How screwed is this motor (leakdown test results)

[90 GSX]

Okay get ready for this... and keep in mind I know the motor was on its way even before I did the leakdown test. It only makes between 13-16 inches of vacumn... On cylinders 1 and 4 I had ~16% leakdown and on cylinders 2 and 3 I had ~14% leakdown. I did the test at 70psi air pressure. I don't know what a good leakdown is, that's why I am asking this question.

I am just pretty much driving the thing until it breaks. I think once I get my hands on another good 6 bolt I'm going to crank the boost up on this motor and have some blow-by fun!!!

Commentary please...

 

[sweet97]

How do I do a leakdown test?

 

[DSMJim]

14 & 16% at 70psi is quite a bit but not terrible by any stretch. You should still be able to drive for quite a while like that.

sweet97 to do a leak down test you must buy a leak down tester from an autoparts store, it's kind of like a compression testere but more expensive. It comes with instruction but in a nut shell you put the cylinder your testing to TDC with all valves closed an screw it into the cylinder and hook up your air line from your compressor. Set the pressure and measure the leak. Once you have it you will understand. It's a bit more complicated than a simple compression check and you must be able to rotate your motor yourself and know where TDC is on each cyl your testing.

 

[90 GSX]

What are you normally supposed to test at? I originally thought I had a bad head gasket between cylinder 2 and 3 because they were noticeably lower than cylidners 1 and 4. However, the coolant level did not change and no bubbles came up. The car doesn't leak anything on to the ground, but I do smell burning coolant smell coming from the engine bay and I can see the steam with my headlights on at night. Maybe I just have a small leak somewhere...

Regardless, I want to start with a fresh motor. Like I said, the car runs and drives fairly well considering the worn short block. What are some leakdown number for a good cylinder and a bad cylinder?

I had another question. If my compression was so much lower on cylidners 2 and 3, why did they have better leakdown than 1 and 2?

Sweet97 - A leakdown tester has two gauges. One measures the input air pressure that you want going into the cylinder. The other measures how much air leaked out of the cylinder. So to get the percentage you take: (amount of pressure that escaped) / (amount of input pressure) and then multiply the result by 100. Anybody want to tell me if I'm right or wrong on that...

 

[sweet97]

Are these testers available at the local auto part stores? I am abou to change my plugs. I want to do a compression test at least. Do I do that with the plugs all out? Thanks, Mark

 

[steve]

Here is an example and a nice table on the second page for the results.

You must be logged in to view this image or video.

http://www.racerpartswholesale.com/long29.htm
http://www.racerpartswholesale.com/long29a.htm

Minor correction:

% leakage = ((cylinder pressure) / (input pressure)) * 100

Steve

 

[truwarrior]

so is it suppose to be tdc or btc on our cars? Those instructions say bottom...

 

[steve]

so is it suppose to be tdc or btc on our cars? Those instructions say bottom...

They say BDC so that the piston doesn't move when you turn the pressure up.

Steve

 

[truwarrior]

So it basically doesn't matter...I would think bottom would be best myself... at if the pressure turned the crank counter clikewise? :

 

[SlowSpyder]

another thing to consider is to do the test when the engine is warm or at operating temps

 

[WatchItExplode]

Eh...you don't need a big fancy tester thing like that. I made a "leakdown tester" by welding a spark plug (with the ceramic smashed out) to a quick-release fitting. screw it in, turn on the pressure, and listen for where your compression leak is coming from.

In my case, oil spewed from my dipstick tube, which obviously indicates worn rings.

 

[thegreatms]

Eh...you don't need a big fancy tester thing like that. I made a "leakdown tester" by welding a spark plug (with the ceramic smashed out) to a quick-release fitting. screw it in, turn on the pressure, and listen for where your compression leak is coming from.
In my case, oil spewed from my dipstick tube, which obviously indicates worn rings.

That sound like its a good qualitative method.

However some people still want to get quantitative data.