hello,
need some info can I use used cyl head bolt and how much newton on torsion wrench I should use?
It is difficult to get new cyl head bolt here so I must use it.
any advice how to install cyl head gasket, may need to put grease or should be both surface clean of any oil etc?
thank you
markus
m20 cyl head bolt used
Moderator: martauto
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chippy1947
- E30 Zone Newbie
- Posts: 50
- Joined: Fri Jul 11, 2014 11:00 pm
Hi i might be from the old school but we never renewed cylinder head bolts mind you things have changed as far as the gasket leave it dry.
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Simple question with a complicated answer.
Original head bolts had a conventional hex. head, were reusable, and were tightened to 40-45 Nm initially, then to 60 - 65 Nm after waiting 15 minutes, then finally angle tightened another 20 30 degrees after running the engine for 25 minutes.
BMW recommend that these bolts are replaced by a newer version on sight, although if I understand the situation correctly, the faulty bolts were only those supplied by one of three manufacturers, with the other two makes being fine. Unfortunately, they are all identical in appearance, and were mixed at the factory, so that any particular engine will statistically have four or five of the defective ones fitted.
The replacement bolts have a male torx head, and are a stretch bolt. There is a narrowed section along the shaft that permanently stretches a small amount when the bolt is fully tightened, so the bolts are single use only, although the odd one has been known to be used twice without incident.
The tightening sequence for these bolts is initially tighten to 30 Nm, then angle tighten 90 degrees, then another 90 degrees. No waiting time or engine running needed.
Block and head faces need to be surgically clean, and gasket is fitted dry.
Original head bolts had a conventional hex. head, were reusable, and were tightened to 40-45 Nm initially, then to 60 - 65 Nm after waiting 15 minutes, then finally angle tightened another 20 30 degrees after running the engine for 25 minutes.
BMW recommend that these bolts are replaced by a newer version on sight, although if I understand the situation correctly, the faulty bolts were only those supplied by one of three manufacturers, with the other two makes being fine. Unfortunately, they are all identical in appearance, and were mixed at the factory, so that any particular engine will statistically have four or five of the defective ones fitted.
The replacement bolts have a male torx head, and are a stretch bolt. There is a narrowed section along the shaft that permanently stretches a small amount when the bolt is fully tightened, so the bolts are single use only, although the odd one has been known to be used twice without incident.
The tightening sequence for these bolts is initially tighten to 30 Nm, then angle tighten 90 degrees, then another 90 degrees. No waiting time or engine running needed.
Block and head faces need to be surgically clean, and gasket is fitted dry.
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Torx bolts, on a M20, are always 30 Nm +90 +90, with no further tightening afterwards.
A once used bolt will have been weakened, but is probably still strong enough for the job.
A once used bolt will have been weakened, but is probably still strong enough for the job.