New problem tighten bolts

[ch1ch2]

JD 302 old construction grade tractor work, horse for a long time.
Two stage clutch. PTO quit clutching. Split the tractor found 1 or the 3 arms broken. JD does not sell a clutch pack assembly, you have to buy individual parts at ridiculous prices.
Bought a new arm and started reassembly. Six bolts attach clutch assembly to the flywheel. Manual says to replace the bolts from grade D to grade F.

New to me. Never heard of grade D or F bolts. Manual says to torque to 120 ft/lbs. Figured out I already have grade F bolts. As I tighten every thing seems normal until @50 ft/lbs and the 2 bolts seem to not get any tighter but like something is stripping. One bolt breaks. Bought 6 grade 8 bolts. Bolts tighten to around 50 ft/lbs and that odd feeling returns. Does not seem to tighten. Pulled it apart again and nothing seems to be stripping. Scared to go on. What should I do??????
HELP!

 

[AWSubie]

Grade F is equivalent to Grade 5. What is the diameter of the bolt shank?

 

[ch1ch2]

Grade F is equivalent to Grade 5. What is the diameter of the bolt shank?

Not sure. I used a 5/8 socket if I remember right, if not it was a 9/16.

 

[ch1ch2]

Grade F is equivalent to Grade 5. What is the diameter of the bolt shank?

From what I found on the internet an F had a lot lower shear strength.

 

[ch1ch2]

The tractor is at my sons house about1 mile away.

 

[ch1ch2]

I see you are in FTW. I called Arrow Bolt in Euless, and they never heard of a grade D or F.

 

[AWSubie]

Once you know the shank size you can figure the torque you need from a chart like the one found here
Bolt Depot - US Recommended Bolt Torque Table

Do not lubricate the threads.

 

[ch1ch2]

Once you know the shank size you can figure the torque you need from a chart like the one found here
Bolt Depot - US Recommended Bolt Torque Table

Do not lubricate the threads.

That is a very good thought!
Maybe the manual is mis-printed. The 120 does seem way out of line for the weak bolts and the chart listings.

 

[ch1ch2]

I went to another bolt companies web site for a torque chart and it shows torque for 1/4 and 5/16 bolts in in/lbs. Maybe the manual is mis-printed in ft/lbs instead of in/lbs.

 

[Creamer]

A 9/16" wrench is for a 3/8" bolt which should not be 120 ft-lbs - 120 in-lbs would be more like it but that does seem a little light.

I am not familiar with the application but is this a light torque load where it is locked some other way and they are more for shear - if so 120 in-lb would be where I would put them.

Do you see what felt like it was stripping?

 

[ch1ch2]

A 9/16" wrench is for a 3/8" bolt which should not be 120 ft-lbs - 120 in-lbs would be more like it but that does seem a little light.

I am not familiar with the application but is this a light torque load where it is locked some other way and they are more for shear - if so 120 in-lb would be where I would put them.

Do you see what felt like it was stripping?

I felt the stripping feel but could not see any stripping damage.

 

[ch1ch2]

I could not see any damage form what felt like stripping.

But we all know if it felt like it striped it probably did.

 

[Creamer]

Do the bolts free thread in fine? Because as the stripping start your threads start to shear but you may not notice it if you just started to feel it and stopped but your thread pitch will have been messed up. If your thread pitch is good so that the bolts freely thread in (may want to use longer bolts to check the threads so they do not tighten up) then you should be good.

 

[ch1ch2]

Do the bolts free thread in fine? Because as the stripping start your threads start to shear but you may not notice it if you just started to feel it and stopped but your thread pitch will have been messed up. If your thread pitch is good so that the bolts freely thread in (may want to use longer bolts to check the threads so they do not tighten up) then you should be good.

I think I will take it apart one more time and run the bolts all the way in without the clutch pack before a put it together again.

 

[ch1ch2]

Thanks to all.

I think the issue is solved.

If not I will be back asking for more help.

I hate it when I think I should have figured it out on my own. Guess I am not as smart as I think I am. At least I am smart enough to ask for help.

 

[Creamer]

Don't feel bad - I get tunnel vision when things just don't make sense. I need to just sit back and think about them. this is a good forum to do so in as we will come at it from a different viewpoint. Good luck in getting it all back together.

 

[bcp]

Deere bolt specs :



Bruce


PS: added heading

 

[MORRISONSTEEL]

Grade F is equivalent to Grade 5. What is the diameter of the bolt shank?

Backwards, F=8, D=5

 

[ch1ch2]

What does JDM stand for? and, ASTM?
I always thought SAE was the standard.

 

[bcp]

JDM is a John Deere standard.

Bruce