1991 BMW 850i

page 12

  1. Ignition waveform analysis
  2. Spare engine refurbish
  3. QuickJack BL-5000SLX


Ignition waveform analysis

So I'm still not convinced that my car is running as well as it should. Replacing the spark plugs and cleaning the distributor contacts (they were covered with varnish since new) made a very noticeable  improvement and MPG jumped by 2 but it still lacks grunt and the idle seems a little bumpy.

There is a lot that can be gleaned by analyzing the ignition signature... The waveform below was simply captured with a digital scope attached to the primary of one ignition coil. The sync signal was from a piece of foil wrapped around one of the spark plug cables but I have a better solution for it in the mail. There is a lot of info on the web about how to interpret what is shown below (here's a good example https://www.motor.com/magazinepdfs/052001_04.pdf ) i'm still learning and will post more results of my findings as well as some fuel injector tests I plan to perform.

The only possible issue I see so far is that the spark line goes much higher than expected (actually clipped in the image below but they are all of similar height). Since I have already tested the cables and both sides of the engine behave exactly the same, I'm not sure if this is because I'm monitoring the ignition coil primary or a real issue. I have a capacitive pickup cable (to monitor ignition secondary) in the mail and should know more soon.



Spare engine refurbish

This engine was purchased March 2016. It came out of a wrecked 850i with only 65K mi. I also got the transmission, seats, rear axle and some modules (2 x DME, EML, TCU). The car this 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 I'm really surprised this didn't suffer more damage. 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.


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

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

I was very pleasantly surprised to find a 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 03/15 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 look pretty much brand new. They cost a whopping $600+ a set... about what I paid for the complete motor!



The water pump was removed and 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...


When this stud came out I saw a bits of aluminum thread come out too! At first I thought it was a helicoil but now I think it was stripped by the breaker as it appears he removed and re-attached the exhaust manifolds (probably to get the engine out of the car). Fortunately the threads go much deeper than the stud 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 test at 60 psi.

Most cylinders had some leakage into the crank case and by jiggling the crankshaft I could often improve this leading me to believe the rings are a bit sticky (engine 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 some carbon build up on them and saw some on the pistons too. intake valve leaks were not consistent... rotating the crank 360 sometimes improved things. Anything less than 10%  is considered good.

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.

Then I noticed the rear coolant manifold was cracked! An easy target 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).

These hubs are a tight fit on the ends of the camshaft. I tapped them off with a slide hammer but a small puller might be 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 th eupper cover so 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 absolutely no discernible wear lip at the top. Carbon build up is not excessive but I'm plan to remove the pistons to clean them up (with a solvent). 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... beginning to whish I had not tried to remove this cover, it was a nightmare to remove in my car's 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 looks like a possible crack in the corner of the lower oil pan but hopefully just a casting flaw. Until I get this on an engine stand I cant remove the oil pans and lower cam chain covers.

I suppose this is the risk you take buying an engine from a wrecked car. I was drawn to this one by the low mileage and I at least got to see the car it came out of. Many times when you buy a used engine you have no idea of its history. Fortunately the main block and heads are looking to be in good shape.


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 has sharp edges) resulting in some minor nicks on the head surface.... Oh well, hopefully this can be 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. This is the rear coolant plate and fortunately they backed out easily although one was a bit tight and had me worried for a minute or 2.


Then other bolts look like this... perfect! This is one of the covers at 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 and drop the pistons out. I think a couple strong guys should be able to lift it now. Still no luck with the valley pan, one bolt stuck. Plan to try some heat on it next but almost ready to give up on it.


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 have 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 this time and it works great, no foul odors and easy on the skin too. This stuff also does an excellent job cleaning the oil deposits in 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.


Did some more cleaning on the engine. No more surprises... everything looking good so far.


With the exception of the valley pan, all the bolts have been coming 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 corroded. As soon as I encounter resistance I back it out and blow off the debris repeating until the tool bottoms out.


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.


I've been wanting a quickJack for a while now but think they are a bit overpriced at ~ $1450 with sales tax here in California. So I kept looking on craigslist for a used one until one came up... brand new. The seller had purchased it for track use but his plans changed and he never even unpacked it! I got it for $950. It's the BL-5000SLX model which is only just long enough for the 850i. If buying a new one I would recommend getting the BL-5000EXT which is a few inches longer and will making placement under the car a lot easier. On the 850i the lifting blocks on the quickjack just barely pickup the jack points with nothing to spare so they must be very carefully situated under the car before lifting.

This is the 12V version... pump shown below. It does not take a lot of juice and can be powered by a small lithium ion battery which I have ordered on Ebay for an unbelievable price of <$10. Until it arrives I'm using jumper cables to a spare car battery.

It's a bit disappointing that the manufacturer doesn't package the pump and motor a bit better (enclose it). I'll come up with something to keep the dust and dirt off it.

My plan is to store the quickjacks under the car and leave everything plumbed up all the time. Blocks of wood under the hydraulic connections are to minimize the risk of me accidentally kicking or stepping on and damaging them


I got the engine mounted on the Harbor Freight engine stand today. Although I'm sure its fine, I added a little 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 cut down head bolts. I don't have an engine hoist yet so used the quickjacks to lift the engine on its dolly by sliding 2x4's under the dolly and straddling them across the quickjacks.


A local classic car shop was having a garage sale today...  I picked up this Napa 2-ton engine hoist for $100. It's not a folding model but is very quick and easy to tear down and takes up little space after doing so. It has a much longer reach than cheaper models with extendable legs. I was able to grab a few other odds and ends at a good price too. It always pays to keep an eye out on Craigslist !


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



I gave this one a light polish.



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


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


I'll be removing the oil pump next.


 Link to Page 13 (not created yet)