I got the bike back together and was able to ride 50 miles today.

So far so good!

I measured cylinder growth today.  Ambient temp was 85 degrees F.  Engine/cylinder temp before starting was 85 degrees F.  Rode for twenty minutes.  On return engine/cylinder temp was 285 degrees F.  Total cylinder growth from centerline of crankshaft to just above the camshaft was exactly .025".

Don't forget that the chain is also growing as the temperature increases.  The coefficient of expansion for steel is 51% of the coefficient for aluminum.  Its a complicated problem.  I intend to attempt an evaluation along with some critical measurements discussed in this thread.  I think it will be an interesting project.  There's a lot of interesting ideas discussed in here.

DragBikeMike wrote on 05/22/18 at 01:06:48:


And just to make this even more complicated.....I suspect the cylinder and head get warm and grow faster than the chain.  The head and cylinder get hot from the combustion process - the chain only gets the heat passed  as it travels from the head to the camshaft to the cam sprocket.....or from the piston though the rod to the crank to the crank sprocket......or from the oil splashed onto the chain.  And the cam sprocket most likely gets a bit warmer than the crank sprocket.

I suspect the chain gets warm far slower than the head/cylinder, and it likely never becomes as hot as the head or cylinder.

When I first removed the pawl from my tensioner, Dave brought up a valid point that the valve springs being much stronger than the tensioner piston spring that at times (I'm thinking shutdown) that the cam could be rotated forward , moving the slack in the chain to the area of the front guide. while when restarting the bike the starter motor develops instant torque and snatches the slack from the chain and MAY cause momentary stress to the pins and possible wear ,this doesn't happens often. ( if the motor was very strong we wouldn't need decompression) What bothers me is what occurs on the other side of the chain, which is now stretched taut, In my case , if my piston was out dealing with 2-3 mm of stretch with only the spring holding it the piston simply retracts , and no extra pressure is applied to the chain . But what stress would occur if my tensioner was set up to retract only 1mm? It could be many times greater than the stock tensioner.Note DBM's statement below in his reply #55"as I continuied to rotate the motor backward, the plunger would retract 8 mm".I believe this same type of action takes place with forward rotation,  a purposed limit of .050 (1/16) will not releave 8mm(5/16) placed on the chain , and due to the nature of the cam being in a certain place for this to occur, the stretch will happen in the very same section of chain each time. limiting the tensioner from full retraction , when the chain is already under stress from the valve springs,  is like putting a thorn in its side.

The calculated growth for aluminum 13.5" in length with 200 degree delta T is .033".  That's using .00001244 for the coefficient.  I attribute the .008" variance to the steel studs that are restraining the cylinder and head.  The coefficient for steel is about 51% of aluminum (.00000633).

The chain is also getting hot.  I initially thought that it would run a bit cooler than the cylinder, but after careful consideration I have concluded (just my opinion) that the chain is running pretty close to the same temperature, possibly even hotter.  The chain is encased in a cavity within the cylinder.  I am measureing the temperature on the surface of the cylinder where it is exposed to ambient cooling air.  The chain isn't getting any cooling air, not much cooling oil either.  If your thinking the oil is cooling off the chain, remember the oil is about 220 to 250 degrees, ambient air was 85 degrees.  So essentially, the chain is in an oven cooking at about 300 degrees.  Just my opinion.

With the chain growing at about half the rate of the cylinder, the difference in length should now be about .012".  So, with the pawl locking the plunger, I believe that the chain is under about -.012" interference at operating temperature.  In other words the cylinder is about .012" longer than the length of chain running from the centerline of the crank to the centerline of the cam.

This .012" difference is the amount you want to compensate for if you decide to make your tensioner soft (i.e. remove the pawl).  So I wanted to try and measure how much the tensioner plunger retracts for a given movement of the slack  side of the chain.

I removed the pawl from the tensioner and set up dial indicators to read plunger movement vs drive gear movement at  the tooth pitch line.  I took a few crude measurements and determined that the chain sprocket on the crank is roughly half the diameter of the drive gear.  The drive gear is about 3 inches so the sprocket is about 1.5", therefore, movement at the sprocket should be about 1/2 the movement at the drive gear pitch diameter.


I backed the engine up until the intake lobe was at a point where any CCW rotation resulted in movement at the plunger and zero movement at the cam.  The valve springs are so strong that the plunger just backs off when you rotate the engine.  When the gear pitch moved .050" the plunger backed off .100".  I did this several times to verify repeatability.  Since the sprocket is one half the diameter of the gear, .025" movement at the sprocket should retract the plunger .100".


The .012" chain interference is roughly 1/2" of .025" so it seems to me that the plunger needs to retract about .050" to make the chain and cylinder run at equal lengths at normal operating temp.  One millimeter is .040", pretty close Dave.  This data seems to confirm Dave's spacer length which restricts the plunger from moving back more than 1mm.  Setting it up for .050" might be just a tad better but that's splitting hairs.

I continued to fiddle with it to see how it behaved without the pawl when rotating in the normal direction of rotation.  The plunger modulates about .09" as you rotate the engine, and at times can make excursions up to up to as much as .15".  The valve springs really are a challenge for this thing.  No way of telling what it's up to when the engine is running.

I noticed that the plunger is a bit rough when its close to fully retracted.  The spring is bunching up a bit and catching on the edge of the chamfer.  I pretty much eliminated that by rounding off the edge of the chamfer in the bore.  I'm not too comfy with all that movin around so I reinstalled my tensioner with the pawl and stock spring.


I hope this data is useful and helps you decide what path to go down.  There seems to be four or five to choose from.  Here is a pic of that sharp edge on the chamfer.


 

After a good night's sleep I realized that I missed a very important point.  Quite some time ago I had made a comment regarding "both sides of the chain".  Both sides of the chain are being subjected to the interference.  When the system is hard (pawl installed) it's a wash.  Nothing can give so it's essentially .012 interference.  But when the system is soft (no pawl), you have a condition where the cam rotates as the cylinder grows.  During normal operation the drive side of the chain is fixed and the slack side of the chain is flexible, the tensioner takes up the slack, and the pawl locks things in place.  With the pawl removed, the drive side remains fixed and as the cylinder grows the cam must rotate clockwise.  So removing the pawl also results in your cam timing advancing just a bit as temperature rises.


With the stock cam, that's probably not much to be concerned over, but if you are running a performance stick, and you want to run a soft tensioner,  you might want to do a good check of clearances.  I haven't had the head off yet but from photos I can see that the intake & exhaust valves have lots of distance between them, so valve to valve clearance is most likely not an issue.  But valve to piston might be something to be concerned about.  If you checked that clearnce with the chain system hard, and then switched to a soft system, there's a good chance your valve to piston clearance may be altered because the cam will be at a different position at TDC, and as such your TDC lifts will have changed.