I try to keep my cams and rockers in matched sets.  The rockers that I run with the DR650 cam looked perfect, so those went into the sausage grinder too.

I’m basically lazy.  The Stage II head was set up with the heavy-duty RD spring kit and DR650 valves.  The DR650 cam does not require the heavy-duty long-travel springs, but if I wanted to convert back to stock springs, I would have to replace all four valves.  No thanks.  I’m not goin through all that hullabaloo.  I decided to leave the head as-is.  It was a good opportunity to see how the DR650 cam handles the higher spring pressure.  The RD springs exert about 28% more force than the stockers.  That means a lot more pressure on the cam lobe.

I’ve been wanting to revisit the cam chain tensioner.  A few guys are running tensioners without the pawl.  Sort of a free-floating setup.  Most are incorporating a hard-stop to restrict backward movement of the plunger to about .04” to .06”.  I ran a setup like that for a little while.

If the valve-to-piston clearance is on the ragged edge (like on the 97mm Flat-Top I built), then I’m not a fan of any play in the cam drive.  But this 94mm Flat-Top engine, with the DR cam and 33mm intake valves, had ample valve-to-piston clearance.  It looked forgiving enough to permit some leeway.  A cam chain tensioner with a bit of back-travel seemed tolerable.  I just have to do periodic checks and adjustments.  Since I ALWAYS inspect the chain tensioner when I do a scheduled oil change, periodic checks won’t be a problem.  A bit of float will reduce some of the stress on the cam drive.

I have an adjustment bolt on my cylinder head that allows me to adjust the arc of the rear chain guide.  That bolt, in conjunction with a floating tensioner, allows me to do periodic adjustments.  This is the setup for the adjustment bolt (which is just a 5/16-NF continuously threaded stud).

This is the modified tensioner.  The plunger goes hard at 10.5mm, so I set it to 12.0mm (cold).  That allows it to retract 1.5mm (.060”) as the engine heats up.  It should be very close to the hard-stop when the engine is at normal operating temperature.  When I change oil, I will check the extension, and adjust as necessary.  Just a simple turn of the adjusting screw will bring the extension right back to 12mm.  I intend to keep track of it and report periodically.  We can all get a better feel for how these floating tensioners behave.

The big 97mm engine exhibited several problems when it failed.  In addition to the transmission failure (heavy pits in 5th gear), there was high vibration and audible noise, excessive crankshaft runout (about .004” TIR), and excessive main bearing play (about .0035”).  Since I didn’t have a good explanation for the runout and vibration issues, I opted to assemble the replacement engine with the stock flywheel.  I thought there could possibly be a connection between the super-light three-inch flywheel and the vibration issues.  There is almost no difference in performance, so I installed the big six-inch flywheel.

I also couldn’t rule out detonation.  To be on the safe side, I retarded ignition timing 2°.  That would also give me an opportunity to see how the ignition timing affects driveability, operating temps, fuel economy, etc.
 
This little timing wheel rig along with a strobe light allows me to verify that the ignition timing is where I want it.  I was lookin for 2° BTDC at idle and 27° to 28° at 4000 rpm.  It’s a shame you can’t tweak it with the engine running.  Maybe someday I’ll work on that.  

The exhaust system got a mild upgrade.   I had built a new high-flow muffler with a larger baffle.  I ran it on the 97mm Flat-Top engine for a few miles.  Not long enough to see how it performed.

The new baffle had a 1.75” ID with 288 perforations in lieu of the 1.65” ID baffle that had 216 perforations.  It reduced the restriction from 31.5” H2O to 26.5” H2O.

This is the new baffle tube.  I think anything larger than this will start to increase restriction.  It wasn’t much louder than the 1.65” baffle.  It’s quiet.

The new adapter polished up nicely.  It was a good cosmetic improvement.