Hey F-I-T ?

I said that if you go to a dealer and buy a replacement bolt today, it will be a grade 8 because the old "High Strength" fastener type is now obsolete. I also said that I trust Albert of Renaissance Tractor's advice who, in his seminars, highly recommends Grade 8, fine thread fasteners, with hardened washers under tall nuts, torqued to the spec for grade 8. I use the torque for the coarse thread, even though you can get a bit more on the fine thread since it has a greater cross-sectional area since the threads are not as deep.

I also said that you can crack any casting you want, including a flywheel if you use a big enough pipe with no regard to measured torque, so to say that 370 lbs, or even 475 lbs will crack an ear and 265 will not is a guess, and only a guess. It is apparane that the engineers wanted to get as much pinch as possible, or else they would have and could have specified a torque reading that even below that of the maximum of a grade 5 or high strength bolt, but thet chose to torque it to the maximum that the fastener could stand. That sounds to me like they were more worried about the strength of the bolt than the strength of the flywheel casting.

It is my opinion, and only my opinion, that the original torque specification was not based on the force that the flywheel "ears" could stand, but on the maximum torque of the "high strength" fasteners of the day. If John Deere engineers had had Grade 8 available to them, I believe they would have specified grade 8 and not grade 5. and increased the specification to 370, but I admit that this is an assumption on my part.

I also said that of the flywheels I have seen cracked, only two that I could see were the result of excessive fastener torque breaking off the ears, but generally other problems such as stress risers from burrs and nicks on the crank splines or on the internal broached splines opf the flywheel caused a stress point that gave way. Many flywheels have cracked over the years, but not just on diesels, and not just around the ears. In the two cases where an ear was broken off on a diesel flywheel, one of those had grade 3 bolts installed. The torque to break the remaining bolt loose was beyond the measurement of my 400 ft-lb wrench, which I had set up with a two foot amplifier, so the torque was probably in excess of 700 lbs. The grade 3 bolt that remained was well stretched.

So, I did say that I like to use grade 8 bolts, torqued to spec for the reasons stated above.

So it sounds like we disagree.

Frank

Whether the bolt used in the "good old days" was grade 5 or grade 8, I am not here to debate either, although I don't believe there is a grade 8 bolt in my John Deere except perhaps for the wheel hubs, and that's even doubtful to me. There is simply no need!

And there is also (to me) no need to apply torque several hundred ft-lbs of torque to a flywheel bolt, and using SAE thread decreases the pitch thus increases the force of a given amount of torque -- oh I now what the charts say -- there is very little difference, but (again) I am not convinced.

I would like to know the actual meaning of a "high-strength" fastener in terms of today's way of grading them. And until I hear some kind of a reliable definition there, I will continue to advise folks to steer clear of using grade 8 bolts in most cases except possibly to fabricate a pin for some work-around thing.

I will grant you that use of ASTM-B7 threaded rod is not suitable for engine head studs & have so advised others. So there are cases where I have listened! Have a Great Day. (PatB)

The main advantage of fine threads is that they leave a greater cross-sectional area of the bolt, and thus a fine thread bolt is capable of greater tensile forces as compared to a coarse thread bolt. So, you can safely use greater torque with a fine thread fastener.

I"m curious about your statement implying "ASTM B7" (assume you mean ASTM A193, grade B7) isn"t suitable for head studs. Why?

Thanks for your contributions - looking forward to your response.

• Fine and Coarse Thread Trivia

The high strength fasteners of old, using 3/4" for an example, was rated at a tensile strength about 20% greater than today's grade 5. Also the max torque to be applied was about 20% greater. You can find that in any older vintage Machinists Handbook.

I listed my reasons, referenced who I regard as a quality resource, used my experience taken from many years and many diesel projects, and and I stated my case.

The debate's over.

Remember. This discussion thread started because of folks saying that letting a diesel coast to a stop using the decompression lever saved crankshaft splines, and as I said then:

Aitn' no way, ain't no how.

Frank

The original, and singular point of discussion from several days ago, which has yet to be answered is:

Does a Grade 8 fastener torqued to maximum (370 ft-lbs) cause diesel flywheel ears to break? And I say you can't answer to the affirmative unless you know what the shear of those ears are. Since no ones appears to have access to that data, it is all suppostion and conjecture.

Again, I can read a fastener chart (there is one on my webpage in fact) and I own a proper 400 ft-lb Proto torque wrench. I've been to Textron Corp's fastener school,...and, I have never had a diesel flywheel ear to crack, though I have seen two flywheels with such cracks, but neither had Grade 8 bolts, so how can the Grade 8 bolt be the problem? Hyper-torquing with an uncalibrated long pipe on a wrench causes this, as well as previous stress risers of sometimes indeterminant origin. And sometimes a flywheel has a flaw that shows up years later.

Does anyone remember the pictures Clooney posted about two years ago of the 1/2" longer original high-strengths he removed? That does not happen at an extra 80 or 90 ft-lbs of torque. If you think it does, put one in your vise through 4 inches of steel. Give it a crank every day and see how much torque it takes over time to stretch it even 1/8". You won't have a torque wrench big enough to measure it.

I wish we would hear from all of those people who had diesel flywheel ears crack from going to a Grade 8 bolt on a diesel flywheel, and then we'll balance those against the number who can't keep them tight, or had to go to taper lock adapters because the previous owner could not either.

The flywheels I have installed this way are tight and they stay tight while running on my dyno. I'm going to stay with Grade 8's, tall nuts, and hardened washers under them so that the force is spread evenly across the ear.

Frank