Stuff-mo-tron

Mon, 07 Jan 2008

Jesse came over yesterday, and helped me get the engine out of the CL. In all, we ended up spending about 6 hours unbolting parts, draining oil, lifting, and disassembling. By the time we were done, the engine was in three major pieces (crankcase/transmission, cylinders, and head).

A quick inspection looked good, but upon peering closer, we discovered some exciting stuff. That's not a good kind of exciting, but I'll be replacing all the damaged parts, so it's not a big deal.

The first thing we did was to look at the cylinder bores. They were pretty clean, but the right one was a bit rusted. This is the cylinder which is uphill when the bike is on the sidestand, so it's more likely to let rainwater in past a sparkplug, or have crud fall in when the sparkplug is out. Still, the bore looked good enough that I wasn't too worried.

The next thing we noticed was that the top of the right piston had an odd-looking dent in it. After pondering it for a moment, I realized it was from a too-long spark plug. Someone had installed a spark plug that was so long that it left a deep divot, and three lines of thread impressions, in the top of the piston. It must have been half an inch too long, which is really long.

Jesse pointed out that some previous owner had installed Helicoils in the heads, to repair or prevent spark plug threading problems. This is generally a good thing, since aluminum heads' spark plug holes are pretty easy to mess up, and they're a pain to fix. Unfortunately, the inserts were far too long, protuding into the cylinders by several millimeters.

This poses a number of problems. The first one that occurred to me was that the exposed coil (which is nothing more than a fancy spring) would heat up to red hot, and lead to pre-ignition. My guess now is that this helicoil business must have been done pretty recently, or it would have burned a hole in both pistons.

The next problem we discovered was that the helicoil was long enough to hit the piston. There are indented rings visible on both pistons, although the left piston is more clearly marked. I think it was the right helicoil which looked all melted at the end, suggesting it had been shedding chunks of coil into the combustion chamber. This theory was confirmed by other evidence.

The left piston was actually the more frightening, from the helicoil standpoint. It has a little silver spot at one point in the circular impression left by the coil, which is where the melting-hot end of the coil was probably liquifying a little bit of piston on each stroke, spattering it across the top of the piston as little bright flecks Jesse pointed out to me. That couldn't have continued for too long before it would have put a hole in the piston, and racing with it like that would have certainly led to piston failure.

After I started cleaning up the head, I discovered more divots on the right side -- this time on the top of the combustion chamber. Something big (like a small nut, or possibly a broken-off spark plug or hefty chunk of helicoil) had gotten in there and been rattled around. It didn't cause any serious damage, though, and I was able to grind down the walls of the craters so they won't provide pre-ignition points.

Also on the head, Jesse pointed out to me that the bike must have been run for many thousand miles without having had the cam chain tensioner adjusted. It's a simple adjustment, just loosen a bolt, and let the spring take up the correct tension, but it's supposed to be done every 500 miles or so. The head has two deep, camchain-width grooves cut in it now, although fortunately they won't cause any problems.

There were also good things we found. The head and valves appear to be in really good shape (minor divots and grooves aside). The cam and rockers are in beautiful shape, and it looks like I have all the important spare parts I need. The inside of the crankcase looks good. I was able to remove the starter and substitute my newly procured starter plug, which will save at least 10 pounds on the bike. It's still got a kickstarter, and push-starting is easy, so the starter won't really be missed.

The cylinders are even now sitting in the queue at Autosport Seattle, and should be done in a week or two. I'm going to take the head into Hill Machine Headworks (which is the same shop that did a beautiful job on my R100 heads lo these many years ago) as soon as I've got it cleaned up.

I've started on the head clean-up, but I need to get together with Jesse again and remove the valve springs and valves before I can make much more progress. This also gives me a good chance to do things like drill a variety of important bolts for safety wire, and work on a laundry-list of other projects on the bike.

I'm glad to be back from holidays, and making progress on the bike again. Of course, I'm worried about time: my new racer clinic is on March 19th, which represents a very definite deadline for getting the bike race-ready. Two months feels like a very small amount of time, although I'll be much more sanguine about things once I get the head and cylinders back from their respective shops. It's the "I have to wait for someone else to do things" factor that worries me right now.

No time like the present, though. I'm back off to the garage to continue grinding carbon deposits out of the exhaust ports!

Written by Ian Johnston. Software is Blosxom. Questions? Please mail me at reaper at obairlann dot net.