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TR5 & TR250 Forum

Leak Down Tester or Air Compressor?

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Rickh Rick Haumesser
Bartlett, TN, USA   USA
I need to do a leak down test on my TR250 and was curious if I could accomplish this without an actual leak down tester by using my air compressor and hose from my compression tester? If I insert the hose from my compression tester into the sparkplug hole (it has a screw in adapter) and the other end to my air compressor, and measure how much pressure drops on my regulator gauge, would that not accomplish basically the same thing as a leak down tester?

Of course I would bring each cylinder to TDC on the compression stroke, and set the brake and keep the car in gear for the test. If this could work, I have a couple of questions:

1- How high should I set the pressure on my regulator?
2- What would be a pass/fail percentage of pressure drop on a TR250 engine?

Appreciate any suggestions, thanks!

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David DPS Avatar
David DPS David S
Louisville, Kentucky, USA   USA
Maybe you could do the leak down test assuming that the gauge was accurate and no fitting leaks. The amount of time jury rigging this might not be worth your time as there are some fairly inexpensive kits for this. Some auto parts stores have tools that they rent cheap (not TR specialty tools of course) or require only a deposit. I would use a purpose made tool and in addition to saving time, I would not have to wonder if it is an engine problem or a tool problem.

Rickh Rick Haumesser
Bartlett, TN, USA   USA
Thanks David. I went ahead and tried my idea this weekend and I am getting some air past the rings, however only a very faint hiss is heard, and the amount of hiss sounded very similar across all cylinders. My gauge on my compressor did not really show any drop in pressure so I am not able to accurately diagnosis percentage of leakage per cylinder. To some degree, I was able to rule out other areas for concern because I did not see any bubbles in the coolant or hear air in carbs or exhaust. My local autoparts do not rent a leak down tester (they did not even know what it was) however I might go ahead and buy an inexpensive tester for the very occasional use and hopefully it will be accurate enough to provide some insight as to what percentage of leakage is occurring past the rings.

Thank you for your input as I value all the help I can get. Have a great day.

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David DPS Avatar
David DPS David S
Louisville, Kentucky, USA   USA
Rick,
You didn't mention if you had problems or just evaluating a recent purchase. I assume you did pressure testing first and also checked if some oil squirted into the cylinders made a difference.

I had to press some pistons out of a TR4A's cylinder sleeves not too long ago. It was amazing how the old leaded gas had left deposits around the rings and below. It was that crap that had locked up the engine and not cylinder wall rust.
Dave

tirebiter Jeff Garber
Dighton, MA, USA   USA
Jumping in on this rather late, I know. My Snap-On brand cylinder leakage tester regulates the air going into the spark plug holes at about 60 PSI. You will always here a slight hiss from the rings. Usually not all that quiet on a cold engine.

The ring gap HAS to be there to avoid seizing when the engine warms up.

If you drop the regulator to about 30 PSI you may hear a more noticeable difference.

It's very difficult to hear exhuast valve hissing due to the length of pipes and muffler.

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