Better to mangle the copper than to mangle the gears.  I’ve done this dozens of times and haven’t put a mark on a tooth yet.

This is the balance shaft bolt.  Same guidance, torque wrench only.  Don’t exceed 35 ft-lbs.

Make sure all the sealing surfaces are pristine, free of any oil or old sealant.  Do a quick inspection to make sure you haven’t forgotten anything.  Apply some assembly lube to the cam lobes, the rocker pads, and the valve tips.  Keep the lube away from the sealing surfaces.  Make sure the plug/cap on the right side of the camshaft is in place.

This plug.  The one you can see on the right side when the head cover is installed.

Installing the head cover is a delicate operation, and you don’t want to screw up the layer of sealant by dragging it across other stuff.  It helps to do several dry runs to figure out the best path to follow, then apply the sealant and do the final fit when you are comfy with the operation.

This is how your sealant should look.  An exceedingly thin layer.  Keep it away from the edges of the cam bearings.  Make sure the oil separator screen is in the breather cavity.

Once the head cover has been installed and the fasteners tightened properly, adjust the valves.  I set mine to .005”.

Reinstall the clutch cover with a new oil filter.  Don’t forget to remove any cleanliness barriers.  Check closely to make sure everything is in order.   Here’s where that red-tag zip tie comes into play.  BTW, don’t forget to remove the red-tag zip tie.

If you have a connection for an oil pressure gage, attach the oil can and fill the trough through the gage connection.  It works good.  You can watch through the intake valve access.  Keep pumping until the trough fills up and spills over.

Reassemble the motorcycle.  Install the decompression solenoid, top motor mounts, carburetor, breather hose, fuel tank, seat, exhaust header, and anything else you removed.  

Fill the crankcase with good quality oil.  Motorcycle oil (10W-40 or 20W-50) rated API-SG is a good choice.  Ready to fire up.

A quick compression check showed that the cranking pressure was still the same, 160 psig.  The early closing intake valve had zero impact on cranking pressure.

Time to try it with the Mac header.  The bigger header wanted less fuel.  I achieved best performance with a #35 pilot jet, #142 main jet, and the needle clip in the fourth groove (rich).

Second Gear 4K to 7K: 3.00 seconds            0.03 seconds slower than stock header

Third Gear 4K to 6.5K: 5.49 seconds            0.25 seconds slower than stock header

Third Gear 4K to 7K: 7.80 seconds            0.15 seconds slower than stock header

Fifth Gear 3.5K to 5K: 5.43 seconds            0.41 seconds slower than stock header

Fifth Gear 3.5K to 5.5K: 8.42 seconds               0.67 seconds slower than stock header

It pulled 7500 rpm in third gear (50-rpm increase).  Based on the acceleration times, it’s obvious that the larger header is a bit slower.  Before the cam change, the larger header was faster.  Why is that?

The short answer, valve overlap.  Now that both valves are open at TDC, the inertia of the hot gas moving out the exhaust system can help evacuate the cylinder, and help pull in a fresh charge through the intake.  A body in motion wants to stay in motion.  A column of hot exhaust gas is a body too, it has mass.

Although the larger exhaust pipe is less restrictive, the hot exhaust gas moves at a lower velocity.  Lower velocity, less inertia, less pull.   At this stage of modification, the smaller stock header works a bit better than the larger Mac header.

If you review Part 4, you will see that when the stock cam was in play, the Mac header performed better than the stock header.  That setup took advantage of the reduced restriction afforded by the larger pipe.  The engine didn’t care much about the inertia of the exhaust gas because both valves were essentially closed during the overlap period.  There was no overlap.

Don’t get the wrong idea here.  Both setups are plenty fast.  You would be hard pressed to tell the difference between the two pipes.  They both feel great with the DR cam.  When subjected to the scrutiny of the stopwatch, the stock pipe is just a bit faster.

It would be great if I had a 1.5” and a 1.62” header pipe to test along with the stock 1.3” and Mac 1.79”.  Hey, a header shootout.  Who’s got pipes to share?
 
Moving forward, it will be interesting to see what happens when we install the ported cylinder head with the 1.5” diameter exhaust port.  Will the tables turn?  Will the Mac pipe work better with the larger port?  What will happen when we bump up the compression ratio?  Which pipe will work better with 10.5:1 CR?  Which will work better with more displacement?  This project is a kick, I’m lovin it.  Build it up piece by piece and test each piece as you go.