use a drill with the extraction bit? The kits I've bought always call for a socket or hand wrench. But your advice is well taken. I lost 1 bolt and several others came loose less then 2,000 miles after the 1,500 mile service. (possibly service tech error). Now I keep an eye on them and you're right, they are going to continually weaken each time they are taken off and put back on. The only other solution is stainless, then good luck drilling them out if they ever sheer!

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post #14 of 26 (permalink) Old 09-30-2007, 04:32 PM Thread Starter
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Are you sure you are suppose to use a drill with the extraction bit? The kits I've bought always call for a socket or hand wrench.
yes. it's a new product. it calls for a low speed (500 rpm) drill operated in reverse. (left twist). the instruction specificy not using a high torque motor, but a right-angle drill is perfect for centering on the bolt. you need the drill's motor to set the threaded collar into the bolt after drilling the hole. in order to preserve the tool, it would be best to using a wrench to remove the bolt after it has been engaged by the collar, however the instructions did not specify that method.
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post #15 of 26 (permalink) Old 09-30-2007, 07:11 PM
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The first oil change I did myself, one of the large bolts had been totally overtightened at the 1000 mile service. I had to destroy the head of the bolt to get it out. Since then, I've been using some stainless steel bolts that I can use a wrench on. I used a little WD40 once, because the first time I replaced the bolts, they weren't stainless steel, and they rusted pretty quickly. I needed the WD40 to loosen things up enough to be able to tighten it all the way.

I've never had a problem with the smaller bolts, other than it taking a while to get off and on. If I start servicing my car more (like if I start to track the car), I may look for some quick release fasteners. Hangar 111 had them for sale, but were more expensive than I was looking for at the time.
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post #16 of 26 (permalink) Old 10-03-2007, 09:11 AM
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Originally Posted by usofrob View Post
The first oil change I did myself, one of the large bolts had been totally overtightened at the 1000 mile service. I had to destroy the head of the bolt to get it out. Since then, I've been using some stainless steel bolts that I can use a wrench on. I used a little WD40 once, because the first time I replaced the bolts, they weren't stainless steel, and they rusted pretty quickly. I needed the WD40 to loosen things up enough to be able to tighten it all the way.

I've never had a problem with the smaller bolts, other than it taking a while to get off and on. If I start servicing my car more (like if I start to track the car), I may look for some quick release fasteners. Hangar 111 had them for sale, but were more expensive than I was looking for at the time.
For the smaller bolts I got an electric screwdriver with a torque-sensing clutch. Now they spin in & out quickly, and there's no chance of over-torquing.

Francis
2006 Chrome Orange Elise: LSD/TC, Nitron SAs with 425/650 springs, BWR 7/8" ("Hardcore") Front Bar, Eliseparts bumpsteer kit, VF Stage 2, 2bular Header + Sport Cat + 8x24 GT3 Muffler, ECU Tune by Jermaine, Smaay's fuel rail, ACT XT clutch, Saikou Michi dual catch can, Moroso pan, Manly's mount inserts & FF Engine Damper
2000 Black Integra Type R - DD: 231,000 miles!
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post #17 of 26 (permalink) Old 10-03-2007, 10:18 AM
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Good post. I had the same problem of the two big bolts feeling like it was stuck when I installed my exhaust, and like usofrob, never had much problems with the smaller bolts.

I use an electric screwdriver as well, and keep the torque pretty low (like 3 out of 6, max), then do the rest by hand.

How do you clean the bolts? With just a simple paper towel or rag, and do you use any solvents? I suppose I can use a chrome polisher wadding that I have, but it seems a bit wasteful for bolts.
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post #18 of 26 (permalink) Old 10-03-2007, 11:31 AM Thread Starter
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Good post. I had the same problem of the two big bolts feeling like it was stuck when I installed my exhaust, and like usofrob, never had much problems with the smaller bolts.

I use an electric screwdriver as well, and keep the torque pretty low (like 3 out of 6, max), then do the rest by hand.

How do you clean the bolts? With just a simple paper towel or rag, and do you use any solvents? I suppose I can use a chrome polisher wadding that I have, but it seems a bit wasteful for bolts.
i just squirt the bolts with some WD40 and wipe them with a shop towel. then i flush out the female receiver really well, wd40 there too. i'm sure there's a better routine/product but that's what i'm going with for now.
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post #19 of 26 (permalink) Old 09-24-2018, 12:34 AM
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Quote:
Originally Posted by usofrob View Post
The first oil change I did myself, one of the large bolts had been totally overtightened at the 1000 mile service. I had to destroy the head of the bolt to get it out. Since then, I've been using some stainless steel bolts that I can use a wrench on. I used a little WD40 once, because the first time I replaced the bolts, they weren't stainless steel, and they rusted pretty quickly. I needed the WD40 to loosen things up enough to be able to tighten it all the way.

I've never had a problem with the smaller bolts, other than it taking a while to get off and on. If I start servicing my car more (like if I start to track the car), I may look for some quick release fasteners. Hangar 111 had them for sale, but were more expensive than I was looking for at the time.
This is not the first time that SS has been recommended. Does that not increase the chance of galling? What material does the SS bolt into? Is it the aluminium frame/cross member?

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Patrick Van Rinsvelt
2005 Lotus Elise 111R Owner
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post #20 of 26 (permalink) Old 09-24-2018, 03:56 AM
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@patvr - Both the large and small undertray bolts thread into zinc-plated steel rivnuts. Stainless steel and zinc are at opposite ends of the galvanic scale, so putting them in contact isn’t a recommended combination. With regards to corrosion, steel is a lot closer to zinc and should fare better than stainless steel.

I’ve been using the 4 large factory-supplied steel bolts for the undertray and diffuser on my Elise for seven years with no corrosion issues. (I drive in rain but don’t generally encounter salt or other corrosion promoting chemicals.) One pair of bolts is zinc plated, the other pair is black oxide. The latter finish is more susceptible to corrosion: if I lived in a corrosion-prone environment, I’d replace these with a zinc-plated set. As long as there is some zinc plating present, the zinc-plated bolts should be fine in corrosion-prone environments. The zinc is designed to be sacrificial, so when the plating no longer covers the steel, the bolt should be replaced. Anti-seize would no doubt extend these fasteners life since probably the most damage to the plating occurs from the wear of repeated removal and replacement.

I suspect the vast majority of undertray bolt problems begin with chronic overtightening of fasteners, followed by corroded fasteners that take excessive torque to remove and end up spinning the rivnut in the frame members. I use an electric 3/8” drive ratchet that stops at 30 lbs ft of torque to run fasteners in and out (even that is probably too much . . . I always aim to stop before the ratchet does and tighten by hand to 15 or 20 lbs ft).

Glen

2011 Lotus Elise SC

Last edited by Glen; 09-24-2018 at 04:24 AM. Reason: add last paragraph
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