Rattle noise at about 4000RPM while coasting. (found the source)

A conrod shop should be able to re-bush the small end and ream it to size. How are the wrist pins?

I do not think your engine damage is due to lack of friction modifiers (ZDDP). Do you know the history of oil change intervals, oil brand and viscosity? Also, how about the filter?

Many boxer owners use Mobil1 15w-50 synthetic auto oil without engine issues. Mobil and Purolator oil filters are popular as well.

I see a lot of wet carbon on pistons and combustion chambers. Any thoughts?

Wrist pins, pistons and rings all good. Would rather not take a chance on the worn conrods.

Oil pump might be more of an issue.

Just out of interest, do you allow your motor to warm at idle for a time before taking off, or fire up and go????

Dont know about previous owner, but I start the bike just before I put my helmet and gloves on.
So it runs for about 2 to 3 mins before I take off.

Methinks to spin a bearing you would have had to have had an interrupted oil supply... And there is scoring on the pump faces. Low oil? Or as you say - motor going while on its side, but it would have had to be revving or been on its side for a period of time to do that - those motors can take a bit... Other thought is water in the oil at some point... Have both bearings been damaged in the same manner?

Just thoughts

viz

It spun a connecting rod bearing in the rod and cap for some reason or another. Maybe bearing wear from mileage and the bearing got loose and beat itself up enought to get loose and spin. It didn't look like it got hot from oil starvation to me but you never know what happened for an instant at some time. It rattled because it didn't have compression forcing it on the crank but was loose with the vacuum at decel.

In a former life we used to have the big end of connecting rods resized all the time. Engine rebuilders do this as a normal practice to make sure the con rod bearing fits correctly. If you can find the spec for the inside diameter of the rod most amy machine shop should be able to do this for you then new bearings and rings and gaskets and ......

Clean it all several times and then keep it all very clean and good luck with the repair. Congrats on the cojungas to take on the job.

Bmw does not even stock undersized big ends. They do not rebuild these motors very often.

2 new conrods cost about 500usd. I have found a good source locally for second hand spares, so I will measure and fit a good second hand pair. At worst I will buy a new set. Its just amazing that I might get away under 1000 usd with rebuilding a 100000miles motor. Of course the labour is free which helps a lot.

The previous owner did not maintain that bike. That is some nasty wear which should not happen at that mileage. I use synthetic Mobil 1 10W40 every 10,000 km's and the paranoia over not using "motorcycle oil" is nonsense propaganda planted by the industry so they can make huge profits. Mobli 1, 4.4 liters $ 24.97. Full synthetic "motorcycle oil" $ 50- $100 for the same volume. Those are some expensive additives. Must be gold flakes or screwthemoverium molecules.

The so-called motorcycle specific oils that we are told we must use are SG, SH API classification oils which are obsolete for automobile engines.

Also, many of these recommended oils lack friction modifiers inasmuch as most motorcycles share engine oil with the transmission and clutch.

So actually, the later API rated SL, SM auto engine oils are likely a better choice for the boxer engine with its separate dry clutch due to a more robust additive package. The friction modifiers in these energy conserving oils can help reduce wear.

However, this engine looks like there was some debris loose in the lubrication circuit that wore the pump, compromised the high pressure bearing surfaces in the lower end and went on to caused bearings to spin on one journal.

Is there evidence of any oil filter media anywhere inside the engine, oil galleries or oil ports in the crankshaft?

Don't stop looking for the cause of the bearing failures.

Keep us posted.

Except for the wear on both ends of the conrods, the wear is surprisingly low on the rest of the motor.

Not sure why the conrod bearings should be more prone to damage.The main bearings look like they had some impact damage. There are some small indentations, as can be seen in the one pic.



The Oil issue, is more of a cold versus hot climate issue for me. At our mild to very hot temps, a 20W40 or 50 would be better. At freezing temps a 10W would be a better bet, as the startup lubrication is much better. But it would probably get way too thin at 40 deg c heat out in the bush over here.

