compression test

[parkze]

I did a compression test on my 2002 Kat 600 today and the compression started getting odd readouts...

test# 1 2 3 4 5
Cylinder 1- 152, 150, 95, 60, 60
cylinder 2- 135, 145, 150, 60, 145
cylinder 3- 150, 150, 145, 90, 65
cylinder 4- 150, 150, 148, 150, 150

Why did my testing have suck up and down readings?

I had the carbs off so it was wide open throttle. I made sure the gauge was screwed in the whole way. I let the air out of the gauge after every test. Should I replace the plugs in the cylinders after I test them, or is it ok to do the test with all the plugs out? Test 4 and 5 were done on a battery charger which I thought may be why they read so low but cylinder 4 proved that thought wrong since it was pretty similar every reading.
Help please...
thanks

[arsenic]

I can't even begin to guess what you did wrong But it was obviously something

[Kfreak]

This may sound funny but, my manual says to do a compression test on a hot or warm motor. I'll have to re-read.

[DoyleDee]

Uhhhhmmmmm first- remove all the plugs and do the test again. If you aren't sure, consult a book and check what you are doing with what the book says..... and just so you know I'm not trying to be mean or anything of that nature- it should be the ((((First)))) thing you do if you haven't done it before.

[BradsKat]

If your engine is warm and everything else checks out (good seal on the gauge, good battery) then maybe the gauge itself is pooched?

[parkze]

heres my newest test with fully charged battery... 150, 60, 145, 65

[kevin2502000]

Squirt a shot of light oil or wd40 in the cylinder before you check it, that makes sure your rings might not be gummed up and sticking.

[StevieB]

I'd go with the high reading from each cylinder. Your gauge could read low sometimes, but I don't think it would ever read high. You probably have a leak. So, you have 152, 150, 150, 150. Very good.

[hardlydangerous]

Make sure you are holding the throttle wide open when testing.
Its best to test the engine when cold for the most accurate reading
put a bit of grease on the sealing o-ring when you tighten in the guage.

[parkze]

OK I called my suzuki dealer and the mechanic there said I needed to hook my coils back up and put the plugs them and ground them out while doing the test. This seamed to have been what I was doing wrong. He told me my results would be all over the place if I did not do this. After doing so 2 times through I came up with the same psi for both tests. cylinder #1- 115 cylinder #2- 162 cylinder #3- 180 and cylinder #4- 178. I have decided that i will be replacing the rings on 1. Or should I just say to heck with it and just do all the rings at once?

[Kfreak]

I did confirm the test procedure and it does state to bring the motor to operating temp.

[The CyberPoet]

I'd literally replace the engine if my readings were 115/162/180/178 freshly warmed.
Why?
Because I'd seriously suspect the oil jet under the piston and those in the heads aren't supplying oil to that piston correctly, or one of the valves chipped, and the amount of work involved in boring/honing/re-ringing a 98+ engine isn't worth it in my opinion (I'm prejudiced in that I live in a hot, humid place ). Easier to find a $400 - $600 engine and simply bolt it in instead.

While I was at it, I'd also tear down the #1 carb float mechanism & replace that, or simply replace that entire carb, as this kind of wear can also indicate that gasoline was flooding the cylinder, washing away all the lubrication for the rings.

Either way, I don't envy your position.

Cheers,
=-= The CyberPoet

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[StevieB]

OK I called my suzuki dealer and the mechanic there said I needed to hook my coils back up and put the plugs them and ground them out while doing the test. This seamed to have been what I was doing wrong. He told me my results would be all over the place if I did not do this.

That is the loopiest advise I have heard in months. No way the ignition has anything to do with a compression test. He's probably STILL laughing at you.

[kevin2502000]

That is the loopiest advise I have heard in months. No way the ignition has anything to do with a compression test. He's probably STILL laughing at you.

I was thinking the same thing but didnt want to hurt his feelings. I found this advice sounds legitimate to me............

Cylinder Compression Check: If you just acquired the motorcycle, you should first do a full inspection before you try to get it running. Please see this page on restoration. If this is the case, I'd do a compression check first because it's easy. First check the quantity and condition of the engine oil. Add oil as necessary. I wouldn't change it unless it's terribly dirty. The engine could be bad so you'd waste the oil change. Hook up or purchase a good battery. Leave out the spark plug and crank the engine for ~5 seconds. This helps to circulate the oil. Let it set for ~15 seconds and do it again. It's not a good idea to continuously crank the engine because the starter can overheat and wear prematurely. Most motorcycles need a minimum of 100 psi in compression to run start and properly. Compression should be checked when the engine is warm, but that's kind of hard to do if the motorcycle is not running. So just hook up a compression gauge and open up the throttle all the way. Crank the engine until the needle on the compression gauge stops moving. This should take no more than 5 seconds. Very roughly, 100-120 psi is good, 120-140 psi is very good and 140 + psi is great. If you don't have this level of compression then you have bad valves and/or bad piston rings. If you want, you can add a teaspoon or so of oil to the engine through the spark plug hole. Then try the compression test again. If compression is higher, then it's likely you have bad rings. The oil will seal the rings and give you better compression. If compression is the same, then you have bad valves/seats and/or valve clearances out of service limits. If you get any bad readings, perform a leak-down test to further determine the source of the leak.

[strn365]

wow something is wrong put a cap full of 10w-40 oil in each cylinder run the test again screw the coil if after you put the oil in the compression goes up in the low cylinders then the walls are scratched and needs to be resleaved and new rings if it stays the same you have valve problems by the way what cause you to do a compression test to begin with