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Pelican Technical Article:

BMW E30 325i Head Bolt Update Fix
Jared Fenton
Wayne R. Dempsey

Difficulty Level: 5
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     So here’s the situation, I’m driving home one night, when all of a sudden, I hear a loud “PINNNNK!” and then sort of a rattling noise coming from inside the engine. Instantly I think to myself “@#*$*#*$! I snapped a timing belt.” Fortunately this was not the case. Luckily I was less than a block from home, and since I always carry a small tool set in the trunk, I decided to do a quick inspection of the engine. I pulled off the distributor cap and rotor and looked inside. The timing belt was still there and tight, so immediately I sighed a huge breath of relief. I then looked all over. Everything seems ok. Then I pull the valve cover off and I see the problem. One of the head bolts has broken, or rather, the hex head has snapped off, and has flown down under the cam. Thank god it didn’t get wedged in between, as it probably would have cracked the camshaft.  I grabbed a magnet and very carefully fished the bolt head out. I put the valve cover, distributor rotor and cap back on and drove the car back to my apartment.

     I immediately started thumbing through my Bentley manual and found out that there was a BMW factory update for the M20 6 cylinder motors. Apparently, the older style hex head bolts have a tendency to stretch due to fatigue and eventually snap, as in the case of my motor. The fix is to update to the newer Torx head style bolts. I called my local BMW service guy and he confirmed that this was indeed a factory service update. The next day, I ordered a set of new head bolts ($25.75 from Pelican Parts)

     So here’s how you do it. First, loosen the hose clamp on the valve cover breather hose and pull the hose off the valve cover. Now look at the bracket that holds the intake manifold to the valve cover. Remove the two 10mm bolts at the top and the two 10mm bolts that secure the bracket to the valve cover. Next, remove the eight 10mm nuts that secure the valve cover to the head. Now pull the valve cover straight up and off. You will now see the valve train.

     Next, locate the head bolts. There are 14 around the inside of the head. I first had to extract the broken bolt out of the head. Since the bolt head broke off, it relieved all of the torque on the threads. This made it relatively easy to remove. I just used two small screwdrivers to turn the shaft of the bolt until it had screwed out far enough for me to just unscrew it by hand. This is where we will begin to install the new bolts. If it is stuck in place, you can use a file to cut a small groove in the top of the shaft, then turn it out with a screwdriver. If the shaft snaps down inside the head, you can use an electric drill, set on “reverse” along with a reverse-thread drill bit, and simply drill until the bit catches the shaft, driving it out of the head.

     BMW specifies that you can replace the head bolts without replacing the head gasket. This means that depending on how mechanically adept you are, the whole fix will take anywhere from 30 minutes to an hour. I really didn’t want to have to pull the head off just to fix a broken bolt! The important thing to remember before you begin is to replace each bolt individually. What this means is that as soon as you remove an old bolt, replace it with the new bolt before you continue.

     Next, I used a small screwdriver wrapped with a rag soaked in brake cleaner and inserted it down the hole. This is important. You want to try to get the holes as clean as possible. If there is any dirt or grime in the holes, it can possibly give you false torque readings when you go to tighten the bolts. You’ll notice that the new bolts are coated with oil. This is to prevent corrosion from building up on them prior to installation. It’s a good idea to keep this oil on the bolts. It will help lubricate the threads when you torque the bolts down. Now grab the new bolt and thread it into the hole. Now using an internal Torx head socket, torque the bolt to 22 ft./lbs.

     Now remove the bolt on the opposite side of the bolt just replaced. This will help to distribute the torque between the new bolts and old bolts. Repeat the process above, first cleaning out the bolt hole, then threading in the new bolt and torquing it to 22 ft./lbs. Just remove and install one bolt at a time and make sure they are torqued to 22 ft. lbs. Make a not of the order of which you install the bolts.

     BMW has a specific process for torquing the cylinder bolts. It calls for three different stages. The first is the initial torque of 22 ft./lbs. The second stage is to torque each bolt a further 90 degrees from the first setting. Once all the bolts have been torqued the further 90 degrees, the last step is to go back and re-torque them an additional 90 degrees. The reason for the incremental torque is to allow the bolts to naturally stretch and expand without snapping them.

     So, make a note of the order and begin torquing all the bolts. All you have to do is put the torque wrench on the head bolt and turn the handle 90 degrees. For those of you not too familiar with geometry, that’s ¼ of a turn. Be sure to mark where you start. I would go like this; Start at no. 1 cylinder intake side, then exhaust side, back to the next intake side, then exhaust side, do it in this order until you run out of bolts to torque.

     Now, go back to the first bolt you turned 90 degrees, and turn it an additional 90 degrees. Now follow the same order again, and turn all the bolts an additional 90 degrees. Once done, you have successfully installed and torqued the head bolts without removing the head.

     One thing you may run into is a bit of engine coolant seeping past the head gasket when the bolt is removed. This will cause the coolant to come up through the bolt holes. Don’t worry; just use a rag to soak up the excess coolant.

