Without having the proper torque specifications, assembling an engine, is just asking for failure.
This is especially true on today’s lightweight engines that use mostly aluminum castings.
Torque specifications are crucial information whenever you make repairs.
So, Most people do not realize that a bolt or a stud acts like a big spring to hold parts together.
As a result, It has to be stretched a certain amount in order to do its job.
Even though there are tools to measure bolt stretch, most people do not own them.
But almost anyone who does mechanical work will have a torque wrench.
Most engine torque specifications require 30w engine oil to get the correct stretch on the bolt.
Using the wrong lubricant will affect the clamping load.
Some specialty fasteners require a specific lubricant. It is important to know which lube, if any, the bolt requires and to use it when tightening it.
A torque wrench really only senses friction. For example, take a bolt with a torque specification of 50 lb ft. Tighten it with no lubrication at all and mark it so that you know where it stopped turning. Now loosen the bolt and apply some engine oil to the threads and under the head of the bolt.
Consequently, when you torque it again it will most certainly turn considerably further, which means it has stretched more. This is why it is so important to know what, if any, lubricant the manufacturer specifies for each fastener.
It is also important to pull on the torque wrench slowly and evenly without any type of jerking motions.
Torque Plus Angle Method Of Tightening
This method of tightening fasteners in engines is relatively new. The reason for it is to get a more consistent stretch in the bolts. Since a torque wrench senses friction, there are a lot of variables that can affect proper tightening.
Start by using the torque wrench for a small initial torque to seat the bolt. Next turn the bolt a certain number of degrees of rotation. Now the manufacturer can be pretty sure that the correct stretch will apply to the bolt.
An example would be to tighten the bolt to 20 lb ft and then turn it an additional 90 degrees. There are torque angle tools available that will work with a standard ratchet. These tools enable you to accurately measure the number of degrees you are turning the bolt. Fel Pro makes a very inexpensive plastic version that is great for the home mechanic.
What About Torque To Yield ?-Torque Specifications
Torque to yield fasteners are stretched to the point that they are just about to “yield” or lose their springiness. These types of fasteners can only be used once and then must be replaced.
Torque Plus Angle Is Not The Same As Torque To Yield !!-Torque Specifications
A lot of people, including professional technicians do not understand that just because a bolt uses the “torque plus angle” method of tightening, it is not necessarily a “torque to yield” (TTY) bolt. For example, Honda has used the “torque plus angle” method of tightening head bolts for many years. I do not think that any of their head bolts require replacing so they are not “torque to yield” bolts.
Not all torque wrenches are universally adaptable to all jobs. It’s important to choose one that features your torque value requirement in the middle of its range. For instance, if you need to tighten a fastener to 100 ft.-lbs., don’t use a torque wrench model that has an upper range limit of 100 ft.-lbs. Instead, use one that features a range of, say, 25 to 250 ft.-lbs. If tightening a fastener to 50 ft.-lbs., use a torque wrench that has an upper limit of about 100 ft.-lbs., and so on. So you may need torque wrenches with different ranges, depending on the type of work that enters your shop.
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