cylinder head machining - blown head gasket?

Question

ok so once a head gasket is blown the cylinder head is removed and sent to an automotive engineering shop.

what exactly do they do to it (in detail pls) and how do they get it to look almost brand new on all surfaces? Are there any sites/books/resources that go more in detail of what is done?

also, how do they know the torques to be applied. I doubt they have a database of all torque settings. Is it just a case of taking the size of the bolt and matching it with the standard torque settings of that size bolt? Also, where do they get turn 2 half turns and wait for 2 minutes? thanks

Answer 1

The head is 'hot' dipped..a cleaning process, then the surface is machined to the next engineering dimension which will remove warping or surface faults.
The torque settings are all in the shop manual, the mechanic just looks them up along with the tightening sequence. The express torquing sequence is necessary to avoid warping the head.
I've never heard of "2 half turns and wiat 2 minutes". Unless directed otherwise in the shop manual, follow the torque sequence several times increasing the amount of torque applied slightly until the specified setting is reached.

There are many books on the matter. Go to your local library and check the engine repair manual for your particular car.

Answer 2

Time to go to school.
Machine shops have all of the specs for almost every engine out there. It is their business to know.
They clean it in a tank of special cleaner and use a special machine to surface the head.
Turn 2 half turns and wait is called Torque to yield. You need a torque wrench and an angle gauge for your breaker bar to turn the bolts the right amount.
Failure to follow the procedure just means you do it again.
You can buy a book on your car from the parts house that goes into more detail.

Answer 3

They take the head and check it for trueness with a straight edge. If the valves need grinding their remove, the head cleaned by vatting in a strong caustic It's then magnifluxed fo.check for cracks. If the head is warped, it's surface ground to true it. The valves and seats or ground, the valve guides checked and replaced if needed, then the valves or re-installed. Every car or truck has a torque setting for the head bolts.Newer cars and trucks have stretch head bolts, that can't be reused. The bolts or torqued down to specks working in a clockwise pattern, starting at the center and working outward. The torque specks will call for pound feet of torque, plus additional amount or turn or degrees.

Answer 4

they usually throw it in a parts washer to remove oil,dirt,sludge,etc.then remove any gasket material that's still stuck to it.then a visual check for how hot things got .a check for cracks by a visual inspection,using a dye and or magnafluxing is next.then a straight edge is used with a feeler guage to check how bad its warped.if the head is salvagable and or cheaper to repair then getting a new one or good used one its resurfaced ,washed again and usually ready to go back on.a lot also pedends on what the costumer wants . a total rebuild or just fix it to make it run again.when it comes to head bolts or other nuts/bolts most do have the info on the shelf in their computers.a chiltons or book alike have all the info you will need for assembly and torque spec's.there are too many factors on things like for example headbolts just to know thier size and then just torque them up.length and the type of metal are just two factors for headbolts.cylinder and engine block design and the type of metal they are made of also are a factor.a lot of and or most of engines of today use torque to yeild headbolts.which means once thier stretched they can no longer be reused or shouldn't be but some people do.things get too complicated to sit here and go any further if you want to learn more they do have books look on the internet thier out there.

Answer 5

Hot tanking cleaning walnut shell blasting valve grinding cyl head oven and fixture to straighten warped heads save lots of material being taken off. many engines these days are chain driven and if you remove .060 from the head surface the chain tensioner will not take up the slack. Factory shop manuals Som of mine are on DVD and CD Machine shops have specifications and data base too. With out the media blasting and cleaning you may never see the crack that will ruin a cyl head. Two half turns and special streach bolts hold engine cyl head to the block and those bolts are replaced when they do not measure the correct thickness at x distance.

Answer 6

Did you use new cylinder head bolts? They can stretch and you should never re-use them, otherwise even with the correct torque and torquing sequence they won't be holding the head down properly, hence repeated gasket failures.