Warning; Long post. Sorry.
- Heads and Cylinders
- Alternator
- Timing Cover
- Timing Chain
- Clutch/Flywheel/Oil Pump
- Connecting Rods
- Cam/Crank
- Cleanup
In my last project I didn’t do a full engine rebuild. In fact I didn’t even take off the clutch/flywheel or timing cover. I just rebuilt the top end. Given this bike is 12 years older and I really want to do a “full rebuild” I will document the engine rebuild in more detail for this project. Starting with the tear-down. It should be noted that I had the engine out of the frame and on the garage floor at this stage. Getting to that positions requires removal of the driveshaft, gearbox and all the electrics.
NOTE HERE THAT I AM AN AMATEUR- and you probably shouldn’t follow my instructions. This is more intended as documenting my experience than as instruction- proceed at your own risk!
There are a number of “special tools” required for various parts of this tear-down but in many cases there are alternatives and the special tool is not really required. A few cases however really require special tools.
It should be noted at this stage that my Ryobi cordless impact wrench remains one of the most useful tools I have purchased. It has allowed me to unfasten seized bolts easily but I seem to be finding more and more uses for it, including in stripping down this engine.
Heads and cylinders
I disassembled the heads and cylinders very much as per the write up for the R65 project. There isn’t really much to be specific about here, particularly if you are anticipating a total rebuild as I am. If you were only resealing the heads, you can leave the piston in the barrel if you are careful.
I removed the valve covers (2 diagonally opposed 10mm nuts between the fins and the central nut). Then I unbolted the 6 head nuts and removed the rocker assemblies and pushrods. It’s important to keep everything side oriented and it’s important also to ensure that the pushrods go back in the same way as there will be established wear facets from how they impact the cam. To achieve this I lay everything out on clearly labeled paper in a corner of the workspace where it can sit covered for a few weeks (months?) until I need it. I’ve already mentioned the infamous blue goo shit show I found under one of my valve covers, but suffice to say it was nasty. Looks like someone simply didn’t have a gasket so tried to use silicone. After the head is removed the barrel (cylinder) can be carefully withdrawn. When you do this you need to anticipate the piston and connecting rod falling down and striking the crankcase on the seal surface. I stuff a heap of shop rags into the case as soon as I’ve opened up enough space, then remove the barrel the rest of the way. I then use a home made puller tool to pull out the wrist pins and release the pistons. It’s basically a length of threaded bar and two pieces of tube on either end and nuts on each end and pulls the pin out as you tighten the nuts. The pistons were pretty coked up but I soaked them overnight in sugarsoap and they cleaned up well.
Alternator
To remove the alternator you first have to remove the front engine cover. In the r65 this is secured with two bolts but in the r75/5 there are three- an additional one at the bottom. After removing all the wires connecting the alternator to the diode board and the engine harness, the three bolts securing the stator (part that is static- doesn’t spin) to the timing cover can be removed.
To proceed with removing the alternator and getting the timing cover off you need to remove the rotor (part that rotates) from the crankshaft nose. Unfortunately removing the bolt from the end doesn’t cut it as the rotor is pressed hard onto the crankshaft. This is the first “special tool” that the manuals call for . Basically the tool is a long bolt with no thread on the first part. It works because BMW engineers (or Bosch??) were smart enough to thread the neck of the rotor. So if a long bolt with no thread on the first part is passed into the hole and then tightened it will engage the rotor but only push against the crank and effectively push the rotor off. This kind of “Reverse pulling” (pushing by tightening a bolt against a dead end) is a recurring theme in motor engineering. Luckily this is the first of many situations where the “Special tool” is not really required. I have found these online selling for as much as $12. Actually all that is needed is a small rod of metal about 6mm by 50mm. I used the cut end of an old blunt drill bit. This is then passed into the hole and the original rotor bolt used as the pusher. This works the same as the tool and costs about 10c.
