Farmall H noise

Got the tractor apart today.All 4 bolts flywheel to crankshaft sheared off.Parts book gives a part number for those bolts.Where can I find size so could pick up nearby.What do you think happened to break them,the 2 locks were still in place. Thanks Bill

Over tightening is a highly possible answer. When a bolt is over tightened, the strength of the bolt is compromised. The holding force is the tensile strength of the threads at the point they (usually) taper into the shank. If the bolt is at 90% of its strength, the bolt has only 10% of its strength left to hold things together when external force is applied. If 50% tight, 50% remains. Bolts torqued to 10% of their strength have 90% left. That is why the use of a torque wrench is now SOP in tire shops. IT applies to all bolts. Engineers know bolt strength, and the specification is the spec. Used bolts can also cause it. they fracture because they are already stretched. If actually loose, the bolts can snap from shock loading, or continued working in shear stress. I hope this helps. The use of other bolts is not recommended the shank size will not be appropriate, and even if grade 8, or titanium, they will not correct rotary shear at the shank. Original bolts are the real thing. Don't split it twice. JimN

Thanks for the input.A friend said the same thing adout overtightening. Bill

and I would offer that when you replace them, they should be at least GRADE 5 bolts.

Looking at how they broke will give a clue to the reason for the failure. They are more likely to fail from being too loose rather than too tight. A properly tightened bolt will be stretched a little bit but not so much they will not return to the same length when removed. (Torque to yield bolts are tightened to a point beyond where they will return to there original length. That is why they are to be replaced rather than reused.)

The friction between the flywheel and the crankshaft is what keeps the flywheel from moving on the crank. As long as the dowel pin is still in good shape it is unlikely that they sheared off. Sheared bolts will have the metal smeared off to one side. A bolt that has sheared on a baler is good example of this type of failure. A more likely cause in your case is they were not tight enough to have been stretched properly This will allow movement/vibration between the crank and flywheel. This little bit of movement causes the bolt to stretch just a bit, maybe less than .001 of an inch. This isn't much movement but over time it work hardens the metal to the point where it becomes brittle. If this is the reason for the failure the metal at the break will be crystallized. Broken head bolts usually display this type of failure.

A bolt failure from being over tightened will usually have a circular pattern in the metal as a result of the twisting.

I just wanted to add to my comment on the GRADE 5 bolts. I absolutely agree with JimN. My comment assumed that shank size to be used was appropriate. What you don't want to do is use "off the shelf" standard bolts. And I also agree DO NOT OVER TORQUE!

Is or was the dowel pin for flywheel still in place? The bolts are only intended to keep the flywheel sandwiched to the crank flange, the dowel pin is supposed to do the torque transfer. New bolts should be available at Case-IH, I picked up a set for an M acouple years ago. Grade five bolts would work, but I would use grade 8 to make sure, the cost wouldn"t be much more.

Matt there were three of us when we split the tractor.The flywheel did not come out with the engine.I think the dowel pin was still in crankshaft end.The flywheel stayed in tube housing.I was afraid flywheel would fall on sonebodys foot.Not sure where the dowel was.
Thanks Bill