Engine Main bearing bolt yielding help 9

[preload]

Hi

I am new to this forum, but used to be in ROM (Read only mode). I am new to the fastening field but have quite a bit knowledge. My problem is we are yielding some bearing bolts right after installation on the cylinder block and crank case joint. I will provide you guys the info on bolt and joint parts and environment.

Bolt – carbon and low alloy steel flanged head 3/8-16 grade 8 bolt.
Joint – both cyclinder head and crankcase are made of Aluminum – copper alloy casting (soft joint compare to the bolt)

We also use a bead of gel seal in between the mating parts (cylinder head and crank case), when in contact, the gel seal uniformaly gets distributed on the mating surfaces. (making the joint even more soft?)

We make two engines V4 and V6. for v4 we have 6 bearing bolts and for v6 we have 8 bearing bolts. The tool used is two spindle dc electric torque angle monitor. For v6 We do bolts 1-2 then 3-4 then 5-6 then 7-8 and again do 1-2 (re torque due to elastic interaction) (I will try to upload a picture for better understanding)

Torque used is 31-15 lbs-ft on each bolt.Min proof load of the bolt is 9300 lbs.

Do you guys know why we are yielding bolts on a soft joint (if it is?)

 

[desertfox]

Hi dimjim

Fair point you make about the hole in the casting; although it won't change the variation between them it does change the actual value of the stress.
To reach 43ksi according to me the hole for the screw would need to be 0.4929" dia based on a .72" flat washer hex head.
Preload what is the hole clearence size in the component? and we touched on embedding previously have you found any marks on the surface of the component under the screw head?

regards

desertfox

 

[preload]

Desertfox,

the dia of the hole is 0.4375" and regarding maks on the underhead surface, yes, but it dosent look like a damage though.

 

[preload]

Desertfox,

Finally I got the clampload specification.

6000 lbs - 8000 lbs and 7000 lbs being the target clamp load. we decided to do torque-angle signature. we also decided (not full confirmed though) not to use any lube oil (just the dry bolts with cad plating). will be doing some tests with dry bolts and get the torque angle graphs and then will go from there. will let you guys know how it goes

 

[desertfox]

Hi preload

Thanks for the update

 

[desertfox]

Hi preload

You might find without lube your clamping load spread will
be greater, and the method your using might not achieve
6000-8000lb clamp force i think the method you are going to use is about +/- 15%.

regards

desertfox

 

[preload]

Desertfox,

I thought torque-angle control is independent of friction. The how lube or no lube matters?

And also we have some room on the higher limit as 9300lb is the min proof load and max spec is 8000 lbs.

 

[desertfox]

Hi preload

We mentioned using ultrasonics to measure bolt elongation
which is very accurate compared to the method your using.
I suggested earlier that you make some joints dry to see if the bolt failure stopped.
If you don't use lube you need a higher torque setting to overcome increased friction, using lube reduces the torque required to achieve clamp load, have a look at some of the earlier posts.
I agree now you have a clamping load you can now clarify a method to achieve that and that if you aim for 7000lbs with lube then yes you can reduce your torque.

regards

desertfox

regards

desertfox

 

[preload]

yup I agree, we will play with torque for sure.
anyway I will et you know how consistent things show up after we do some experiments with dry bolts. and if we are consistently holding the clamp spec then we are good to go.

 

[yates]

Does this thread get the record for most posts ? Who said fasteners were simple ?