Bericht: Motoruberhohlung E28S M5

Gentlemen,

Last Sunday, I visited the seller of a used M88/3 cylinder head somewhere in Germany. I didn't buy it on the spot as I found three spots of which I was not certain. Despite the advice of a fellow board member I didn't take it with me directly but took some pictures to have them assessed by an engine repair shop before making a final decision.

From an operational point of view, the cost of the trip is higher then the asking price of the head so I could have bought it unseen. My only risk was that I would receive a crap head which is not usable and loose some money. Hypothetically, I could have sold it through the 'bay of e' afterwards but I am not a person to do that. Nevertheless, the engine repair shop that I consulted (and who will rebuild the engine in the upcomming months) gave me enough confidence so I took the plunge and bought it last week. I expect it to arrive in the upcomming week.

As mentioned, I consulted a local engine repair shop last week. I won't mention names yet, but the shop owner has experience with the M88/S38 heads and is aware of the NLA status of the M88/3 head. He conformed that cracks are common but according to him these can be repaired reliably. Although that is not my prefered appraoch, BMW AG forces me to do so with their policy to declare M88/3 heads as NLA!!!

Thums Up for the Mobile Tradition department grrrrrrr . To be honest, I contemplated about selling the E34S and E28S due to this unreliable behavior of BMW AG and buy a classic Mercedes Benz instead. After all, MB Classic center has a much better reputation for supplying even cosmetic parts for their classic cars then BMW. :crying:

On the other hand, that doesn't make sense after all as such a decision would be based on frustration and I would have regretted such a decision down the line. In any case, I need to find a way to 'hedge' the logistical problems that BMW imposes to the owners of her classic cars.

With other words, the engine will be rebuild and the head will be repaired. A groce estomation.

Cylinder head
- Routing away the cracks.
- Filling the routed spots with new alloy
- 24 new valve guides
- 24 new valve seats
- 24 new valves
- Gasket set

The head completely assembled and ready for fitting: ~3k Euro ex VAT

Cylinder head
- New main bearings
- New piston rod bearings
- New piston rings
- Machining the engine block.

Provided the pistons are OK: ~1k Euro ex VAT.

Assembly of the engine is quoted for 500 Euro ex VAT. Off course, I want new chain-guides, chain-sprockets, oilpump etc etc so it will add up a bit more.

I have started making preparations to lift the engine block. First, I removed the exhaust headers to gain some clearance.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img330.jpg]

These headers are a nice piece of art. Safely stored away.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img331.jpg]

Tapping of the old fluids (in this case the less then 1500km old Castrol TWS 10W60.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img332.jpg]

Next step is the removal of some heat shields and the remaining auxiliary parts.

Some would argue that it didn’t make sense for a 378km single distance trip to inspect a cylinder head with an asking price that is lower then the net-cost of the trip. If I would have to use my E34S M5 that would certainly have been the case, but I didn’t want to risk the chance that the cylinder head is nothing more then scrap metal. The seller (Andreas Heuer, owner of ‘E28 power’) did send me a few digital still images, but their resolution and quality were too low to make a decision so I took the plunge and decided to inspect it on site. We used my fathers Audi A6 2.5TDI for this trip, saving a few pennies on petrol cost. As I wrote in a previous post, I didn’t buy the cylinder head directly as it did show some faults and I wanted an expert opinion about two of the artifacts. Andreas did describe the artifacts on the phone beforehand, so they didn’t come as a surprise. Let’s zoom in onto two of the defects.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img335.jpg]

The red arrow points to a groove around the intake side of the combustion chamber for cylinder number three. The green arrow points to bubbles in the casting. It is unknown weather these are caused by the casting process or by another phenomenon.

This groove itself has a depth of roughly one millimeter. This is too much for machining down the cylinder had as there is no oversized head gasket available because of the unique construction of the valve train due to which it is impossible to re-torque the head bolts once the engine is assembled. To allow such a construction, the head gasket is made from high-grade steel [1], hence why it costs so much more then the normal head gasket of the SOHC M90 engine (E12 ///M535i) that uses the same engine block as the M88/3 engine.

