CBX250RS-E Engine Rebuild 30/03/2012

Cor valves are difficult!

I attempted to some make sort of impression on the carbon that is welded to the valves with a coin but all I ended up with was a valve with a bit of coin added to it in orange streaks. My Dad saw me trying this and took a valve off me, and then proceeded to put it in his lathe and attack it with the tip of a flathead screwdriver! The graunching noises were unbearable to my mind but the valves appeared to have come through the experience unscathed, and missing all of the deposits to boot! Filled with confidence the next task was to fit the new stem seals (four 12208-413-003P, £18.96 total), which was relatively easy in the grand scheme of things although the old ones put up a bit of a fight. They simply pop on and off the top of the guide which is a bit like a barb, I was quite pleased with the progress.

Then came putting the valves back together with their springs. What a nightmare! If I ever want new springs fitting to anything again I'm getting a workshop to do it! Getting the collets or cotters or whatever you want to call them to fit back in where they should proved an impossible task by the normal route, they simply wouldn't stick in the groove that they're supposed to occupy at the top of the valve stem. Instead we (poor dad gets roped into more than he should) had to compress the springs and the valve cap quite a way down, get the collets to sit in the gap between the stem and the cap and then slowly undo the spring compressor tool to let the cap and collets slide up the stem and hopefully have it all locate into place. This was a tricky business with much frustration and use of dentistry tools, but eventually we had one done:

And then, with the experience we had gathered, the rest followed a bit more quickly..

This all took at least two hours of poking, prodding, compressing and undoing. If only my paranoia of breaking valve springs wasn't so strong! Anyway, so we now have four inner springs (14761-KE5-003, £9.60) and four outer springs (14751-KE5-003, £12) fitted and ready to go. I'll also show you how much cleaner the valves are now:

They are that clean on the back, too. I didn't bother to touch the valve seats as I have used this head and the compression seemed just fine, and frankly I have no idea at all what I am doing if I start grinding away at stuff.

I am somewhat concerned by the rust that can be seen in the top right of that picture though, it is from the previous head gasket and whilst being fairly smooth now it is still not as good as the rest. Could it affect compression if I don't clean it up to a mirror shine? I don't really want to take sandpaper to it as it'll end up being uneven, surely? And I don't really want to get it skimmed because the compression ratio is already 10.5:1 so there's not much metal to spare..