Calling all die hard engineering types - i've got a real stumper here and I'm fresh out of plausable suggestions.
So, I've just rebuilt a little honda 125 twin engine and got it back in the bike. I had to split the casings and take out some bits that I had dropped into the bottom of the engine (circlips and a washer and a few other bits and bobs ) anyway, all that curse word is out. New pistons, rings, honed out, new stem seals, lapped valves etc etc- all good. I didn't know if I had rebuilt it 180 degrees out or not as there is no real way of telling my firing stroke without power going to it (CDI ignition) so I put it all in.
The problem is this.
I turned it over on the key (no kickstart) and it just sounded like the starter was turing over and nothing else. Hmm. Took the cover off and sure enough, it's all connected and doing as it should. (turning over the right way against the ratchet)
Wazzed the plug out and had a look whilst turning it over - piston going up and down, valves in and out - lovely. but no sound at all - no compression whatsoever and no exhaust noise. In fact you can turn the engine over, with the spark plugs in, with your hand on the fly wheel pretty easy.
Plug back in - same as before.
Put it in gear, ignition off, and turn the engine over using the back wheel and ther is loads of compression and proper exhaust noise. To proove the point, when I stick it in first and push it, the back wheel just skids unless I sit on it, and hten it's quite tough.
The engine is very simple. In the top end there is just pistons, bores, 4 vavles, one cam. Thats it.
How the hell can an engine that simple do that? There is no compression purge valve or anything - there's no kick start. I'm totally stumped. Please help!
So, I've just rebuilt a little honda 125 twin engine and got it back in the bike. I had to split the casings and take out some bits that I had dropped into the bottom of the engine (circlips and a washer and a few other bits and bobs ) anyway, all that curse word is out. New pistons, rings, honed out, new stem seals, lapped valves etc etc- all good. I didn't know if I had rebuilt it 180 degrees out or not as there is no real way of telling my firing stroke without power going to it (CDI ignition) so I put it all in.
The problem is this.
I turned it over on the key (no kickstart) and it just sounded like the starter was turing over and nothing else. Hmm. Took the cover off and sure enough, it's all connected and doing as it should. (turning over the right way against the ratchet)
Wazzed the plug out and had a look whilst turning it over - piston going up and down, valves in and out - lovely. but no sound at all - no compression whatsoever and no exhaust noise. In fact you can turn the engine over, with the spark plugs in, with your hand on the fly wheel pretty easy.
Plug back in - same as before.
Put it in gear, ignition off, and turn the engine over using the back wheel and ther is loads of compression and proper exhaust noise. To proove the point, when I stick it in first and push it, the back wheel just skids unless I sit on it, and hten it's quite tough.
The engine is very simple. In the top end there is just pistons, bores, 4 vavles, one cam. Thats it.
How the hell can an engine that simple do that? There is no compression purge valve or anything - there's no kick start. I'm totally stumped. Please help!