At the conclusion of Part 9, we had a 692cc high compression engine.  It had a high-flow K&N air filter, high-flow 38mm carb, ported head, DR650 cam, high flow exhaust system, and a lightened flywheel.  The Wiseco 97mm flat-top piston increased displacement by 40 ccs, compression by about 3 points (8.5:1 up to 11.4:1) and tightened the quench clearance to .040”.  To hold the power, it needed a beefed-up clutch.  It ran great.  Tons of power, excellent fuel economy, and cooler operating temps.
 
I wanted to put some miles on it before I wrote the final report.  So, once the Big Bore Flat-Top had 6200 miles on it, I changed the oil & filter (3rd oil change), checked chain tensioner extension (14.4 mm), adjusted the valves (.007” as-found), cleaned the air filter, checked compression (225 psi) and started writing.   But something wasn’t right.  After a few miles, the vibration and audible noise seemed higher, the clutch felt like it was slipping, and the oil got black.

When I did the service at 6200 miles, I changed out the oil drain plug.  I had been running the old-style non-magnetic plug.  I had a newer magnetic drain plug, so I installed it.  No particular reason, it just seemed like a good idea.  So now I had like 50 miles or so on a fresh oil charge, and the engine was noisy, and things seemed to be shakin more, and the oil was black already.  Best take a look.

Oh my!  That’s not good.

8/25/23  As it turns out, I believe these chips came from the LH main bearing.  At first I suspected the chips were from the failed 5th gear, but later on I discovered that the main bearing had also failed. I simply missed the bearing failure.  DBM

Since it’s magnetic, the sludge was very hard to remove.  Wiping with a towel gathered some nasty black stuff, but I couldn’t get it all.  The magnets refused to let go.

I did a cursory check of left-hand crank runout.  Cursory because it’s almost impossible to get an accurate runout, other things are moving the crank around.  The cam chain is tugging on the right-hand side, and the rod is pushing and pulling on the crank pin.  I figured it wouldn’t hurt to take a runout.  The runout was .0040” TIR.  The runout spec in the manual is .0020” TIR, but that’s checked with the crank assembly on V-blocks.  I set the indicator up to check axial play.  

The crank moved to the right +.0020”.

I checked axial play on the spare engine crank, and it was only .0005”.  That seemed more like it.  The manuals don’t provide a specification for axial play, but .0030” seemed like it was excessive, especially when compared to the spare engine.

I wanted to see how the transmission bearings were, so I checked the input shaft and the output shaft.  The input shaft had .0000” up & down, but .0022” axial play.  The input shaft on the spare was tighter, up & down was the same, but axial was only .0010”.
 
Comparison of the output shafts showed similar results.  The output shaft was .0010” up & down while the spare engine was .0000”.  The axial movement on the output shaft was a whopping .0050” while the spare output axial play was only .0010”.

It was obvious that the engine in the bike was way looser than the spare engine.  I have no idea how many miles are on the spare, or how it was treated before I got my hands on it.  I have only logged about 1500 miles on the spare.  That was on the 97mm Pop-Top project.

Similar deposits were on the output shaft splines.  Don’t worry, I didn’t check axial play with the pulley removed, I just wanted to see if it made a difference.  It does.

The top ring looked terrible.  I’m used to seeing a nice, uniform polish 360° around.  This thing looked like it had been through a meat grinder.  That might explain why the compression was down about 15 psi.

The combustion chamber and piston top looked fine.  It wasn’t detonation.