[DeTomaso] Shift Happens - Broken Motor Mount Bolt

Dave Londry davel at trguys.com
Tue May 15 14:59:51 EDT 2018


It is a good piece - pretty much as taught in old-school ME courses.
And Marks is simply-the-best reference.
Dave


On 15/05/2018 11:48 AM, Mike Drew via DeTomaso wrote:
> Larry,
>
> Very interesting! Thanks for sharing!  It contradicts a lot of commonly held wisdom, which might not be as wise as I thought!
>
> Mike
>
> Sent from my iPad
>
>> On May 14, 2018, at 20:37, Larry Stock <larrys at panteraparts.com> wrote:
>>
>> Mike not to bore everyone with a bunch of engineering specifications for
>> each comparative bolt design, you all can read about all these details
>> here at
>> http://tinelok.com/grade-5-vs-grade-8-fasteners/
>> The conclusion basically sums it up;
>> Getting back to the original question, “which fastener grade should I
>> use?” We hope it’s very clear by now that grade 8 fasteners are far
>> superior to grade 5 fasteners. If this is so, then why do the automotive
>> manufacturers use some grade 5 fasteners? The automotive OEM’s use what it
>> needs to be safe and nothing more since there is a difference in cost
>> between grade 5 and grade 8 (or metric 8.8 and 10.9). Since the OEM’s
>> manufacture millions of vehicles each year, the difference in a few cents
>> per fastener adds up to a lot for them.
>>
>> Larry Stock
>>
>>
>>
>>> On 5/14/18, 7:37 PM, "Mike Drew" <MikeLDrew at aol.com> wrote:
>>>
>>> Larry,
>>>
>>> Grade 8 bolts are stronger in tension and weaker in shear. They are more
>>> brittle, and they break when Grade 5 bolts bend.
>>>
>>> The fix is to use Grade 5 bolts―as originally installed (for a reason).
>>> The engine subjects the bolts to shear loading and Grade 8 bolts will
>>> snap when Grade 5 bolts distort. A distorted bolt is still doing its job
>>> after a broken bolt isn’t!  (Thats also why A-arm bolts are Grade 5
>>> instead of Grade 8).
>>>
>>> There are lots of other applications where Grade 8 bolts are appropriate.
>>> It depends on the nature of the job they are being asked to do. But
>>> neither Grade 5 or 8 bolts are ‘better’. They are instead ‘different’.
>>>
>>> The Ford engineer guys are no dummies.
>>>
>>> Scott―you should be able to support the engine from below (or suspend it
>>> from above), then unbolt the bottom half of the engine mount, remove the
>>> through bolt, and withdraw it. Then you can remove the other upper mount
>>> bolt (hope it isn’t broken too) then remove the upper mount. Then you can
>>> determine if you can extract the broken bolt with an EZ-out. Frame rails
>>> might make access difficult, so you may have to unbolt the other side
>>> mount and raise it up with a hoist to get better access.
>>>
>>> If the bolt is broken off inside the block and the EZ-out doesn’t work,
>>> you may need to take the block to a shop that can do EDM, Electro
>>> Discharge Machining, and have it zapped out. Or perhaps a machinist can
>>> extract it for you. Dismantling the engine might be part of either of
>>> those operations however....
>>>
>>> Mike
>>>
>>> Sent from my iPad
>>>
>>>> On May 14, 2018, at 11:04, Larry Stock <larrys at panteraparts.com> wrote:
>>>>
>>>> There should be 2 bolts Scott, so I assume you sheared the other one
>>>> also.
>>>> Since you so good with that camera, shoot me a photo of the other side
>>>> as
>>>> well, I¹d like to see what the bolt heads indicate what grade of bolts
>>>> you
>>>> had in there. Factory came with grade 5, and after Radial tires were
>>>> invented and installed the true nature of the difference of a monocoque
>>>> vs
>>>> Unibody became evident with the shearing of the grade 5 bolts with the
>>>> engine being engineered as stressed member of the chassis. The fix has
>>>> been to use grade 8 or higher to keep that engine as a stressed member
>>>> brace of the chassis design. More Grip, more stress.
>>>>
>>>> Larry
>>>>
>>>> On 5/14/18, 10:47 AM, "DeTomaso on behalf of Scott Mead Photography"
>>>> <detomaso-bounces at server.detomasolist.com on behalf of
>>>> scott at scottmeadphotography.com> wrote:
>>>>
>>>>> Hi Everyone -
>>>>>
>>>>>
>>>>> I was under the car this weekend, diagnosing my paperweight of an A/C
>>>>> system, when I noticed something a little unnerving: The right-front
>>>>> motor mount bolt had sheared off in the block, and the motor had
>>>>> shifted. With the hole in the motor mount no longer lining up with bolt
>>>>> remnants, there's no way I can "easy out" the bolt. Aside from pulling
>>>>> the engine/ZF, can I take out the other bolt, loosen the bolts on the
>>>>> other side and (using a block of wood under the oil pan), jack the
>>>>> engine up a bit to re-align or remove the motor mount to extract the
>>>>> bolt? Are there any other options I haven't thought of?
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>
>>>>> Scott (caretaker of 5638)
>>>>>
>>>>>
>>>>>
>>>>> SMP-Slogo
>>>>>
>>>>> PO Box 1190
>>>>>
>>>>> Lake Arrowhead, CA 92352
>>>>>
>>>>> T: 626-660-8075
>>>>>
>>>>> E: scott at scottmeadphotography.com
>>>>>
>>>>> W: www.scottmeadphotography.com
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