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

 

[Dex]

Hack saw! What is that? More power! That is why the sawall was invented!

 

[firemanpat2910]

Yes I use grade 5 bolts. I do agree that a slip clutch is far better. I do not know what grade is reccomended on my cutter,nor am I suggesting that anyone uses a higher grade bolt than their unit is rated for. On the other hand I know of one cutter that has a link pin in it, It never shears and the drive shaft has some definate wobble to it. But a grade 2 in mine will snap as soon as it is engaged.

 

[Soundguy]

What rpm do you engage the pto at? Do you feather it in?

Soundguy

 

[firemanpat2910]

Rpm as low as it will go. no feathering on mine its on or off. Or if there is a way to feather I have not figured it out. Pto does not use the clutch on my Ford 2910 just slide the lever and its on.

 

[Soundguy]

Rpm as low as it will go. no feathering on mine its on or off. Or if there is a way to feather I have not figured it out. Pto does not use the clutch on my Ford 2910 just slide the lever and its on.

If your trans is the ford independent trans.. like the 8x2, etc.. with the left ankle pto engage lever, ( like has been used on my 1975 ford 5000 thru my 2002 NH 7610s ) then you can indeed feather it.

In your operators manual, there should be a section on engaging / disengaging the pto. In my manual it states to set idle low, slowly slide the lever forward to engage.. (actually uses the word 'feather' ).. It states to not be in the middle range for more than a few seconds, so as to not prematurely wear the pto clutch. Same info for disengage.. very low rpm.. so as not to wear pto brake, slowly disengage lever, and feather it out.. not staying in the middle range for more than a few seconds so as to not wear the pto clutch.

Jerking a pto load to start it is a horrible thing to do to a tranny and the implement.. if it can be prevented. And that grade 5 shear pin... If it's repalcing a grade 2.. that's also a red flag. ( if you do have the 8x2 tranny.. it's fairly bullet proof.. however.. you can stack the caseing plumb full of 5$ bills to repair it if it shells out....and that's just the parts.. not counting labor. )

I have seen some electric solenoid engaged independent pto clutches.. and those can be problematic with shock loads.. not much to do about them.. unless they have a soft engage feature...

Soundguy

 

[Ford960]

The PTO shaft for my 5' BH uses 5/16" shear bolts and I started going through them left and right because I was using grade 2 bolts as recommended by Bush Hog. Then I noticed that they were talking about 1/2" bolts so I switched to a grade 5 bolt and haven't had anymore problems.

I just bought a used heavy duty 5' bush hog with a slip clutch and had to shorten the PTO shaft off my light duty cutter. The slip clutch has 3 tensioning bolts and 2 clutch discs. But I see that there are no springs under the bolts and they appear to have been replaced with a stack of washers.

Now I have to find out what springs I need to get and set up the correct tension for the clutch to work.

If it would just stop raining.

 

[Ford960]

Hack saw! What is that? More power! That is why the sawall was invented!

Even better is a 4" grinder w/cut-off wheel. Cut my shaft yesterday in less than a minute and without all the shaking and jarring of a recipricating sawz-all.
In fact that 4" grinder is the best thing that I ever bought at Harbor Freight for $17.99. Next time that I get to HF I'm going to buy another one because if I wear out this one I would go into severe withdrawals.

 

[Soundguy]

The PTO shaft for my 5' BH uses 5/16" shear bolts and I started going through them left and right because I was using grade 2 bolts as recommended by Bush Hog. Then I noticed that they were talking about 1/2" bolts so I switched to a grade 5 bolt and haven't had anymore problems.

What are you refering to when you say that "they were talking about 1/2" bolts".

Is your machine setup for 5/16 or 1/2?

If there is some slop or play in the yoke to shaft coupling area.. then that will cause premature shear pin breakage. Incorrect sized pins/bolts will also cause premature breakage. Using incorrect grade shear pins, without manufacturer approval.. can cause expensive tranny and gear box repairs.

I'd much rather go thru a few grade 2 pins ever time i mow ( or fix the deficiency ) rather than replace the tranny in my tractor even once!

Soundguy

 

[normde2001]

Did you, by chance go from a gear shift tractor, where you engage the PTO, then slowly let out the clutch to get it going, to an HST, where you engage the PTO, and it is instantly turning at engine RPM speed?

 

[Soundguy]

I hadn't thought about the HST issue.. or how they come up with independent clutch. I had just assumed that the pto clutch would allow feathering there too.. but again..I've not used any HST tractors in a while.

For what it's worth, gear shift tractors can have independent pto too. And from what i can find int he resource books.. a NH 2910 either has an 8x2 or 8x4 optional tranny..

Anyone with an HST care to drop in and give info about your pto clutch setup.. list makes and model, and size.. etc. any other helpfull info you might have too.

Soundguy