Extremely confusing compression 83' kz1100

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14 May 2015 17:57 - 14 May 2015 18:13 #672146 by cafebrat
Hey guys,
I have noticed that my 83' kz1100 ltd is loosing oil pretty drastically and quickly, along with smoking consistent with throttle coming from my crankcase breather filter. No smoke coming from the exhaust at all though. So as far I could tell it would be labeled as blow-by. So I did a dry an wet compression test to try and figure out what the rings were like and I got some really confusing compression numbers. They're as follows:
DRY: #1 -175 psi. #2-150 psi. #3-155 psi. #4-180 psi
WET: #1-250 psi. #2-260 psi #3-240 psi #4-285 psi
My clymers manual says anything between 130-160 psi is "normal" and that when comparing numbers between dry and wet, any more than 10-15% increase shows worn rings and bore. My confusion is that the dry numbers show normal, or even higher than "normal" and the wet numbers show a massive wear on the rings/bore.
I know my valves are in spec because I did them last year and other than losing so much oil mysteriously and the smoking from the crankcase, the bike seems to run good. It has a ticking noise coming from the engine as well but I've been told by some mechanics that it's normal to hear some ticking, although I disagree and lean twards the ticking, smoking, oil loss and compression to all be somehow related. Thanks in advance to anyone who can lend a hand.

83 Kawasaki Kz1100 LTD
81 Honda cm400
72 Suzuki T500 Titan** 2-stroke B)
Last edit: 14 May 2015 18:13 by KZQ. Reason: Make thread searchable

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14 May 2015 19:02 #672154 by 650ed
Replied by 650ed on topic Extremely confusing compression 83' kz1100
Ignore the wet numbers - they pretty much are meaningless.

Here's why -

Even a very small amount of oil added to a cylinder can make a big difference in the compression readings. I have seen more than one person advocate adding "about a teaspoon" of oil to each cylinder when doing a "wet" compression test. That may not sound like much oil to many folks, but a teaspoon is actually right around 5cc, and that is a lot. As an example of how little oil it takes to change the compression ratio I offer the following diagram. It uses a hypothetical cylinder with a total volume (cylinder & head) of 100cc and a dry compression ratio of 10:1. A little oil added changes things quite a bit, so if different amounts of oil were added to different cylinders one can see that the compression ratios might vary a lot. This example is not precise and is not any specific engine and it doesn't take into account oil that may seep past the rings, etc. It only is meant to demonstrate in very general terms how adding oil can change compression ratios. You can see how quickly the compression ratio jumps as oil is added to the cylinder. Ed

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1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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15 May 2015 07:15 #672215 by cafebrat
Replied by cafebrat on topic Extremely confusing compression 83' kz1100
Thanks for your repy, That certainly explains the very high "wet" test numbers. So if I'm not paying attention to the wet and just the dry, do the dry numbers seem okay or should I be worried that cylinders 2&3 are worn and causing blowby? Like I said before, Im losing a lot of oil and can see smoke coming from the crankcase breather as if it were a smokeing exhaust. I can blip the throttle and see a direct increase in smoke being blown out.

83 Kawasaki Kz1100 LTD
81 Honda cm400
72 Suzuki T500 Titan** 2-stroke B)

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15 May 2015 09:15 #672237 by SWest

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15 May 2015 09:56 #672247 by 650ed
Replied by 650ed on topic Extremely confusing compression 83' kz1100
Are you sure you haven't overfilled the oil? Are you checking the oil level using the site glass with the bike level on the centerstand? No offense intended, but some folks have been known to check the oil with the bike on the side stand and then overfill it. Ed

1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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21 May 2015 15:37 #673039 by cafebrat
Replied by cafebrat on topic Extremely confusing compression 83' kz1100
The bike has a little over 20k on it, which only adds to my confusion since I don't think 20k would be all that much wear on the top end. And no offense taken, but I'm not that stupid haha, I always fill my oil with the bike on the center stand and get it right in-between the min-max lines.
While we're on my shitty engine topic... Does anyone know if the engine models a1, a2, and a3 would be compatible to swap into my 83 kz1100 L1 LTD?

83 Kawasaki Kz1100 LTD
81 Honda cm400
72 Suzuki T500 Titan** 2-stroke B)

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