Leakdown Test Help Needed

[kdietz]

How do I keep the piston from moving off TDC when the air pressure is applied to the combustion chamber?

My instructions say to remove both spark plugs, but it seems to me that if you left the other spark plug installed if would help to keep the piston in place?

[Don D]

High gear with the rear brake set. From my perspective exact tdc is not essential but you have to be on compression and valves closed.

[kdietz]

Makes sense....thanks 

I didn't notice that the wheel was turning as the air was applied....duh!

[Herko]

I've had good results with this:
Tranny in high gear.
Bring cyl being tested at or near TDC
Using a "stout" drift, punch or similar, place it between the swingarm and rear brake caliper and align the nearest hole in the rear brake rotor and slide in the drift (securely deep enough) to lock wheel.
Cautiously add the test pressure.
Slight settlement movement will likely occur.

YRMV.
Do not try this at home.

[Admiral Akbar]

High gear with the rear brake set. From my perspective exact tdc is not essential but you have to be on compression and valves closed.

Only works with mouse motors... Max

[Hillside Motorcycle]

High gear, brake, and have someone sit on the bike.

[TXChop]

Yup, i do as Scott says. Sometimes letting the rear wheel down on the ground helps...Also if flying solo at ratchet tie down around the rear brake lever had helped me in the past.

[FLTRI]

Same as Scott and TXCHOP and if no one is available to hold the brake, we use a tiedown w/ratchet around the pedal to the crash bar or footrest depending on the configuration.