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Discussion Starter · #1 ·
Hello everybody, this weekend after cleaning the carbs last week, This weekend I adjusted the valves, 4 of them were out of spec and the other were at the bottom end of the spec, so I adjusted them so to be at the middle of spec range.
So now carbs and valves are Good.
Now before the first start, the bike had 120psi on cyl 1,2,3 and a great 30psi on cyl 4.
After I was able to start the bike, before valve adjustments and carb cleaning, I got it up to temp and now on cyl 1,2,3 I still had 120 Psi, and on 4 now I had 110Psi.
Today I get the bike to run a bit, performed a compression test, and nothing has changed, 120 on the first 3, and 110 on the 4th.
So I decide to go ahead and perform a leakdown test, and I got 4% on cyl 1,3,4 and 3% on cyl 2.
According to the specs, the cyl compression should be between 139-230psi, now having a compression of 120Psi, means some major tear and wear on the rings or valves or head gasket and should be associated with a pretty bad leakdown test result.

So I tried the compression test gauge with the shop air, and it was not too far off, maybe 5-10 Psi.
and to try the Leak Down tester, once I was done with the test on cyl 4, I just started to rotate the crank shaft, and the and as soon as the valves moved the leak value went sky high

End result is that at this point If I have to believe the leak down, my engine is in good condition, while if I have to believe the compression test, my engine is close to trash... which of the 2 you think is more reliable?
 

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Generally you would use a compression test to give an indication of the health of an engine. Then use leak down to pin point the weak/problem areas.
They are used together to diagnose engine problems. You can’t use one and ignore the other.
 

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A leakdown is the test you do to confirm low compression. Yours seems to have confirmed the opposite.
When you adjusted the valves, compression climbed back up in the one cylinder that showed low compression. That seems to have been the source of the problem. Prior to leakdown testing, wet-or-dry compression testing determined the source of the loss. After a low test, a little oil is squirted into the cylinder and if that makes a difference, the leak is past the rings. If not, the issue is at the valve level.

After all is set in order, it's how it runs that counts.
 

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Discussion Starter · #4 ·
So Am I too optimistic thinking that with those results I can conclude that the engine overall is healthy and not worth to be taken apart for a full rebuild?
 

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1993 Zx-7 L Model, 2006 ZX-10R
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A leakdown is the test you do to confirm low compression. Yours seems to have confirmed the opposite.
When you adjusted the valves, compression climbed back up in the one cylinder that showed low compression. That seems to have been the source of the problem. Prior to leakdown testing, wet-or-dry compression testing determined the source of the loss. After a low test, a little oil is squirted into the cylinder and if that makes a difference, the leak is past the rings. If not, the issue is at the valve level.

After all is set in order, it's how it runs that counts.
So Am I too optimistic thinking that with those results I can conclude that the engine overall is healthy and not worth to be taken apart for a full rebuild?
After seeing those numbers; I would've done the irresponsible thing and test how long it'll run before needing a rebuild. All the while searching for and accumulating parts for said rebuild. I'm a glutton for punishment. I like servicing the bike so much, I do it twice.
 

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Discussion Starter · #6 ·
After seeing those numbers; I would've done the irresponsible thing and test how long it'll run before needing a rebuild. All the while searching for and accumulating parts for said rebuild. I'm a glutton for punishment. I like servicing the bike so much, I do it twice.
well, that is exactly what was in my mind... I still need to rebuild ALL the hydraulic lines, rebuild all master cylinders, Find the brake rotors, Steering bearing and swing arm bearings... Good news is that all of those things are sort of easy to find, and would get the bike in a safe to ride condition (of course I'm missing all the front fairing too DISASTER!!! lol)
My dream scenario is to get the bike street worthy and safe as it is, mean while hunt for the hard to find parts body work and engine, so that once I got a spare engine all build up I can go for for a frame up restoration, and finally get my dream bike alive.
Doing so, while riding, I can find all little things that are in need and 1/2 enjoy it until I gather all parts for the frameup restoration. I'M TOO IMPATIENT OF A PERSON! :)
 

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Hello everybody, this weekend after cleaning the carbs last week, This weekend I adjusted the valves, 4 of them were out of spec and the other were at the bottom end of the spec, so I adjusted them so to be at the middle of spec range.
So now carbs and valves are Good.
Now before the first start, the bike had 120psi on cyl 1,2,3 and a great 30psi on cyl 4.
After I was able to start the bike, before valve adjustments and carb cleaning, I got it up to temp and now on cyl 1,2,3 I still had 120 Psi, and on 4 now I had 110Psi.
Today I get the bike to run a bit, performed a compression test, and nothing has changed, 120 on the first 3, and 110 on the 4th.
So I decide to go ahead and perform a leakdown test, and I got 4% on cyl 1,3,4 and 3% on cyl 2.
According to the specs, the cyl compression should be between 139-230psi, now having a compression of 120Psi, means some major tear and wear on the rings or valves or head gasket and should be associated with a pretty bad leakdown test result.

So I tried the compression test gauge with the shop air, and it was not too far off, maybe 5-10 Psi.
and to try the Leak Down tester, once I was done with the test on cyl 4, I just started to rotate the crank shaft, and the and as soon as the valves moved the leak value went sky high

End result is that at this point If I have to believe the leak down, my engine is in good condition, while if I have to believe the compression test, my engine is close to trash... which of the 2 you think is more reliable?
I'd do a leak down test like what others had mentioned. That way you can figure out where the pressure loss is coming from. Although I'm biased I'd use the Motion Pro 08-0740 Leak Down Tester. See attached.
 

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Discussion Starter · #8 ·
I'd do a leak down test like what others had mentioned. That way you can figure out where the pressure loss is coming from. Although I'm biased I'd use the Motion Pro 08-0740 Leak Down Tester. See attached.
Dang... you are SUPER Technologically advanced :) That motion pro looks, very good... I'm still at the stone age using a good old school 2 analog gauges tool :)
 
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