1991 BMW 850i

page 13

  1. Spare engine refurbish

Spare engine refurbish

This engine was purchased March 2016 and came from a wrecked 850i with only 65K mi. I also purchased the transmission, seats, rear axle and some modules (2 x DME, EML, TCU). The car these came out of looked to be in great condition but had suffered a nasty collision on the front passenger side. The engine mounts tore away and the engine was pushed back in the bay. The fan had broke off the fan clutch, passenger distributor cap and rotor were cracked along with some minor damage to the spark plug wires and wiring harness. At this time I couldn't see any further damage but there was more (read on).

The engine sat on this dolly for a couple years until I got around to it...


The engine harness is complete and in nice shape (better preserved than the one on my car was) but still much of the outer jacket has hardened and turned brittle. The wires inside are fine. I started removing the outer jacket and re-wrapping it with silicone tape. There is some minor damage to the wires feeding the passenger side coil and the passenger side MAF connector is broken but both are easily repairable. It will be a nice spare harness when finished.

This shows how the harness is attached to rear of engine.

I was pleasantly surprised to find a near brand new set of intake manifold adapters installed on this engine!

The installer was too lazy to remove the labels. The parts have a 2013 date code cast into them but the label below shows a 03/15 date code so my guess is these were replaced just shortly before the car was wrecked. They still have a very pronounced ridge on the sealing surfaces and still feel soft and pliable, they look pretty much brand new. These cost a whopping $600+ a set... about what I paid for the complete motor! Original parts often crack and become hardened after 20+ yrs but many avoid replacing them due to the cost.



The water pump was removed and it also looks pretty much brand new!

All of the exhaust manifold studs stayed in place on the passenger side.

But not on the drivers side many backed out. The studs are steel but the nuts are copper.


When this stud came out I saw a few bits of aluminum thread come out too! At first I thought it was a helicoil but I think it was stripped by the breaker as it appears he removed and re-attached the exhaust manifolds (to get the engine out of the car). Fortunately the threads go much deeper than the stud was installed so a longer stud should make up for the 1/8" or so of damaged thread.



I did a leak down test on the engine today (results below). I performed the testing at 60 psi.

Most cylinders had some leakage into the crank case but by jiggling the crankshaft I could improve this leading me to believe the rings might be a bit sticky (engine was cold and not run in about 18 months).

2 cylinders had very noticeable leakage at the intake valve. None of the exhaust valves leaked. Many of the intake valves have carbon build up on them and on the pistons too. intake valve leaks were not consistent... rotating the crank 360 sometimes improved things. Anything less than 10%  is considered good so this engine looks to be in great shape.

Leak down results were best with the piston at TDC. Either side of TDC (valves still closed), there was noticeably more leakage past the rings.

I will be pulling the heads and will clean up/re-seat the valves and make absolutely certain I don't overlook more damage.


The valve train looks is in great shape on both sides of the engine with no noticeable cam lobe wear! All of the rocker arms and lifters appear to be great shape also (upon removal).

None of the banjo bolts were loose.

I then noticed the rear coolant manifold was cracked! This is easily damaged I suppose, sticking out the way it does.


And then I found this...

I knew the distributor was cracked and rotor damaged but had no idea the casting it attaches to also. It looks like the distributor was pushed towards the engine which cracked this casting and allowed the rotor to hit the distributor which sheared the dowel pin in the rotor hub. This pin is normally retained in the hub so my challenge will be to remove the piece lodged in the end of the camshaft and make sure the camshaft is not damaged (it looks to be ok). I'll look out for a used casting on Ebay...

These hubs are a tight fit on the ends of the camshaft. I popped them off with a slide hammer but a small puller would have been a better choice.

Below is just a reminder for myself of where this bolt and spacer goes.


 Hopefully no more surprises but the heads will be coming off next. And the valley pan... another nightmare as all the bolts are seized in place (2 broken off and 1 more to go).


I checked the run-out on the camshaft on the side that got hit and don't see any issues, less than .001" and the cams turns freely in the head with the valve rocker arms removed.


The first head is off. I had no problems removing it.... I gave each head bolt a whack with a hammer first then loosened them off by hand in reverse order to the tightening sequence. The bolts came out looking like new but unfortunately these are one time use (stretch bolts). The right side cam chain guide is held in with just one bolt in the upper cover and easily removed. I forgot to brace for the spring releasing when removing the cam chain tensioner which resulted in oil squirting everywhere but nothing escaped!

The cylinder bores look great with no discernible wear lip at the top. Carbon build up is not too bad but I plan to remove the pistons and clean them up (solvent in ultrasonic bath). I'm not planning to remove the rings, hoping solvent will clean around them.

