Techni-Tips – May ’88

Techni-Tips – May ’88

by | May 17, 1988

Possible Fire Hazard

If you own a four cylinder BMW (1600, 2002, 320i, 318i), be aware of a possible oil fire hazard . The upper xhaust manifold studs thread directly mto the upper end of they cylinder head, which is exposed to oil lubricat­ ing the valve train. If a stud becomes loose, oil will seep out the threads of the stud and directly onto the hot exhaust manifold. Ifthe stud backs out completely enough oil will flow out to almost certainly cause a fire.

In recent years, I have seen this too often. One engine fire is one too many. On every tune-up service, I recom­ mend that the exhaust manifold heat shield be removed and the nuts secur­ ing the exhaust manifold be checked for tightness. This check should be done with the engine cold. If all goes smoothly, you should only need two tools: a IOmm socket/ ratchet and a 12mm end wrench. Use the IOmm socket to remove the four heat shield bolts. This will expose the four upper exhaust manifold studs and 8 x l 2mm copper exhaust nuts. Both the upper and lower exhaust  nuts should be checked and tightened as required. On occasion;fr will find an exhaust stud that has backed out and rattled loose for awhile. This loosens up the threads and makes for a poor fit. In this case you should take the stud completely out, clean the 8mm hole in the head and the threads on the 8mm stud and reinstall with a liberal amount of thread sealer such as permetex .

Bolts or Nuts Frozen?

There will be times, when working on your car, that you will encounter fasteners that just will not budge. If you apply undue force onto a frozen nut or bolt, you will most likely shear the bolt or the round head . Neither one of these alternatives is pleasant. A bolt with a rounded head simply may be impossible to get out using conven­tional tools. A sheared bolt or stud will require special pliers or drilling and easy-outing the remaining piece. This is usually not an easy task, therefore, learning how to avoid these problems is important.

The novice mechanic can find out the shea_r force of a bolt or stud by performmg the following simple task. Find an assortment of 6mm and 8mm bolts and nuts. Place a nut into the center of a vice. Insert the appropriate bo.lt into the nut and tighten. Try tight­ening the bolt slowly until it breaks. Notice the hardness rating on the bolt. The hardness will usually be printed on the bolt head. An 8.8 grade bolt is softer than a 10.5 grade and so on. After a few tries with various common 8.8 grade bolts you will find yourself antic­ipating when it will shear.

If you have a good feel as to when a fastener is going to shear, then you11 know when to stop. If you encounter excessive resistance on any fastener, try using a penetrating lubricant and lightly  tapping  the  fastener  with  a small hammer to vibrate the penetrant into the fastener. Let it sit for at least Yi hour.  Once  a frozen  bolt  is  cracked free, then work the bolt back and forth a little to loosen it up. Try unscrewing one turn and then  Yi turn back  in. In this manner , continue to remove any hard to remove fasteners.

It seems you can always see the results, in  cuts  and  bruises , on the inexperienced  mechanic.  When  too much effort is exerted on a fastener the  hand  often  times  encounters  a immovable  object  which  is  usually sharp. Think about what you are doing. Play little “what if ‘ scenarios in your mind when working on on your car (or whatever). What if . . . this bolt shears while trying to remove it? Where will my hand end up with 60 pounds  of unimpeded force and inertia? Anyone who  has  worked   on  any  kind  of machinery  could  probably  relate  to this. Be careful.

Alignment Tip

Many BMW owners have been ripped off because they thought that BMW front suspensions were like those of American cars, and needed expen­ sive alignment on a frequent basis .

There are three measurements of front suspension geometry – caster, camber, and toe-in. Caster involves the degree of rake of the front struts camber measures the verticle positioning of the wheels (if the top of the wheel leans out, it is positive, if the bottom is out, it is negative), and toe-in (or toe­ out) indicates whether the front wheels are running parallel. The normal set­ tings are not necessarily horizontal / ­ vertical / parallel , but rather what was designed into the car

On a BMW, the only normal adjustment is that of toe-in. If the caster or camber is out, it is usually an indication that a very solid obstruction has been encountered, and quite possibly will require replacement of one or more suspension components or even cold bending of the strut assembly.

Rough streets, over a period of time, have a very bad effect on BMW tie­ rods and center track rods. If your car “clunks” as it encounters pavement separations or chuck-holes,  and the tie-rods and or track rod has not been recently replaced , you might be read y for a bit of maintenance.

Harmon Fischer
Bayou Chapter, BMW CCA


This article was originally published in the May 1988 edition of Zundfolge