The most plausible explanation for this groove is coolant that escapes through a leakage path between the cylinder head and the cylinder head gasket where it changes into a gaseous state and explodes under high temperature. The bubbles (green arrow) could be the result of the casting process during production. According to the machine shop, both faults can be restored by routing out the damaged spots, fill them with new alloy and skim it to specs.

This cylinder head does not suffer from the cracks between the intake-and exhaust ports as is the case with so many M88 / S38 heads. But if one takes a closer look on the following picture, a small hairline crack can be seen between the exhaust valve-seats (purple arrow).

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img336.jpg]

Normally, such a small hairline crack is nothing to worry about, but not to my requirements. Although I still prefer a new cylinder head, BMW’s policy to declare the M88/3 heads as no longer available forces me to rely on craftsmanship instead of process control. Maybe (and I hope) they will change that policy in the future. If the BMW Classic department (formerly Mobile Tradition) want to reach the same level as the Classic center from ‘Das Haus’ they have to reconsider their policy. Nuff said.

Based on above pictures, the machine shop that I will use for overhauling the engine thinks that the cylinder head in Schöningen is usable so I agreed to buy it. A week later, the parcel with the cylinder head was delivered on my doorstep and after a visual inspection moved to my workshop where it resides in the same rack that I use for storing engine parts on.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img337.jpg]

In any case, both cylinder heads need a significant amount of work and if I will use the cylinder head that I bought from Andreas, I assume that I need an oversized head gasket as well. According to member Stevie, these can be custom made from a third source. Another option is to use the solution that member jrobbo used when he had to rebuild the engine of his E34S ///M5 in 1999 [2]. He used a laser cut steel shim as compensation for the machining losses to straighten the cylinder head in combination with an OEM head gasket.

To make this project work, I will need short lines to the machine shop, hence why I have decided to do business with one in my near vicinity. When some engineering decisions need to be made, I can convince myself without the need for long distance traveling.

References:

[1:] M88 engine description by BMW Motorsport Gmbh (page 5)

[2:] Engine rebuild description written by member jrobbo as published on the M5 springboard and later on the E34 M5 FAQ’s.

I proceeded with the removal of ancillary parts last Monday evening to prepare the short engine block for lifting. The cranckshaft sensor came off rather easy, but my attention was put to the patch close to the connector.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img340.jpg]

I removed the insulation tape to inspect the wiring. The two signal wires and the shielding braid have been damaged in the past and very poorly repaired. I will have to replace this sensor with a new one at a cost of over 200 Euro's for the part alone.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img341.jpg]

The alternator is the next part that came of.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img342.jpg]

To avoid further damage to the DME wiring loom, I removed it fully. This will allow me to inspect it more closely and repair the poorly repaired patches that have been described in this thread earlier.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img343.jpg]

I have to disconnect the oil lines from the oil filter house, but when that is done and the engine is unbolted from the gearbox and the engine mounts, the engine is ready to be lifted.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img344.jpg]

It doesn’t make much sense to buy an engine-crane just for this occasion, so I borrowed one. The downside is that I had to wait for it becomming available. We first gave it a try on Wednesday evening 3-December.

With most of the preparations done, we ‘only’ had to unbolt the gearbox und engine mounts. I had a distinct preference for keeping the gearbox in place. It is bolted to the engine with eleven bolts of different lengths and sizes, but all of them require a so-called inverse TORX nut. Stahlwille, a German tool manufacturer, offers these in a few sizes as special tooling for BMW.

I don’t really know how it is possible to remove the gearbox without removing the engine, as four of the bolts are almost impossible to reach. Maybe there is a special tool or the engine needs to be lowered, but even so, three of the upper bolts have to be removed without seeing them. Better make sure you have the right high quality tools for that and don’t over torque these bolts as you’ll regret it when having to remove the gearbox again.

