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1986 K75 C w/ Luftmeister Turbo
Table of Contents (Hyperlinked) 1)Introduction 2) Turbo Charging 2.1 Basic Concepts & Terminology |
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Disclaimer: I do not warrant that ANYTHING on this page is complete or correct. I know a lot about K bikes from owning quite a few and being a "shadetree mechanic" on them for several years but am anything but an expert on turbocharging, the details of engine management systems or exhausts aside from having a basic understanding of how such things work. What you see here is what I've gleaned from other places on The Internet and from individuals I've come across who know a lot more about this stuff than I do. This page is just a place where I document things I learn/discover as I go along for my own personal edification. I merely put it up on this site in case anybody else is interested in this topic. In many places I will oversimplify things in order to be concise. The purpose of this page is to give an overview, not explain the intricacies of turbo engineering and design. If you find something that you feel is wrong or misinformation then please let me know at smithduck@gmail.com. |
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Very Brief History: Back around the 1980s, Luftmeister was a SoCal-based company that specialized in aftermarket parts for BMW motorcycles, including exhausts and turbo installs/kits. With respect to turbocharging two valve K bikes, aside from some custom K75s made for attempting speed records and a few "street" models, it is my understanding that the only "mass produced" K bike turbo setups were for the K100, with approximately 200 being produced and installed or sold as kits. Therefore, a Luftmeister turbo'd K75 is a rather rare brick. Luftmeister Documentation: I do not have any operating or maintenance documentation for the Luftmeister turbo setup. If you have anything of this sort for either K75 or K100 Luftmeister turbo systems then I'd be VERY interested in getting a either a hard or PDF copy of what you have. Heck, even Luftmeister R Bike turbo documentation from the late 80s or early 90s would probably be helpful to some extent. If you have anything like this and are willing to share it then please email me at mailto:smithduck@gmail.com |
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(Short version) The bike was listed on a SoCal Craig's List. Here's one of the pictures and the text of the CL ad:
I was OK with the asking price and knew someone in SoCal who was willing to pick it up for me and hold it until I could get it home to Seattle so I bought it in late August of 2013. My original plan was to fly down from Seattle in September sometime and ride it home up the coast since I've done that several times before but when the end of September came, for a variety of reasons, I decided just to have it shipped home instead. Since SoCal to Seattle is a straight shot up I-5, I was able to get a decent shipping deal on door-to-door shipping from Power Sports Services Northwest out of Salem, OR. |
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On Thursday, October 10, a little after noon, the bike was delivered to my home in Seattle. The odometer read 114K+ but records that came with indicate the instrument cluster was replaced at 2,200 mile so maybe it has 116K on it. Regardless of supposed miles, it's in pretty darn good shape for a K of that age and I'm very happy with my purchase.
It had a couple of issues. First, by the bent front brake lever (which I'd noticed in the CL pictures prior to purchase) and the cracked right mirror glass, I could tell that it had been dropped on the right side. Non-issue to me as I have a good brake lever and mirror to replace those. Both of the engine covers are in nice shape and there aren't any signs that it has ever been crashed. Though not perfect nor comprehensive, it did come with some documentation of its history from which I was able to discern the following: 1) According to the documentation that came with it. It was originally sold from Huntington, NY to a buyer in San Diego as a K75T. The K75 "T" model was a US-only model put together by BMW NA to make the K75 a better touring bike before the K75RT came out in 1990. It was manufactured as a K75C and then had a standard K100 headlight surround, a large handlebar-mounted windscreen and luggage installed. Here's a picture of one that I Googled up:
How it ended up with the current C fairing is unknown to me. 2) In late 1986, the steering was recalled/repaired by BMW. 3) The instrument cluster was replaced at 2,200 miles. 4) In January of 1988, at about 20,000 miles, a previous owner installed modified cams. I don't have any details beyond that but my guess is that they were modified to improve the lower end of the power curve. 5) In March of 1988, at about 23,000 miles. The Luftmeister turbo and exhaust were installed. I guess that that's probably when the Luftmeister shock was also installed. 6) In November of 1990, at about 41,000 miles, the engine was balanced and the valves were ground. 7) In May of 1991, at about 47,000 miles, the splines on the final drive and the drive shaft were replaced. The transmission was modified in order to make the gear ratios taller: +4% on gears 1-4 and +9% on fifth gear. 8) In March of 1992, at about 58,000 miles, the valves were checked/adjusted, the front wheel bearings replaced and the splines lubed. 9) In August of 1992, at about 64,000 miles, all of the coolant hoses were replaced and the clutch replaced. 10) Not sure when but at about 84,000 miles the splines were lubed at a BMW dealer in San Diego. 11) At about 86,000 miles the front brake lines were replaced. 12) At about 112,000 miles the steering head bearings, throttle and clutch cables and rear wheel were replaced. My guess is that the rear wheel was replaced due to wear on its drum brake surface. There was no documentation on more mundane maintenance tasks like oil and filter changes but, given what else was done to this K75, my guess is that those were done regularly since the bike generally seems to have been very well taken care of. The California license plate on it is very old and faded so I'm pretty sure that it's the original license plate from 1986. It has near new Bridgestone Spitfire tires installed and came with a half-sized 20 Ah AGM battery manufactured in May of 2012. The city cases that came with it are in pretty good shape and have the newer round locks on them. In going over the bike it seems as, although not mentioned in the documentation, other parts like the starter and center stand have been replaced. Side stand? |
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2.1 Basic Turbo Concepts & Terminology
The diagram above depicts a typical basic turbo system. It utilizes the energy of the exhaust flow to spin a turbine wheel connected to a compressor wheel in order to compress the intake air and increase its density. This higher density air provides more oxygen to the combustion chamber. However, compressing the air makes it warmer (decreasing its density) so including an intercooler (a radiator for air) in the system reduces the air's temperature, thus increasing it's density. Since turbos spin in excess of 100,000 RPM, the bearings on the shaft between the turbine and compressor wheels are constantly fed "fresh" engine oil to lubricate and cool them. The pressure control valve (a.k.a. wastegate) on the turbine side of the turbo regulates the turbine speed and boost pressure while improving boost at lower speeds. Turbocharged engines can be further optimized to obtain maximum engine power by modifying the cylinder head to make it flow better as well as altering valves and valve cams to optimize them and get maximum output from a turbo.
