Monday, September 22, 2014

Honda Express Muriatic Acid Wash / Seized Cylinder Repair

How To perform a Muriatic acid wash on a Honda Express NC50 DR Racing 70cc (46mm) cylinder jug.

Wash away the sadness...

Ad clicking is great too...

Honda Express Moped nc50 1978 engine cylinder repair using Muriatic acid wash technique. Highly caustic and dangerous! Will even dissolve iron. This amateur attempt is used to repair a multiple soft-seized Honda Express Moped cylinder jug. The object is to use the acid to remove the aluminum left by soft-seize on cylinder jug wall. DO NOT ATTEMPT. DO AT OWN RISK. NOT LIABLE FOR ANYTHING SHOWING IN VIDEO.

With all that being said... Here are links to the items I used to perform this Honda express cylinder jug repair:
Feel free to leave feedback and suggestions on video, process, and/or any questions.

Honda Express Moped Engine Soft-Seize Cylinder Jug Piston Seizure : Woops!

Honda Express moped... 

"Houston, we've had a problem here"

Back on Mar 28th 2014 I had taken out my newly "upgraded" honda express nc50 noped for some test riding. The prior weekend I had take in out as well and experienced some technical difficulties... ie. It died on me. Once fully assembled with the following parts, I was able to start the honda noped first-shot. It was great. Now, keep in mind, I used the following stock express moped Mikuni carb settings on pilot run:

  • Idle : 22.5 
  • Main : 185 
  • Needle setting (clip position) : default 
The "low end" throttle was very poor, being sputtery and slooooow on the go. But, when I was in the 15-20 mph range... the moped FLEW! Because I was breaking in the new setup and honda carb, I never had the throttle more than 1/2 and kept the speed to 30-35 mph (measured by the Trail Tech vapor speedometer).

The moped ran excellent for 30+ miles and unfortunately my Trail Tech vapor temperature gauge is not installed correctly, so I was running without and monitoring of engine temp. On my way home there was a half mile or so of flat open back-roads and I decided to test max honda nc50 acceleration. I was probably between 35-38 mph and the honda noped began to "buck" (like I was jamming on the breaks) and then finally the engine died and I cruised to the edge of the road.

At the time, I didn't understand the problem. I thought it might be electrical or perhaps something went wrong with the carburetor and the engine lost fuel. As see in this forum post, I experienced a Honda Express Cylinder Jug Soft-Seize. As you can see for the honda express parts photo at the beginning of this post, I had soft-seize the engine a few times 5-10. After the piston and piston rings had melted to beyond functionable, I was unable to start the moped because I lost all compression I had.

I thought the cylinder and piston were shot and I would need to drop at least $150+ for a new engine kit. Some suggestions I received included:

Of those options I choose the Muriatic Acid Wash technique, because is was the least expensive. $60 for the Honda Dr 70cc 46mm upgrade piston. $7.29 for the Muriatic Acid. Some chemical resistant gloves, baking soda, Rubbermaid tub, goggles, air mask, paper towels... all things I already owned.

Next post reveals the video documentation of the process.