1991 BMW 850i

page 2

  1. Top end dismantle
  2. Banjo bolts
  3. Intake manifold refurb
  4. Fuel injector refurb
  5. Valley pan cover
  6. Engine wiring



I removed the intake manifolds today. You can see that someone previously tried to seal them with red gasket maker.

Removing them was a relatively easy job except for the 2 hidden nuts closest the firewall on the driver side - these were tough to get to and I'm sure even more difficult to put back on when I reassemble.

The passenger side valve cover was not terribly dirty but the drivers side is filthy and obviously leaking for a long time. I had already cleaned the passenger side cover in the pic below.

The valve covers came off next...

This is the passenger side

I was pleasantly surprised at how clean it is.

As expected, loose banjo bolts; this one was the worst but another was only finger tight.

Thankfully the head bolts are all good (non are loose or broken).

The cam lobes are all in excellent shape, showing little to no wear.

This is the driver side...

Non of the banjo bolts were backed out on this side but the one closest the firewall was only finger tight.

I'll pull both rails out and clean them up when I receive new sealing washers. I will apply loctite to the banjo bolts.

All of the cam lobes look great on this side as well except the one closest the timing chain which does show slight wear on the leading edge. This cam is at the very end of the oil chain. Tightening the Banjo bolts should help this. I plan to remove/inspect the rocker arm and lifter later (I will be replacing the valve stem seals).



I ordered a couple of spare rocker arms and lifters as well as a tool to compress the valve springs to service these parts. The cam damage above is minor and may be polished out with some fine emery cloth.

The intake manifold couplers were removed and cleaned today. As is common, they have some small cracks in them but appear structurally sound. I have purchased a set of gaskets to use with these instead of the more common practice of using gasket goop (which I may use as well). New replacements are about $125 ea and there are 4 of them so replacement is $500! And they are just plastic!


I cleaned the Cosmolene off the intake manifolds with Paint stripper (worked great) and then painted the box section black and sanded off the letters - they look much nicer now.

There is a temperature sensor at the end of each intake manifold... a simple thermistor I believe. I measured about 2.5K ohms at ~ 65 deg.F and this went down to ~ 1K ohms with a little heat applied. Both sensors measure about the same resistance so I will assume they are both good.

I got the last 2 fuel hoses out (you can see the feeders under the brake booster in the pic below). These are very difficult to get to and had never been changed - I had to loosen the clamps for these from underneath the car. I have a small heat gun that I use on all hoses prior to working them loose - a little heat helps a lot as 23 yr old hoses in the vicinity of the engine are no longer soft and pliable and can be very difficult to remove. These 2 were not too bad, actually still quite soft and flexible.

There are 7 fuel hoses under the hood of this car; 4 at the rear bring fuel in from 2 ea fuel pumps to 2 ea fuel rails. Each rail has 6 fuel injectors attached and a fuel pressure regulator (FPR) at the forward end that feeds excess fuel back to the tank. There is a return hose under each FPR that feeds excess fuel back to the rear of the engine via a  metal 'Y' connector under the intake manifolds and then one last hose at the back of the engine couples the return to metal hardline. I am replacing them all. Many of these cars have gone up in flames due to failure of one or more of these fuel hoses!

You can see the mass of rear coolant hoses in the pic below. Many connect to the heater control valve and aux pump which are presently removed. I believe these are all original too (23yrs old) and all will be replaced. They are not in bad shape but if one of them decides to leak they are difficult to get to once everything is back together so best to do it now as a preventative measure.


I have started to clean up the valley pan area and the front of the engine - both of which are caked in oily grime....


I repaired the MID last night with a brand new LCD and cable. This time I went with a cable that is glued on (a solder iron with a rubber 'T' tip is used for this) - it is a much better solution than the Pixelfix approach I tried the first time (which caused my LCD to crack). I used the pixel fix cable on my 740i cluster with good results but their solution is not a good one for this car.  I did not take any pictures of this repair job - it was a delicate operation. Most people choose to send their MID out for repair but my goal is to fix everything myself!

I dismantled the front of the engine today and began cleaning this section of the engine.

Belts, tensioners, water pump, hoses, etc are all removed and it is only now that I can appreciate how massive this engine is - it's a monster!

I spent several hours cleaning 20+ years of grime off the front of the engine. There's still more cleaning to be done but it is starting to look presentable now.



Today I cleaned the fuel injectors using a quick and dirty setup which you can see below.

I purchased a few injector connectors on ebay and wired one up to a push to make switch and a DC Power supply (set to 5V). At this voltage the injectors draw 300mA when energized. My air compressor is set to about 25PSI and connects to the top of the injector via a short section of clear PVC hose which is a tight fit over the end of the injector.

To my surprise, a few of the injectors did not activate at first and I thought they were bad but then after energizing them a few times they began to work and seemed fine there after. I tested them multiple times and they never again failed. It may be just that I am using 5V when they are probably intended to be used at more like 12V. I'll double check them again in a few days just to make sure they are OK but I don't anticipate any problems.

I disconnect the air compressor line, squirt some cleaner down the pvc  hose to depth of about 2" above the injector then re-connect the air compressor. Press the switch to activate the injector and the cleaning fluid flows though the injector. I basically check that they all sound about the same, draw the same current and spray evenly. According to my service records these injectors have about 70K mi on them and were last cleaned 10K mi ago. I doubt they were cleaned this way.

