shear bolt blues, need advice

[kossetx]

I ran the same shear bolt on my 5' shredder for 14 years with my old 25 hp tractor. I mowed down some nasty stuff. If I could push it down with the tractor, I could shread it up.

New 40 hp tractor, same shredder. The shear pin shears if I even approach something larger than 1.5". I replace the bolt daily when my wife drives the tractor. I'm using too many bolts just mowing a pasture. A new 6' shredder is in the near future so this one can go back on the 25, but in the mean time do I go to a slightly higher grade bolt to use on the 40? The current shear bolt is a grade 1, I think. No marks on the head. If I remember right the next grade bolt has 3 marks. I know the bolt is to protect the gearbox, but I don't want to constantly be replacing the bolt either. Advice? TIA, MP

 

[firemanpat2910]

with my old shredder anything less than a grade 5 breaks when I engage the pto even if blades are clean, clear and in the air. You might check and be sure blades pivot freely and the stump jumper is tight. these will make mine shear also. Do you know what brand cutter you have? I cant imagine designing one with a weak grade bolt. A slip clutch would be a cheaper alterative to a new cutter
Bolt Grades

Grade - 2

Low Carbon Steel. Economical for use in non-critical applications where the fastener is not subject to extreme temperatures or stress.

Grade - 5

Medium Carbon Steel, Quenched and Tempered. Has greater tensile strength than a Grade-2. Yield-to-tensile ration is the lowest of all heat-treated steels.

Grade - 8

Medium Carbon Alloy Steel, Quenched and Tempered. Has greater tensile strength than a Grade-5. Designed for use in high stress applications.

 

[Doc_Bob]

I ran the same shear bolt on my 5' shredder for 14 years with my old 25 hp tractor. I mowed down some nasty stuff. If I could push it down with the tractor, I could shread it up.

New 40 hp tractor, same shredder. The shear pin shears if I even approach something larger than 1.5". I replace the bolt daily when my wife drives the tractor. I'm using too many bolts just mowing a pasture. A new 6' shredder is in the near future so this one can go back on the 25, but in the mean time do I go to a slightly higher grade bolt to use on the 40? The current shear bolt is a grade 1, I think. No marks on the head. If I remember right the next grade bolt has 3 marks. I know the bolt is to protect the gearbox, but I don't want to constantly be replacing the bolt either. Advice? TIA, MP

Sounds like the shear pin is doing it's job. I assume more HP through PTO=more strain on shredder=more heat=possibly more damage to implement if shear pin does not "fail". Be careful, the shear pin is failing for a very good reason. Is the gear box rated for the PTO HP of your new machine?????????????
Bob

 

[BB_TX]

Here is a link to bolt grades and strengths. There is a pretty substantial jump in strength as you go up. Seems a lot of people use grade 5 and even grade 8, but I would be hesitant to. I shear something like 4-5 a year on a 6' cutter with 27 PTO hp.

http://www.textronfasteningsystems.com/eng_tools_f/grades.html

 

[john_bud]

Kossetx,

I agree with Bob! Do you really want something stronger than a grade 2 bolt, but weaker than a grade 5 INSIDE the tractor or cutter to take the shock and break? The extra stress can form cracks in housings and other areas - not that it will - but it surely can.

Errrr - makes me shiver thinking about it -- errrr...

Why not just get a whole PTO driveline with slip clutch from Surpluscenter.com for under a hundred bucks? Last I looked they had new 60 hp ones in stock for either $79 or $89.

jb

 

[RobJ]

What size sheer bolts are these? 1/2"?

 

[kossetx]

Pat, The blades are free and the SJ tight. I was wondering if anyone uses a higher grade bolt. You are saying you do right?

Rob, Yes, 1/2".

 

[SPYDERLK]

#1,
Im thinking your old 25 hp tractor PTO clutch slipped a little under shock loads and spared the shear bolt. The new, higher hp tractor has a proportionaly stronger pto clutch that wont slip before the bolt shears. What HP gearbox is on the bushog? If its a 100hp you can probably put in a larger shear bolt and safely foist the slip duties on the 40 hp pto clutch.
Larry

 

[Soundguy]

Unless you are good at replacing transmissions.. you NEVER use a higher grade shear bolt than recomended by the manufacturer.. The no mark on is grade2.. 3 marks is grade 5. Only do it if you have the extra cash laying around for a new mower.. or new pto section for the tractor.

It's quite possible that your 25hp tractor didn't have quite enough torque to run the 5' mower and shear the bolt... in other words.. the mower may have bogged down a bit when it hit a load, and that bogging actually allowd the laod to clear without shearing the bolt. I notice that on my 8n. If I hit an ant mound with my 27 hp 8n and 5' mower.. i simply drop engine rpm for a few seconds.. If I hit that same ant mount when i had my 33 hp NH 1920 the engine rpm never dropped, and the shear pin died immediatly. it was the momentary bog down in the engine rpm that was lowering the load and thus not shearing the pin..

Int he same way.. your bigger tractor has excess 'nads' for a 5' mower.. and the shear pin is seeing it...

Stick to the grade 2 shear pin... Perhaps consider a slip clutch....

Soundguy

I ran the same shear bolt on my 5' shredder for 14 years with my old 25 hp tractor. I mowed down some nasty stuff. If I could push it down with the tractor, I could shread it up.

New 40 hp tractor, same shredder. The shear pin shears if I even approach something larger than 1.5". I replace the bolt daily when my wife drives the tractor. I'm using too many bolts just mowing a pasture. A new 6' shredder is in the near future so this one can go back on the 25, but in the mean time do I go to a slightly higher grade bolt to use on the 40? The current shear bolt is a grade 1, I think. No marks on the head. If I remember right the next grade bolt has 3 marks. I know the bolt is to protect the gearbox, but I don't want to constantly be replacing the bolt either. Advice? TIA, MP

 

[john_bud]

here's the link for a $79.95 60 hp slip clutch. It may be too long, but that's why God invented hack saws...

http://www.surpluscenter.com/item.asp?UID=2006062908082639&item=1-1917&catname=


jb