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How Do I Do A Compression Test Properly?


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#1 noeman

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Posted 09 January 2019 - 07:26 PM

I want to do a compression test this weekend on my 99h/g30. Never done one before so I've done a lot of reading on the forum/internet. Just a few things are confusing me.
Do I need to disable the fuel pump to stop fuel getting in whilst doing the test? If so how?
Some people say pure a small amount of light oil in the cylinder prior to test?
And just to confirm I need to warm up the engine first?
I've read my G30 is high compression and I need to be getting around 150psi, does this sound right.
Thanks for any help.

#2 nicklouse

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Posted 09 January 2019 - 07:32 PM

battery charged. plugs out. open the throttle wide. (a friend my make it easier). also good to check the valve clearances are right.

 

screw the gauge in spin the engine over until the needle stops rising. make a note. repeat till all 4 done. then do again in the opposite direction. so 1234 and 4321 helps show and issues due to battery drain.

 

a squirt of oil in the bores after doing the test and repeating can help show up worn piston rings.



#3 noeman

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Posted 09 January 2019 - 07:41 PM

Thank you for your reply. So no need to disarm the fuel pump? I thought I read that somewhere. Makes it easier if not 🙂

#4 nicklouse

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Posted 09 January 2019 - 08:04 PM

Thank you for your reply. So no need to disarm the fuel pump? I thought I read that somewhere. Makes it easier if not

never bothered as it needs a vacuum in the engine to suck the fuel out of the carb and as you dont have any plugs in it is not sucking much.



#5 noeman

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Posted 09 January 2019 - 08:09 PM

Ah yes, that makes sense.

#6 Richard19

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Posted 10 January 2019 - 10:33 AM

Is it best to take all 4 plugs out before you start?



#7 nicklouse

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Posted 10 January 2019 - 10:37 AM

Is it best to take all 4 plugs out before you start?

yes



#8 Richard19

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Posted 10 January 2019 - 10:53 AM

 

Is it best to take all 4 plugs out before you start?

yes

 

 

Cheers.






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