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"Make 4WD Mechanix Magazine and the 'Tech and Travel' Forums your online resource for Jeep, 4x4 truck, powersports and dual-sport motorcycle maintenance, troubleshooting, repairs, rebuilding, engine tuning, upgrades, backcountry trail prep and overland travel tips!"Moses Ludel, Publisher

How-to: Cylinder Leak Down Test on Honda XR650R Motorcycle Engine!

In this engine diagnostics and troubleshooting how-to HD video, Moses Ludel discusses cylinder leak down testing. The magazine's Honda XR650R motorcycle is the candidate. Learn how to perform a cylinder leak down test on any internal combustion engine and why this is a superior tool for pinpoint engine diagnostics.
 
Honda XR650R motorcycle engine Setting piston to TDC for cylinder leak down test
 The Honda XR650R cylinder leak down test begins with setting the piston at top-dead-center (TDC) of the compression stroke. TDC can be found with the timing mark or piston height reading, using a dial indicator and fixtures. A "two-stroke timing kit" with piston TDC finder will work here. This motorcycle engine is a four-stroke, single cylinder "thumper".
 
     Caution: Make sure the piston is at TDC on the compression stroke with all valves closed. If the automatic decompression start/release mechanism is holding the valves open at TDC on the compression stroke, loosen the rocker arm adjusters enough to establish valve clearance and seat the valves completely...A leak down test requires all valves to be seated.       
 
Demonstrate functions of a cylinder leak down tester Snap-On MT324 cylinder leak down tester
This HD video describes how the leak down tester works. At left, Moses Ludel demonstrates how the gauge tester registers leakage. The gauge reads in percentage of leak. Percentage of leak is the amount of air leaking past the valves, piston rings, head gasket or a casting crack.
 
Custom homemade adapter for motorcycle leak down testing Running cylinder leak down test on Honda XR650R motorcycle engine
At left is an adapter made for the Snap-On MT324 leak down tester. Honda XR200R, XR350R and XR500R four-valve, single cylinder motorcycle engines have a small, difficult to reach spark plug. This Snap-On MT324 gauge has been a shop mainstay since the early 1980s. Maintained properly, this equipment will serve for a long time. At right, the actual leak down test with compressed air reveals considerable air loss at the upper cylinder of this XR650R Honda motorcycle engine. 
 
Exhaust valve leak detected at Honda XR650R tailpipe. Air leakage at the intake air box 
At left, the air leak past the closed exhaust valves is considerable. At right, sealing the exhaust pipe tip causes air to rush out of the air intake box! This engine's extreme 95% cylinder leakage is largely due to leaking intake and exhaust valves.
 
Normal versus abnormal cylinder leak down readings Dirt seepage paste air filter on Honda XR650R motorcycle engine
At left, any piston ring "blowby" can be read as air seeping into the crankcase. In this engine, the majority of leakage is intake and exhaust valve issues. There is also air leakage into the crankcase. At right, the air box shows abrasive debris at its edge. Dirt seeping into the air intake stream can cause intake and exhaust valve pitting or score the cylinder's Nikasil liner. Nikasil wear at the top of the cylinder is evident when looking through the spark plug hole.
 
     This engine required an upper cylinder tear down to confirm the extent and cause of damage. It is clear that the damage is severe enough to cause substantial compression loss. We will now rebuild the top end of this Honda XR650R motorcycle engine. Follow the step-by-step "how-to" coverage right here at "The Off-Road Motorcycle Channel"! 

Cylinder barrel removal during upper engine rebuild

     In this instructional HD video series, Moses Ludel rebuilds the top end of the magazine's Honda XR650R motorcycle engine. Low compression led to the tear down. (See the HD video how-to on the cylinder leak down test.) The tear down led to a sublet of the cylinder head and cylinder for machining and reconditioning at L.A. Sleeve Company. For an overview of the teardown and removal of the cylinder head and cylinder barrel for inspection, click here!

     The rebuild of the Honda XR650R upper engine is now available as a 54-minute HD video step-by-step upper engine how-to rebuild!  Rent the entire program, including the bonus segments on valve adjustment and tuning, at Vimeo On Demand.*

     *For those doing only a valve adjustment on this four-stroke engine (and other four-strokes with conventional rocker adjusters), a valve adjustment standalone video is also available at Vimeo On Demand.  Each video rents for a 30-day period, allowing enough time for parts delays, machining sublets and other time constraints or challenges! 
 
Curious how this iconic and "bulletproof" Honda XR650R motorcycle engine got to this wear point in less than 1000 original miles? Get the whole story in Moses Ludel's comments on carburetor jetting and air filtration—exclusively at this 4WD Mechanix 'Tech & Travel Forums topic—click here!
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