Modern Vespa

If you need more clamping force use a bigger bolt. Don't over stress an under sized one.

Sure, but we are talking about TTY's here and the fact they should never be re-used. Although you make a good, but unrelated point.

crescent wrenches and vice grips come in many sizes. If you collect enough of them, you don't need no fancy 'tools' to fix stuff.
If your crescent wrench is destroying the nut, switch to vice grips.
It's okay to hit your crescent wrench or vice grips with another crescent wrench or vice grips if the nut won't budge.
If you can dodge a wrench, you can dodge a ball.
While still extremely possible, you are less likely to screw a TTY fastener up with a crescent wrench than the other kind.
You can't skin a squirrel with a torque wrench.

I think you'll find you can! lol.

Yep, you beat that squirrel enough with that torque wrench, the skin will come off.

Wait, shouldn't we be cross-posting this in Protips ?

Agreed. All MV members should know how to skin a squirrel with a torque wrench.

As I understand it TTY bolts actually irreversibly stretch when properly tightened, that is, the bolt is perceptibly longer when you take it out than when you put it in. Not sure how many times you can re-use it before it either stops stretching (overtorqued) or breaks. Certainly, in a critical location, I don't want to find out. I doubt you get the proper clamping force when you reuse it either. Maybe not that important in some roles.

I think the only time I ran across them was on the output flange on the transmission of my old Airhead. Would have been a pain in the butt (not to mention catastrophic) if they failed. So I ponied up the couple of bucks, and rode it for 25 years after without a problem, at that location anyway.

If you torque to yield the first time using a torque wrench to see what torque was applied to get it to final position, you could get a good grasp on how much torque to apply when re-installing. I'm thinking beam type here, not a clicker. Torque is torque. Torque to yield is a good way to get a more accurate clamping force.

Torque to yield exists because of automated assembly lines. It is easier for robots to do properly. Back when the first robots started to appear on the assembly lines, it was easier to get them to turn a nut a certain amount than to turn it to a specific torque setting.

Torque to Yield has been about for decades and decades and has nothing to do with production line assembly. TTY must still be torqued to the correct torque, and only then can it be tightened by degree. So tty actually adds more complication to the assembly process. But it has distinct engineering advantages when designing engines allowing for smaller fixings, holes etc and greater strength and accuracy, less failure rate. But bolts should never be reused due to high failure rate if done so. To reiterate, TTY has to be torqued first, then set by degree. Depending on which assembly torquing machinery is being used it needs two different processes to be carried out. It's far easier for robots to just torque a fastener than tty it and has been for decades.

This would make for fascinating reading if only you were right. What I think you are saying is that TTY was around a long time, and came into being about when automation started appearing on assembly lines, but has nothing to do with that. It's just a coincidence. What decade do you think it first appeared on an assembly line, and where?

I wonder why you think I'm wrong Motovista. Please explain. You certainly come out with some amusing "corkers" Lol.

TTY's have been about since not long after the introduction of alloy cylinder heads on engines. It was realised too that ttys could be used to solve issues elsewhere on vehicles even before that.

A main reason for tty introduction on engines was head gasket failure rates were high on engines with cast iron block and alloy heads. The expansion rates are different. New ways of clamping were needed to allow for the movement caused by the different expansion rates. The use of ttys allows for this extra movement without compromising clamping force. or breaking the bolts or studs (see link below explaining why ttys were introduced).

TTYs didn't come about because of engine assembly robots finding it easier to fit them as you are saying. They came about because of engineering requirements/needs.

https://dannysengineportal.com/torque-to-yield-bolts-what-are-they/

Incidentally, the first assembly robots were introduces in some car plants in the 1920's, but the computer controlled era started in 1961 onwards and really kicked off in 1969. Robots have nothing to do with the tty introduction. I designed my first engine with ttys in 1980 but ttys existed before then. The aircraft industry used them long before that.

Stromrider, not trying to get too far off topic but wonder if you know if there is a difference between TTY and just bolts tightened by the "torque turn" method. They both use a low initial torque plus a set number of addition degrees to get to the final clamping load.

I recall some time back in the 1980's working on a Deutz Diesel air cooled engine. I had no manual for it. I talked to the dealer and was told the torque for the head nuts was something like, Snug them evenly to about 35 Lb./Ft. then turn each one in a crisscross pattern 90º at a time till I got a full turn on each one.

kshansen, the bolts you were using were almost certainly tty bolts.

Well for the Deutz the dealer never suggested replacing the studs that held the head and cylinders to the crankcase. I would have thought if that was a standard procedure for that engine they would have done that to make another sale. But who knows?

As for some of the other engines I worked on like the Cat diesel C13 I just checked and the main and rod bolts are torqued to 111 Ft./Lb on mains and 95 Ft./Lb. on rods and both are then turned another 60º. Neither the disassembly manual or assembly manual mention anything about replacing bolts.

I was on tour of the International/Ford 7.3 Power Stroke Diesel Production line at the International Engine Plant in Indianapolis and they were using a torque wrench on the head bolts that tightened all the bolts at once in the proper order, so they to make the machines to torque bolts no problem. And the Power Stroke does not use TTY bolts so they were torque to spec.

We were allowed to talk to the team on the line and they would answer questions. Ford Plant didn't allow that.

Many years ago when I was working on Rolls-Royce Diesel engines, the prescribed method of tightening the connecting rod big end bearings was to "snug" the nut down, and then measure the length of the bolt with a micrometer. The bolt was then tightened until it had stretched a specified amount, again measured with the micrometer. The bolts, which were of a "waisted" design were very accurately made, with a ground finish on the fitted diameter and length, and were changed at every overhaul. Don`t know if that is "torque to yield" or "torque to stretch" !!