     Now, place a new valve cover gasket on the cylinder head and re-install the valve cover. Thread the eight 10mm nuts back on and tighten using a criss-cross pattern. Now re-install the bracket between the valve cover and the intake manifold. Re-tighten the four 10mm bolts that hold it in place. Now re-connect the breather hose to the valve cover and tighten the hose clamp.  

     Well, there you have it - it's really not too difficult at all.  If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.  Your continued support directly affects the expansion and existence of this site and technical articles like this one.  As always, if you have any questions or comments about this helpful article, please drop us a line.

Comments and Suggestions:
Dario Comments: I bie Head bolt New i Want to know nesesari put old washers to tork the Head
July 17, 2016
  Followup from the Pelican Staff: The washers have to be installed with the bolts. They should also be new. - Nick at Pelican Parts  
Victor Comments: Ok so the image didn't upload. I meant this:

3 5 11 13 9 7 1 front of engine facing the radiator
2 8 10 14 12 6 4 exhaust side
February 17, 2016
  Followup from the Pelican Staff: Thanks for the part numbers. - Nick at Pelican Parts  
Victor Comments: For clarity, we're talking about this sequence for removal and replacement with initial torque @ 22 ft-lbs right?
February 15, 2016
  Followup from the Pelican Staff: I don’t have the torque info.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
ryan Comments: do you soak the headbolts in motor oil?
March 19, 2015
  Followup from the Pelican Staff: Soak no, lightly coat the threads and bolt head washer, yes. - Nick at Pelican Parts  
eric Comments: What year did BMW go from hex to torx on the M20 engine?

I have a n April 90 e30

January 1, 2015
  Followup from the Pelican Staff: I don't know.
I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
diagnosticator Comments: For clarification of terms used in my prior post, specifically, stretch type bolts increase in length when tightened, applying the required preload necessary for the fastener to perform correctly in the intended application, are tightened so that the length of the bolt shank is stretched into the elastic range of the fastener material, not the beyond the elastic limit point into the yield range of the bolt material. Depending on the material, once a preload in the elastic range has been applied, the fastener must not be retightend after the preload has been removed by loosening the fastener, and must be replaced with a new bolt of equal or higher quality and or performance specification.
August 17, 2014
  Followup from the Pelican Staff: I would add, replace the bolts each times they are loosened with the factory part. Not a substitute from a hardware store. - Nick at Pelican Parts  
diagnosticator Comments: Using a torque turn angle gauge is not really all that necessary. The bolts are designed to stretch when turned the total 180 degrees, and the tension in the bolt shanks when tightened into the yield range of the steel, results in a uniform clamping load on the head gasket. The tension produced in the bolt shanks by stretching, does not depend on absolute accuracy for the exact degrees the bolt is turned. A few degrees +/- 180 degrees will result is practically the same clamp load on the gasket as if exactly 180 degrees was measured. Eyeballing the 180 degrees, as 2 times 90 degrees is accurate enough. Being more accurate with the angle gauge, will not produce a more accurately applied bolt tension or clamp load on the gasket. As background for why the factory uses stretch bolts, when a bolt is stretched into the yield zone of the material, the tension does not increase much at all while the material is stretching with additional turning angle degrees. With the head clamping the gasket with the bolts stretched, functions similar to a giant spring compressed from above, holding the head down on the gasket/block. This allows the head to move around a little when the block twists from the torque reaction of the crank and the reaction forces against the head from the combustion pressure in the cylinders, and from the expansion and contraction of the head and block from temperature changing between cold and hot.
August 17, 2014
  Followup from the Pelican Staff: To avoid problems or doubt during repairs, I follow the factory recommended procedure. If BMW instructs me to use a torque-angle gauge, I use it. - Nick at Pelican Parts  
Steve Comments: Follow-up to my previous post. Just replaced each of my head bolts for the 2nd time and found using the angle gauge to be damn near impossible. In my case, I had to use a 1/2" to 3/8" adapter for the e-torx socket which made it difficult to position the little holding arm on the angle gauge reliably. Furthermore, you can forget using it with the 2 bolts closest to the firewall.

I ended up doing the 22ft/lb initial torque and then drawing a nice, straight line across the top of the bolt with a sharpie. Then turn 90 + 90 so your line is nicely vertical again. Easy.
May 24, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Steve Comments: Would you say the use of an angle gauge is mandatory when doing this? I've already installed the head bolts, but performed the 90 degree turns by hand/eye only. I'm trying to decide if I should replace them one at a time and use an angle gauge this time round...
April 29, 2014
  Followup from the Pelican Staff: I would say so, yes. - Nick at Pelican Parts  
Jun Malan Comments: Thanks for sharing an excellent explanation for the cylinder bolts replacement.
April 23, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
325e Comments: Hello Pelican,

I want to change the headbolts without removing the cilinderhead of my 1987 325e. But which bolting sequence should be used? The undo sequence starting at the outside bolts or the torqueing sequence starting with the bolts in the middle of the head.

March 18, 2013
  Followup from the Pelican Staff: When removing, start at the outer bolts and work your way inside. When tightening, start in the center and alternate the sequence as you work your way outward.- Nick at Pelican Parts  

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