I suspect that this was my problem, as I doubt that #231 still has the original clutch after 23 years, but that can be investigated later on. With little space to work, removing these bolts is a serious challenge, even with the cylinder head out of the car. The following picture shows two of the upper bolts that were really tight. We managed to unbolt the right bolt on Wednesday evening, but no such luck for the more accessible bolt on the left.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img349.jpg]

This bolt can be seen from underneath the car and with some halve inch extension tools it can be reached, but even with the right nut, it didn’t turn. By that time, it was already 11:00PM so we called it a day and my acquaintance who helped me with this stage thought he had access to suitable tooling. We agreed to give it another try again on Thursday evening Wednesday the fourth but something came up in between so we postponed it to last evening (8 December).

My acquaintance brought a few nuts that have the distinct function of finding grip in damaged heads. I don’t know how these are called, but these nuts have a few sharp blades that penetrate the bolt surface in perpendicular direction to allow a fair amount of force to be applied without loosing grip to the head. Fortunately, my halve inch ratchet has a very small pitch, which came in very handy in the crowded working space. It didn’t take much time before the troublesome bolt came off.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img351.jpg]

I don’t want to reuse the bolts anyway so I don’t care. With nine bolts removed and no other bolts in sight, it was time to position the engine-crane and attach the chain to the lugs on the engine block. But the engine didn’t move forward. Also disengaging the clutch didn’t help. We then removed the starter-engine and the alloy engine mount on the exhaust side to get some more clearance when we discovered two more bolts sitting in the way. Problem was that these are even more difficult to access. Blunt said, there is no room to put on a halve inch nut. We tried of course, but to no avail. I finally decided to remove the engine and gearbox together, so we unbolted the gearbox support, removed the slave cylinder, gearshift, disconnected the propeller shaft and some wiring. Before reattempting to lift the engine, we first installed some of the bolts between the gearbox and engine to prevent the remaining bolts being overstressed.

This time, everything worked like a charm and the gearbox/ engine assembly was ready to be lifted.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img352.jpg]

Even though the radiator had been removed, the clearance is very tight (less then halve a centimeter). I needed to place the hood in a close to vertical position to gain enough clearance for the engine to be raised high enough for the gearbox to be maneuvered over the front nose but other then being hard work that was not really difficult.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img350.jpg]

Before calling it a day, we separated the gearbox from the engine. The two remaining bolts were very tight and could only be released with air-powered tools. With other words, the gearbox had to come of anyhow.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img353.jpg]

I have to strip the engine a bit further to prepare it for shipment to the machine shop. But with most of the removal work being done, I can focus myself on restoring functionality.

I have stripped the engine block from all the removable parts.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img354.jpg]

The pulleys and the harmonic balancer are for the machineshop as I don't have a breakerbar for the 36mm hub nut. Also not advisable with the engine hanging on the crane. The only other part that I could not remove is the bracket for the A/C pump because two of the 13mm bolts are only accessable after removing the harmonic balancer.

We removed the clutch shortly after seperating the engine and gearbox.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img355.jpg]

The gearbox with the release bearing. Looks rather messy. It appears that the seal of the prise-shaft is leaking. I think that most cars suffer from this.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img356.jpg]

Damn, what do I hate this. A dealer replaced waterpump with less then 3k km on it. This should not have happened if the cooling system has been run on low mineral coolant (glycol). Just replacing the waterpump and topping up the coolant clearly is not enough. Looks crap to me.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img357.jpg]

With the engine out of the car and the wheels a few inches higher there is much more work to do some simple work of cleaning up the engine bay and do so cosmetic work.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img358.jpg]

I just dropped of the engine block and two M88/3 cylinder heads at the Machineshop. According to the owner of the shop, the bores looked and felt pritty much OK. In the new year, he will start stripping the short engine and cylinder head to clean all the parts.

I'll try to post regular updates from time to time.

Nothing news to report about the engine. I wanted to visit the engine shop last week, but my schedule didn't allow that; probably next week. I didn't do anyhting to #231 since removing the engine. I am not in a critical time-path at the moment so I used the holidays as an argument for a time-out and thus kept a low profile. I ended this break yesterday, when I removed the subframe.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img361.jpg]

A close up of the surface that is bolted to the chassis. Looks OK after all these years; It is a bit wet though. As this car has not been used in bad weather, I assume this is caused by coolant spill, that cannot be avoided when tapping of all coolant. It is contaminated with dirt and I want to have it sand blasted, galvanized and powder coated.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img363.jpg]

By removing the subframe, I have better acces to the front cross member of the chassis that needs attention. It's the only rust spot on #231. I got a good tip from Richard Baxter how to treat this POR15. (thanks Richard).

