After assembling the pistons and cylinder barrel several times using the technique in the Honda shop manual, I decided to try something different this time, and I think it's much better. The book procedure is to put the pistons on the rods, then slide the cylinder barrel onto them. I always found it hard to get the compression rings into the bores using that method, and I even broke a ring once doing it that way.
My new procedure is to put the pistons into the bores while the cylinder is on the bench. Then I slide the barrel onto the studs, holding it above the face of the crankcase with clamps on the four outer-most studs. The gap is about 2 inches. Then I install the wrist pins and cir-clips.
A few details:
- Tuck pistons 1 and 4 all the way into the bores, and leave 2 and 3 sticking out just enough to allow the wrist pins to be installed. Connect rods 2 and 3 first, then 1 and 4.
- Before putting the pistons in the bores, install one cir-clip in each, so that you only have to install one cir-clip per piston after installing the wrist pins. All wrist pins have to go in from the outside (i.e., from bike's left for 1 and 2 and from bike's right for 3 and 4). There is not enough room to insert the wrist pins for 2 and 3 from the center out.
- Think through how you're going to position and rotate the crank during the procedure. A little planning pays off. You want to be able to rotate 2 and 3 well up into the bore while you work on 1 and 4, so there's no chance you'll pop them out.
- With the pistons sticking out enough for wrist pin clearance, the oil-control rings are just out of the bore. So you have to be very careful when pushing them in.
- Resist the urge to force the wrist pins. If you get the piston and rod lined up properly it'll slide in smoothly with only finger-tip pressure.
- It's a good idea to cover the crankcase opening with a rag while installing the cir-clips, to reduce the risk of one falling into the crankcase. Even so, having a magnet on a stick handy is also a good idea!
- Once you have the wrist pins and cir-clips installed, very carefully work 1 and 4 all the way into the bore. Things get a bit tricky to do with only two hands at this point, but you can safely tap the top of the cylinder lightly with a dead-blow hammer to work it onto the pistons, if you're very careful.
- Once the rings are all in the bores the barrel should slide down very easily, with only ring friction restraining it. If there's any binding or force required at all, something is wrong. The first time I did it got the arm of the chain tensioner caught under the barrel, which took me a minute to figure out.