I am still cleaning up, and will keep it posted.

Detonation, severe spark knock can stretch the big end of rods enough to cause a bearing to spin. So can severe lugging, maybe with detonation however the pistons show no sign of damage do they. Erosion of top ring groove is common under these conditions. Were any rings broken?

More likely it was on its side too long running.
Or blew out a sight glass and lost oil before it was noticed.

Lack of ZDDP would cause pitting on the cam shaft, lifters, push rods, etc. It has no effect on plain bearings at all.

Rod

Are those solids (debris) I see in the oil channel on that main bearing insert between the two lube oil ports?

Not sure. Cleaned it up without noticing. The pics come out so clear that I notice things afterwards only.
I did however find small flakes of metal and brass from the big ends in the sump part of the motor.

OK, here is some history on the previous owner.

She rode this bike mostly long distance off tar routes. Although she used the bike past its offroad potential some times, she never over revved wheelied etc. But the bike was properly utilized.

Althought she is a girl, she can ride! A picture is worth a thousand words:

Well at-least she was having fun and the bike wasn't a hangar-queen.

OK< I finally managed to get all the parts together, and I am busy re assembling the lot.

Some notes on buying parts. This would probably apply to most makes.

1. Take the manual and go through each page to get what you need
2. Even then you will probably not get everything. Allow for some extra time.
3. BMW took about 3 weeks to source the parts locally. With constant reminders from me.
4. I decided to add the conrods to the crank, and found out that only 2 bearing shells were supplied. BMW only supplies 1 shell per box, and not 2 as per everybody else.
5. I got lucky and got 2 shells from the other local BMW shop. Luckily I took the sample box, as the were going to supply me with roller bearings to fit as big ends. As the guy gave me the correct bearings, he asked how I decided to get the "red" shells. I asked what do you mean red shells. Did not know there were different colours. He said there were blue ones as well. My next question was the obvious, "what is the difference?" His answer was the obvious " Don't know" :huh. So I called the previous shop which I gave my VIN number to, to try and find out why they got me the red bearings. His obvious answer: "I told him I wanted the red ones, as I saw the red colouring on my old bearings." :huh By now I was seriously worried. I looked up all over Google, and found that the red bearings are standard, and the blue bearings are +0.25mm. All my components measured within original wear limits, but I would have cut the crank if I had known.
6. If the manual says "DO NOT re use bolts" then do not re use bolts. Like the conrod bolts. It says so clearly in the manual. Unfortunately I did not read that far during the dismantling, but I read that on the assembly. Needless to say, that both dealerships that provided me big end bearings failed to mention this. Now I am without these and have to carry on until after the weekend. I called, and the are only available ex JHB, and possibly 2 days. Luckily You can do the conrods after the motor is back in the bike.
7. So, the parts are expensive due to the cost of stock keeping. But do not expect to see any stock at your local dealership. Even when you sit with the parts salesman and go through the manual, do not expect to get all the parts you need. And do not expect them to guide you.
8. May faith in dealerships took a further knock with this. I could only imagine the mechanic starting the assembly, and seeing he did not have the conrod bolts, just using the old ones. This would have resulted in an exploding motor about 5000kms down the line. Just out of warranty. :eek1

Cracked con rods can not be re-sized when spun. For popular car engines bearings with oversize OD are available to the big re-builders. I vote for engine on its side too long. Lack of ZDDP will not cause bearing failure. This was not due to non-motorcycle oil. .That would be early wear of the cams and lifters.

Rod

Are you sure about that? Red and blue. BMW Max Fiche says red is cover side and blue is rod side. Only the part number tells which are +0,25 mm. http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51556&rnd=08102012 Engine picture #11_2806 Pekka :eek1:eek1:eek1

Some pics through to current stage.

Sorry about the quality. It was bright outside, stuffing up the backlighting.

Box of spares. About a shoebox full.



Damage to the wallet. About $850 USD.



Biggest of the many pieces of welding slag found when cleaning the casings. (one corner was welded where bashplate came off)











Gearbox added: