As always, thanks for the great info guys. I’ll let you know what I find inside the head. I used a cheap endoscope and it looks like the valve is seated OK but has a little bit “missing”. I forgot to mention that when I took the cover off a small brass colored 10mm bolt fell out! Yep, it was one of the camshaft bolts. So who knows other joys I will encounter but I will completely strip the engine as I really know nothing about the history of this engine and also winter is just starting here🥶.

@roach374 The bike does sit a bit lower at the front and you can see that from the angle of the horizontal lines on the engine cases. This, in my opinion, really helps transform the K75 from a hefty tourer to a racy looking cafe (plus a ton of other work) As you might be able to see from the pictures, I have also mounted the clip ons above the trip tree which means the bike sits even lower. Mounting the bars here gives me a bit more turn lock clearance to the tank and it feels ergonomically correct for me when I sit on the bike.
I’ve not ridden this one yet, but I have modified the stance on previous bikes and I have always liked the way they feel. However, remember I am not a professional.

You also have to decide where to mount the Retrorides suspension as that will also affect the stance, as you suggest. I have not seen any exact measurement information for placement of the bracket so I just eyeballed it by tack welding the mount before final welding, to get the swing arm angle correct (in my opinion). Note also that the bracket has to be mounted maybe 3/4 inch towards the center line of the bike to make sure the  arm and suspension unit tracks parallel to the center line. This is part of the reason that you need to put the triangular bracket near the frame mount.

The real proof will come with testing of course, but that is a ways off. Rainy day here so I’m going back to work in the garage to get the head off and see what is happening to the valve train.

kenrams wrote:You also have to decide where to mount the Retrorides suspension as that will also affect the stance, as you suggest. I have not seen any exact measurement information for placement of the bracket so I just eyeballed it by tack welding the mount before final welding, to get the swing arm angle correct (in my opinion). Note also that the bracket has to be mounted maybe 3/4 inch towards the center line of the bike to make sure the  arm and suspension unit tracks parallel to the center line. This is part of the reason that you need to put the triangular bracket near the frame mount.

Here's the resource I'm looking at for the mounting point: 


That 109mm between the mounting point and the (I think?) rearsets mount is supposed to be the "sweet spot" (according to RR). Your mileage may vary.

The Mount point affects what angle the swing arm settles with respect to the flat road surface and the picture shows this as maybe an acute angle of roughly 10 degrees. If you, for example place the mount higher up the frame this angle will increase - ask me how I know🥴. I think this angle should be the same as the factory bike. Also, I found it really tricky getting this just right as I work by myself. You need to completely build the suspension and connect the mounting bracket to it first. Then offer it up to the frame to get the correct angle and mark the weld point. Remove the bracket, clamp it to the frame as accurately as you can and lay down a decent tack weld. Test fit the suspension again and if you are happy weld it up properly. I probably took 3 tries at it as I was working alone. Took me a few hours but this part is super crucial, so I suggest getting a friend to help and it will go smoother. 
One thing I should mention is that you are adding a very thick ( maybe 5/16” ) bracket and that will take a lot of heat to get good penetration. That very heat will almost certainly cause distortion of the frame at the Mount point if you have the frame removed from the engine. So, if you can, leave the frame attached to the engine for as long as you can for the weld. 
One other thing to note is that the geometry of the K75 is slightly different to the K100 pictured. So maybe all the measurements are not the same. On my bike I have the crank cover lines tilting forward slightly as I like what it does to the stance.

kenrams wrote:Took me a few hours but this part is super crucial, so I suggest getting a friend to help and it will go smoother. 

What would you have done differently, with a friend?

kenrams wrote:One thing I should mention is that you are adding a very thick ( maybe 5/16” ) bracket and that will take a lot of heat to get good penetration. That very heat will almost certainly cause distortion of the frame at the Mount point if you have the frame removed from the engine. So, if you can, leave the frame attached to the engine for as long as you can for the weld.

You do need to take the frame of the engine at some point though, to get at the other side of that triangle / bracket, right? (Just checking...)

Thanks for all this info, super interested in following along with your build!

An extra pair of hands can hold the rear end up to the correct angle while you are getting happy with placing the bracket and marking. I tacked it in the wrong place a couple of times and I think if someone was helping I would have nailed it first time. 

Yep, you will need to remove the frame to get at the rear of the bracket, but do as much welding as you can with it connected. Your going to have to lay down a number of beads as you want this mount solidly welded, so that will mean more heat to be dispersed. Just take your time as this is a crucial weld and needs to be super strong all over.

OK, once the sprockets came off it was plain sailing. I have the head off now and happily have no chipped valve with associated damage. looks to me like it is just the valve seat that needs lapping. As you can see from the photo below, I used a trick I learned from the might Interweb. I shone a bright torch into the exhaust port and can clearly see the issue of light escaping from the inlet valve seat on #3. Exhaust #1 & #3 are also poor.. I'll lap all the valve seats until I see no light leaks and put the engine back together. 

Hey Kenrams, jus swinging by to see if you've got any updates! I'm almost done with my own Retrorides conversion and frontend swap, and curious to see what you did for a seat on that subframe.

I believe I read on this website that we can have 16* of travel from flat with the gearbox uni joint. so a  total of 32* degrees of swing before you start to stress the uni joint. But where in here I read it, I've no idea.

So the project went on the back burner due to other interests taking preference but I've been back in the shop a bit more recently and plan to spend more time on the K75 build. 
So here's some updates:
* Head, camshaft chain & camshafts back on
* Cleaned injectors  and fitted new rubber bushings/clamps
* Replaced "ugly" airbox with exposed K&N setup. Not only do I prefer the look but this also creates some space under the frame that I may use to create a deep metal tray for electronics/battery in the near future.
* I got fed up sitting on the floor so made a frame to hold the engine so I could move it around easily
* Replaced the rear main oil seal and checked the clutch (almost brand new)  
* Checked water pump and replaced red o-ring.
* Painted covers

The next job is to check the valve gaps fit the gearbox and covers.

Building bikes is not my main focus but I do love the "process". In the last few days, I have made some progress as I have decided I really want to get this bike on the road before spring arrives. In the last couple of weeks I have 
* buttoned the engine back together after doing the valve shims. Only 3 shims had to be changed - from 2.5mm (which I guess is the default) to 2.45mm. So I was pleased for the further confirmation that the engine is probably in good health. As stated earlier, the pistons and cylinders displayed no wear on inspection.
* I painted all the engine covers (with rattle can HT enamel). Results are pretty good and much less bother than powder coating.
* Replaced water pump seal 
* installed the new rear main oil seal and mounted the new clutch. Lubricated all splines with Guard Dog GD-525 Moly.
* Made and painted a support bracket for the air filter assembly
* Fitted new throttle body rubber bushes

The next task is to build a new, minimal wiring harness to work with a Motogadget

Refitted the frame to check on new air filter setup to check frame clearance. It looks perfect! And look at the space that is freed up - maybe I can use that for something.....






As I had done all the top end work, I fitted the starter and tested 
1. That the starter gear Sprag clutch worked OK 
2. The engine turned over correctly after all the top-end work that I had done.

All good!

Now I can concentrate on the wiring harness. Lots of people seem to be intimidated by the complexity of the wiring on K bikes but I plan to simplify the wiring quite a bit. I have read a lot about this and I think the most comprehensive is Zach Ross's post here. https://www.k100-forum.com/t11686-m-unit-wiring-bmw-k 
After I finish studying Zach's post plan to create a minimalist harness by
1. Remove all the ABS stuff
2. As discussed earlier, due to the 25% increased capacity of the radiator and the fact that the K75 runs much cooler than K100, I am removing the temp sending circuitry and all other fan related circuitry. 
3. Using the motogadget removes all the other relays (apart from the FI relay) and fuses. I will still have a starter relay and definitely add a main circuit breaker.
4. Removing the Throttle Butterfly circuit. 
5. As I am relocating the ECU I will probably have to shorten all the wires for the sake of neatness.

Here's the stripped down harness without all the light stuff or switchgear. It looks way less intimidating

Man, there is a lot of things to be done when building a custom project. There are also many, many decisions to be made which you simply cannot rush or you will regret it at some future date. So, I have made a lot of progress but it's not really obvious to the casual observer. 

A lot of time has been spent on wiring. After seeing the space that was freed up by removing the plastic air box, I decided to relocate the FI module and battery/starter relay to the new space. Changing the wiring was really easy and looks very neat and functional. I also had to get the welder back out and make mount brackets. While I had it out I fixed some of the tack welds on the frame which actually took a lot of time. 

Another ton of time has been spent understanding the electrical system and simplifying the harness. The main doc reference I used  is Bert's wonderful guide: https://bmwmotorcycletech.info/K100%20troubleshooting%20Starting.pdf  

Rearsets from BSK have been ordered as I no longer have access to the CNC machines I previously used to fabricate my own. I have found a custom bike painter so will be sending out the parts for paint as soon as I receive the GSXR front fender I purchased. Yes, this bike will be ridden in the rain and I hate seeing customs that do not have a front fender. I also have a local powder coater so will send the frame out at the same time.

I need a rear tire but I like the stance of the bike so may stay with the Avon 130/90 x 17

Here's a picture of where I am currently with the build

Hey kenrams , like what i see so far , im about to embark on cafe - ing 2 k75s ,s  . i wont be going the retrorides route , although i do like the look , its just a cost thing . like yourself i will be tearing down the harness and simplifying it and getting rid of anything that is just not needed . love the idea to build an engine trolley , brilliant , i think that will have to be an addition to my garage , lol , been wondering about the best way to move the engine around once out of the frame

Hey Madhatter,

It is definitely important to plan ahead as the motor - even without the gearbox fitted is pretty darn heavy! The stand still allows access to the head, water pump, and crankcase. It is very rough and ready and I built it very quickly with little thought (or even great measurement! )

Next time I'll fit casters to make it easier to move around. Also,  just a thought, but if you make the base longer it will be stable enough to support both the gearbox and the rear swing arm.

Progress update. So it has been a little while since I posted but have actually been working on the bike pretty consistently the last six weeks. I want to dispel the myth that taking on a project like this is a straightforward series of quick steps that you can see on time-lapsed videos on the internet. It actually is a number of big tasks like frame modification and front fork replacement and a myriad other smaller tasks requiring multiple decisions that you have to make BY YOURSELF! Most of which you will get wrong the first time. And you probably have no previous experience to help you make the correct decision. So you will make lots of mistakes but lots of learning  

Easily the most time consuming task has been the wiring. Using the motogadget m-unit to eliminate fuses and relays is a wonderful way to simplify the electrical system and to force you to really understand how these bikes work from the electrical point of view.  However, be prepared to spend many hours poring over wiring diagrams and Internet videos.

Here's a list of what I have done/accomplished lately.
1. Wiring loom pretty much finished just needs tidying and final checking. All switches work correctly through M-unit. Bluetooth setup is awesome! Two 50A isolation circuit breakers were added for over-the-top safety.
2. Seat made using an old KTM seat/foam I had lying around and upholstered locally in Fletcher, NC by James Autoupholsery - they are excellent. 
3. Multiple brackets fabbed and welded
4. Fuel tank pump, hoses and filter replaced
5. Motodemic brackets for headlamp and Woodcraft clips ( with 75mm risers for comfort) fitted
6. Switch wiring run through bars.
7. Exhaust manifold modified to fit new exhaust.
8. GSXR levers and new braided brake lines fitted.
9. Fitted a new front tire to the GSXR front rim. I have a new SportDemon for the back still to do. I may do the bearings if they feel shot.
9. Tested starter, fuel pump, spark plug operation - all good! 

So I have fuel and spark and the next step is to tidy up the wiring, put the fuel onto the fuel rail and see if it starts - so fingers crossed.

