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Old 03-23-2015, 02:15 PM   #1
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DIY leak down test fun!

I've done my first attempt at a leak down test with my new tester. It is a model that has two pressure gauges (0-100). It was not an easy job to do by myself with the car on jackstands.Much easier on a lift. I want to redo the test (glutton for punishment) but I want to clarify a few things.
1. Engine warm, right? I've heard warm and cold.
2. I have used a balloon on the adapter hose to discern the compression stroke of #1 cylinder, as well as the others. Is there an easier way? I figured that if I followed the firing order that might be an indicator.
3. TDC is difficult to ascertain in the boxster with the chopstick method because you need to crank from the inside then check the stick, and repeat and repeat for each cylinder! Am I missing something?
4. I pressure up the tester using the adjustment knob once the connections have been completed (compressor-tester-cylinder). This is the right procedure?
Any enlightenment here would be greatly appreciated!
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Old 03-23-2015, 02:36 PM   #2
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I've done my first attempt at a leak down test with my new tester. It is a model that has two pressure gauges (0-100). It was not an easy job to do by myself with the car on jackstands.Much easier on a lift. I want to redo the test (glutton for punishment) but I want to clarify a few things.
1. Engine warm, right? I've heard warm and cold.
2. I have used a balloon on the adapter hose to discern the compression stroke of #1 cylinder, as well as the others. Is there an easier way? I figured that if I followed the firing order that might be an indicator.
3. TDC is difficult to ascertain in the boxster with the chopstick method because you need to crank from the inside then check the stick, and repeat and repeat for each cylinder! Am I missing something?
4. I pressure up the tester using the adjustment knob once the connections have been completed (compressor-tester-cylinder). This is the right procedure?
Any enlightenment here would be greatly appreciated!
For the most accurate results, the engine should be warm.

The easiest way to find TDC on each cylinder is by pulling the plugs and rotating the engine by hand while someone checks the piston position.

Once at TDC, pressurize the cylinder and measure the indicated % leakage, them move on to the next cylinder and repeat.
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Old 03-23-2015, 02:47 PM   #3
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So is it easier to follow the firing order to avoid excess manual labour (cranking by hand) or numerical order? Not trying to be tedious but since I'm doing this by myself (no assistant) I'm trying to limit my skinned knuckles and wearing patience!
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Old 03-23-2015, 05:19 PM   #4
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So is it easier to follow the firing order to avoid excess manual labour (cranking by hand) or numerical order? Not trying to be tedious but since I'm doing this by myself (no assistant) I'm trying to limit my skinned knuckles and wearing patience!
Obviously, if you follow the firing order, the next cylinder to fire will be the one requiring the least crank rotation to come to TDC.
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Old 03-23-2015, 05:40 PM   #5
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Thanks JFP!
Geometry quiz: so about how many degrees? 120? (1/3 of a revolution).
(4 stroke engine = 720 degrees for each cycle / 6 cylinders = 120)
Seriously, this way I would only have to balloon test once (for the first cylinder) to know which is the compression stroke on the other cylinders.
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Old 03-23-2015, 07:07 PM   #6
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Newart,

I hope you find no significant leaks -hot or cold !

Last edited by Gelbster; 03-23-2015 at 07:37 PM.
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Old 03-23-2015, 07:33 PM   #7
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Thanks.
The hole will show me TDC for cylinder number one and 4 (?) both on the compression stroke and the exhaust stroke. ��
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Last edited by NewArt; 03-24-2015 at 02:48 AM.
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Old 03-23-2015, 09:25 PM   #8
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I've only done this on GM V8 engines, so I have no experience with the Boxster. Can't even imagine how difficult this would be on a flat mid engine. The best way to find TDC is probably to get someone to help you. You turn the harmonic balancer and they watch the chopsticks. It's a tedious process, but I think you got it covered.
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Old 03-23-2015, 10:07 PM   #9
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Hi,

warm engine is the way to go. Cold engine does have different compression.

Does leak down test mean a crompression test for each cylinder is does that mean an engine pressure loss test?
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Old 03-23-2015, 10:44 PM   #10
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Originally Posted by Smallblock454 View Post
Hi,

Does leak down test mean a crompression test for each cylinder is does that mean an engine pressure loss test?
Leak down = engine pressure loss test - over time. It is more accurate than a simple compression test, but I've always found that a compression test (done correctly) will give you the correct results and that a leakdown will just confirm it more ecurately.
Plus a compression test is a hell of a lot easier than a leakdown - especially on a mid engine flat six configuration.....
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Old 03-24-2015, 11:03 PM   #11
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Quote:
Originally Posted by NewArt View Post
Thanks JFP!
Geometry quiz: so about how many degrees? 120? (1/3 of a revolution).
(4 stroke engine = 720 degrees for each cycle / 6 cylinders = 120)
Seriously, this way I would only have to balloon test once (for the first cylinder) to know which is the compression stroke on the other cylinders.
This is a diagramm of the firing order:



Hope that answers your question.

Regards Markus

@Steve Thinker: thanks for explanation
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Old 03-25-2015, 04:08 AM   #12
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Thanks Markus, I already know the firing order, I just wanted to verify the degrees of rotation between TDC of each firing cylinder in the sequence. ��
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Old 03-25-2015, 07:10 AM   #13
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Well, OK. So, let's see.

We have a 4 stroke Boxer engine. That means we have 3 pairs of pistons that work together like that:



So 1 and 4, 2 and 5, 3 and 6 are pairs.

Let's take a closer look at 1 and 4. So 1 and 4 are allways at the same position and at OT. The difference where we are in the "stroke cyle". So if 1 is at OT and before ignition - all valves closed. 4 has all exhaust valves open and all exhaust gases are out of the cylinder.

So if 1 is at OT all valves closed and you crank the crankshaft 360 degress 4 is at OT all valves closed.

Because we have a 6 cylinder engine, there are 4 clinders left. First, they work also as pairs. So the same logoc as above. But they work with a different timingcycle because of the crankshaft has a 60 degree offset for each pair.

In combination with the firning order i think now you should be able to make a spreadsheet and note all OT and crankshaft turn degrees for your engine pressure loss test.

Animation: https://youtu.be/JDYHyGNFR5Y

Regards Markus
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Last edited by Smallblock454; 03-25-2015 at 07:18 AM.
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