There is still one stuck bolt in the valley pan that does not want to free up... I'm beginning to wish I had not tried to remove this cover as it was also a nightmare to remove in my present engine. Bolts that don't want to come out are the worst part of this job. I had one bolt in the upper timing case cover that started to tighten up as I removed it but taking my time I was able to get it out. I'm not sure why it is that some bolts come out covered in what looks like black carbon and others come out looking like new.

As I disassemble the engine I'm always looking out for damage...

This looked like a possible crack in the corner of the lower oil pan but was just a casting flaw.


My inexperience showed itself today... upon inspecting the head I removed I noticed some nicks on the mating surface. Clearly when I was rocking the head back and forth to break it free from the gasket I must have let it touch one of the dowel pins (which have sharp edges) resulting in some minor nicks on the head surface.... Oh well, I will have this machined out as it does not look to be very deep.

I was more careful with the 2nd head, the technique is to lift and lower the low edge until the head breaks loose and then lift it straight up.


Here you can see the corrosion I'm finding on many of the bolts, particularly those on coolant covers. This is the rear coolant plate.


Some bolts look like this... perfect! This is one of the covers from the rear of the head. The difference seems to be oil casings=clean bolts, coolant casings=corrosion!


Here's a look at one of the heads. Looks like carb cleaner will get most of the crud off. I will most likely bring these to a machine shop for refurb.


Here's what it looks like now. I plan to buy an engine stand tomorrow which will allow me to get the oil pans off, then remove the front chain covers. I think a couple strong guys should be able to lift this now. Still no luck with the valley pan, one bolt is still stuck in there. I plan to try some heat on it next but almost ready to give up and break it off.


Casualties so far:

  1. Rear coolant manifold (cracked)

  2. Front upper engine casing (cracked)

  3. passenger side distributor, rotor and rotor hub (dowel pin)

  4. Wiring harness passenger side MAF connector broken and wires to coil damaged. Some Ignition wires on passenger side also damaged (where connect to distributor).

  5. 2 x broken bolts in valley pan and 1 more that refuses to come out.

  6. Slight damage to head surface (self inflicted)

Nothing too serious yet.

At this point I paused to clean up and inspect all of the parts I've removed.

The intake manifolds were covered in Cosmolene. The one standing up has not been cleaned yet, the one on the ground has had a first pass.

I used Citristrip to strip these... it works great and with no foul odors. This stuff also does an excellent job cleaning oil deposits from the runners! The black tub is a concrete mixing tub from Home Depot and a perfect fit for this job.

It took 2 passes to clean them up to where I was happy with them.

This one is now ready for paint.

I used High temperature paint (Aluminum and Satin Black).

And then sanded away the BMW logo with sand paper.


After some more cleaning on the engine.... no more surprises, everything looking good.


With the exception of the valley pan, all the bolts have come out relatively easy.

This is a thread chaser, used to clean out threads. It is essential to run this tool in/out on all threaded holes especially on the coolant casings which always seem to be crudded up. As soon as I encounter resistance I back it out and blow off the debris and repeat until the tool bottoms out. All of the threaded holes have cleaned up nicely.


I had mistakenly assumed the crank pulley hub was the same as the M62 motor for which I already have a special holding tool but it turns out they are not the same! Why BMW can't standardize on one size hub I don't know.

I made this tool from a pre-WWII 19" equipment rack side rail, it is heavy steel and at about 6ft long has plenty of leverage!

A 3/4" socket and breaker bar are essential for this job, this bolt is super tight!


The engine is now finally mounted on a Harbor Freight engine stand. Although I'm sure it is fine, I added some extra support under the oil pan for peace of mind... its a lot of weight hanging out there. To secure the engine to the stand I used four of the removed head bolts (cut down in length). I don't have an engine hoist yet so I used my quickjacks to lift the engine on its dolly by sliding 2x4's under the dolly and straddling them across the quickjacks.


All the casings are off the engine block now. I've inspected them carefully and the good news is non are damaged.

Here's a nice shot of the oil pump, chain driven off the crankshaft.


Here are the low timing chain covers.

The upper oil pan.


I found 3 x M6 bolts with  missing (broken) spring washers. Two of them were in the oil pan and the third I found in the oil pickup screen along with a small piece of silicone sealant.


The cam chain tensioner has only light wear. Unfortunately you cannot buy just the plastic piece otherwise I would replace it.


I cleaned up the metal casings today and inspected them carefully... they all look great. Getting them clean took quite a bit of work. I use Citristrip to clean off most of the gunk, it works wonders on oil stains. After that I scrub them thoroughly with dish washing soap. Every threaded hole was cleaned with a thread chaser.

The rear half of the upper oil pan received a light coat of paint since it is somewhat exposed under the car. I don't plan to paint any of the other castings.

