Low compression

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Bodom
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Low compression

Post by Bodom » Thu Aug 06, 2015 7:42 pm

I've had my 8 for 5 years and loved every second driving it. Unfortunately it seems like I now have engine compression issues. A rebuild is quite expensive. Does anyone have any advice?

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zoom
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Re: Low compression

Post by zoom » Thu Aug 06, 2015 8:25 pm

First advise is to detail what makes you say your compression is low.
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Bodom
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Re: Low compression

Post by Bodom » Fri Aug 07, 2015 7:11 am

I have hot start issues and low performance. I had the engine tested and is came back with the flowing reading when the compression was tested:
The front rotor had the following readings: 65psi / 74psi / 78psi at 221 revolutions per minute.
The rear rotor's readings were: 74psi / 78 psi / 75psi at 225 revolutions per minute.

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Re: Low compression

Post by zoom » Fri Aug 07, 2015 8:51 am

So if you look at the mazda guide in this thread viewtopic.php?f=44&t=6661 you are definitely below the low mark. however not significantly. My suggestion is that you look at getting a decarb done (get someone who knows how to do it properly on an 8), personally id do it twice over a few weeks. Once that is done then i would do another compression test, if that doesn't help then look at premixing. If that helps then start saving for a standard rebuild.
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Re: Low compression

Post by Bodom » Fri Aug 14, 2015 5:21 pm

Thanks for the advice. I did the decarb and the numbers after is:
Front 82/78/77 @ 201
Rear 86/88/85 @ 207
I really appreciate the advice!

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Driffill
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Re: Low compression

Post by Driffill » Fri Aug 14, 2015 5:28 pm

Replace that starter motor, and then check the compression again. 250RPM is the speed you want to be comparing compression readings against. You could also try pre-mixing and seeing if that has any effect on comp and drive :)
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Re: Low compression

Post by zoom » Fri Aug 14, 2015 5:49 pm

Good to hear. I'd drive around for a bit and do another decarb. But also as driffill said. You might want to look at your starter.
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Re: Low compression

Post by Sir_Smeghed » Sat Sep 05, 2015 2:04 pm

220 rpm is pretty slow, upgrade to a high torque starter and minimum 700CCA battery.

My RX8 has (Front) 68, 68, 67 @323rpm, (rear)63, 59, 63 @326rpm. My car was running rough but with the high torque starter and 720CCA battery as you can see the turnover speed is great. I replaced the coils, leads and plugs and even with the low compression my car now runs beautifully, a bit down on power but is still seems to kick along well enough to put a smile on my face.

I have found the coils to be particularly susceptible to failure, but they are also prone to lead and plug failure.

I spoke to a number of rotary mechanics who informed me that almost all of the issues they have dealt with on RX8's were starter motor, battery, coils, leads, plugs and the RX8 flooding syndrome which can apparently occur randomly on any RX8.

Oh, I have found someone in Brisbane that sells good quality, japanese made high torque starters brand new for $195.

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Re: Low compression

Post by skc » Sat Sep 05, 2015 4:03 pm

Let me know how your starter turns out. I am rebuilding and would be interested in upgrading my starter.
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Re: Low compression

Post by Sir_Smeghed » Thu Sep 08, 2016 12:35 am

Starter is amazing, it's a Japanese starter as well not a Chinese knock off.

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