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keisers1001
08-27-2004, 02:40 AM
There is no reason to beat a dead horse; I know that this subject has been discussed in detail, but I have not seen any calculations made. I was installing my bhj balancer and the mustang bolt (it is the same thread length as stock). I noticed that there was only about 5-7 threads engagement into the crank (approx .400”). I read all of the posts on this matter and it seems that there are some people that are not convinced of the potential risk of using the stock length bolt. I decided to run a quick calculation on the potential of stripping the threads out (bolt only):

Bolt size: M14 x 1.5
Shear diameter of the bolt (I used pitch diameter) = .50”
Shear area of the bolt: (.5 x pi x .4)/1.5 = .418in^2
Tensile strength of the bolt: 145000psi

Recommended torque = 130 ft.lbf = 1560 in.lbf
Load on bolt = 1560/(.1*.55) = 28364 lbf


Shear strength of the bolt: approx .5 x tensile (to be safe) = 72500psi
Shear stress = 28364/.418 = 67856 psi tensile stress


According to these numbers, these threads are close to shearing.

Conclusion….use these shorter bolts at your own risk!!!!!!!!

I reccommend a 50mm length.

XR7 Dave
08-27-2004, 08:05 AM
What about the stress on the threads themselves? I would think that you are at closer risk of stripping out the threads than shearing the bolt. However, I have a feeling those numbers are going to be a little more difficult to calculate. :D

TBone95
08-27-2004, 10:18 AM
What about the stress on the threads themselves? I would think that you are at closer risk of stripping out the threads than shearing the bolt. However, I have a feeling those numbers are going to be a little more difficult to calculate. :D

Dave,

That's what he did, and it seems pretty close to me. He at least got the shear area very close, I don't have time to check his load equation.

Using "Ase=pi*Knmax*te*n*Le" I came up with .410in^2 shear area for the external threads. If the load is correct then a longer bolt would definately be a good idea to reduce that stress. How much that stress is important with a pressed on balancer is another matter...

-Travis

Rich Thomson
08-27-2004, 11:03 AM
Excellent math data to further justify the use of a longer bolt. A 55mm long bolt will get the thread engagement back to about stock depth of .80" I choose a 60mm long bolt because the crank thread depth with a 60mm long bolt still allows for a 10mm margin before bottoming out. But any length is better than the stock bolt length of 40mm.

I have also spoken to BHJ and they have sent their findings to George over this counter bore issue. Hopefully we will see a updated BHJ FAQ coming soon. I do know what BHJ's position is but will wait for George's post.

keisers1001
08-27-2004, 12:55 PM
Excellent math data to further justify the use of a longer bolt. A 55mm long bolt will get the thread engagement back to about stock depth of .80" I choose a 60mm long bolt because the crank thread depth with a 60mm long bolt still allows for a 10mm margin before bottoming out. But any length is better than the stock bolt length of 40mm.

I have also spoken to BHJ and they have sent their findings to George over this counter bore issue. Hopefully we will see a updated BHJ FAQ coming soon. I do know what BHJ's position is but will wait for George's post.

Be very careful with the 60mm!!!! I used a 60mm (all that they had in stock at the time) but had to trim it about .300". The threads bottomed out in my crank at the exact same time the underside of the head made contact with the washer. This could potentially result in a false loading of the bolt.

John

Rich Thomson
08-27-2004, 06:42 PM
Be very careful with the 60mm!!!! I used a 60mm (all that they had in stock at the time) but had to trim it about .300". The threads bottomed out in my crank at the exact same time the underside of the head made contact with the washer. This could potentially result in a false loading of the bolt.

John

Before installing the balancer check, clear and clean the crank threads with the bolt. I used the bolt as a tap to verify nothing was in the threads to stop it.

This were part of my findings. All measuremants were done myself with digital calipers for accuracy.

Stock bolt length is 40mm
Stock washer thickness is 5.5mm
Available thread depth is 34.5mm

Longer "60mm" bolt length is actually 57.2mm
Stock washer thickness of 5.5mm
Available thread depth is 51.7mm

Crankshaft thread depth is 42mm
Total crankshaft depth is 47mm

Now the BHJ is designed to fit the same as the OEM. A step in the crank snout which is 2" from the front of the crank stops the balancer from pressing down over the crank any farther. The extra 12.7mm added to the front of the balancer has to be factored in.

12.7mm additional material in the snout
42mm crankshaft thread depth
54.7mm total length from face of BHJ snout to bottom of threads in crank

54.7mm total snout/crank thread depth available w/BHJ
- 51.7mm total thread depth available on the 60mm bolt
===========
3mm or .118" additional depth before running out of threads in the crank

Which is 2.5 threads on the bolt

I do see your issue. A 55mm bolt would work better and offer more margin. I will switch to the shorter bolt now.

Thanks!

ThunderDave
08-27-2004, 06:51 PM
I may be replacing my balancer soon with a BHJ. Does the new bolt come with the balancer, what size is it and who would have the 50mm bolt if that one is not suitable? Also, is the BHJ ready to install or is there a mod for it to fit the crankshaft?


Thanks,

David

Rich Thomson
08-27-2004, 07:42 PM
I may be replacing my balancer soon with a BHJ. Does the new bolt come with the balancer, what size is it and who would have the 50mm bolt if that one is not suitable? Also, is the BHJ ready to install or is there a mod for it to fit the crankshaft?


Thanks,

David


I wrote a BHJ How-To. I sell replacement bolts. I do not sell the BHJ balancers. Contact www.spinningwheels-sc.com he has a bulk order coming to him next week.

BHJ Install How-To (http://www.mn12performance.com/mn12how-to/BHJ/BHJ-install.html)

ThunderDave
08-28-2004, 06:44 AM
I wrote a BHJ How-To. I sell replacement bolts. I do not sell the BHJ balancers. Contact www.spinningwheels-sc.com he has a bulk order coming to him next week.

BHJ Install How-To (http://www.mn12performance.com/mn12how-to/BHJ/BHJ-install.html)


Yeah Rich, if I get one, it will be from Victor. I've already been in touch with him.


Thanks!

David