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img362.jpg]

Sidenote: I agree with some other members in the E34 section that it is much easier to lower the subframe then to lift the engine for replacing the sump gasket.

With the engine out of the car and the subframe removed, there are no more restrictions to clean the left-and right 'engine supports', the official name of the longitidual steel bars that are part of the forward structure. According to the parts catalogue, the individual parts are still available, but not as a whole.

I removed the heatshield from the exhaust manifold after which the brake lines comming from the ABS-pump are exposed. Both engine supports where contaminated with dirt. The surface to which the subframe is bolted too showed some spots of light corrosion which is not uncommon after all these years.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img365.jpg]

After spraying an aerosol with 'cold-degreaser', most of the dirt dripped of quitte easily. I only needed to wipe of the remaining dirt with a towel. This exposes the painted metal.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img366.jpg]

IMHO, the overall condition is very good. There is some minor corrosion; that is the result of friction between the subframe and the engine supports. Although this friction is minor (at least when the bolts are properly torqued), twenty-three years and 155k km of service leaves traces.

The only thing that needs to be done is sanding the surface lightly; chances are that only the paint finish is damaged and not the primer underneath. In any case, the grinded surface will be treated with a few layers of zync-primer.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img367.jpg]

The right side engine support after cleaning (picture above) with the exhaust manifold heat-shield removed. A detailed picture of the brake lines and the right inner-sill (picture below)

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img368.jpg]

I received a small update from the engine rebuilder who just started working on the engine by taking it apart and measuring the bearings, cranckshaft, pistins etc.

I have to wait untill Monday before I can take detailed pictures, but he informed me that the cranckshaft and bearings are OK, but the clearance between the pistons and cylinders is between 0,12mm and 0,16mm. According to him this is twice as much as regular.

I did call my dealer for factory specifications, but they have no such data for the M88 engine, only for the S38 that apart from the B38 engine has the same bore. The chief-mechanic send me the data by fax so will compare them with the obtained results before drawing conclusions.

According to the engine rebuilder, the measured wear is twice as much as what is normally accepted. He suggests going oversize and use new oversize pistons.

I had the subframe bead-blasted and powdercoated. Looks much better then before.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img369.jpg]

The TIS specs for the S38B35 are:

Bore: 93,40mm (+0,01/-0,00)
Bore-midsize: 93,45mm (+0,01/-0,00)
First oversize: 93,60mm (+0,01/-0,00)
First oversize: 93,80mm (+0,01/-0,00)
Surface roughness: 0,2 ... 0,4 (Ra [mu])
Max allowable ovality: +0,005/-0,005 (mm)
Max allowable conicity: +0,01 (mm)

Whilst on my way to work this morning, I made a small detour to see the fully disassembled engine from my M88/3 which was carried out by member Javier who coincidentally works for the engine shop that we selected to carry out that work.

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The engine block in disassembled state.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img401.jpg]

The six pistons.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img402.jpg]

The internal parts layed out on a table.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img403.jpg]

Just a randomely selected cylinder (this case #6). clearly visible is the machining pattern (grooves). Clearly visible is [d1] The brown tinted surface on top of the cylinder and [d2] the cleaner looking surface from the bottom up until one third of the height. The surface in between [d3] is used by the piston-springs and wear out over time. With other words, there diameter of the bore that is 'used' by the piston springs wears out in time and with heavily worn engines, a ridge can be felt on the cross-over points between these surfaces that may prevent the removal of the piston without damaging the cylinder walls. If that is the case, the cylinder needs to be bored anyway so that doesn't matter. Javier did make a report with measurements that he carried out to determine the wear of the engine.

