It’s a Hercules K105X from 1972 and needs a LOT of work, but I really couldn’t say no to the offer. This will probably be my main project for 2026.
It’s pretty much complete aside from the missing battery cover and the engine turns over by hand. I had some trouble getting it into neutral, there’s definitely something wrong with the gearbox or the linkage. The tank is completely rusted inside, I’ll probably need a new one.
It might be a long shot, but does anyone in this community have experience with these bikes? The K125 is supposedly pretty similar.
You must log in or # to comment.
Alright bud, congrats, this is how I got into motorcycling as well, albeit on a different make/model.
Some things to check, if you’re already aware of this stuff my bad, but maybe you’ll find some useful info here:
- The tank is probably fine, I used electrolysis+washing soda to derust that fucker over an afternoon. POR15 is great to permanently block water from being a problem again after the initial derust.
- Carbs are going to need careful cleaning, I never tried berrymans (gallon of noxious chemicals sitting around is not my vibe), but I do recommend ultrasonic cleaning. The rubber is likely degraded (pinholes, dry rot), see if you can find people making aftermarket replacements which use viton, resistant to ethanol in modern gasoline
- For the future, never spin a motor without putting some oil into the spark plugs holes, the piston rings will gouge the fuck outta the piston walls. Gouges = reduced compression, which = lower engine power, besides burning oil. Clean around the spark plugs to prevent any grit from falling in. Pull out the spark plugs, borrow an endoscope camera from AutoZone or whatever, check inside the cylinders for rust or for circumferential gouges left by the rusting piston rings as well. Nobody ever drops a little oil into the pistons before putting them away, the small amount of humidity that sneaks in causes flash rust. You’ll be honing the cylinder wall, it’s a bit of work but not too bad.
- Whether you hone or not, best way to check engine condition is using a compression tester, fill the engine with the right kind of oil (should meet at least JASO MA2, no friction modifiers!! They make your clutch permanently slip), plug a charged spare battery in (even a jumper from your car), hook a compression tester to one cylinder while the other cyl has its spark plug thoroughly loosened but not removed (otherwise it may jet oil out into your shop, you can also use some paper towels). Crank, crank, crank, check the tester for the max value. I don’t know this bike, but look for at least 110psi compression, with approx. symmetric values on both cyls.
- Save money and use cheap oil during restoration, the filter will catch the important debris as you keep reusing the oil, because you’ll find that as you get closer and closer to proper operating status, you’ll be emptying/refilling the oil to get at internals for inspection/adjustment, thus no need to keep using brand new oil. Definitely use the right stuff on the final fill though, and please recycle the old stuff and the filters at the place you bought the oil.
Plenty of other work to do, as your life is in your hands, but you’ll learn a lot, and have fun too. Keep an eye out for corroded electrical connections too, there’s a wiring diagram in the manual that’s pretty easy to follow.
The official service manual is your friend, take the time to read the job first before going for it. Crazy I gotta say that, but I’ve seen other people really fuck some moto jobs up.
Have fun, keep us posted on your progress!
Wow, great advice, thanks for taking the time for this write-up!
I’ve worked as a car mechanic, so I’m not completely clueless but I don’t have any experience with motorcycles.
I thought about cleaning the tank myself but I’m not sure how to go about conserving it. Do you have any tips how I could apply the coating on the inside? The tank kinda does a inverted U-shape around the frame and the filler hole is not very large.
The carb seems to be a pretty common model from Sachs and there are a lot of manuals available. Not so much for the bike itself unfortunately, there’s pretty much zero documentation to be found. Most of the parts including the engine, brakes and gearbox seem to be from Sachs as well, so I’ll probably be able find some more info on those separately.
I have not tested for compression yet but I did put some oil in the cylinder and let it sit for a bit before turning it over. I’ll see if I can get it running before I decide on the actual scope of this project, but it’s definitely going back on the road in any case!
Nice, you’ll find bikes to be away easier to work on than cars haha. Maybe email this guy? https://www.pentonpartsusa.com/catalog/8a repair sachs.htm
For the tank, I basically turned the tank upside down after taping up the fill port, and reached a bent coat hanger in via the removable petcock, electrically isolated from the tank body with the highest of technology: used chopsticks. Coat hangers usually have a thin plastic varnish, so scrub the wire with steel wool first.
