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compression test
https://www.ausmini.com/forums/viewtopic.php?f=2&t=86652		 Page 1 of 1
Author:  Diesel27 [ Sat Jul 26, 2014 7:05 pm ]
Post subject:  compression test
just carried out a comp test and only have 120 psi, would have expected more?
Author:  MiniVLT [ Sat Jul 26, 2014 7:42 pm ]
Post subject:  Re: compression test
Did you do the test with a warm or cold engine?
Author:  Morris 1100 [ Sat Jul 26, 2014 7:44 pm ]
Post subject:  Re: compression test
120 is pretty normal on a stock motor.
Author:  mini_mad_matt [ Sat Jul 26, 2014 8:45 pm ]
Post subject:  Re: compression test
I wouldn't be particularly concerned unless they varied a lot from cylinder to cylinder
Author:  Monaco [ Sat Jul 26, 2014 9:36 pm ]
Post subject:  Re: compression test
Depends on the gauge too. It is more the variance across the cylinders that is important. Did you have your foot flat on the accelerator pedal?
Author:  Scoop [ Sat Jul 26, 2014 9:41 pm ]
Post subject:  Re: compression test
Monaco wrote:
Depends on the gauge too. It is more the variance across the cylinders that is important. Did you have your foot flat on the accelerator pedal?

How does the accelerator pedal matter?
Author:  Morris 1100 [ Sat Jul 26, 2014 9:48 pm ]
Post subject:  Re: compression test
Scoop wrote:
Monaco wrote:
Depends on the gauge too. It is more the variance across the cylinders that is important. Did you have your foot flat on the accelerator pedal?

How does the accelerator pedal matter?

You need to accelerator open to get a proper compression reading.

It is hard to get compression from a vacuum.
Author:  Convertible Mini [ Sun Jul 27, 2014 6:06 am ]
Post subject:  Re: compression test
You need Air to compress air!
Author:  Scoop [ Sun Jul 27, 2014 10:07 am ]
Post subject:  Re: compression test
So your saying no air enters the engine if you dont have the accelerator open. Or just not enough for the compression test.
Author:  Irish Yobbo [ Sun Jul 27, 2014 11:47 am ]
Post subject:  Re: compression test
Scoop wrote:
So your saying no air enters the engine if you dont have the accelerator open. Or just not enough for the compression test.


The butterfly is almost closed to restrict air down to idle speed, so less air.

For an accurate reading you will want a strong battery and a foot on the accelerator. You're supposed to do it with a warm engine too.

If you get a low reading, put some oil in the cylinder and try again. If the compression jumps up dramatically, your rings are worn.

I would say that 120 is a little on the low side, but it's not reconditioning territory yet.. A new modern engine (which has a good starting system and higher compression ratio) will read about 200psi, my mini reads ~145psi (998 with no mods).
Author:  Diesel27 [ Sun Jul 27, 2014 12:34 pm ]
Post subject:  Re: compression test
cheers Irish that is what I wanted to hear.
120 compared with 145,
Author:  smac [ Sun Jul 27, 2014 5:08 pm ]
Post subject:  Re: compression test
Diesel27 wrote:
cheers Irish that is what I wanted to hear.
120 compared with 145,

Which could just be the difference between two gauges.
Author:  Morris 1100 [ Sun Jul 27, 2014 5:23 pm ]
Post subject:  Re: compression test
smac wrote:
Diesel27 wrote:
cheers Irish that is what I wanted to hear.
120 compared with 145,

Which could just be the difference between two gauges.

Could almost be the difference between brands of head gaskets. :lol:
Author:  MiniBob [ Fri Aug 01, 2014 1:03 pm ]
Post subject:  Re: compression test
Compression is also reliant on good valve seal / adjustment.
If there is a bit of carbon present or the tappets need doing then the figure will be lower.
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