Javier was not present this morning so I had to do with the measurements for [d3] that he wrote down.

cyl #1 [d3] = 93,48mm
cyl #2 [d3] = 93,47mm
cyl #3 [d3] = 93,47mm
cyl #4 [d3] = 93,48mm
cyl #5 [d3] = 93,48mm
cyl #6 [d3] = 93,48mm

I discussed these results with his collegue and additionally measured [d2] that turned out to be 93,45mm for all six cylinders. The bore wear is determined by substracting [d3]-[d2] or 20umtr to 30umtr for all six cylinders. The original diameter is what is strange. According to the BMW specifications this must be 93,40mm ('size 0'). Coincidentally, 93,45mm matches the so called 'size 00' in the technical information. Above 'size 00', there is 'size 1' and 'size 2'. Both are oversize (93,60mm resp 93,80mm). Unknown to me is were 'size 00' is used for but it does list a matching piston sized 93,40mm.

The pistons in my engine measured.

piston #1 [d] = 93,35mm
piston #2 [d] = 93,33mm
piston #3 [d] = 93,31mm
piston #4 [d] = 93,32mm
piston #5 [d] = 93,32mm
piston #6 [d] = 93,35mm

There are no inscriptions anymore what the original construction size is, but I assume it is 93,35mm, the matching piston for 'size 0' since for 93,40mm the wear must be visible on the piston. So someone must have decided in the past to machine the bore according to 'size 00' whilst using the pistons for 'size 0'. This equates to 50umtr or 30% of the allowed piston-to cylinder wall clearance (0,15mm) !! I have no clue who is responsible, but it sure is strange. Sounds like some cost cutting measures by a dealer who had a warranty claim (or something like that).

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img404.jpg]

A randomely selected main bearing journal on the cranckshaft. Their diameter measured 59,97mm for all but one that measured 59,98mm.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img405.jpg]

A few (lower) main bearings still in the main bearing caps. After 155k km these still look excellent.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img406.jpg]

Some other (upper) main-bearings. Also these are still excellent.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img407.jpg]

A randomely chosen piston rod with the rod-bearings still installed. Also these bearings didn't show a sign of wear. Their journals on the cranckshaft measured 47,98mm for all six.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img408.jpg]

One of the chain guides. Well worn and thus in need for replacement.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img409.jpg]

The timing chain sprocket on the cranckshaft. The tooths are a bit too sharp so also these will be replaced.

The disassembly and analysis of my M88/3 engine is almost complete, so it is time to draw some conclusions. The facts at a glance:

1: The valve clearances for all intake-and exhaust valves were to small.
2: The cylinder head gasket has S38 printed on the topside.
3: The engine wiring loom has been damaged on two spots.
4: The original bore diameter of all six cylinders is 93,45mm, matching ‘size 00’
5: The pistons in diameter are close to the value for ’size 0’

Facts 4 and 5 combined led me to believe that the engine needed serious repairs at some stage in the cars life. Normally, if an engine needs to be bored, a matching set of pistons must be used as otherwise a significant part of the engine-life is wasted. From the factory, BMW manufactured the M88 and S38 engine with a 0,05mm clearance between cylinder wall and pistons. As maximum clearance BMW specifies 0,15mm for a worn engine. This has not so much to do with oil consumption, but more with the maximum tilt of the pistons during cold start.

I rule out excessive piston wear, as these are not designed to come in contact with the cylinder wall. There are no (visible) signs of scoring either, so I can safely conclude that the pistons are originally 93,35mm in diameter, matching the criteria of ‘size 0’ in the TIS. The difference in measurement recordings can be explained by measurement tolerances and metal expansion / retraction due to temperature cycles.

The main question is: What caused the 93,45mm bore size what should have been 93,40mm? The difference seems to be minor, but bare in mind that the maximum specified piston-to cylinder wall clearance is 0,15mm. Subtract the initial manufacturing clearance of 0,05mm (the tolerances are ignored for simplicity) results in a mere 0,1mm as maximum wear. As a rule of thumb, one can assume that an M88/S38 engine lasts 300k to 350k km before needing a rebuild (abuse excluded). With these figures, the slope of the engine wear can be determined to a value between 0.00000029 and 0.00000033 mm/km.

