Rodrigo Alvarez

Tinkering as a way of life

K75 Restoration: New endevour

For the last few years I’ve wanted to restore a classic motorcycle. I’ve been looking around on second hand sites but it is hard to find reasonable prices in Spain. You can’t expect to pay less than 2k€ for a larger than 500cc motorbike and even in that case, the state of the engine can’t be trusted.

I laid my eyes on a 1990 BMW K75 that has been parked in my neighbourhood for the last two years. The bike is in a hideous state and its colour isn’t helping. I believe BMW calls it “Topaz Red Violet “, I call it; Ugly Purple.

The beast

I purchased the Carfax for a few euros and found out that the last time the bike had passed an inspection was more than two years ago. For what I know, that bike has been in the street at least that time. In the Carfax report I found the owner and wrote him a letter to encourage to sell it to me for a symbolic price. After a few back and forth emails we agreed on 200 euros, with me being in charge of paying the taxes related to the transaction.

About the reason he had it abandoned on the street; “One day I was going to take my daughter to school, the bike started, I went out of the garage and suddenly the bike stopped and wouldn’t start again. Being in a hurry, we took the car and I never worried more about the bike”. Weird…. Though, it suggests that something electrical might be wrong. Also while in the street a car knocked the bike over and he was left a note with contact details for insurance purposes, the guy never bothered to fix the bike.

General State

Bad to very bad… The fall must have broken foot rest plates (PNs 46711457234 & 46711454485). Broken headlight glass. Cracked (need to check) crankcase cover. Bent front brake lever & handlebar.

I would later find out that the back spring is upside down….

And of course, the time in the street has taken its toll. It has rusted forks, rusted gearbox oil plug (07119919143).Cracked vacuum plugs (13547694924). Rust in the battery strap (61211459044). Sulfate in battery holder and rusted Vibration dampers (PN61211233028 male/male M6 thread 8mm length. 15mm height rubber part and around 22mm wide in thickest point for reference). Brakeswise, the front brake works, but the back brake doesn’t have any fluid in it. The oil level seems reasonable though…

On a closer inspection after the purchase, the petrol tank is installed incorrectly, missing (PN16112309163) vibration dampers and missing retention clips (07129934336). The Battery is around 5 volts but should be at least 12V. However, good news! The clock is still running and its on time!

Fuses are all ok.Coolant level cannot be determined and the state of the spark plugs is abysmal. I believe the HT leads on this bike need solid terminals but the installed spark plugs have screw terminals (Recommended spark plugs Bosch X5DC or NGK D7EA). Maybe is this the cause for not starting? Weird….

Let’s try the easiest thing first.

I’ve purchased a new battery (EXIDE GEL 12V 19AH GEL12-19) and new spark plugs, as I would’ve done this anyway ( NGK D7EA + nupsies to turn threaded terminal to a solid one), I’ve also purchased the vacuum plugs that were on the same site for some change. Spark plugs hey have been tested by connecting them to the HV leads and grounding them to the chassis. They all create a strong blue spark. Injectors have been removed from the throttle bodies and they all spit petrol. Still The bike wont start….

An engine needs four things to run; Fuel, air, compression and spark, I am pretty sure on all of them but the compression…. but that will be for the next post as I need to purchase a compression tester.

Shout out to my dad who helped me push the bike to our garage! It is really a heavy bike to push around!