Can 4 Grade 8.8 Bolts Hold an 800lb Diesel Engine on an Engine Stand?

In summary: M12 would have a shear strength of 608 N/mm squared, M14 would have a shear strength of 910 N/mm squared. using a1...M12 would have a yield strength of 448 N/mm squared, M14 would have a yield strength of 592 N/mm squared.
  • #1

great forum.

i have searched the internet for 2 days to figure out the following, but with no luck.

i am going to remove my diesel engine which weighs 800lbs and bolt it to an engine stand.

i will be using 4 hex bolts with dimensions, 3 1/4'' long, just over 1/2'' thick, 13 threads per inch, 1 1/4'' thread pitch, marking 8.8 on head.

i am trying to figure out if 4 of these bolts can hold the 800lb engine?

i assume this method of strength is shear strength??

can someone tell me what one of the above afformentioned hex bolt can hold ??

thanks in advance...
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  • #3
bruca003 said:
... i am trying to figure out if 4 of these bolts can hold the 800lb engine?

i assume this method of strength is shear strength??
That could be a dangerous assumption. Are you also guessing the weight of the engine?

Not possible to provide meaningful answers without knowing the design of the stand.
  • #4
the weight of the engine is 800 lbs. the engine stand is rated to hold a 2000 lb engine.

after some research, the hex bolt is;

8.8 metric class, 8.8 mark on head, steel material,

tensile strength = 800 N/mm squared, 116000 psi

yield strength = 640 N/mm squared, 93000 psi

thanks again.
  • #5
i have pulled big block engines out of cars with two 3/8 bolts and an chain hooked to an old farm tractor with hydraulic forks..think i was about ten years old... was my younger not know better years..i would remove as many parts *** possible once placed on the engine opinion..
  • #6
Maybe if we keep this thread alive, a real mechanical engineer (or student thereof) will answer. I'm not one. The engine will probably get bolted to the engine stand before the theoretical discussion reaches a conclusion. Nevertheless, the engineering aspects would be interesting to discuss.

This link says that for fasteners, an empirical guide to shear strength is 60% of "minimum tensile strength". Is "minimum tensile strength" the same as "yield strength"?

The way the typical engine stand works is that there are 4 bolt holes on one end of the engine block where the transmission is normally attached. A vertical plate on the stand is bolted to the engine block by 4 bolts into those holes and the engine is held only by it's attachment to the plate. So the length of the engine block is going to matter. The block is going to be like a cantilever beam, only supported at one end. (There should be plenty of exercises in mechanical engineering texts about such beams!) I think a long engine block will exert more tension on the bolts than a short one of the same weight.
  • #7
I would recommend no more than 60% of yield strength in tension and 30% of yield strength in shear. It is better to design to a fraction of yield (metal deforms permanently but does not break) versus tensile (failure) strength.

I would flush your arrangement through all the formulas in:

Also consider bearing stress and shear tear out for the plates the bolts go into. Let me know if you need these formulas.
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  • #8
Probably your question is bit vague. What kind forces, moment are expected on the bolt. If it is just axial force, that is encountered by the bolt, then you asre good to go even with smaller bolt dimension.

Any by the way what is the length of thread engagement

For a less detailed calculation, I would suggest the calculators in the below link
  • #9
Bruca 003,
Your question is a bit vague. A picture would be a great help.

Please state how far apart are the bolts and the overall size of the engine(for CG).

It is not a good idea to calculate the direct shear stress only; bending stress also needs to be calculated ( with the possibility of torsion also).

If the bolts are to be under pure tension only, the bolts are more than enough to hold the engine.

I hope this helps.
  • #10
Stephen Tashi said:
Is "minimum tensile strength" the same as "yield strength"?
No. "Tensile strength" is an unclear, abbreviated term meaning tensile ultimate strength, not tensile yield strength.

bruca003: In post 1, are you saying your bolts are M12 x 1.75? Or are they M14 x 2? (The number after the "x" is thread pitch, in mm.) Measure the diameter of your bolts accurately in mm. And measure the axial length of, say, ten or fifteen threads, in mm. Let us know.

Assuming your engine and engine stand are the same as for this", then it appears the vertical bolt spacing is h1 = 164 mm, and it appears the distance from the bolts midpoint to the engine center of gravity (CG) is a1 = 360 mm (or less).

Using h1 = 164 mm, a1 = 360 mm, and yield factor of safety FSy = 1.70, it currently appears M12, property class 8.8 bolts will work, assuming you torque them to 42.0 N*m, and assuming you have a thread engagement length (Le) of at least 16 or 18 mm. However, please let us know if your h1, a1, and Le dimensions are different, because it can make a big difference in the stress results.

As saurya08 mentioned in post 9, what is the vertical spacing between your upper and lower bolts (h1)? And what is the horizontal distance from the bolts midpoint to the engine CG (a1)? Also, what is the upper bolt thread engagement length (Le) in the tapped holes? What is the tapped hole material? And are the threads of the upper tapped holes greased, or dry?
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1. What does the "8.8" in Grade 8.8 bolt strength refer to?

The "8.8" in Grade 8.8 bolt strength refers to the material strength of the bolt. It is a metric system that indicates the tensile strength of the bolt, which is measured in Newtons per square millimeter (N/mm²).

2. How is the strength of a Grade 8.8 bolt determined?

The strength of a Grade 8.8 bolt is determined through a series of tests, including tension, shear, and hardness tests. These tests measure the bolt's ability to resist forces and deform under pressure, which ultimately determines its strength rating.

3. What is the maximum load capacity for a Grade 8.8 bolt?

The maximum load capacity for a Grade 8.8 bolt varies depending on the size and length of the bolt. Generally, Grade 8.8 bolts can handle tensile loads ranging from 60,000 to 90,000 pounds per square inch (psi).

4. Are Grade 8.8 bolts suitable for all types of applications?

Grade 8.8 bolts are typically used in high-stress applications where shear forces and heavy loads are present. They are commonly used in construction, automotive, and machinery industries. However, it is important to consult with a structural engineer to determine if Grade 8.8 bolts are suitable for a specific application.

5. What are the benefits of using Grade 8.8 bolts over lower grade bolts?

Grade 8.8 bolts offer a higher level of strength and durability compared to lower grade bolts. They are able to withstand higher loads and provide better resistance to shear forces and deformations. This makes them ideal for use in critical and high-stress applications where safety and reliability are essential.

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