Compared to the original bore size, the cylinder wall wear on my engine is determined at 0,03mm. Combined with the very good condition, i.e. minimal wear on crankshaft, bearings, camshafts, the true life of my M88/3 engine can be assessed to between 91k km and 104k km. Granted, this is an educated guess, but I can safely assume that this is within a ten percent accuracy, setting the limits to 82k and 115k km. However, the mileage indicator on #231 shows 155k km, meaning that the engine must have been opened once before. Corrected for the calculated true life, this must have occurred between 40000km and 73000km. Chances are that the factory warranty had already expired and that #231 was still in the hands of the first or second owner and the repair was covered under goodwill or a used car warranty. In that case, it was the seller’s responsibility, most likely a main dealer.

The logic is that if the pistons are original, they measure 93,35mm nominal. By increasing the bore to ‘size 00’, the piston to cylinder wall increases to 0,10mm! Although still within limits (0,15mm max), roughly halve of the engines operating life expectancy is wasted, meaning the engine wear reflects that of an engine with 150k to 175k km. A dealer would call this a successful repair with the problem shifted outside their liability or possibly outside the cars technical and economical life. The customer would not notice that the trade-off in engine life is at least 77000km just to save on a new piston set!

One may argue that this occurred at the factory already in 1985, but I think that is unlikely for a variety of reasons. First, if this engine block has been rejected initially due to a tolerance issue, it is very unlikely that the engineers would have enlarged the bore to ‘size00’ without using a matching piston set. Second, the engine wiring loom has been damaged and this would not have occurred at the factory. Lastly, the cylinder head gasket that came out of this engine has S38 printed onto it. This designation did not exist at the time #231 was manufactured in October 1985, let alone the manufacturing date of the various single parts some of them being stocked months before.

This evening, I started with one of my secundary goals that is so easy with the engine out of the car. When I removed the subframe, the mating surface of the chassis-beams were a bit corroded. Just some 'fly-rust' and nothing serious, but something that needs attention.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img410.jpg]

With some light sanding, I could remove the corrosion and the old primer coat.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img412.jpg]

More serious are some welds deep in the engine compartment. A dremel came in handy and allowed me to remove the rust between the sheet metal plates on the borrom of the following image. The weld right next to it was attacked by corrosion as well, but nothing serious.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img411.jpg]

P.S: The bracket for the AC condensor will be replaced.

The cracks between the valve seats are not uncommon to cylinder heads of the S14/S38 and M88 engine families, but in most of the documented cases, these cracks appear only between the exhaust valve seats. In that respect, the condition of #231’s cylinder head is more serious with cracks between the intake-and exhaust valve-seats and cracks between the exhaust valve-seats and the spark plug holes. I have doubts about the maintenance being carried out by the previous owners before I took over ownership of #231. Already in the spring of 2001, I had to replace two expensive parts that were manually modified for some reason.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img413.jpg]

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img414.jpg]

Both facts combined led me to believe that the condition of the cylinder head is not necessarily related to the piston to cylinder wall clearance being out of specification. The cause of the cracks between the spark plug holes and the exhaust valve seats may be over tightening of the spark plugs combined with high temperature rises in a short period of time (dT/dt) or with other words, plain abuse by ignoring a proper warm up phase.

With the valve seats affected by these cracks, their stability is lost and valve clearance affected. Even if I had adjusted the valves in between, an engine failure could not be avoided and would have occurred sooner or later. With the removal, disassembly and failure mode analysis, the second phase of this project is almost completed. The third phase, the actual rebuild will formally start next week after I have given the approval to proceed. The third phase will start with determining the usability of the cylinder head. After the visual intake inspection, Thomas Hoop from the ‘Twentse Motoren revisie ‘ gave the preference to using my original cylinder head, as it had not machined before. The overhaul of the cylinder head is a difficult route, but necessary as using the cylinder head ‘as-is’, is not an option and replacement cylinder heads are not available through the BMW dealer network anymore. This is my main worry so my project planning is as follows:

1: Confirm the usability of the cylinder head.
2: Purchasing the parts that have a time-critical impact.
3: Machining and overhauling the cylinder head with new valve guides and valve seats.
4: Machining the engine block.
5: Assembly of the engine with new oversize pistons (93,55mm), matching piston rings, intake-and exhaust valves, new timing chain and associated parts etc.

