The timing chain is in good condition.  The measured distance over 21 pins is 5.035”.  The wear limit is 5.070”.  This is the original chain.  I’m impressed.  I use a couple of sprockets and a ten-pound weight to hang the chain for measurement.  It makes the job a lot easier and ensures consistency.

When I removed the cylinder head, the gasket was dry.  Prior to going to an external feed system, this gasket was always full of oil when I removed the cylinder head.  A welcome sight, no oil on the gasket.  Note how clean the deck is just behind the intake valves.

Once the cylinder was out of the way, I had a clear view of the transmission input gears.  All is well.  No pitting.

The gear spray tube is also in good condition.

The area on the circumference just above the compression ring has the same sandblasted texture that I saw on the pop-top.  The sandblasting is in those detonation suppression grooves, and it is confined to the back side of the piston.

That ring land has a visible crack running vertically all the way through the land.

And you can see how the combustion gas was blowing by the compression ring.  That brown coking/shellac tells the story.  The hot combustion gas just blew through the circumferential crack in the ring land and overwhelmed the oil scraper ring.

So, the oil system mods are a keeper, but it’s back to the drawing board with the piston.  I have no idea how this thing ran as good as it did with that piston damage.  I also can’t explain why this thing gets into the detonation biz with the 97mm flat-top but not with the 94mm flat-top.  I understand that the larger bore raises the compression ratio a bit.  I guess it's just on the ragged edge of detonation and the bore increase takes it over the cliff.  I figured increasing the pocket volume by 5cc would have resolved that issue.  Guess not.

The problem might be related to the cam.  Of all the available cams, the DR650 cam has the earliest intake closing event.  I might try revisiting the Web 402.  I have a 402 but it is lightly scored up.  I might be able to polish it.  I’ve got lots of oil pressure now, so maybe the 402 will hold up.  I’m also gonna try a bit less compression, see if I can get cranking pressure down to 190 -195 psi.  In addition to those two changes, I’ve got about 2 degrees of ignition timing I can play with.  So, bring the compression ratio down to 9.7, install a cam that closes the intake about 8 degrees later, and pull out 2 degrees of the ignition advance.  Maybe that’s the secret recipe.

I hope some of you find this project interesting and informative.  More to come.