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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / March 2006How to read head bolt tightening specs?????
I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that is leaking oil through the head gasket They are: Step#1 - 22 ft-lb Step #2 - Torque angle 90 degrees Step #3 - Torque angle 90 degrees The proper tightening sequence is also provided. I have 3 questions: Q.1. - Since these specs are for assembly, it would mean (I guess) that a new gasket is being used. And this might mean that the specs are not really applicable to my situation since the gasket I have has been in service for a long time. Or it might be that these specs only apply to a situation where the head is completely dissassembled. Does anyone know????????? Q.2. - I would guess that what the specs say is that every head bolt is tightend in the proper sequence to 22 ft-lb, then 2 more sequences are performed where a quarter turn is applied to each bolt. Is that what the specs are saying???????? Q.3. Heck- what if I just tighten the bolts uniformly in the proper sequence in an effort to stop the leak???????? Would there be any great harm in that????? Thanks in advance. All responses are appreciated. - Ben > I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that is > leaking oil through the head gasket [quoted text clipped - 14 lines] > long time. Or it might be that these specs only apply to a situation where > the head is completely dissassembled. Does anyone know????????? You are to bolt down the head using that procedure and specs no matter what the situation. > Q.2. - I would guess that what the specs say is that every head bolt is > tightend in the proper sequence to 22 ft-lb, then 2 more sequences are > performed where a quarter turn is applied to each bolt. Is that what the > specs are saying???????? That is correct. It's also known as a "torque to yield" method. The bolts are designed with a certain amount of spring or 'stretch' specifically for this application. > Q.3. Heck- what if I just tighten the bolts uniformly in the proper > sequence in an effort to stop the leak???????? Would there be any great > harm in that????? There would be if BMW says the bolts must be replaced after each use. Many torque to yield designs require new bolts every time they are removed from the engine. Chances are, if your bolts *are* actually too loose, then head gasket damage has already occurred from improper clamping force between head and block. You may as well change the head gasket in this case, or expect the oil leak to continue. Toyota MDT in MO >I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that >is [quoted text clipped - 18 lines] > where > the head is completely dissassembled. Does anyone know????????? If a new gasket was used it may compress just a liitle bit more than a used gasket would. I don't think that it would drastictly effect the torque. > Q.2. - I would guess that what the specs say is that every head bolt is > tightend in the proper sequence to 22 ft-lb, then 2 more sequences are > performed where a quarter turn is applied to each bolt. Is that what the > specs are saying???????? Correct. > Q.3. Heck- what if I just tighten the bolts uniformly in the proper > sequence in an effort to stop the leak???????? Would there be any great > harm in that????? Nope. Just as long as you realize that a retorque might not stop the leak. Are the head bolts loose ? Replacing the gasket would be a better idea if the car is driven much. > Thanks in advance. > > All responses are appreciated. > > - Ben >I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that >is [quoted text clipped - 18 lines] > where > the head is completely dissassembled. Does anyone know????????? Yes, those specs are for heads being installed with new gaskets. > Q.2. - I would guess that what the specs say is that every head bolt is > tightend in the proper sequence to 22 ft-lb, then 2 more sequences are > performed where a quarter turn is applied to each bolt. Is that what the > specs are saying???????? Right > Q.3. Heck- what if I just tighten the bolts uniformly in the proper > sequence in an effort to stop the leak???????? Would there be any great > harm in that????? You will only make your problems worse by attempting that. > Thanks in advance. > > All responses are appreciated. > > - Ben You would be best served by stating your exact problem along with the year and engine size of your car. I assume you are dripping oil... where about is it coming from? If the head is leaking, it needs to come off and be checked. You can't retorque these heads. The bolts are torque to yield bolts. They need to be replaced after you do the repair. They can't be reused. When they are torqued, they are designed to strech. After they stretch, they can't be used again. |
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