Ok, some of you may have seen the overhaul of my 1973 Cb250 (Link in my signature). Well, I didn't have time over the summer to completely finish the bike, and after taking it for a little spin, I lost compression on one cylinder.
I didn't have time to rebuild the top end, or the option to bring the bike back to university with me. Luckily I did have a spare motor which I brought back with me. I was planning to get it rebuilt and upgraded before Christmas so I could take it back, quickly swap motors and be done. Unfortunately, I have only just got round to starting work on it so that looks less likely as the days pass.
Anyway, save the essay, here's the start of the engine tear down and rebuild.
Obviously started by pulling the rocker cover off. The cam/timing chain was not present, neither were the rocker arms. So I will probably end up pulling the rockers from the current blown motor (after checking their condition), and getting a new cam chain.
I haven't managed to pull the valve springs yet, but will be getting hold of a spring compressor soon. The valve area (my lack of knowledge now becomes apparent) seems in pretty good shape. No dings or dents, just some carbon build up. The intake (the smaller ones?) valves seem to be pretty rusted from what I can see without pulling them, and the exhaust valves seem to be ok, just covered in carbon again.
Im not too sure about the gasket/surface area. It looks free from obvious deep scratches and dents, but Ill inspect it with a DTI later. It does seem to be covered in lots of small scratches.
The valve springs seem pretty clean and in good shape too, but again, I will be able to tell better once they are removed.
I didn't have time to rebuild the top end, or the option to bring the bike back to university with me. Luckily I did have a spare motor which I brought back with me. I was planning to get it rebuilt and upgraded before Christmas so I could take it back, quickly swap motors and be done. Unfortunately, I have only just got round to starting work on it so that looks less likely as the days pass.
Anyway, save the essay, here's the start of the engine tear down and rebuild.
Obviously started by pulling the rocker cover off. The cam/timing chain was not present, neither were the rocker arms. So I will probably end up pulling the rockers from the current blown motor (after checking their condition), and getting a new cam chain.
I haven't managed to pull the valve springs yet, but will be getting hold of a spring compressor soon. The valve area (my lack of knowledge now becomes apparent) seems in pretty good shape. No dings or dents, just some carbon build up. The intake (the smaller ones?) valves seem to be pretty rusted from what I can see without pulling them, and the exhaust valves seem to be ok, just covered in carbon again.
Im not too sure about the gasket/surface area. It looks free from obvious deep scratches and dents, but Ill inspect it with a DTI later. It does seem to be covered in lots of small scratches.
The valve springs seem pretty clean and in good shape too, but again, I will be able to tell better once they are removed.