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Jon-D

Leak Down Test – Procedure

3 posts in this topic

Yesterday I purchased a leak down tester from Harbor Freight and plan to test out my bike but have a few questions.

Do I need to have the engine warm to conduct the test or can it be cold?

How much difference in the reading would I see between a cold and warm test?

Does the piston have to be at TDC, or do I just have to make sure the valves are closed (piston near TCD)?

Is there a way, or do I need to lock the piston at TDC to prevent it from moving during the test?

At what psi do you normally run the test?

Thanks Guys!

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Yesterday I purchased a leak down tester from Harbor Freight and plan to test out my bike but have a few questions.

Do I need to have the engine warm to conduct the test or can it be cold?

Warm would have everything in its normal conditions and expanded to where they would be. but Cold would be easier. I'd try cold for convenience but if the results are poor I'd try it warm...more like operating temps.

How much difference in the reading would I see between a cold and warm test?

Try them both...I believe Warm would be closer to riding conditions.

Does the piston have to be at TDC, or do I just have to make sure the valves are closed (piston near TCD)?

Yes...TDC, make sure your valves are adjusted to spec as well.

Is there a way, or do I need to lock the piston at TDC to prevent it from moving during the test?

Put it in gear and hold the rear brake in case it does but I believe a problem would show in the test. I always did it in park in my car so wasn't an issue.

At what psi do you normally run the test?

I thought I remembered 80-90 psi and normal is 5-10% leakage??

Thanks Guys!

Here is the procedure...if it didn't come with instructions.

1. Take out the spark plug.

2. Bring the cylinder TDC (top dead center) so that all the valves are closed.

(on the XR650R you line up the "T" with the mark on the inside of the case)

3. Install the leakdown tester into the plug hole.

4. Apply the compressed air and modulate the knob to get a steady reading

from both faces on the gauge.

5. LISTEN to where you can hear the compressed air.

* At the crank case: Not sure a good place to listen on XRR (don't know if you'd hear it back at the filler hold in the frame? but if its a different bike where the oil filler hole is in the case like other bikes that would work but It might force oil out...Maybe best to try it when oil is drained if dealing with that situation. (Not need in the XRR)

* At the tailpipe: It is your exhaust valves if you can hear it (or even feel puffs on your hand) at the tail pipe.

* At the intake manifold: (through the airbox. Make sure gas is turned off and slide of carb is open)

hopefully you are just playing with your new tester and not trying to fix a problem!

Hope this helped.

JT

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Hey, thanks for the reply. yup, just playing with the tester. I tried it on the bike yesterday just to see what would happen and I did hear a small leak from the exhaust valves. I listened for a leak from the oil vent hose but did not hear anything so I was pleased with that. not sure if I am setting the gauge correctly though, the % loss gauge was reading kind of strange, to the point where I focuses on hearing any air loss rather then the % loss. I will have to give it another try.

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