48cc engine overhaul

makoman1860

New Member
Jun 6, 2008
4
0
0
Good Day All,
Im new to this forum, but not to these "wonderful" 48cc bicycle engine kits. Ive done 3 conversions, and I have found the following overhaul points to be very helpful.

1-Tear the engine down to every last nut and bolt
2-De-burr all edges on the case
3-lap mating surfaces on surface plate
4-Machine the case to accept "normal" 30mm OD crank seals, and use decent Corteco seals from CR seal.
5-Replace the crank bearings with SKF units
6-Replace the jackshaft bearings with SKF sealed ( not shielded ) units
7-Actually align , redrill, and helicoil most of the holes in the case
8-Replace the cylinder studs with stainless (english threaded units)
9-Re-true and polish the crankshaft journals, especially where the seals ride
10-Deburr and chamfer everything slightly, these engines are full of burrs and sharp edges.
11-chamfer and polish the edges of the ports in the cylinder
12-lap the cylinder and cylinder head to make sure they are flat
13-lightly hone all the edges of the piston rings, and check the fit in the piston.
14-De-burr the primary reduction gears, glass beading works well for this
15-Clean and relube the clutch idler bearings with high temp nlgi-3 grease
16-Bush the clutch shaft in the sprocket cover with a bronze bushing
17-Ultrasonicly clean every part (if you can) and assemble with a decent lube one the engine parts, high temp grease on everything else, and a removeable sealer on the gaskets.
18-Assemble using allen head good quality fasteners
19-Seal the excitation coil in the engine with epoxy
20-I have run blendzall 455 at a 32:1 ratio in all of mine with great results.

This probably seems like overkill, and it does take a bit of time. But boy are they reliable after that! All of the kits I bought, from various suppliers, had quite a lot of grit, dirt, metal chips, bad bearings, and all had torn crank seals. Just a good cleaning, de-burring, and hand fitting, and sealing up would make a world of difference. Anyone else gone this far to save a buck?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Not a bad thing to do if you are motorhead enough to do it, some people (we love you anyways...) don't know which end of a screw driver to hold, so this would be out of the question.
 

spad4me

New Member
Jan 20, 2008
472
0
0
Arizona Bullhead
Good Day All,
Im new to this forum, but not to these "wonderful" 48cc bicycle engine kits. Ive done 3 conversions, and I have found the following overhaul points to be very helpful.

1-Tear the engine down to every last nut and bolt
2-De-burr all edges on the case
3-lap mating surfaces on surface plate
4-Machine the case to accept "normal" 30mm OD crank seals, and use decent Corteco seals from CR seal.
5-Replace the crank bearings with SKF units
6-Replace the jackshaft bearings with SKF sealed ( not shielded ) units
7-Actually align , redrill, and helicoil most of the holes in the case
8-Replace the cylinder studs with stainless (english threaded units)
9-Re-true and polish the crankshaft journals, especially where the seals ride
10-Deburr and chamfer everything slightly, these engines are full of burrs and sharp edges.
11-chamfer and polish the edges of the ports in the cylinder
12-lap the cylinder and cylinder head to make sure they are flat
13-lightly hone all the edges of the piston rings, and check the fit in the piston.
14-De-burr the primary reduction gears, glass beading works well for this
15-Clean and relube the clutch idler bearings with high temp nlgi-3 grease
16-Bush the clutch shaft in the sprocket cover with a bronze bushing
17-Ultrasonicly clean every part (if you can) and assemble with a decent lube one the engine parts, high temp grease on everything else, and a removeable sealer on the gaskets.
18-Assemble using allen head good quality fasteners
19-Seal the excitation coil in the engine with epoxy
20-I have run blendzall 455 at a 32:1 ratio in all of mine with great results.

This probably seems like overkill, and it does take a bit of time. But boy are they reliable after that! All of the kits I bought, from various suppliers, had quite a lot of grit, dirt, metal chips, bad bearings, and all had torn crank seals. Just a good cleaning, de-burring, and hand fitting, and sealing up would make a world of difference. Anyone else gone this far to save a buck?
I just bookmarked this post for reference.

Thank you.
 

