U.S. General cylinder leakage gauge questions

[natemoore]

If anyone here is familiar with Harbor Freight's U.S. General cylinder leakage gauge set, I'm not understanding this thing.

First, the left gauge has the regulated air and the right gauge has a percentage leakage scale, 0-100%, with 100% being at about 8 o'clock and 0 % being at about 4 o'clock and 50% at 12 o'clock.

I put the no.1 cylinder at TDC on the compression stroke by turning the crankcase until the timing mark was at 0 and the ignition rotor was pointing at the no. 1 spark plug wire.

When I connected the gauge and cranked up the pressure to 70 or 80 psi, the right gauge went all the way past 0 % leakage all the way down to the 6 o'clock position. Since I could hear and feel the air coming out of the oil fill hole (and it was quite a breeze) I assumed that the gauge should read something in between 0% and 100%.

So, I bench tested the gauge by hooking it up to compressed air and putting a blow gun on the other end, assuming I could simulate a perfect engine and a worn engine by how much I depressed the blow gun's handle.

Got the same weird behavior.

The directions that came with the tool said to hook it up with the regulator closed, then slowly increase the air pressure until leakage dial read zero. "Now you can read the percent leakage." Doesn't make sense to me.

Help. Thanks.

 

[Bifflefan]

Re: U.S. General cylinder leakage gauge questions

you have to hook up the air and adjust the pressure to read 0 when its not connected to the engine adapter. then when you plug in the adapter with it in the engine it should give you a reading of the leak %.
If you have a 4 stroke you may not be on TDC compression. you may be on TDC exhaust. try rolling the engine over one more time to TDC and recheck it.

 

[natemoore]

Re: U.S. General cylinder leakage gauge questions

you have to hook up the air and adjust the pressure to read 0 when its not connected to the engine adapter. then when you plug in the adapter with it in the engine it should give you a reading of the leak %.
If you have a 4 stroke you may not be on TDC compression. you may be on TDC exhaust. try rolling the engine over one more time to TDC and recheck it.

Even if the rotor is pointing to no. 1 spark plug? I thought each piston fired once each complete revolution of the distributor rotor. Am I mistaken?

BTW, the Harbor Freight instructions had the set up steps out of order: hook up to cylinder then do the calibration. Typical. Put together any Wal-mart patio furniture lately?

Thanks.

 

[Bifflefan]

Re: U.S. General cylinder leakage gauge questions

Even if the rotor is pointing to no. 1 spark plug? I thought each piston fired once each complete revolution of the distributor rotor. Am I mistaken?

Thanks.

that is true of a 2 stroke. a 4 stroke fires every OTHER turn. You didnt say what kind of motor it was so i just put that in there.

 

[natemoore]

Re: U.S. General cylinder leakage gauge questions

Learn something new just about every month! Thanks. It's a 4 stroke.

 

[dontask]

Re: U.S. General cylinder leakage gauge questions

Even if the rotor is pointing to no. 1 spark plug? I thought each piston fired once each complete revolution of the distributor rotor. Am I mistaken?

BTW, the Harbor Freight instructions had the set up steps out of order: hook up to cylinder then do the calibration. Typical. Put together any Wal-mart patio furniture lately?

Thanks.

Yes you are correct, the spark plug gets fired each time the rotor is at its contact position inside the distributor cap. The rotor and the cam are in sync. The crank is a 2 to 1 turn in relation to the cam. Two turns of the crank gets you one turn of the cam & rotor (4cycle). A 2 cycle can get its firing information directly from the crank or flywheel.