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Discussion Starter #1
Do a compression test on my zx-10r yesterday, because is running like crap.

I retime the cam (106-102) recently and put a thin head gasket, check the valve clearance and it was running O.K until last night.

So I do a compression test and weird result happen.

First the pression built on the guage coming up to 120 around, but the pression just go down to zero. So I redo test on each cylinder, same results.

Soooo I take anothe compression tester redo the test and same results ????


So why it run O.K before and now , can't figure.

I will check the valve clearance again to see.

If it's O.K I will put the cam to their standard position and do a compression test again.


It seem that the motor built pression but for some hidden reason don't hold it ????


Kind of head sratching there.

Fisrt time I saw that....:dontknow::dontknow::dontknow::dontknow:
 

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Yeah, I would be checking clearance and cam timing very closely although it sounds like it is building compression. Do you have a leak down tester? My compression testers don't drop pressure unless I press the relief button and a cylinder will not hold compression unless all of the valves are closed (i.e. TDC). But the compression tester gauge should hold the maximum pressure until you press the relief button. Sounds more like a bad tester. The leak down tester will tell you the rate of leak down (test at TDC).
 

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Google "leak down tester". They are almost as common as compression testers. But, your compression tester shouldn't lose its pressure. If it reads a certain pressure it should stay there until you press the button. That would be a problem with the tester, not the bike.
 

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Well finally I built myself a leak down tester, that thing take me a fair amount of try guess and finally I got something very efficient.

This thing lead me to what I was suspected......LEAKING HEAD GASKET......

Imagine when I put pression (100lbs/po2) on cylinder 1 at TDC the pression leak on other cylinder.

First thing I was thinking that was the valve, sooo I put some water in the intake (because sound comme from the intake (air leaking by there) ) to see if the air coming from bad valve = NO.

But the air still coming from other intake.


So well I put of the cylinder head off and yes the seal between cylinder are not exactly efficient.

So tonight I will put another head gasket and I will perform the test again on each piston at TDC to see if everything ares sealed (witout the camshaft in place).

I will put the camshaft and do a test agin at TDC. But with the water test seem no air coming from a bad seal of valve (clearance on valve already checked are O.K (A bent valve for example will gave you a large clearance over the spec) and another sign are the valve never touched the pistons so I'm not afraid for valves.

The leak down tester are an amazing tool. If anybody want to see it I will take pics.
 

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Discussion Starter #7
Well head gasket was put on and when I performed the lek down test on cylinder 1-2-3-4 now the leak seem to come from the base.

Maybe it's normal because the test is performed at bdc (ie the piston on the bottom of his stroke).

I will put the camshaft in place and test the bugger at TDC for each cylinder.

Anyone tried to do leak test at bdc witout the cam in place..... maybe not.


The wall of the cylinder are nice and smooth without any rail (who is the indication of ring wear), but like I don't know the historic of this motor it's very hard to know if the ring if they was put off was installed in the right order.

I will perform a leak test with the cam install at TDC tonight if I'm not catch by a thunderstorm like yesterday.

Thanks for help or experience.
 

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If the engine hasn't been run recently the cylinders will be dry. Squirt a few drops of oil into the cylinders around the edge of the pistons to get the rings lubricated and see if that changes anything. The test should be done at TDC of the compression stroke. Not sure how you made your leak down tester but you can buy one for less than 50 bucks.
 

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Discussion Starter #9
Leak down test performed

Replace the head gasket and after that performed the leak down test. Less then 5% loss so I'm good. Need to put out the thermostat because the spark plug wires was stuck under it. replace everything with the seal and a liitle of silicone in case.

Start the motor....run like shit so put off. Put out the cam cover and fu...water in the oil, drain the oil pan and fu... again water in the oil...grey oil...

So I think the water pump seal bust, put out the water pump and the pump are perfect, seal O.K etc.


So after that I Checked visually the block and the cylinder head for cracks or something ....Nothing....


The head gasket are new and the torque on the bolt applied follow the pattern give in the repair manual.


So now I'm at the point to put out the cylinder head and pass through magnuflox to look if their any cracks.

Really I'm tired of this motor, seem it's haunted.


This one new problem I don't understand really.


As I'm tell nothing seem wrong with the water pump.



Head gasket are straight forward installation and theirs only one way to put it sooooo.

This new thing just kill me.:headshake::headshake::headshake::headshake:
 

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Any one got this before? Grey oil usually are sign of busted water pump but no it wasn t the case. I will do leak down test again and put water in the intake and exhaust port to see at tdc if they re any bubble. Next thing will be do a hydrostatic test to the head. Did a broken valve guide could cause that or a damn crack somewhere ? When i put the head on no crack are visualy detect.
 
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