Getting closer to running. Turned over well on pressing the starter, fuel pump ran, and got a promising couple of seconds burst of engine firing. Only took 18 months! The engine sounded good for the time that it ran. Unfortunately, when the engine died the starter stayed firing. Fortunately I had fitted the battery isolation breaker so was able to kill the starter easily. Checked the battery -an expensive Anti-Gravity which was new 18 months ago - and found it is down to 75% capacity on a full charge - even after a full overnight charge. So guess I'll need to replace it. The starter relay is expensive and not really designed for servicing but it can be (broken) open and "fixed". I took a bit of emery paper and cleaned it up ( see below). 



and after some emery paper cleaning



I have another battery that I'll try next.

Yesterday I received a brand new upgraded AntiGravity battery - a Hi-Power 460CCA 1601. This was a bit overboard but it is still a small form factor and I would rather be over specd on power and not get the starter relay fused again.

So, nn the first attempt to start I found out I hadn't connected one of the water hoses and got coolant everywhere! At least I now knew that the water pump that I had serviced was working  

On the second attempt to start I found out I hadn't tightened one of the fuel hose clamps and got fuel all over my garage floor.

The third attempt was the charm. It started right up with no unexpected mechanical noises or clicking after the valve head work I had done. this also meant that the new harness I had made - partly due to all the relays I had removed - was working correctly. Major relief and satisfaction as I had never heard this bike running. The exhaust note is very nice - not too loud but not exactly quiet  

After being in pieces for over 18 months, it is now beginning to look like a motorcycle once more. I have located a painter and hope to get painting completed before the end of March so I can have the bike on the road in April. 

Here are the latest photos of the project.

Now that I've confirmed the electronics & new harness work, it is time to break it all down and do all the tidying up jobs like finish up tidying up the frame welds - I am not a welder so there will be a certain amount of grinding involved! here's a couple of breakdown shots :






Finishing off the seat cowl before I send it out for paint. ( Note there is quite a bit of metal covered by Bondo,  to support the side legs )

So while everything is out for paint - it's shocking how much it will cost! - I've gone back to work on the frame. Lots of welding to tidy up which will be made easier now I've got a new helmet that makes it much easier to "follow the puddle".

I've found that decisions made earlier in the build get rethought when new ideas come into my head. I decided that I didn't like the FI computer and battery shelf that I had welded up when I looked at the bare frame. So as the FI computer had plenty of cable slack I decided to move that under the seat hump, removed the old shelf, and create a new custom battery tray for my new Anti-Gravity battery. I also decided to move the starter relay mount closer to the battery.

The painter did a fantastic job and I was actually hugely surprised with how quickly he scheduled and turned around my project. Figuring out how to paint a custom bike is a huge decision. I am not a huge fan of fancy paint schemes and believe that cafe bikes should be stripped down and simplified where possible. I also love the work of Russell Mitchell of Exile Cycles. I started off thinking the bike should be BMW metallic black and that is what I went with. 

The seat cowl that I made especially looks brilliant. 

So the next task is to finish up the details on the frame. It has to be good as I am powder coating the frame so I can't use any filler. 

Well done.
Looks incredible!

Getting closer! The paint is finished and the frame and rear wheel are back from the powder coaters. I've spent the last couple of weeks working on finalizing the electrics and other smaller details. Here's where it's at now before I put the bodywork back on.....

Whose radiator are you using? It doesn't appear to be BSK's as their thermostat housing isn't round. Is it from KPartsHolland?

It's not from either of those guys. I can't fully remember as I got it about a year ago but as always I presume I just googled custom K100 aluminum radiator and came up with an ebay item like this one. 
https://www.ebay.com/itm/264980793872?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1CdZYQ7HvTaePWZnzYIdGaw28&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=264980793872&targetid=4581046489808870&device=c&mktype=&googleloc=&poi=&campaignid=418640322&mkgroupid=1239149842233245&rlsatarget=pla-4581046489808870&abcId=9300602&merchantid=51291&msclkid=f606c3189fb01b86751ba1722be67121

This is one-third bigger than the stock K75 rad and I am using Evans Expansionless coolant so I have eliminated the ugly fan and the expansion tank. Note I don't do any city riding and all my riding is on the backroads and twisties of the Appalachian mountains. The stock thermostat and mountings fit reasonably well. And I like the racing look!

