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Rebuilding the Honda XR650R Motorcycle Upper Engine

dirt motorcycle dirt motorcycle forum off-road motorcycle dual-sport motorcycle dirt bike discussion dirt bike how-to dirt motorcycle how-to Honda XR

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#1 Moses Ludel

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Posted 28 December 2013 - 04:54 PM

The magazine's Honda XR650R is slated for remote field service and use as an HD video platform.  Reliability is essential.  I ran a compression test when the engine refused to start.  The results became an HD video how-to when I moved from the simple compression test to a full-fledged cylinder leak down test.  Want to know more about a leak down test?  Click here for the 4WD Mechanix HD Video Network feature and details!

 

High cylinder leakage called for a top end inspection and repairs.  I moved to a tear down, part of the top engine rebuild.  Both the tear down and the rebuild/reassembly will be covered at the magazine as HD video 'how-to'.

Attached File  Cylinder Leak Down Test-8.JPG   96.97KB   0 downloads Attached File  Honda XR650R Engine Teardown-8.JPG   92.29KB   0 downloads

At left is the cylinder leak down test covered in the HD video how-to. At right is the actual top engine tear down, part of the current rebuild. See both HD videos at the magazine for details! 

 

Here is Part 1, the top engine tear down: http://www.4wdmechanix.com/Honda-XR650R-Motorcycle-Upper-Engine-Rebuild-Part-1-Tear-Down-How-to.html.

 

Expect more details as the sublet work and reassembly become Part 2 of the how-to HD video series!

 

Moses



#2 DavidEasum

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Posted 02 July 2014 - 06:34 PM

Question for you, Moses:

 

Is there a difference between the compression stroke and the exhaust stroke on the XR when the cam is out? I’m worried that if I’m 360 degrees off on reassembly, I’ll put it back together with the ignition firing on the wrong stroke. Or does the ignition simply fire every time the crank goes around so that it doesn't matter? 

 

D.



#3 Moses Ludel

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Posted 29 July 2014 - 07:17 AM

David, for the Honda XR650R, the ignition fires on each TDC of the piston, two times during the four strokes.  Specifically, the ignition fires at the top of the compression stroke and top of the exhaust stroke.  The exhaust stroke firing keeps the spark plug cleaner and otherwise will not affect performance. 

 

Simply put, for valve timing, as long as the piston is at top-dead-center (TDC) on the Honda XR650R, you can align the camshaft sprocket properly.  Your only concern is to have the camshaft and its sprocket tensioned on the pull side.  To accomplish this, always bring the piston to TDC without going too far and needing to back up.  This way, there is pull tension on the camshaft sprocket and no chain slack.  This prevents a valve timing error due to chain slack.

 

Following the camshaft and sprocket installation, I always recheck the valve timing after installing the chain tensioner.  After installing the tensioner, rotate the crankshaft in its normal direction of rotation, orienting the cam sprocket marks properly.  Bring the piston slowly to TDC and stop there.  Tension applied at the backside of the chain, the cam sprocket timing marks should be exactly where you want them with the engine running.

 

Moses





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