Lower inner timing chain cover.

Lower outer timing chain cover

Upper inner timing chain cover

Upper outer timing case cover. This part was damaged on my engine so I purchased a used replacement. Unfortunately, the replacement had a couple of cross threaded holes and was about to return it but the seller offered a partial refund and I repaired it with time-serts...

Here's the time-sert kit and holes drilled out ready to be tapped. These are not cheap (this kit cost $75) but they are the best thing out there for thread repair. The tools set includes a drill bit to drill out the hole, a counter sinking tool that bottoms out at the right depth, a tap, and insertion tool and 5 x inserts (more can be purchased separately).

This hole has been re-tapped...

And here's the finished product with the time-serts installed... better than new!


Rear main seal holder.


The oil pan mounting holes are often dimpled from over-tightening which can affect the seal after a new pan gasket is fitted.

I used an M6 bolt and a large nut to flatten these out... it worked great!



Now to dismantle and clean the oil pump... Prior to removal I checked the chain slack and measured about 11.5mm. It is supposed to be 10mm. I doubt it makes any difference but the tie wrap on the oil pump chain marks it's front side so I re-install the same way.

Here are all the pieces cleaned up. These casings appear to be magnesium alloy. There is no noticeable wear anywhere on this pump.


This is how I dismantled the pressure valve. After removing the circlip the piston was stuck in place, I had to blow it out with compressed air. After I cleaned it up the piston moved freely again... It needs to pushed in to install the retaining clip and a drill press works great for this but you need to secure the pump (I made a bracket). Don't try to hold it by hand because if you slip the spring will shoot the piston across your shop!


I finally got back to the valley pan cover. It took a lot of work to get this off and as you can see I ended up breaking 3 of the M6 bolts. Fortunately there is a short stub left that I can grab with vice grips. But before I try to back them out....


I recently came across a tool called a Bolt-Buster. It is an induction heater used to heat up seized bolts without using a torch. Unfortunately they cost about $500 but I figured I could make one using parts left over from a previous project. This is nothing more than a high power oscillator using a pair of FQA11N90 FET's. It can get pretty hot so I wrapped it in cardboard and installed a fan to blow air across it. It draws 15 to 20A at 12V. If you run it for more than a minute or 2 the coil will start to overheat (you can see the enamel coating starting to blacken in pic below), so need to be careful with it.

Slip the coil over a bolt and it will glow red hot in about 30 seconds!


It took some work but I eventually got them out...

The inductive heater worked but lacks the power to get the bolts good and hot when bolted into the engine. I need no make a higher power version.

By working these back and forth I was able to get them out. 2 of them only took about 15 mins ea but one was stuck in there real good and took me several hours over 2 days to get it loose. One trick I tried was to connect a car battery across the bolt... running a few hundred amps through it gets it nice and hot! Eventually it broke loose and when it does I work back and forth with a good soaking of penetrating fluid.


All the threaded holes have been chased. For the head bolt holes I made a chase using an old head bolt with a slot ground into it (using a Dremmell tool). The slot will catch the crud in the threads.


Pistons and Rings

Some time ago I purchased a stash of BMW 850 parts... amongst them was a partially rebuilt engine block. The seller was an experienced engine builder and had installed new rings and bearings. The block had clearly been cleaned and lightly honed. Unfortunately the rest of the engine was not available. It has been sitting in my workshop since and I figured why not use this to practice removing and installing pistons!

The bottom end bearing caps are still loose and the bolts look brand new as they should be (they are one time use). These alone cost ~ $200 a set!

Here's one of the pistons I removed.


Just as I was told, the rings are brand new Goetze and cost anywhere from $300 to $450 for a full set!


The Pistons were relatively easy to remove. I pushed them out from underneath with a long wooden dowel. There's not much clearance for the end of the con rod so you have to  be sure it is positioned correctly for the piston to come out. It is easy for the end of the con rod to jam in place, at least with the block positioned as I have it (not in  an engine stand).


To re-install the pistons I purchased an ARP tool. This is a tapered tube 84mm dia that works really well... much easier than I was expecting. In fact I removed and reinstalled two of the pistons 5 or 6 times and every time it worked perfectly.

The blue masking tape on the con rod is to avoid scratching the bore.


With the piston and tool positioned as below I simply pushed down on the piston with both thumbs and it popped right into place... every time! Just remember to keep the tool and piston well lubed.

This gave me the confidence I'll need to tackle the engine I'm rebuilding.


I don't normally buy tools from Snap-on but this piston ring remover was only $16.00 shipped so I ordered one.

I found it relatively easy to remove the rings from this piston. Note these are brand new rings which might make this task easier (I don't know).



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