I purchased a kit of o-rings, spacers, filters and pintle caps and replaced these on each injector. I doubt this was really necessary but many people choose to do this. If you send your injectors out to be cleaned, this is what they do and most cleaning services will also flow test them.

Pull the filters out of each injector using a screw. I pressed the new ones in using a drill press with a 1/2" socket around the injector body (15mm I think).

Here they are all tested and cleaned up with new O-rings, filters, spacers and pintle caps.

As I dismantle this car I like to clean up and test every part I remove so reassembly can be trouble free. I try not get too far ahead of myself (too many parts needing cleaning/testing). A few days ago I removed the water pump, belts, tensioners etc and so today I got caught up again by cleaning these parts. This is a good practice because if anything needs to be replaced, I can order it now and have it ready at time of re-assembly. In this case I noticed the O-rings for the water pump and thermostat appear different sizes but I'm pretty sure what I ordered were both the same so I will investigate this.

Now I'm ready to start tackling the Valley pan... this is a cover over the main water jacket that cools the cylinders on the inside (middle) of the engine. It is a common place to find a coolant leak in BMW V8 and V12 engines. I have done this job on both my 740i and 540i (V8's).

With the main coolant return pipe removed you can now see that the valley pan was not leaking at the O-ring in the middle of this pipe as I had supposed but in fact looks to have been leaking at some of the mounting screws (gasket failure). It has obviously been leaking for some time based on the amount of  (the light brown crusty stuff).

What an oily mess ... and I have already cleaned up a lot of it! Most of this oil probably ran down from the leaking valve cover gaskets and intake manifold seals. It will look a lot nicer soon.

I've been dreading this next step for a while. According to the message boards I read, the valley pan bolts on this engine are notorious for being seized and breaking off when trying to remove them. I have read several posts reporting 1 or more broken bolts when doing this job! I will be proceeding with caution as I do not want this to happen to me...

I started out giving each bolt a healthy whack with a big hammer via a 1/2 extension and then a good squirt of penetrating fluid. Then I went at them with a cheap Harbor Freight 3/8" air impact gun. This gun does not have the power to break these bolts (I set the air pressure low) so it is a safe first bet and I got all but 3 of them out like this. I'm debating now what to try on the remaining 3 which are not budging. First I will let them soak up the penetrating fluid overnight. Most likely I will then try applying heat from a small butane torch and then maybe try my 1/2" impact gun. There is a very good chance these will simply break off if I use a convention wrench to loosen them. Professional mechanics always use impact guns as there is a much higher likelihood of removing a seized bolt without damage.


I got 2 of the 3 stuck bolts out after applying some heat. Unfortunately the 3rd broke off! And to make matters worse, the cover was still securely held in place by what was left of the 3rd bolt. After trying to pull the cover off for a few hours I gave up and spent some time thinking about what to do next. I used a dremel and small dental bur to mill away the cover around the stuck bolt. I only had to go down about 2/3 the hole so the gasket surface is still just fine, after this I was able to pop it free.

You can see what I did here. It looks a little worse than it really is but should have no effect on the cover's ability to seal as the gasket surface is untouched.

The valley pan was full of coolant. I just sucked it out using my shop vac.

I ran a chaser down each of the valley pan bolt holes - they all cleaned up nicely. I think the biggest problem is dried coolant which gets down the threads and leaves a residue that is very hard. Just cleaning up the gasket surface was quite a chore.

And here you can see the remains of the bolt that I still have to deal with.


Armed with some helpful suggestions from forum members I went after the broken bolt today. Soaked it in penetrating fluid overnight, heat it up a couple of times, gripped it tight with vice grips and worked it backwards and forwards for at least an hour with absolutely no movement. Then all of a sudden it just popped loose! and out it came... what a relief!


I got busy on other things and haven't touched the car in almost 8 months! I'm a little worried that I've forgotten where some of the pieces go or more importantly the order in which things must go back together!

This weekend I stripped and repainted the valve covers. I used High temp black gloss paint from Harbor Freight. The valve covers are almost completely hidden from view once the engine is back together so it doesn't really matter what color they are.

I also installed 2 new crank position sensors  as the wires on the original parts were brittle and cracked. I had to remove the power steering pump pulley to remove the pump mounting bolts so I could push the pump aside and make room to swap out the lower sensor.

Then I started to work on the engine wiring harness - the black plastic sheath had become hard and brittle and is cracked/falling apart in several places. Fortunately the wires inside are still soft and flexible.

The secret to removing the old stuff seems to be to heat it up (which softens it up) then score a line along it with a utility knife and peel it off. Cutting it when cold just results in small pieces breaking off and flying everywhere..


I re-wrapped the wiring harness using vulcanizing silicone tape and applied a teflon spiral wrap where the harness touches the engine covers. The teflon wrap was an Ebay purchase. This stuff is ideal for protecting wiring that is in close contact with a hot engine.

I cut the single blue wire that goes to the alternator and installed an inline connector.

Later changed the inline connector to a waterproof connector. I spliced in a piece of brown teflon wire to the harness but this is the normally blue wire.


The Engine ground strap was corroded and falling apart. I picked up a replacement on Ebay for $10 !



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