Engine Compression

  • Spectre1982
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Engine Compression

01 Feb 2013 17:16
#570258
Checked the compression in my engine yesteday. My shop manual says the minimum should be 124 PSI and not deviate more than 14 PSI between cylinders. The spark plug in No. 1 cylinder looked a bit oily. The other three were normal. Here are the readings.

1 - 100 2 - 110 3 - 120 4 - 110

This set of numbers was taken after putting a little oil down the spark plug hole.

1 - 122 2 - 118 3 - 125 4 - 120.

What do I need to do to restore my compression? I'm hoping new rings is all I need. When replacing the rings do I buy a standard set?

Thanks.
1982 Kawasaki KZ750 Spectre

1978 Kawasaki KZ200

1985 Yamaha XV1000 Virago



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  • 4TheKZ1000
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Re: Engine Compression

01 Feb 2013 17:34 - 01 Feb 2013 17:36
#570262
Have you checked valve clearance?

When you did compression check.....you must have throttle wide open.... to get correct numbers.
Last edit: 01 Feb 2013 17:36 by 4TheKZ1000.

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  • Spectre1982
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Re: Engine Compression

01 Feb 2013 18:16
#570269
Valve clearance is in spec. I didn't have the carb on when doing the compression test. I had them off for an unrelated issue.
1982 Kawasaki KZ750 Spectre

1978 Kawasaki KZ200

1985 Yamaha XV1000 Virago



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  • 4TheKZ1000
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Re: Engine Compression

01 Feb 2013 18:32 - 01 Feb 2013 18:33
#570275
Leakdown test done?

How many miles?

Sounds like it a tired motor.
Last edit: 01 Feb 2013 18:33 by 4TheKZ1000.

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  • Spectre1982
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Re: Engine Compression

01 Feb 2013 20:31 - 01 Feb 2013 20:35
#570290
No, I don't have a leakdown tester. The motor has 9,000 miles on it. I guess it's time to get another tester.
1982 Kawasaki KZ750 Spectre

1978 Kawasaki KZ200

1985 Yamaha XV1000 Virago



(Avatar picture is from Alleycatscustoms.com)
Last edit: 01 Feb 2013 20:35 by Spectre1982.

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  • 4TheKZ1000
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Re: Engine Compression

01 Feb 2013 20:47 - 01 Feb 2013 20:48
#570293
9,000 miles.....maintained and oil changes.....you should be ok.
Last edit: 01 Feb 2013 20:48 by 4TheKZ1000.

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  • wireman
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Re: Engine Compression

01 Feb 2013 21:05
#570294
If it was sitting for some time you might just want to try putting some miles on it to seat the rings back up a little and retest it
posting from deep under a non-descript barn in an undisclosed location southwest of Omaha.

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Re: Engine Compression

01 Feb 2013 21:33
#570297
I got it last year. I put 2,000 miles on it. It's been sitting over the winter, but just a couple of months. I'm not sure how well the previous owner took care of it asside from it being in the garage. When I went to pick up the KZ from him he hopped on another bike and did a monster burn out. I'm assuming the KZ got pretty rough treatment.

I'm shimming the valves because they're getting close, but still within spec. I suppose I could just blow compressed air into the sparkplug hole and listen for any leaks and their location. I figured since I've got it apart for the shim job I should go ahead and do the rings and all the gaskets. When I took off the valve cover gasket it was pretty dried out. I think the leakdown test will tell me more.

Thanks guys!!
1982 Kawasaki KZ750 Spectre

1978 Kawasaki KZ200

1985 Yamaha XV1000 Virago



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Re: Engine Compression

01 Feb 2013 21:41 - 01 Feb 2013 21:44
#570299
Really dont know your experiance with bikes....but this is good advice for anyone.

Take your time and do it right....look it over really good.....you dont want to go back in later..... B)

Dont over-torque bolts.....use a torque wrench. Watch cam cap bolts and sparkplug threads.
Last edit: 01 Feb 2013 21:44 by 4TheKZ1000.

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  • donthaveakawman
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Re: Engine Compression

01 Feb 2013 22:56
#570306
the engine should be warmed up when testing the compression, that way the pistons have tome to swell up/expand with the heat and seal better to your cylinder walls.
I would find some upper cylinder lubricant to put in the gas such as marvel mystery oil(which you could put in your car engine oil as well, but not recommended for your bike oil). what upper cylinder lubricant does is protects from wear and tear on your piston rings and cylinder walls.
If you want to go further you could replace the piston rings, which you would need to take the whole top end off.

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Re: Engine Compression

01 Feb 2013 23:04
#570308
Spectre1982 wrote: I got it last year. I put 2,000 miles on it. It's been sitting over the winter, but just a couple of months. I'm not sure how well the previous owner took care of it asside from it being in the garage. When I went to pick up the KZ from him he hopped on another bike and did a monster burn out. I'm assuming the KZ got pretty rough treatment.

I'm shimming the valves because they're getting close, but still within spec. I suppose I could just blow compressed air into the sparkplug hole and listen for any leaks and their location. I figured since I've got it apart for the shim job I should go ahead and do the rings and all the gaskets. When I took off the valve cover gasket it was pretty dried out. I think the leakdown test will tell me more.

Thanks guys!!
Carefull spinning that motor over to do a leakdown test with valve cover off on j series motor B)
posting from deep under a non-descript barn in an undisclosed location southwest of Omaha.

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Re: Engine Compression

01 Feb 2013 23:55
#570317
use anti seize compound for the spark plug threads.

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