CBX250RS-E #2, October 2015

The red framed CBX had been in the shed for over three years, only touched to steal its rear wheel with all straight spokes to get #1 through its MOT, and again to steal the speedo drive after #1 broke the driving tab off its own because the cable was stiff. CBX #1 is now quite properly on the road, and I am finding it a joy to ride - it has only served to vindicate my original thinking that these bikes are the pinnacle of correct, basic motorcycle design. Meanwhile the K100 and TRX850 both need serious and invasive servicing, so there's only one thing for it.. Take the easy way out and put this thing back together.

A long time ago I removed the barrel and piston from engine #2 with the knocking main, in the hope of maybe using it in this bike. I can't use the bike's original piston because it has a valve stuck in it, but maybe the barrel will be okay with its new hone marks? A quick measure suggests that's a stupid idea, as that barrel has been freshly bored to the next oversize, so I have no choice but to bolt the different barrel on. I'm not too keen on this because it does show some scoring:

I was reliably (?) informed that these marks are not terribly important as they are near the top, and perhaps the rings won't sweep past them.. I don't know, but I have no choice. The bore was also sporting a light coating of rust after sitting in the shed for three years, as were the piston rings.. I scraped off what I could, the uppy downing will take care of the rest right?? After a liberal covering of oil on both cylinder and piston, I attempted to squeeze the rings and slide the cylinder down over it.. As if. The rings eventually went in and allowed the cylinder to come past, but I have no idea if any of them broke. I don't think they did, but it's impossible to know - it's really a job for two people, one to squeeze the rings in while the other lowers the cylinder. Anyway, after a small hiatus #2 was finally being rebuilt!

I had the head refurbished by Zoom Factory in Harbury at the same time as I had the head for #1 redone. I replaced both inlet valves as they had clearly been kissing the piston, which cost £47 shipped from Econohonda in New Zealand. I also had both heads "refurbished" (ruined) by Coventry Boring And Metalling who are clearly not used to things as high tech as eighties Hondas, if they hadn't refused the workshop manual perhaps they would have had more of an idea of what to do. Half the springs were upside down, and they had attempted to lap the valves in rather than perform the correct three angle cut.. I paid £16.80 for the privilege. The work at Zoom Factory was £86.40 but it is of the highest quality, I would use them again. Despite the cylinder and piston being free as I had them sitting around, I have also needed to use a base gasket which was £4.44 from CMSNL and soon a head gasket, £10.73 again from CMS. I also had to buy a single dowel pin from ebay as I just couldn't free one more, so annoying! Anyway, I was left with a head looking like this:

You may be able to see a few marks from the valve head rattling about, left in the aluminium. These may create hot spots, but the engine is not of a particularly high tune and fuel here in the UK is a minimum of 95 RON so I doubt it'll be a problem somehow. This head had also sat at the foot of my bed since January 2013, wrapped up in its own bag.. How time flies. Not any more though, stick that head gasket on!

And then stick the head on!

This engine building lark is easy, right? Thankfully all the bolts torqued correctly, despite the aluminium threads still being full of copper grease. 50Nm still seemed more than tight enough, so I'll say it was fine. While poring over the engine, I found a bit of wire that was loose for some reason.. Someone who had rebuilt this engine before had lovingly crafted a strange loop that was meant to keep something in place, but I don't know what. It was chewed, and possibly what caused the timing to slip.. Looking around a bit more I noticed this thing, sitting behind the pulse generator:

Can't have that there, can we? Best free it..

This fits with the other part that I found. I think someone didn't trust the front tensioner blade to stay in place, so decided to try and tighten it down.. Even though the head holds it in place. If this owner is out there, reading this - please don't put bits of wire inside the engines you are building. There is no need. And please don't use copper grease on everything, it's even around the inspection cap mixed with oil so some has been washed away, lovingly swirling round all those bearings acting as a fine grinding paste.

Anyway, with the head on it's time to do the fun bit - time it up. Simply put the cam idler gear in the chain so that the lines on it are flat along the top of the head when the T mark on the flywheel lines up with the little inspection mark on the alternator casing. Easy, right? After faffing about with letting the tensioner off and skipping the chain around the teeth of this gear about six times, we finally have the marks almost straight:

They're not quite perfect but moving the chain a tooth either way would be further out, so this has to be right. I blame a slightly stretched cam chain. With that fiddly job done, fitting the cams is easy - just plonk them in, with the lines on the cams lined up with the marks on the idler gear.

 These are the cams and rockers out of engine #2 with the knocking mains, by the way. In CBX #1 they make a horrible racket, as can be observed here:

I think this is probably due to the low oil pressure that engine has. Hopefully, this set of valve gear will be quiet in this engine.. It used to be, at least. Eventually, the bike looks like this:

Looks a lot healthier already, no? The rocker cover bolts don't seem to want to go into the cam holders inside, the threads come out with bits of aluminium on them but I'll worry about that some other time, along with finding a tank that doesn't leak. And rear wheel bearings. And all the wiring. Carbs next!