Timing cover
After the alternator has been removed the timing advance unit (points) needs to be removed (single nut on the end of the camshaft and two screws for the timing plate) and then you can tackle the timing chain cover. The timing cover has a lot of bolts and there are a few different types so it’s worth keeping some kind of diagram or photo to help you remember when it’s reassembly time (next year!!!). Basically they are all the same except for two second from the top that are a bit smaller and three which are actually threaded nuts.Also, the washers here are unusually thick and hard to replace so keep them safe. In the picture below I have marked the standard bolts in yellow, the shorter ones in red and the threaded nuts in blue. Also, the area in green shows where the crank bearing is behind the case. You also have to remove the tachometer drive cable on the left (as you sit on the bike) by loosening the small clamp bolt. I also removed the crank and cam seals here- I just used a standard seal puller.
After the bolts are removed the timing cover can be removed… right?? Wrong. It’s pretty tight. Mainly cause the crankshaft has a nose bearing which is mounted in the cover (behind where you removed the alternator). Again there is a special puller tool for removing this but I wouldn’t bother. It would be easy enough to make one up (for example a steel bar across the crank shaft tip with two bolts in the cover at the sides) but I was able to easily get my cover off as follows:
I applied some heat to the area around the crankshaft nose with a heat gun. I gave the cover a few taps with a rubber mallet from behind (note- I had already removed the starter motor giving good access to this for a mallet). Then i just pulled and gently rocked the cover from side to side until it came off.
Timing chain
Removing the timing cover reveals the timing chain linking the crankshaft pulley and the camshaft pulley underneath. On my bike there were immediate signs that the timing gear hadn’t been changed in a long time (ever?)! First, the timing chain has a big angle in it where the chain tensioner pushes it. This shows that the chain has stretched. Secondly, the tensioner itself is badly grooved (you have to take things apart further to see this). And thirdly, and most worringly, there is evidence of severe chain slap on the crankbearing carrier. There are even chips of aluminium here.
The r75/5 has the old style double row timing chain. This chain has no masterlink- that is it is a continuous chain put on at the factory as the crank and cam are installed. If you want to remove this chain intact you have to reverse the way that did it at the factory- that is remove the cam and crank (or crankshaft pulley) simultaneously. However, as it is clearly in need of replacement I just cut through it with bolt cutters and a small cutting wheel on my Dremel.
Clutch/Flywheel
Removing the clutch plate assembly and then the flywheel is necessary to; replace the rear main oil seal, replace the oil pump seal. Also if you are planning on removing the crank and camshaft and rebuilding the whole engine! It’s also another area where the manuals call for a number of “special BMW tools”. I have found so far that I haven’t needed them. First remove the clutch actuation arm, bearing, and rod from the back of the gearbox. Actually you have to do this to get the gearbox out of the frame so you probably did it before you removed the engine. There is a small circlip which holds the lever arm pin in place. Remove the circlip, then the pin, then the arm, then the rod and piston/bearing assembly.
Once the gearbox is out with the clutch arm off you can set about removing the clutch plate assembly. This is a friction plate/diaphragm spring arrangement exactly the same as a car clutch. It is secured to the flywheel with 6 bolts around the edge, but if you just unbolt these blindly the spring could cause the assembly to come out (at you) under pressure- this is where the special tool comes in. They are basically just three long threaded bolts with nuts on them. First you remove three of the original bolts 120degrees apart (ie alternating bolts) and you leave the others in place. Then you screw in the special bolts into the holes where you removed the first three and lightly tighten down the nuts. Then you remove the other three bolts. This allows you to gently one by one loosen the last three a turn at a time with your “tools” and allow the clutch assembly out. To be honest, you can buy these online but I’ve seen people asking as much as $20 for them.. or you can just get three long M10 bolts and some nuts from your hardware store for about $2. Added to the list of inessential “special tools”.
Once the clutch plates are off I keep them in order as they came off in a corner of the workspace where they won’t be disturbed. I will be replacing all the clutch components for this build so not so important.