Bit of a setback. the bike fired up almost immediately which was good. I did this a few times just to check everything. But on the fourth run the bike just cut out after about a minute and refused to restart and didn't quite sound right during turnover. Checked the fuel and that was good. The plugs were soaked so dried them off and confirmed that the spark was good. A compression test revealed that 1 and 3 had no compression! So I took off the headcover and found a couple of metal pieces so I knew something was toast. investigation revealed the exhaust cam had sheared off the part that inserts into the driven sprocket. I guess somehow I messed up with the torquing of that bolt (35-43ft-lb). An expensive lesson about triple-checking everything!

Edit :  I've just re-read the manual and it states to use Blue Loctite on the bolt before torquing. As I found no Blue Loctite on the thread I am now sure it was my mistake! And yes, the inlet cam bolt was not torqued either!!!

Ouch! Last engine I rebuilt I forgot to tighten those bolts at all and remembered only after I'd refitted the camchain cover. There's just enough room to get a torque wrench ring spanner over the bolts without removing the camchain cover. Phew!

As part of my penance for being a wally, I removed the cover just in case there were other things I had missed! One thing that struck me was that I had to remove the water pump cover to get at a couple of the Allen bolts at the bottom of the timing cover. Of course, this meant I had to drain the cooling fluid first and will have to reseal it which is a pain. This is/was a poor design of the cover and they could easily have allowed access to the timing cover bolts using cutouts or even access holes.

So, it's been a while since I posted an update. Since April, I have been riding lots of off road trails locally in NC and also on Backroads Discovery Routes ( https://ridebdr.com/) on various bikes - a DR650, a KTM 790, an R1200GS, and recently on an R1250 GS (what a machine!)

We are moving back to the UK (Alnwick, Northumberland) so I had to get a move on and finish the K75 as I wanted to ship that back. 

As stated earlier I had to replace the intake camshaft, but when I put it all back together it would not run and there was a pretty bad engine oil leak. Long story short I drained the coolant and took the timing, water pump and head covers off again. Three issues became apparent. The rubber gasket on the crankshaft cover had moved out of the channel and did not seal properly with the timing cover. The crankshaft seal was just floating BEHIND the hall sensor. It is not super clear in the manual that the seal actually sits in the timing cover. I got a new seal but it was pretty tricky to install properly as the lip of the seal wants to fold over as you insert the timing case. This really tried my patience but I solved the issue by inserting the top of, I think, a can of WD40 to open up the lip of the seal and then offered up the timing case to the shaft  The circumference was not quite large enough so I used sticky tape till it did the job.
 
The main issue however was the inlet camshaft gear. Unbeknown to me it had also been damaged by the bolt that came loose. The small locating bump that inserts into the notch of the camshaft was mostly worn away by the spinning action when the bolt came loose. This meant that when I put it all back together and torqued down the camshaft sprocket I somehow managed to screw the alignment up! So another learning opportunity! I replaced the sprocket and triple-checked the camshaft positions and didn't just rely on the triangular alignment cut outs on the sprockets! 

I wanted to make sure the timing was spot on this time so I used a dial indicator to accurately find the firing point (0.24mm BTDC) and used a hall Sensor LED tester to position the Hall Sensor correctly.

After all that, the bike fired up the first time and passed the mile shakedown first ride. Tickover is a bit high and there is a bit of a noise coming from either the alternator or maybe the clutch. I look into that sometime after I get back to the UK. Otherwise, it has turned out well, and looking forward to riding in the UK next spring.

As you can see from the video, I had to change the rotors and I also had to get a new rim. When I purchased the project I never checked the condition of these - mistake!