ok ummmm can bad spark plugs/wires, bad battery (causing slow cranking) cause low compression tests?
my mechanic said even motor oil level can cause different compression levels.

 

You might want to get a new mechanic...

Spark plugs and wires can't affect a compression test. I think it could if he takes out both the leading and trailing plugs on the same chamber though.

Oil level can't really affect compression test. But it oculd if the car wasn't warmed up and the oil hasn't lubricated the motor.

Heres the low down on compression. You want at least 6.0KG or is it 85psi per chamber and want it uniform for every chamber..as well as per rotor.

Make sure the motor is warm/opperating temp. Make sure that you depress the throttle.

Danny

 

I dont see how bad wires and plugs can cause the compression to be low, a bad battery or a bad starter that doenst doesnt crank like normal will cause a lower compression reading. Compression varies from temperature and cranking speed, theres a chart in the manual. If you car was so low on oil that you bearings are not being lubed and that it was causing enough friction to actually slow the rotors from turning, then yes it will cause a lower reading. But if that were the case your engine would be toast soon anyways.

 

all he said was it may be due to the slow cranking on the starter or battery.
the spark plugs and wires were my stupid questions. hehe.
he also told me that since my motor only has around 7000km its not fully broken in and the compression could still go up. is that right guys? this mechanic is like the best in town. everyone says hes the best in town.

 

7000km? KM stands for kilometers. He probally means 7.0KG/cm2.

That would be a pretty good compression.

You need to make sure the motor spins at least 250rpm. If the battery or starter is weak, you wont' get that speed. ANd yes, compression should rise as you break in your motor.

Danny

 

Where can I buy a rotary compression testing unit ??

 

I think you misunderstood his question. He only has 7000 km on his engine since rebuild/replacement. I would check the compression again later.

 

ah..thanks for catching that Rated R1. I'm just not used to seeing mileage as KM.

I believe a rotary comrpression testor costs anywhere from 900-2000 US dollars.

danny

 

Why exactly do you need a rotary compression tester??

 

i just replaced the starter tho. maybe i need a new battery for the slow cranking. after i relocate the battery and break it in alittle more i will do another compression test again. thanks guys.

one more question. if the compression is low due to slow cranking. how much will it be off by? 1.0kg/cm^2?
what i mean is; is the difference signifigant?

 

I think the mazda manual has a sliding scale to account for change in RPM. I am not 100% positive thoiugh.

 

The rotary specific tester records the compression values for each combustion face as a separate number. A standard compression tester will only tell you what the compression is for the highest rotor face. You can pull the check valve out of a standard tester and sort of use it to check a rotary's compression, but it's not really accurate.

 

?

 

www.mazdatrix.com, $1,640.00 plus shipping.

Better yet, borrow one.