Lucky Day

Reverend Bill’s Lucky Day.

Rescue Rig

When you look from the long view, some crises turn out to be very propitious.  

Backtrack a week to the 11,000 mile valve adjust.  Clearances seemed really tight, pre-adjustment, but I blamed it on the long interval since the 3,000 adjustment.  Even after the adjustment there was a loud ticking that I attributed to a slightly loose valve, and better loose than tight.  Turns out I set the valves on the exhaust TDC instead of the Compression TDC.  Caption would read: "Oblivious Stupidity."  The bike ran fine, and the ticking was “curious”.

Ready, set, GO!

All week long, the bike ran great, even at 70mph at 9,200 rpm (near redline).  3pm Saturday rolling along I-5 at 65mph the engine died.  No odd noises, no drama.  Felt like it ran out of fuel or blew a main fuse (don’t ask how I know). Pulled the plug to confirm spark and noticed the exhaust valve hanging down into the cylinder and not moving with the motor turning over.  Called my lovely wife to bring the van, and went out to the Rat City Roller Girls.  Work on it tomorrow…….

Carb, exhaust header, plug, upper mount and valve covers off, ready to remove the head.

Sunday, unloaded the bike and tore into it.  Amazingly, the cylinder was unscathed, with just a bit of carbon worn off one spot.  The intake valve was fine, as well as the exhaust valve seat.  After pulling the camshaft out of the head it was evident the valve failed right at the stem top where the cotters secure the stem in the spring keeper. The top 3mm end  of the valve stem was roughly peened on it’s top by the rocker.

The valve stem was bent , requiring it be driven out, but the valve guide appeared intact.

Desk Trophy, Indeed

So the failure cause appears to be high RPM valve stem failure at the cotters due to excessive rocker impact secondary to some idiot adjusting the valve while it was on the cam! Doh!!  Then, of course, after the valve dropped down into the cylinder, the piston bent the valve stem.

Are we lucky because the interfering parts didn’t kablam the motor? Hell yes.  But it gets better.

Last year I purchased three TW200 in various states of disassembly, and built a motor out of the best parts of the three.  This left a number of TW parts, including two exhaust valves!

Head Gasket in Good Shape

Reassembly proceeded, with the discovery that one of the cam chain tensioner guides was excessively worn, so the T-Dub got a new cam chain guide while we were in the engine, and a tensioner adjustment.

Top of Piston has an arch of carbon pinged off the surface. Cylinder bore is smooth.

By 930pm the project was complete with the bike ready for the morning commute.  It ran like a champ today, with no smoke to indicate a valve guide issue. The valves will get another check tomorrow- just to be sure!

Bottom of head, intake valve circa 2006, replacement exhaust valve 1986. Engine still in production.

Special thanks go to Paul Bullard who stopped on I-5, Tim Bowman who drove by on a mission, to JT for moral support and Scot Iverson for the use of his valve spring compressor.

830PM: She Runs!

So how lucky was it? The engine failed causing a valve to drop into the cylinder and the bike did not grenade!  And there was a spare valve in my shop! What’s the lottery up to?

930PM: Repair complete and tucked in for the night.