S90: New Airbox!

Got a new inline airbox from eBay.  No filter, of course, but otherwise seems in about the same shape as the rest of the bike.  The screws holding the covers on are froze solid, and partially stripped.  But if the impact driver can't get them off, it'll be a breeze to Dremel them.

What actually gave me some trouble was that the bolt holes on the frame (one above and one below the airbox) were very dirty and caked with rust.  At first I couldn't even get the top bolt to go all the way through.  I hit it with some PB Blaster and then tried to clean out the debris a bit.  Finally I put a big dollop of anit-seize on each 6x16mm bolt and worked it in and out a couple times.  That seemed to do the trick.

I was happy to see that the carb and the airbox were lining up perfectly, although I'm still missing the short rubber connecting tube that will eventually link them up.

CM91: Clutch Disassembly

Took the clutch apart today.  Here are the steel plates and friction plates, stacked in the reverse order that they were removed.

I measured the friction plates to check for wear, and found that the A and B plates were actually much thicker than they should have been.  But I was comparing against the table in Clymer's and I'm not sure how valid it is for the CM91 since it doesn't list that model by name.  The type and arrangement of the steel plates didn't correspond to any diagram in the book, either.  I'm not sure if the CM91 clutch is just different, or if non-stock parts have been used during a past rebuild (which wouldn't surprise me).

There were two steps that were a real pain.  The first was getting these springs below in and out.  The book recommends using the tip of a small Philips head, but I had more luck using slip joint pliers to gently compress and maneuver the spring around.

The other tricky job was getting the cover screwed back in once you want to start reassembly.  You have to push the cover down, compress the big springs (pictured below), line up the screws and get at least one threaded - all the while pushing down hard enough on the cover so the screw can reach the hole.  An irritating juggline act, though I feel like it wouldn't be hard to work out a neat trick to make the whole thing easier.  I'll also have to see if the forums have any sage advice.

S90: Valve Compressor Tool

Getting the valve out was actually somewhat anti-climactic.  Turned out to be a lot easier than I was expecting.  Hardest thing was getting the keepers lined up when I was re-installing the valve, but just another of those little things that probably get easier each time you do it.

Here's the 19mm bit (the tool comes with 5 sizes) sitting on the valve spring collar as I begin to compress it.

After removing the keepers and collar, the inner and outer springs can be removed.

 Some shots of the valve itself.

S90: Wear Limit

Nice long Saturday morning garage session.  Actually got way more accomplished than I thought I would, especially considering I didn't know exactly what I wanted to work on.  But I did have a new micrometer and caliper to play with, along with the new valve compressor tool, so I figured I'd dig into the S90 top end again.
 
The caliper and micrometer I'm using are dirt cheap compared to top end measurement tools, but they seem to be sturdy and accurate enough for this type of shade tree work.  I did get different answers when I measured the same part with first the caliper then the micrometer.  Maybe one needs to be zeroed a little better, but it could also be my "technique".

I took measurements on the camshaft, rocker arms and rocker shafts, valve stem, and valve springs.  The only thing that seemed to be past the wear limit was the right side end of the camshaft.  The wear limit in Clymer's said 0.705" and the micrometer was reading 0.7045".

One odd thing I also found was that when measuring the inside diameter of the rocker arm bore, I was getting a measurement of 0.390".  But the standard was 0.3937"-0.3943" - meaning the hole was actually smaller than standard factory settings...?  I probably took a bad measurement, though, because the outer diameter of the shaft measured 0.392".  In other words, the shaft would be too big to fit into the rocker arm!  Clearly not the case...