Hello all,
My 17yr old son just picked up a 89 K100rs that he’s going to strip and build to match his 87 535is.
We’ll probably be asking some questions on here(we’ll try the search function first). For starters it’s a clean bike with non functioning ABS that we’re going to eliminate. Only real issue with the bike is it won’t start when cold unless you fog her throat with a little eather. Then it fires up and purrs like a kitten and runs hard, we’re assuming it’s a failing fuel pump or blocked FF.
We’re looking forward to the project!

Welcome Winmag

Hi i take it the bike starts ok when warm,with the Ks if we presume to assume shit happens
Easy start products are not recommended,if the engine spins at a good speed,on starter do compression test and start from there,good luck with the project.

After failure to start check the spark plugs. Are they wet or dry?
Regards Martin.

OK, so we are pulling it all down. Since it's snowing it gives time.
We'll check valve clearance and do all the typical stuff.
Searching the forums I think we may go with K75 pistons and hone then re ring it.
My son has a 82 320i, 84 533i, 85 535i and a 87 535is. The motorcycle looks to be typical 80's BMW technology. 

As far as the no start when cold, we cranked on it for 5 minutes and got no heavy fuel smell out of the exhaust.  There's no excessive fuel smell in the oil either. Had the same issue on the 85 535i and we installed a 255lph in tank pump and bypassed the external fuel pump and it literally starts with a tap of the key, and it has 244k miles on it. Since then we've converted all the cars to a in tank only pump. Not really concerned since we're going through it. We'll post pics as we progress.

winmag4582001 wrote:Only real issue with the bike is it won’t start when cold unless you fog her throat with a little eather. Then it fires up and purrs like a kitten and runs hard

Welcome. If it purrs and runs well, why would you consider changing the pistons and re-ringing it?

winmag4582001 wrote:OK, so we are pulling it all down. Since it's snowing it gives time.
We'll check valve clearance and do all the typical stuff.
Searching the forums I think we may go with K75 pistons and hone then re ring it.
My son has a 82 320i, 84 533i, 85 535i and a 87 535is. The motorcycle looks to be typical 80's BMW technology. 

As far as the no start when cold, we cranked on it for 5 minutes and got no heavy fuel smell out of the exhaust.  There's no excessive fuel smell in the oil either. Had the same issue on the 85 535i and we installed a 255lph in tank pump and bypassed the external fuel pump and it literally starts with a tap of the key, and it has 244k miles on it. Since then we've converted all the cars to a in tank only pump. Not really concerned since we're going through it. We'll post pics as we progress.

you wouldn't hone it at all
the cylinders are lined nickasil , and there is virtually no wear to talk about , k75 pistons fit straight in , same bore and stroke

starting issue , more likely a fuel pressure regulator - injector clean issue , the correct bmw pump has a backflow valve which maintains pressure for a good while along the pressure rail , if the pressure regulator weeps internally a bit, as they can do , could take some time to get fuel to pressure along the fuel rail for the injectors .

just do the irregular maintenance required for any neglected engine and im sure you will be surprised

welcome aboard

Charlie99 Thanks for letting me know about the cylinder lining. My son and I are new to street bikes. Been into cars forever. We’re eager to open it up and play. He read somewhere that the K75 pistons were higher compression, that’s the reason behind finding a set for it. The boy has a lot of energy and I have to give him credit, he’s a better mechanic and electrician than most adults I know. LOL Thanks for the replies!

Nice project. Good luck with it.

Fuel filter - NAPA 3032