With the clutch off you can access the 5 bolts that secure the large flywheel to the back of the crankshaft. The cordless impact wrench was used here. HOWEVER IF YOU INTEND TO ONLY REPLACE YOU MAIN OIL SEAL you should be careful here. If you remove the flywheel, the endplay on the crankshaft can allow the shaft to move slightly forwards in the crankcase when you remove the flywheel. This can lead to the inner thrust washer coming off its pin in the crankcase (a disaster). So if you intend to replace the main seal but don’t want to remove the crankshaft you need to find a way of apply moderate (not big) pressure to the nose of the crankshaft to ensure it stays pushed back in the case. There is a special tool for this and various other methods such as a block of some kind in the timing cover or a strap over the tip. As I was completely disassembling the engine I didn’t need to worry about blocking the shaft at this point.
Next I was able to remove the oil pump cover. This is the early style with phillips head screws. They were very tight, but came off without incident with the impact wrench and a screwdriver attachment. You could use a manual impact driver. Under the cover is the seal to be replaced and you can withdraw and inspect the outer pump drive- you need some kind of outward force applying tool here. I carefully used circlip pliers. Inspect the parts for any signs of wear or damage. I had been worried about this due to the blue stuff and metal shavings mentioned above, but the pump surfaces were pristine. If you intend to go further and remove your camshaft you will need to remove the small (3.2mm). woodruff key in the back of the cam.
Connecting Rods
Before you can remove the crankshaft you have to remove the connecting rods for the two cylinders. These should be snuggly wrapped in shop rags at this stage so that they don’t move around and mar the cylinder sealing surface of the crankcase.
By carefully moving the connecting rod you can access the bolts that hold the two halves of the rod together. These are a special kind of star drive pattern- again I have seen shops online selling these as a “special tool” for Airhead conrod bolts for about $25 for the socket, but I was able to buy a good quality complete set of these at my hardware store for about $50 so worth thinking about.
Removing the bolts, you will discover that the two halves of the connecting rod shell do not come apart easily! That is because they are held together with a quite tight fitting pin which you can see in the photos. To help get them apart I reinstalled the old bolt a few turns into the thread of the shell and gently tapped on the end of the bolt via the socket and an extension bar. Doing this I was able to get the two halves apart. Be careful not to let the small half drop into the case where it might damage a surface.
Camshaft and Crankshaft
Ok so this is where things got a bit interesting. I really wanted to remove these to fully disassemble the engine and inspect internal component wear such as the crank journals, main bearing, thrust washers. I also wanted to replace the timing chain sprockets (note- you definitely do NOT have to remove the crank and cam to replace the sprockets).
I had read a lot about the process of removing these including my manuals and various websites including Bob Fleischer’s epic bmwmotorcycletech.
And despite this I managed to have my first serious f*ck up of the project so far. But more on that later.
To remove the camshaft you need to line up the holes on the sprocket to access the two hex bolts that secure the cam carrier to the case. Then you can get an allen key in and remove them and withdraw the camshaft (you have to have removed the oil pump woodruff key from the back of the cam-see above). To remove the sprocket, place the camshaft in an oversized pipe so it is resting on the sprocket. Then heat the sprocket significantly with a torch or heat gun. Use a socket or smaller pipe slipped over the end of the camshaft to allow you to tap down on the cam without applying ANY pressure to the delicate threaded cam tip. Don’t do like me and try and use a puller. Even if you think you have the tip protected with a socket. Or your tip will bend. And then you’ll have to order a “new” old camshaft at considerable expense and time delay from a guy in Germany. And you’ll be sad. Consider yourself warned.
To remove the crankshaft, first use the Cycleworks tool to remove the sprocket and nose bearing as shown. Heat helps here. Once they are removed, the Cycleworks tool has a plate that can be used to pull out the crankshaft front bearing carrier assembly from the crankcase. Then the crankshaft can be gently manoeuvred out of the case by tilting it to allow the counterweights to come out. The inner thrust washer- the large copper disc at the back of the case can be removed from its pins.
Cleaning things up
I followed the usual process for cleaning up the crankcase. Lots of degreaser, high pressure water, lint free rags and then lots and lots of elbow grease. I used scotchbrite pads and WD 40 followed by fine steel wool and Autosol aluminium polish to get things looking good.
