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How to do a leakdown test?


kenward1000

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Did a compression test on the 3.0L/280Z based engine in my 240Z.  #1 = 195, #2 = 165, #3 = 170, #4 = 185, #5 = 150, #6 = 175.  Want to do a leakdown test to see what's going on in #5.  Have a leakdown tester which I've used on vintage motorcycles.  Have looked on YouTube and searched the forums, for a leakdown test procedure to use on an L28.  For each cylinder, need to test at TDC on compression; how do I determine that for each individual cylinder?  Thanks.

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You can put your finger or a rubber plug over the empty spark plug hole for the cylinder you're working on. As you turn the engine towards it's compression stroke you'll feel the pressure push against you. You should also be able to see the position of the valves for that cylinder.

I might be wrong, because it's been awhile since I did a leak down test on mine, but the cam lobes possibly have the "bunny ears" look for all cylinders at TDC compression stroke just like when observe no.1 at TDC.

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I attached a breaker bar on the front crank nut 27mm IIRC. then with the air pressure on low about 15-20 psi I would hand crank it until i would feel pressure, then slowly continue until the pressure would just go away then a bit more (trying to get the piston dwell in the middle). remove the breaker bar (you dont want it attached when full pressure is added as it can suddenly move if the TDC is not just right), and then pump up to about 90-100 psi. getting the TDC setting just right takes a little bit of practice but not hard.

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5 hours ago, Reptoid Overlords said:

I might be wrong, because it's been awhile since I did a leak down test on mine, but the cam lobes possibly have the "bunny ears" look for all cylinders at TDC compression stroke just like when observe no.1 at TDC.

Do the bunny ears point up or do they droop down?

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Again, I could be wrong about that, but this is the "bunny ear" position on cyl no.1 TDC compression stroke.  I'm fairly certain cylinders 2-6 will do the same when they are at TDC on the compression stroke.  Hopefully if I'm wrong, someone will chime in and say.  Sorry my memory degrades as the beard gets whiter.  Last time I checked valve lash I believe I just felt the compression as I turned the engine, but your leak down needs to be a bit more precise.  
IMG_20190902_101946_optimized_optimized_optimized.jpg.401253b6ee156a2e4a60fa0fc1d073d4.jpg

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