Electrolysis will ‘pull’ rust from every spot that has line-of-sight with the wire. Considering the u-bend, seems like you may have to do two runs of electrolysis for removing the majority of the rust, then follow it with something like evaporust to get anything that got missed.
Glad to hear you put oil in the cylinder first, I really wish I had known that when I first started haha.
Maybe email this guy? https://www.pentonpartsusa.com/catalog/8a repair sachs.htm
That looks promising, thanks!
The only rust repairs I had to deal with so far were frame and underbody stuff on cars with plenty of space but I’m excited for the challenge. It’s definitely a welcome change to be able to work on something while sitting comfortably and not constantly bent over an engine bay or crawling around under a vehicle :D
I really appreciate the advice!
the filter will catch the important debris as you keep reusing the oil, because you’ll find that as you get closer and closer to proper operating status, you’ll be emptying/refilling the oil to get at internals for inspection/adjustment, thus no need to keep using brand new oil.
It’s a two stroke.
👍 Still useful info for the anyone in the future doing this kind of work.
Just a random passerby with no motorcycle experience -
That green is awesome! Bummer that the tank will need to be replaced.
I really like the color too. I’ll see if I can get it refurbished for a reasonable price before I go shopping for a replacement. There are a few pics of others in the same color online, so maybe I can get a matching one.
Quote “this will probably be my main project”. Yep. Everything that Rubber says plus … tank may be ok. Start by washing it out with petrol and ball bearings (take tap and filter off). Also consider adding an external filter in your new fuel lines before the carb. Gearbox may be the reason it was left to die, or may be straightforward - you will have to get it open. Resist the temptation to turn the engine over again. Post lots of photos. Have fun.
Yeah, this bike has been sitting since the early 80s as far as I know. Pretty much everything will have to be inspected or replaced. Thankfully the wiring is not very complex but it’s still messy. I got the indicators to work after connecting a battery, so not all is lost :D
In-line filter was what I did with my motorcycle.
If it’s you first bike, I recommend changing the front breaks to discs.
Keep original parts for when you handle traffic sufficiently well to add the difficulty of very crappy breaking.
On a similar note, at least reshine the mirrors in the front/rear lamps so people see you.
Edit: forgot the most important part: great purchase and great project.
PS: change all the hoses and gasket to models that are compatible with mixed fuel/ethanol or you’re in for a very bad surprise if not trashed engine.
Thanks for the advice! I’m all for keeping things original but I agree, the brakes definitely look like they could use an upgrade.
if you spend another 4000 it could be worth as much as 1200.
Hard/impossible to find parts. You can try and de-rust the tank, but they usually rust up quickly or if you coat them, the coating eventually flakes off.
My advice: part it out.
I’m located in Germany and surprisingly parts are not hard to find at all. I always check the availability before buying a vehicle and there’s still plenty of companies manufacturing spares, from the light switches to the springs and down to the gearbox. I think it helps that Hercules’ lineup shared a lot of components in the 70s. I already found the missing battery cover freshly painted for 22 Euros.
This project isn’t about selling or making money. I just enjoy the wrenching, as long as it may take :D
This thing will be literally impossible to find parts for. Everyones always fooled by the big stuff, but there’s bound to be some random bolt or valve or something that was a problem on these and that you’ll never be able to find, and then you’ll be like 2k deep into something and shit out of luck. Not to even mention the struggle of finding someone capable that’s willing to touch it when you come up against something you can’t do yourself. Save yourself the money pit OP, find something else, as I know this sounds harsh, but this ain’t it.
I appreciate the concern but I know what I’m getting myself into. My last project was a wrecked classic car with a seized engine and I now use it as my daily driver. I don’t have to get it back to museum condition, I just want it safe and drivable. In the worst case I will buy a second one to part it out. These things are still pretty cheap around here. There’s even a club for the K105 and K125.
ok, have fun, but these bikes were never good. They made an optomistic 12 hp, had terrible brakes and suspension.
Thanks, I didn’t expect much anyways :D
My own take (having plenty of old bikes in various states of disrepair) is either buy another for spares, or ditch orignality and engine swap it (ax100 is cheap and half a chance of fitting)
I’m pretty sure I know your garage x)
There’s no way lol. Pretty sure less than 10 people have been in there in the last 30 years.
Haha, its a joke about a genetic chaotic garage. everybody has one of those at home x) “mine looks the same” ;)
