Cylinder Leak Down Test on a Harley Davidson Twin Cam Motorcycle (how to)

[@orgillmathew]

About time someone made a simple explanation how to do a job cheers mate 🤙

[@sophtayl]

Thanks for youvideo and taking the time. Which gear are you in when you do the test? Assume you have the wheel in the air hence the foot on the brake? Hoe do you accommodate backlash rotation around compensator and transmission? All things I'm finding to confound the ussue in measuring.

[@harleyloco1853]

I put the bike into 6th gear pull the plugs to rotate the motor over to find TDC on the cylinder im testing. The reason for the rear brake is that the air will push the piston straight down so a reading would not be possible. This wont put any wear or danger to the conpensator or trans. If you do not wont to let the brake off and let the motor turn you could disconnect the air line and bleed the air back out the top of the leak down device. Thanks for watching appreciate your time

[@sophtayl]

@@harleyloco1853 thanks for your prompt reply. The issue I was trying to explain is that applying the brake doesnt stop the piston moving as it is applied to the wheel but doesn't control the other backlash I refer to. I have been putting the wheel on the bench (after confirming TDC and rotating the wheel backwards to remove belt tension) and doing the pressurising. Occasionally the piston still strokes part way down even without wheel movement (as would happen with the brake applied). In theory, the stroke should still be on both valves closed, but depending on the lift and timing of cam lobes may cause some leak down (mine is stock so shouldn't be an issue). I was wondering if you controlled for this or not? in my case, I ended up loosing push rods/ rockers and still had leakage out of intake

[@harleyloco1853]

@@sophtayl well the piston has to be all the way up the cylinder TDC anything less it will get blown back down. . Aslong as your at TDC you can perform the test. The leak tester showed me a good healthy motor. I also do a sound check ear by the headers by the breather and take the oil cap off and listen for any bubbling etc from inside the motor. You should not be getting any leak out of the intake that shows a leaking valve.

[@sophtayl]

​@@harleyloco1853​yes agree. if the piston isnt perfectly on tdc then the pressure pushes it down. a lot of leakdown tests appear to recommend 100psi for a true reading (lower pressures appear to be less accurate) which will definitely move a piston (unless perfect tdc), mine went to 35psi and still moved the pistion... but agree with all your comments. and yes, ultimately the intake (which should be wedged open), exhaust and oil tank filler told me more about my issues. Suffice to say, a build is being planned... Thanks for sharing

[@harleyloco1853]

@@sophtayl best of luck with it all buddy Ride Safe