Low Front Rotor Compression
08-09-2017, 11:42 AM
#1
New Member
Thread Starter
Low Front Rotor Compression
Help! I just got my 8, which I have been wanting for 5 years... And it broke down!!
So I was on the highway and it lost power unless it had high revs.
I took it to a mechanic and he changed the oil lines because they rusted out which caused the problem he says. Now the compression in the front is 60% lower than the rear. It starts extremely rough, the gas pedal needs to be pressed the whole time, and it won't idle unless it's being revved. Any advice would be great!!
So I was on the highway and it lost power unless it had high revs.
I took it to a mechanic and he changed the oil lines because they rusted out which caused the problem he says. Now the compression in the front is 60% lower than the rear. It starts extremely rough, the gas pedal needs to be pressed the whole time, and it won't idle unless it's being revved. Any advice would be great!!
08-09-2017, 02:15 PM
#3
New Member
Thread Starter
No not before the purchase. I know I should've now though. 
But after the oil hoses rusted through and were replaced compression became really bad. It drove fine before.
But after the oil hoses rusted through and were replaced compression became really bad. It drove fine before.
08-09-2017, 06:21 PM
#6
What am I doing here?
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Those aren't compression numbers. That's just something somebody pulled out of their *** (or the equivalent by using the wrong tools).
A proper rotary compression test will have 8 numbers:
3 pressures and an RPM for the front rotor.
3 pressures and an RPM for the rear rotor.
I'm trying to figure out how rusty oil cooler pipes lead to bad compression. I'd start looking for other things like a vacuum leak or bad ignition components.
A proper rotary compression test will have 8 numbers:
3 pressures and an RPM for the front rotor.
3 pressures and an RPM for the rear rotor.
I'm trying to figure out how rusty oil cooler pipes lead to bad compression. I'd start looking for other things like a vacuum leak or bad ignition components.
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gnarlydreadsdude (08-09-2017)
08-09-2017, 08:15 PM
#7
New Member
Thread Starter
I had a feeling the oil pipes weren't leading to bad compression. I'm currently stuck in an area where all the mechanics are rotary air heads unfortunately. Thank you very much!!
08-10-2017, 11:07 AM
#10
Registered
Those aren't compression numbers. That's just something somebody pulled out of their *** (or the equivalent by using the wrong tools).
A proper rotary compression test will have 8 numbers:
3 pressures and an RPM for the front rotor.
3 pressures and an RPM for the rear rotor.
I'm trying to figure out how rusty oil cooler pipes lead to bad compression. I'd start looking for other things like a vacuum leak or bad ignition components.
A proper rotary compression test will have 8 numbers:
3 pressures and an RPM for the front rotor.
3 pressures and an RPM for the rear rotor.
I'm trying to figure out how rusty oil cooler pipes lead to bad compression. I'd start looking for other things like a vacuum leak or bad ignition components.
10:1 compression (14.7 psi x 10) = 147 psi perfect compression (just a hypothetical formula, obviously not taking heat/expansion into account)
Front rotor 87/147 = .59 or 59%
Rear rotor 138/147 = .94 or 94%
Even though its incorrect way to conduct a compression test, I can't see how a correct test would somehow overcome those numbers.
Last edited by strokercharged95gt; 08-10-2017 at 11:11 AM.
08-10-2017, 12:29 PM
#11
What am I doing here?
Join Date: Mar 2006
Location: 2017 Miata RF Launch Edition
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Mostly it's a matter of not trusting the result of somebody who can't do it right to begin with.
Put another way, if he can't be bothered to do the right test, how do we know he's even doing the wrong test correctly?
Also, based on OP's description, I don't really trust the guy's abilities.
Put another way, if he can't be bothered to do the right test, how do we know he's even doing the wrong test correctly?
Also, based on OP's description, I don't really trust the guy's abilities.
