Retorqing Head

I have a 1990 525i that had its head rebuilt with new rocker arms, valve guides etc. this summer. It was losing antifreeze which we traced to the two hoses that go to and from the engine back into the
throttle housing. (the hoses are probably 1/2" diameter) and the gasket for the throttle housing. When we fixed these, we noticed that the radiatior had some oil at the top of the overflow bottle on the side of the radiatior. The mechanic theorized that there must be a leak from the oil cooler lines going into the radiator because I don't have any antifreeze in the oil, the engine isn't overheating and the radiatior blow-out plug is intact, so no extra pressure from the engine into the cooling system, and no white smoke upon startup or any other time.
He thinks this is left over stuff from the summer's debacle and we just didn't flush it out of the engine. But just to be on the safe side, we replaced the radiatior along with the hoses. Bled the system as best as we could (does anyone have a foolproof system for doing this?) and we still get some oil at the top of the overflow bottle. Where could this be coming from?
He wants to retorque the head just as a precaution, as we did not retorque it after the head installation. What do you think of this idea and do you have any specs for the retorquing?
Thanks for reading this lengthy post.
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I believe that the headbolt tightening sequence prescribed in the manual specifies a three stage process. The final stage doesn't specify a torque value but rather requires running the engine until it warms up and then tightening the headbolts by an additional angle(30 to 40 degrees as I recall). I can't imagine that your mechanic skipped this step as it would almost guarantee a blown head gasket the first time you applied full throttle. But on the other hand if your mechanic has already performed this final stage, is he now suggesting doing it again by tightening the another 30 or 40 degrees. That doesn't sound like a good idea. I also believe that once a head gasket is leaking it can not be fixed by tightening the head bolts. I think you should continue your search for another source for the oil you're finding. Keep wicking the oil out periodically and perhaps it will go away eventually.

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My previous car was a 1990 525i. Did you use NEW head bolts? These bolts, I'm almost certain if I remember correctly, cannot be used twice. The actually stretch and need to be thrown away and go with new ones when you re-fit the head.
Regards, KJB

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Yes, you are correct. You can't use old head bolts. We did use new ones. My mechanic isn't advocating taking the head off and using a new gasket, he is thinking just to tighten the bolts that are already there. We know you can't loosen these and retighten them. Thanks for both replys. We didn't start the engine and retorque on the third step. Maybe that is where we went wrong.
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JoeBeem wrote:

The last step is a 90 degree turn on each bolt. It will not matter if the car is started or not. I have never heard that it should be started. When I last did an M20 engine's headbolts I remember doing the whole procedure with the engine stone cold.
--
-Fred W

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Agree with Fred. My old M20 powered E28 snapped a headbolt. I did all the research etc. etc. and used the Bently manual and there was no requirement to warm the engine then do the last step. It was all done cold.
Howard
Malt_Hound wrote:

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My apologies gentlemen, Referring to the Bentley Manual I see that the sequence that includes warming the engine applies to the original Hex Head bolts and that if you have installed the updated Torx Head bolts that warming the engine is not included in the sequence. It states for the Torx Bolts 1) Torque to 30 Ft-Lb in sequence from the center of the head outward in both directions 2) Tighten an additional 90 degrees in sequence 3) Tighten an additional 90 degrees in sequence

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Jack wrote:

I do not want to appear to be picking on you Jack, but that is close, but no cigar. It is 30 Nm (22 Ft/lbs) for the first step.
--
-Fred W

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No problem Fred. Right you are. I guess I got the 30 Ft-Lbs from the Hex Head spec.

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There's lots of purists out there who will tell you what you can and can't do with BMW engines, but I reckon it's all just a conspiracy to sell more parts to the unwary public. The last M20 I worked on had a head which was bent like a banana (0.5 mm, 5 times more than factory recommended max) after being overheated. I had to change the block but when it came to the head I just tightened the middle six torx bolts by about an extra 135 degrees, reasoning that that would straighten it out and prevent any further problems. I used a new head gasket though. It seems to have worked, as I still thrash that car more than my wife and haven't had any complaints from either.
Steve

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