With step one being confirmed, I placed the order for six new pistons today. My planning of the completion of the third phase by the end of Mai still stands, but this depends on Thomas and Javier’s operational planning. I’ll try to post some updates from time to time.

Before installing the revived subframe , I had to do something about the surface rust on the front chassis beams. Member 'richardbaxter' brought an American marine product to my attention, which is known as POR15. POR stand for Paint Over Rust and is a primer coating that can be painted over rusted surfaces. It goes to far to describe the differences to other etching coatings in detail; for that I refer to the POR15 website .

Since I wanted to try it out first and don't need a large quantity, I was seeking for a starter kit that contained all the substances. It was available on the US website, but not from the Dutch resellers who prefer to sell the normal containers for way too much money. I couldn't order the kit directly in the States, but was refered to their German distributer, Ronald Hoeseler who offered the starter kit for 18 Euro's which is very reasonable compared to the US$ price. The DHL shipping cost almost outweighed the value of the kit itself, but the kit was delivered in four working days.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img415.jpg]

The kit contains a bottle with 'marine clean', which is a highly concentrated degreaser that can be dilluted with water up to a 1:10 rato. The second bottle contains 'metal ready' fluid, which leaves an etching layer on the cleaned metal. The metal container contains the POR15 primer coating. It is available in black, silver, grey and transparrant, but since #231 is salmon silver, I ordered the silver primer coating. Two latex gloves, a pencil and an instruction leaflet are included as well.

Since I already cleaned and degreased the affected areas some time ago, I only used the 'marine clean' to remove the last contaminations. I mixed the 'marine clean' with water in a 1:10 ratio. It takes some time to dry, after which the 'metal ready' can be applied.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img416.jpg]

The last step is the application of the primer coating.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img417.jpg]

I added three thin layers which is recommended for industrial applications. The curing time is two to five hours. I'll leave it for overnight so that will do.

The cylinder head has been blasted to remove the debries and get a full insight in the depth of the cracks. Clearly visible is that the crack (indicated by the green arrow) runs deep into the exhaust port. The true extent of these cracks was only reveiled after the blasting process. The other exhaust valve port (yello arrow) has similar damage, although not that bad as the crack is limited to just underneath the valve seat itself. The other exhaust valve ports have similar damage. It was only a matter of time before these extended to the water galeries.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img420.jpg]

The last step for preparing the cylinder head for the metalurgist (alloy specialist) is the removal of the valve seats. The first one was done in my presence.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img421.jpg]

With a dremel tool, an incision is cut in the valve seat to relieve the tension so it can be removed.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img422.jpg]

After the removal of the valve seat, the crack can be seen in its entity. The crack extends from the combustion chamber, alongside the mating surface of the valve seat, well into the exhaust port.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img423.jpg]

The valve seat from another exhaust port. The purple arrow points to a similar crack of cylinder #2. Also visible is the difference wear inflicted difference in the valve-seats slope. Due to this, the valve seat does not seal off properly and affects valve clearances as well.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img424.jpg]

The remaining twenty-three valve seats will be removed today after which the cylinder head will be dropped of at the metalurist's. The following picture shows a cylinder head from an Opel/Vauxhall Ecotec engine that suffered similar damage after a mere 150k km on Liquid Petrolium Gas (LPG). The valve seats have been renewed, but need to be machined before installing the valves.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img425.jpg]

Last thursday evening, I painted the lower front cross member with POR15 to neutralise the corrosion underneath. The primer paint fills the gap between the spotwelded plates rather nice.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img426.jpg]

I also installed the front subframe earlier this evening. As I have no complaints about #231's handling and the visible inspection of the bushes and control arms reveiled no defects, I decided against replacing the control arms and bushes. I did use new nuts and bolts though.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img428.jpg]

I also did not replace the pitman arms as there is no need to do so.

[Blockierte Grafik: http://rwoe.150m.com/tmp/20080301/img427.jpg]