Found engine rescue.

[cayminlast]

In April 2024 I spotted a rusty old bicycle engine on a junkyard truck, got it for free from the guy, soaked it with verious lubricants ect. and put it in a bucket till about a week ago, when I took the head off, the piston was like new, not a hint of carbon and the cylinder looked almost perfect. I suspect the owner must have got frustrated and discarded it, there were obvious signs of a head gasket leak and the studs were loose enough that they came out with the Acorn nuts attached. Everything looks okay except for the carb and the clutch shaft bearings feel gritty. Should I bother even trying to revive this little fire breather?

 

[DAMIEN1307]

It's worth a try based on what you described...Just get rid of the acorn nuts on top and replace them with open ended nuts so you will be assured to have the head torqued on tight...Make sure those cylinder studs are totally bottomed out into the bottom end of the motor with some blue locktite just on the threads going into the bottom end...I started doing mine that way sometime back and have been quite happy with the results that have required less retorquing of the nuts to hold the cylinder in head down properly.

 

[cayminlast]

It's worth a try based on what you described...Just get rid of the acorn nuts on top and replace them with open ended nuts so you will be assured to have the head torqued on tight...Make sure those cylinder studs are totally bottomed out into the bottom end of the motor with some blue locktite just on the threads going into the bottom end...I started doing mine that way sometime back and have been quite happy with the results that have required less retorquing of the nuts to hold the cylinder in head down properly.

I appreciate your tips and it's worth a try for sure. I built a 4 stroke 50cc bike last year and eventually sold it, a lot of parts were custom so there are enough left over parts to keep it a budget build. My son donated his old mountain bike which is an excellent candidate. Thanks for the encouragement.

 

[Gordy]

Sounds worth trying to save. Wash the bottom end out with a bit of premix gas. Clean the carb. There's probably not much you can do about the clutch bearings. Just clean everything well and get it ready to go. Good luck!

 

[cayminlast]

I managed to get a few pics after stripping, cleaning and investigating the rescue. The piston is untouched, just as is looked when the head came off.

 

[Gordy]

I managed to get a few pics after stripping, cleaning and investigating the rescue. The piston is untouched, just as is looked when the head came off. View attachment 223464

Doesn't look like it's even been run. You're gonna need a new ignition system. If you have it torn down that far might as well replace those clutch bearings.

 

[cayminlast]

Doesn't look like it's even been run. You're gonna need a new ignition system. If you have it torn down that far might as well replace those clutch bearings.

Yes, I split the case and replaced the bearing, removed the seal on the crank side only, no case gasket so I used high torque/temp gasket maker per the instructions, the mating surfaces were'nt perfect, a bit gentle persuasion and lots of test fitting it's good. The hollidays might slow me down a bit, but I'm getting excited and all sorts of idea's are hatching in my imagination. Thanks Guys.

 

[Gordy]

Yes, I split the case and replaced the bearing, removed the seal on the crank side only, no case gasket so I used high torque/temp gasket maker per the instructions, the mating surfaces were'nt perfect, a bit gentle persuasion and lots of test fitting it's good. The hollidays might slow me down a bit, but I'm getting excited and all sorts of idea's are hatching in my imagination. Thanks Guys.

Sounds like you've got things under control so far. I look forward to seeing what you come up with

 

[Chainlube]

Do you know @inspectorcritic? He got caught in a snow storm and had to toss his brand new bike in the ditch.

 

[michael whiteman]

Doesn't look like it's even been run. You're gonna need a new ignition system. If you have it torn down that far might as well replace those clutch bearings.

Gordy, I'm betting if he checks the coil winding with an OHM meter he will find it to be OK. The rust isn't going to affect the magnetic field at all. Have a wonderful Christmas my friend.