Author Topic: 3ma compression psi  (Read 1604 times)

Tzr250si

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3ma compression psi
« on: December 14, 2019, 10:41:21 AM »
Hi what should the compression be with carbs off on std bore
Thanks

busa1300

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Re: 3ma compression psi
« Reply #1 on: December 14, 2019, 12:31:23 PM »
My 3XV2 with 19,000km tested at 165psi.....3MA shouldn't be far off
Smoking for over 35 years.
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tasswipe

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Re: 3ma compression psi
« Reply #2 on: December 14, 2019, 02:35:15 PM »
Is that cold or hot?

busa1300

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Re: 3ma compression psi
« Reply #3 on: December 14, 2019, 02:58:36 PM »
On my 3XV2 it was tested cold
Smoking for over 35 years.
TZR250SP...3XV2
RZ350-RZV500R where it started and why
RGV250 VJ21L-VJ22FL-VJ22N-VJ23T MotoGP street fun
RS250 Track day
KD80 cherry popper - JR50 for the kids - and a pile of GT750J parts

Tzr250si

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Re: 3ma compression psi
« Reply #4 on: December 14, 2019, 05:47:58 PM »
thanks I've just checked mine I'm getting  50 psi cold with no carbs or exhaust on

tasswipe

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Re: 3ma compression psi
« Reply #5 on: December 14, 2019, 07:05:46 PM »
My tz last year measured 145 psi cold

Tzr250si

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Re: 3ma compression psi
« Reply #6 on: December 14, 2019, 07:11:19 PM »
was that with carbs and exhausts on

busa1300

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Re: 3ma compression psi
« Reply #7 on: December 14, 2019, 08:47:17 PM »
Carbs and pipes on.
Throttle wide open.
Cold....

Smoking for over 35 years.
TZR250SP...3XV2
RZ350-RZV500R where it started and why
RGV250 VJ21L-VJ22FL-VJ22N-VJ23T MotoGP street fun
RS250 Track day
KD80 cherry popper - JR50 for the kids - and a pile of GT750J parts

Tzr250si

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Re: 3ma compression psi
« Reply #8 on: December 15, 2019, 10:21:58 AM »
Ok thanks i will put carbs and pipes on and retry if the pv seals are leaking will it cause low psi    ?:-|

James P

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Re: 3ma compression psi
« Reply #9 on: December 16, 2019, 02:52:56 AM »
Is the 'compression tester' used here of the type which connects in place of a spark plug? If so, I presume it is necessary for the engine to be 'turned over' (through top-dead-centre) to obtain the reading ?:-| .

If the above is true, it should only give a meaningful (maximum) reading once the exhaust port is closed. Therefore, it shouldn't matter whether the carbs or exhausts are fitted or not. Also, the condition of the power valve seals should not affect the reading. It would also appear that a two-stroke engine's secondary compression ratio would affect the reading, limiting the ability to compare readings from one engine to another.

Although I may have the wrong end of the stick, this device only seems (possibly) useful for a basic check of the piston rings and cylinder-to-head seal (gasket, o-rings etc.). For the readings to be of much use, one would have to know a baseline setting for a near identical engine in 'new' condition and also be aware of a minimum figure below which the engine will definitely require reconditioning.
I envisage that one could recondition an engine and then use a compression tester throughout the same engine's life to keep an eye on ring wear and leaks, but factors such as temperature (as alluded to already) and oil residue in the bore must surely affect the readings ?:-| .

I have never used one of these devices, so perhaps I have missed the point :-[ . If so, I'm open to someone setting me straight!

Thanks & regards,
James


Edd

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Re: 3ma compression psi
« Reply #10 on: January 06, 2020, 01:39:40 PM »
Hi Guys

From my experience its important to understand what and how the reading was obtained. I was taught that you connect your psi reader on a cold engine you open the throttle and you kick it over 5 times and take your reading around 110 to 120 psi is a good reading.

Edd
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