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Turbocharger: The turbocharger is a model RHB5 manufactured by IHI Turbo. This turbo was used in quite a few cars back on the mid-late 80s so rebuild kits are readily available from eBay and other online vendors. Turbo Boost: The boost is the amount of additional pressure the turbo compressor generates above ambient atmospheric pressure. (14.7 psi at sea level) On this K75, the boost is ..... Turbo Oil Supply: The oil supply to the turbo bearings is fed from ??? and is fed back into the engine's oil sump Intercooler: The intercooler is a normal sized automotive intercooler that was cut down and customized via TIG welding to fit on the K75. Air Bypass Valve: This K75 has an air bypass valve (and a second air filter by the rider's right knee) which allows the engine to aspirate normally until the turbo spins up and blows a gate shut in order to minimize turbo lag off of the line. Headers: The headers that go from the cylinder head to se were also custom made by Luftmeister for the K75 turbo system. Exhaust: The exhaust is a Luftmeister custom and is a single piece from the turbo exhaust outlet to the end of the exhaust can. Engine Mods: Although it is my understanding that Luftmeister generally did not do any engine modifications for their street turbos, the service records that came with this K75 indicate that modified cams were installed about 3,000 miles prior to the turbo being installed. I have no other details than that but assume that the cams were modified to improve the low end and/or mid-range power. The service records also indicate that the engine was balanced and the valves were ground at about 47,000 miles - about 24K after the turbo was installed. Again. I have no specific details on what this specifically entailed. Fuel Pressure Regulator: ???? Fuel Injectors: ???? Rev Limiter: ????
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Engine/Fuel System
TO DO LIST: Adjusted Valves
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Controls
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Drive Train |
Suspension/Tires/Brakes |
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Lighting/Electrical
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Body/Cosmetic
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Luggage/Seat |
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Engine & Fuel System |
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Oil & Filter Change: Don't know when the last oil change was on this bike. Did an oil change with an OEM filter, Shell Rotella T6 Synthetic 5W-40, new crush washer and O-ring. From doing a little surfing, it seems as though the Rotella T6 Synthetic is a good oil for turbos. Since the turbo bearings are very dependent upon oil I'll employ an oil change interval of 5,000 miles for this bike.
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Clutch: As a matter of preventative maintenance, while I had the transmission of I took the clutch off to inspect it and replace the clutch nut O-ring. The old O-ring was still pretty pliable and the rear main seal looks new so I'm pretty sure have been recently replaced. I installed a brand new O-ring anyway since it's only a $2 part. The clutch looked pretty good but, since I had it on hand, I installed a nicer clutch with a near new clutch plate.
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Head: Text
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Head: Text
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Head: Text
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Head: Text
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Head: Text
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Drive Train |
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32/11 Paralever Final Drive: The bike came with a K75 32/10 drum brake final drive that all K75Cs came with. I replaced it with a 32/11 paralever from an early K1100LT in order to get 9% "taller" gearing and to convert the rear brake to a disc. I'd prefer a black final drive and swing but I had this one and a swing arm for it on hand so that was the most expedient/cheapest way to go. The paralever setup also helps the bike handle better and gets rid of the "jacking effect" of the monolever setup under high torque.
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K1100 Transmission: In order to support the front of the paralever strut from the bottom of the final drive, I installed a K1100 transmission.
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Clutch: While I had the transmission off I took the clutch apart to inspect it and replace the clutch nut O-ring.
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K1100 Peg Plates: In order to clear the "hump" in the paralever swing arm at the rear of the right peg plate, I installed K1100 peg plates.
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Synthetic Gear Oils w/ Moly Additive: I filled the transmission with BRAND??? 75W-140 and the final drive with brand???? 75w-90 synthetic gear oils. I also added Guard Dog Moly Additive to both to reduce friction/wear and make the transmission shift as smoothly as possible.
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Suspension - Tires - Brakes |
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Head: Text
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Head: Text
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Head: Text
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Controls |
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Head: Text
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Lighting & Electrical |
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Head: Text
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Body & Cosmetic |
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Head: Text
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Seat & Luggage |
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Head: Text
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Rotella T6 Synthetic & New Oil Filter
