Fresh built KZ900 blows low compression ??

Hey,

I'll try to make it short. I rebuilt the motor, and it probably has about 45 minutes RUN time, none of that has been ridden. Most is just idle and trying to get it tuned. I can never get the thing to run right. It's been about 6 months sinced I've worked on it, because I lost all my patience with it and am now ready to start working on it again. Before I parked it last, I did a compression test and read as follows, in order of cylinder 1-4: 20psi, 0psi, 120psi, 120psi. I have no clue why it blows such low compression, and really am lost as to why cylinder 2 can blow 0 psi. It's not a wrong reading, I did it multiple times. It's a good guage too, there is no fault there. It never actually ran on all 4 cylinders, had a rough idle and only ran on 2 cylinders, the higher I revved it the other two would kick in and start to work.

And ideas as to where I should start looking and/or testing?

Sounds like you have valves not closing. Do a leakdown test.

APE Jay wrote:

Sounds like you have valves not closing. Do a leakdown test.

Jay has it pegged (who could expect less? ) What do you mean by 'rebuilt the motor'? What did you do?

cuddies say yee 925 wrote:

Hey,

I'll try to make it short. I rebuilt the motor, and it probably has about 45 minutes RUN time, none of that has been ridden. Most is just idle and trying to get it tuned. I can never get the thing to run right. It's been about 6 months sinced I've worked on it, because I lost all my patience with it and am now ready to start working on it again. Before I parked it last, I did a compression test and read as follows, in order of cylinder 1-4: 20psi, 0psi, 120psi, 120psi. I have no clue why it blows such low compression, and really am lost as to why cylinder 2 can blow 0 psi. It's not a wrong reading, I did it multiple times. It's a good guage too, there is no fault there. It never actually ran on all 4 cylinders, had a rough idle and only ran on 2 cylinders, the higher I revved it the other two would kick in and start to work.

And ideas as to where I should start looking and/or testing?

If not already done, would start by assuring all valve clearances are within specs.

Hopefully, good seating of each valve was checked and no valves got bent during reassembly.

Good Fortune!

definately check valves,what was done on rebuild?

No, there are no bent valves. Motor has 6,600 original miles, then my dad parked it for 20 years. Motor was locked up from sitting, so it got torn down. I didn't touch the bottom end at all, and top end has stock replacement pistons, stock rings, and fresh head. I did all the work myself and am very confident in it. I never could get the exact valve clearances, but they were always very very close. Maybe a ring cracked or something. I will have to wait to see, it has to be torn down again no matter what

Even with a cracked ring, or no ring for that matter, you'll have better than 0 compression!

Deffinately already solved... Valves are not closing correctly, if at all!

Or you forgot to install the head gasket... :laugh:

kidding.

GL.

Exactly! That's why I don't know HOW # 2 is blowing 0 psi.

Perhaps cam timing was incorrectly performed on reassembly.

Good Fortune!