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--- techtalk:evo:engmech04a [2019/02/12 03:39]
hippysmack [To Remove Lower Cover]
+++ techtalk:evo:engmech04a [2019/02/17 15:39]
hippysmack [About Relieving Valve Pressure]
@@ Line 87: / Line 87: @@
 ====== Before Removing Lower Cover ======
+===== About Relieving Valve Pressure =====
+See also [[techtalk:ref:svcproc16#hydraulic_lifter_-_disassembly_inspection_assembly|Hydraulic lifter disassembly - inspection - assembly]] in the REF section of the Sportsterpedia. \\
+(also known as "Bleeding the Lifters") \\
+You are not actually doing anything but allowing the oil time to leave the lifter body out of the holes in the each lifter before removing the lower rocker mounting bolts. \\
+Due to viscosity of the oil and hole locations, it usually takes 20-30 minutes.
+Internal clearance and parts determine bleed rates. ((bustert of the XLFORUM http://xlforum.net/forums/showthread.php?t=2039673&highlight=bleed+lifters))
+**The 86-03 FSMs state to rotate the crankshaft so both valves are closed on the head being repaired**. \\
+Then remove the two 5/16" rocker arm retaining bolts first and remove the rocker arm shaft. \\
+In theory, you've already relieved the valve spring pressure by rotating the engine over until both valves are closed. \\
+But you haven't relieved lifter preload against the valves which still puts upward pressure on the rocker box. \\
+They also do not state to wait 20-30 minutes before removing the bolts. But if you don't, the bolts will have more pre-load from the lifters. \\
+And that pressure is still on the rocker arms and also the rocker box. \\
+So, removing the two 5/16" bolts first would relieve the lifter pre-load / valve pressure for you. \\
+This removes lifter preload from the valvetrain. \\
+However, with the rocker bolts in place other than these two, that would send the pressure release down to the cam bushings by jolting the camshafts all of a sudden. \\
+This could cause the camshafts to crook sideways and gouge the bushings. \\
+**They 04-Up FSMs still state to rotate the crankshaft so both valves are closed on the head being repaired**. \\
+**But they changed the sequence of removing the bolts**. \\
+Removing them in the proper order also prevents potentially warpage of the cover(s). ((Screw Loose Dan of the XLFORUM http://xlforum.net/forums/showthread.php?t=1488750)) \\
+It also mentions making sure that both valves are closed prior to removal for each cylinder (separately) of the rocker box you're removing. \\
+**Lifter Preload**: \\
+Lifters have about 2" of internal travel length (down to up movement).
+The pushrod lengths are designed to be in the middle of lifter travel. \\
+This means the pushrods should be compressing the lifter springs down by app. 1" with both valves closed. \\
+This spring load is even more with the lifter pumped up with oil. \\
+Total static lifter spring pressure with both valves closed is a combination of your individual pushrod lengths, amount of oil and initial pre-load in the lifters. \\
+You can't change the length of solid pushrods or the initial lifter preload. \\
+But you can relieve some spring pressure by allowing the oil pressure to bleed down from the lifters before removing the lower rocker arm bolts. \\
+Non compressed lifters also have a small amount of preload by themselves and even being bone dry of oil. \\
+|Photos of a dry lifter. (L) assembled - (R) with spring pressure at rest. On dry assembly, the pushrod cup is \\ relatively easy to push in with you finger to install the retainer clip. If oil was poured into the lifter body and \\ then the cup was compressed, it would be more difficult to push the cup down to install the retainer. ((photos by Hippysmack))  ||
+|{{:techtalk:ref:svcproc:lifter_disassembly_2_by_hippysmack.jpg?direct&300|}}|{{:techtalk:ref:svcproc:lifter_disassembly_6_by_hippysmack.jpg?direct&300|}}|
+**Cam lobe positions**:
+Rocker boxes should really only be removed and installed when the cams are positioned such that the lifters are let all the way down. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=5041422&highlight=rocker+box#post5041422)) \\
+Compression TDC is the best place to do this, because it's just about exactly halfway through the valve-closed window. \\
+If you install the rocker boxes at overlap TDC instead, both valves are slightly open. So it's important to be able to tell compression TDC from overlap TDC. \\
+Ten minutes or so is a pretty normal amount of time for lifter bleed down. \\
+It may take longer if it's particularly cold or if you're using heavy oil. \\
+But if you're sitting at overlap TDC, you may never see the valves close because the lifter will shorten as far as it goes and still be too long. \\
+**There are two TDC's for EACH cylinder**. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1874585)) \\
+The reason there are two TDC's for each is that a 4-stroke motor requires two full revolutions of the crank to complete it's 4 cycles. \\
+Therefore the piston passes through TDC twice; \\
+On one of those TDC's, both valves are closed (compression TDC). \\
+On the other one, both valves are slightly open (overlap TDC). \\
+You want to be at or near compression TDC to remove or install a rocker box. \\
+**So it's important you know how to tell the two TDC's apart**. \\
+The way you do that is to watch the valvetrain motion as you're turning the engine. \\
+You can't tell by just putting it at TDC and looking at the position of the valvetrain. \\
+When you're at overlap TDC, the valves are barely open, and it will appear they're closed. \\
+So watch the motion of the valvetrain as you rotate the motor forward. \\
+**With the rocker boxes removed, that means watching the pushrods**. \\
+When you see the intake pushrod moving down, you're on the compression stroke. \\
+Proceed from there to the next TDC and you're at the right place. \\
+It doesn't have to be precise. Both valves are fully closed from about halfway up the compression stroke to about halfway down the following power stroke. \\
+Compression TDC is about halfway between those events, so it's a good reference point, but the window is fairly wide. \\
 ===== Bolt Removal Sequence =====
-The FSM is quite clear in the proper order to remove the bolts. ((Screw Loose Dan of the XLFORUM http://xlforum.net/forums/showthread.php?t=1488750)) \\
-Removing them in the proper order also prevents potentially warpage of the cover(s). \\
-It also mentions making sure that both valves are closed prior to removal. \\
 **It's important to allow the lifters to bleed down**. \\
@@ Line 141: / Line 204: @@
 If yours are not painted or labeled, check the lengths. The exhaust pushrods are longer than the intake pushrods. ((Turbota of the XLFORUM http://xlforum.net/forums/showthread.php?t=31258&page=3)) \\
 Mixing intake and exhaust pushrods can result in bent pushrods,damaged valves, pistons and more. \\
-**Note**: The intake pushrods have an orange colored painted band. The exhaust pushrods have a purple band. \\
+**Note**: The intake pushrods have an colored painted bands. Newer pushrods may be labeled instead of painted. \\
-(newer pushrods aren't colored but are labeled instead) \\
+But they are still different lengths.
-They are of different length.
 **Remove the inner rocker cover as a unit**: \\

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