Egor

New Member
Jan 30, 2008
714
0
0
Hurricane Utah
Good job. I take all mine apart and have a look, but not that much attention. I finely found someone that knows about sharp edged rings on a two stroke. I found some seals that fit the engine perfectly, and the bearings are a must, mine were lumpy when turned. I do a lot of porting and I have a mod for the carb that works well. Oh I found a way to shut up the speaker affect of the right side cover, smear the inside with Silicone rubber, it will dampen the noise. I hope you enjoy this forum as much as I do. Have fun, Dave
PS: Let me know if you would like to do some porting. I would like to have someone enjoy the affects.
 

makoman1860

New Member
Jun 6, 2008
4
0
0
Good job. I take all mine apart and have a look, but not that much attention. I finely found someone that knows about sharp edged rings on a two stroke. I found some seals that fit the engine perfectly, and the bearings are a must, mine were lumpy when turned. I do a lot of porting and I have a mod for the carb that works well. Oh I found a way to shut up the speaker affect of the right side cover, smear the inside with Silicone rubber, it will dampen the noise. I hope you enjoy this forum as much as I do. Have fun, Dave
PS: Let me know if you would like to do some porting. I would like to have someone enjoy the affects.
Hey Dave,
I myself have re-timed the ports on one of my engines, along with a new intake manifold, walbro "pumper" carb , changed ignition timing and tuned pipe/silencer setup. The end result?-The power of a 1970's vintage 50cc dirtbike engine, with the lifespan of a yugo. In all seriousness the crankshaft is the weak link in the engine for power development, with the driveline short behind. The crankpin to crank-web fit isnt the greatest, and the materials very 1940's vintage (cheap 1940's). Also the piston being a long trunk design is too heavy for high RPM use. After that ordeal I stuck to just making them decently reliable with good runability, and have been having a ball with that!
 

stude13

New Member
May 28, 2008
404
0
0
north bend wa.
i recommend viewing worlds fastest indian, you guys may start casting your own pistons or decide to buy a subatu or tanaka and go on a looooong ride
 

makoman1860

New Member
Jun 6, 2008
4
0
0
i recommend viewing worlds fastest indian, you guys may start casting your own pistons or decide to buy a subatu or tanaka and go on a looooong ride

Heh,
Your not too far off. If I wasnt stretched so thin with other avenues of engine driven machines I would probably toy with this some more. Right now its a reliable way to get around airport and shop.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Hey Dave,
I myself have re-timed the ports on one of my engines, along with a new intake manifold, walbro "pumper" carb , changed ignition timing and tuned pipe/silencer setup. The end result?-The power of a 1970's vintage 50cc dirtbike engine, with the lifespan of a yugo. In all seriousness the crankshaft is the weak link in the engine for power development, with the driveline short behind. The crankpin to crank-web fit isnt the greatest, and the materials very 1940's vintage (cheap 1940's). Also the piston being a long trunk design is too heavy for high RPM use. After that ordeal I stuck to just making them decently reliable with good runability, and have been having a ball with that!

What model and size of Walbro?
 

Egor

New Member
Jan 30, 2008
714
0
0
Hurricane Utah
Yea, all I do is to get it to run good now, like you said it is like a 70's dirt bike the only thing is you can not do any sustained runs. I think if you get them to run excellent and then treat them carefully they will last. One thing that I like is the mileage increase, with the engine running so effortlessly the mileage goes way up. I took a few things off mine also, the timing being one, I also leave the compression alone. The porting being the most radical thing I do, and that is conservative at best. Have fun, Dave
 

Egor

New Member
Jan 30, 2008
714
0
0
Hurricane Utah
Egor Long Run? 15 Miles to work is that too long for sustained ride?
I should have been more clear, I meant sustained full, or high speed runs. A 15 mile ride should be a cake walk for these engines. When I first built my bikes I was looking for a good top end, not that I was going to ride that fast but I wanted to see what they would do. Now I ride the speed that I would pedal if I were willing to do that. LOL, I do think if I were to start riding to work every day I think I would use an over the rear wheel kit with full suspension. just my opinion. I keep the engine in the frame bikes because I like the way they look. Its a George Wyman thing, I still need to take to the tracks to see what it was like. Have fun, Dave