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Car Forum / BMW Cars / March 2006How do I interpret head bolt torque 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 advacne. All responses are appreciated. "Ben Martin" <discflo@yahoo.com> wrote in message <4ZhWf.18510$%d.12686@tornado.socal.rr.com>: >I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that is >leaking oil through the head gasket. [quoted text clipped - 23 lines] >sequence in an effort to stop the leak???????? Would there be any great >harm in that????? The instructions are designed to pre-tension the bolts and then stretch them by 'just the right amount'. If all you're trying to do is stop a leak you've got two choices: 1. Do it properly: Replace the head gasket and the bolts. 2. Bodge it and check the other bolts are tightened to at least 22 ft-lb and then add a 1/4 of a turn each (or so). There is a risk something *might* snap if you do this; but probably a minor risk. Personally I suspect I'd go for '2' and only go for '1' after trying '2' a couple of times and it failing. [[ This message was both posted and mailed: see the "To," "Cc," and "Newsgroups" headers for details. ]] > 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????????? head gasket replaced. you don't reuse head 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???????? yes, but they're stretch bolts and have to be replaced. don't reuse them. > 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????? yes, the bolts could break or threads could strip. replace the gasket and use new bolts... > I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that is > leaking oil through the head gasket. I would just nip them up a bit. Tighten each bolt slightly, in turn, and see if it makes any difference. If it still leaks you could tighten them a bit more. Use your judgement but I wouldn't tighten them more than about 10 degrees. Do this at your own risk and don't blame me if you break something. If it doesn't work you need to change the gasket or just live with it. You could do a compression and leak down test to actually see if the head gasket is leaking. If it is leaking, putting more clamping force on it will not fix it. Once a head gasket starts to leak, it needs to be replaced. >I obtained the "Cylinder Head Assembly Specifications" for a BMW 325 that >is [quoted text clipped - 31 lines] > > All responses are appreciated. > You could do a compression and leak down test to actually see if the head > gasket is leaking. If it is leaking, putting more clamping force on it will > not fix it. Once a head gasket starts to leak, it needs to be replaced. A head gasket seals 4 different environments from each other. Combustion Chamber, Oil galleys (crankcase), Water galleys (cooling system), Outside world. A compression or leak down test will only check the integrity of the head gasket seal between the combustion chamber and the others. It will not, for example determine of there is a breach between the oil passage and the outside world, as is suspected in this circumstance.  Signature-Fred W
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