Tech Tip #172: A Five Point Checklist on Deutz Head Bolts and Torque Values

From time to time when assembling your engine, you might run into a bolt for a bracket or part and no matter how long you stare at your workshop manual, the toques setting can’t be found.  This tip will help you understand how to determine what your bolt “is” and what you need to torque it to.

1)  SAE vs Metric Grade Standards

As a rule, with SAE or standard bolts, the more hash marks on the top of a bolt, the higher the grade. Grade 5 bolts typically have three hash marks on top and Grade 8 bolts have five hash marks. The chart below shows how to tell a Grade 5 bolt from a Grade 8 bolt.

Metric bolts however will have the grade number on the head of the bolt.  This will not be 5 or 8 since metric bolts use a different scale for harness.  They should say 8.8, 10.9 or 12.9 on the head of the bolt. Even though the grade numbers differ from the SAE bolt, the higher the grade still means the bolt is harder.

This is what specifies what the hardness of your bolt is which is important when choosing a toque value.  The higher the grade the harder the bolt is.  Softer bolts stretch when over torqued whereas harder bolts might not break until they are put under pressure.

2)    Torque Values

Modern diesels such as those manufactured by Deutz and Perkins often have a very complicated three or four head bolt tightening process which involves tightening the bolts sequentially to specific torque values and a final step consisting of tightening the bolts to a specific angle. This is known as “yielding” or “toque to yield”

We have listed below torque values by size of bolts and thread pitch. Note that this list shows values for bolts that are both installed and torqued dry as well as with lubricated threads. Note that these torque values below are for noncritical components only, if you are unsure if the part you are installing is critical to the engine, stop and check your workshop manual. For help with installing cylinder heads, main caps, connecting rod, and valves on your Perkins, Deutz, or other industrial engines, take a look at Tech Tip #10: Torque Values and Valve Settings and Tech Tip #30: Installing a Cylinder Head. Still need help?  You can e-mail us at info@foleyengines.com or call us at 866.753.2979 and we will be happy to help.

3)    Deutz 912 Cylinder Head Torque Considerations

We had an odd situation with one of our customers. They were installing a set of new heads on his F6L912 Deutz diesel. Besides new heads, he bought new head bolts and washers. He was tightening down the head bolts in the correct, sequential pattern until he felt a change in the resistance. It was discovered that the new washers had stuck to the bolts and the 912 head bolts and washers turned together as one during the initial torque.

At some point the washers loosened their grip on the bolts and this created this unusual feeling.  This is why it is important to follow the workshop manual. If you look, it states, for this engine to “lightly oil the bolt” not just the threads.  This step could have saved our customer from fearing the worst as well as a possible heart attack.

5)    51 Bolt Torque Specs by Size and Grade

The chart below is presented showing bolt torque value by size. We wish to thank the AERA for preparing this chart.