3387560-00-3-89_torque_plus_angle

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CAPSCREW TORQUE PLUS ANGLE

Foreword

Bulletin No: 3387560-00 3/89

This program has been developed to familiarize customers, sales and service personnel and other interested indiTorque Plus Angle method used on Cummins Diesel Engines.

Introduction -- Frictional Torque -- Preload -- TPA Capscrew

Cummins Eng





2. Our customers continue to demandhorsepower from our engines.



3. At the same time, these customersdemanding a limit on the size and weengines.



4. To realize more horsepower from amust increase cylinder pressures. Higpressures require optimum joint integ

head to block surface.



5. Today's engines can have cylinderexcess of 2,000 psi. The resulting forchigh cylinder pressures cause consta

relaxing of the capscrews that secureto the block.



6. If capscrew clamp loads are not cocontrolled, this constant stretching aneventually lead to fatigue failures. Co

clamp load requires that each capscreproperly.



7. In the past, we used torque input tocapscrews. Conventional torque methadequate for joints that can withstand

variations in clamp loading.



8. However, the conventional torque msufficient for more critical joints that reconsistent clamp load.



9. Below the elastic limit of the capscrfor a given capscrew is directly propotorque. Beyond the elastic limit, the ca

be yielded, and permanent deformatio



10. Only about 10 to 20 percent of theused in preloading, or stretching, the remaining 80 to 90 percent is used in

friction in the threads, and the frictioncapscrew flange and mating surface.



11. This means that capscrews can btorqued and have varying preloads, dfrictional forces acting on the capscre

capscrews are torqued to the same vwith high friction joints will have less pones with low friction joints.



12. To reduce this variation in capscrnecessary to stretch capscrews beyolimit into permanent deformation.



13. Stretching capscrews beyond theonly reduces variations in preload, buachieve more preload for a given size

capscrew.



14. The best method for insuring that preloaded beyond their elastic limits iangle method. Also referred to as torq

torque to yield, this method reduces tcapscrew breakage. To understand hangle reduces clamp load variations, understand the three following relatio



15. (1) As explained earlier, torque inproportional to capscrew preload belofor a given capscrew.



16. (2) Different amounts of friction amcapscrews cause variations of this relhigher the friction of the joint, the lowepreload for a given torque input.



17. (3) Until you reach the elastic limicapscrew is stretched is proportional preload. Above the elastic limit, the cayield, and becomes permanently defostretched.



18. As we mentioned earlier, straight produces a wide variation of capscrewclamp load due to joint friction.



19. Here we're using these same capthe stretch vs. preload curve after initsame preload variation has resulted iamounts of stretch in the capscrews.



20. By turning these capscrews throu'X', an equal amount of stretch is addcapscrew, and the capscrews have babove their elastic limit. The pitch of tdetermines the stretch for a given ang



21. The resulting preload is not only hless variation among the capscrews abecause the stretch of the capscrewsclosely controlled than the friction in t



22. Increased control produces a joinable to handle the higher cylinder preengines ...a joint that assures better rimproved durability.



23. A frequently asked question is "Wtorque value put capscrews beyond thand reduce preload variations?"



24. This is not possible because the tput a high-friction capscrew into yieldfriction capscrew.



25. Cylinder head capscrews that reqplus angle method of tightening are idsymbol for angle ( < ), plus the degreerequired after initial torquing of the ca



26. In addition to the flange head desmarks have been added to the capscsimplify the tightening process. The mexample are for a capscrew that is to degrees after initial torquing.



27. With this capscrew, torque to the specification, and then mark the cylinpoint adjacent to one of the single macapscrew head.

Always check the part number to be sconfiguration is being used during pis



28. Then rotate the capscrew until thecylinder head is between the next twoan arc on the capscrew head. In this edegree nominal rotation is specified; hrotation of more than one flat and lesswill achieve the desired preload.



29. When using the torque plus anglecapscrews are tightened into the yieldpermanently stretched from their origdoes not adversely affect the capscrefunction normally.



30. These capscrews can be used maand should be acceptable throughoutengine; however, as a precaution agathe capscrew in the block, a maximumspecified for each particular capscrewSpecifications Manual for each enginexceeds the specified limit, the capscreplaced.



Formated by -- Servi

Cummins Diesel Sales and Servic35A/1/2, Erandawan

31. Refer to the various engine TroubRepair Manuals, or Shop Manuals forangle values, and capscrew reuse gu

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3387560-00-3-89_torque_plus_angle