bitboy
23.06.2021 17:07:17
How do you reuse torque to yield bolts?
See full version: How do I know if my head bolts are torque to yield
How do you reuse torque to yield bolts?
Subsequently, question is, how much torque is required for tightening the cylinder head? If an engine produces 1,500 pounds of pressure and the cylinder head has 8 bolts, then each bolt must be tightened to 187 foot-pounds of torque to secure the cylinder head to the block. more
You can identify a torque-to-yield or stretch-style fastener by the narrow shank just below the washer face and before the thread run. A bolt of this design is intended to be installed in the plastic range and cannot be reused after being tightened once. [links]
Torque-to-yield (TTY) head bolts are designed to stretch when used. Once stretched, they are not as strong as before. Consequently, they cannot provide the same amount of clamping force and may break or shear off if reused.
One may also ask, how do you know if a bolt is torque to yield? here
GM Tech Tip: Torque-To-Yield TTY Fastener Use And Reuse. A fastener with a torque + angle specification must be tightened first to the torque part of the specification and then tightened further by the addition of the specified angle. The angle must be applied relative to the mating fastener. more
Post by MostMint » Mon Dec 03, 2018 9:09 pm more
On the bottom is a bolt I removed from the engine. On the top is a new torque to yield bolt.
I have a 1995 gen 1 small block Chevy with a cast iron block and cast iron heads and for decades that combination used reusable head bolts. Now they want to sell me the TTY bolts but I want to reuse the factory head bolts assuming they are standard bolts and not TTY. Thoughts ?
Post by MostMint » Mon Dec 03, 2018 7:18 am more
Post by wxo » Mon Dec 03, 2018 1:30 pm [links]
How can I tell if the one on the left is torque to yield? more
Getting to the precise yield zone (for maximum clamping force) is accomplished by tightening bolts to a certain torque spec, then turning the bolts a pre-determined number of degrees. Rotating the bolts a set amount of degrees and putting the fasteners in the yield zone will account for “clamp load scatter” or variations due to conditions such as assembly lubricant type, bolt and bolt hole thread condition, and surface finish of the fasteners. more
Bolts are elastic by nature, meaning that within their elastic range, they'll stretch as the load on the bolt increases. As long as the bolt is not stressed beyond its proof load (the maximum load a bolt can withstand and still behave in an elastic manner), it will return to its original length once the torque is relieved. However, conventional bolts can be an issue when they are used on aluminum heads, given that the expansion rate of this type of head can stretch typical bolts past their yield point. This can be overcome by designing and offering better fasteners to address these conditions.
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While this sequence is more complicated, especially since every head bolt must be tightened this way in a certain order, it provides much more consistent clamping force which creates a better seal. more
We didn’t need them in the 1960′s or 70′s! The simple answer is engine materials are different. Aluminum cylinder heads expand at a different rate than cast iron blocks. As an engine warms up, bolted together parts have to move against each other or slide on their gaskets.
While the first step in the tightening process is normally stated as a torque figure it is done so; only to provide a uniform baseline from which the true load is then applied. This is commonly referred to as a preload or snug torque. more
A typical tightening specification would look as follows: more