how well does a compression test acknowledge health of an engine? a recent test on an 84 13b (se) w/ 100K miles had these results:

rotor 1: 7.6, 7.6, 7.8 and for rotor 2: 7.9, 7.9, 7.9

How does these look?

Thanks

J

 

if those are 76, 76, 78 and 79, 79, 79, I'd say you're close to needing a rebuild. If it's something other than psi being measured, I have no idea.

 

Should be enough for the engine to run.

Does it run? Are you having problems with smoking or starting??

 

I've been told the car runs as a daily driver the past 8 years and the recent test yielded those numbers. The numbers were given to me by the owner, i'm considering whether to buy the car or not. By the way, the ac does not work, radio does not work nor the antennae.

 

Well, Mazda recommends 100+ PSI I believe - my buddy's Rx-7 race car is at 150 PSI...

Honestly? Those numbers are pretty low if the owner made a mistake and put decimals where none were needed.

 

Sound like you need to keep shopping.

There are pleanty of RX's in the Ocean.

 

What if the unit is in kilo Pascal, kPa?

If that is the case, then the compression should be around 100psi.

Nelson

 

Guys, those are readings from an actual rotary engine compression tester. That engine is fine as compression goes, I would buy it.

 

:

Those numbers are terrifice, probably 110 psi or higher, the low end is 6.4 (if I remember correctly) so that is outstanding. Buy buy buy!

 

The other thing that's important (and not mentioned yet) is that all 3 pulses on both rotors are very close to each other - this is a good indication that all the side seals and corner seals are in good shape as well.

There is a premium for good SE's, so given the engine numbers you provided, I'd go for it. The engine is the heart of the machine - if you get a good, strong engine, you can work on the rest to get it back to excellent running condition.

Let us know what you decide to do,

 

Ahhh so...



Thank you for the info.

I learn everyday!

 

 

Man some of you guys are really ignorant.
Those numbers are in metric units.

Anything around 8 is really good. So don't worry that motor is good compression-wise. However that doesn't mean that the motor is not leaking or anything. All that mean is that the apex seals are still there. It really doesn't show anything else.
If the motor has only 100,000miles it is a good find and it has another 100,000+ miles if you take care of it.

Cheers

 

Excellent! Buy it! Because the owner has the test seems to me like he at least cared about the car enough to find out, ya know? Maybe he took good care of the rest of it too as far as maintenence?

~T.J.

 

These figures are proberly in Bar, these look perfect for a car with 100K miles on it.
New engines run 9 bar, worn engines 5.5 or lower
Looks like the owner has taken very good care of the car/maintenance

Buy it!

 

Hey abeomid,

Just because some of us have never seen a rotary compression tester does not make us stupid.

It may just mean that some of us have never delt with roatry engines before. And i've been in the automotive business for 8 years!

 

Since you are the expert... If they are metric what are the units then, Kilo Pascals? That can't be right....


-(i'm ignorant)

 

To clarify for all. Mazda (using metric system) measures pressure in kg/cm2. Min is 6kg/cm2 or 85psi and max dif between rotor faces is 1.5 kg/cm2 or 21psi. The conversion is kg/cm2 X 14.22 = psi. So one quick one would be 7.8 X 14.22 = 110.916psi. And to go the other way just devide the psi by 14.22 and youll get the kg/cm2.

 

You can't really blame them. Most of the people who make that mistake are American, and Americans (on average) tend to think everything is Imperial, even though they're one of the FEW countries still using that outdated system.

Guys, our cars are Japanese. Japanese use metric. Our bolts are metric, our tools are metric, and rotary-specific compression testers are metric.


Just taking another chance to rag on the yanks :P
Jon

 

I am not saying you, or anyone else is stupid. But even though people look at the numbers and see it's pretty low for PSI (it's impossible to have such a low compression in PSI, it basically shows 0), they still say the motor is bad. Just for the reason of saying something u shouldn't post it up. I hope i didn't offend anyone. If I did I am sorry.

I see this often on here that people that might not know the answer to the question just answer something anyways.

I just had to rant.....

 

The SI unit of pressure is Pascals, not kg/cm2. So the Japanese are not using the correct system of units either?

7.8 kg/cm2 = 764.92 KPa = 110.94 lb/in2 = 7.65 Bar = 7.55 standard atmospheres

Unless the compression tester has the units labeled on it, I would be hesitant to assume what they are. Especially since Bar is a widely used metric unit.

Doesn't Canada use Imperial units, not the US?


-(stupid)

 

No, Canada is all Metric.

When I refer to Imperial I mean ft, miles, gallons etc... I realize that the US has a "US gallon" and other things that make it slightly different than what Canada and the Brits *used* to use as the Imperial system, but it's easier to say "Imperial measure" than "that freaky US system that doesn't make any sense because it's not metric but it's not really Imperial either... it's something they made up as they went along"

I mean WTF? Farenheit is based on the freezing temperature of a full Saline solution and (roughly) body temp. (0-almost 100F). They missed the body temp one by a little more than a degree, but who can blame them? the system's hundreds of years old.
The metric system is based on the freezing and boiling of water. 0-100. Water freezes at 0, boils at 100.

And the measurements like inches, ft etc... are based on the body of some guy who died long long ago. I'm not sure what the basis for a metre was, but EVERYTHING else is based off that single metre. Just devide or multiply by tens.

As for kg/cm2 vs. pascals, I'm not sure why they used kg/cm2 for the compression. I've commonly seen both types of measurements used and quoted, though the weather network uses kPa... I'm not sure.

But at least it's less of a stretch of the imagination to say "maybe it's kg/cm2" instead of saying "hey, they put decimals in at random, it's actually supposed to be PSI"...

Jon

 

Basis of meter had something to do with the circumference of the earth divided by some really big number. Actually thats how they got a kilometer IIRC. Then divide down to get meters, etc.

 

How do airplanes in Canada measure airspeed?... Metres were just as arbitrary two marks on a stick. The problem is that as measuring devices get better the original standard is no longer what it was to start with. This continues to happen.

Actually using kg/in2 instead of KPa is more confusing since the two numbers are similar for a given pressure. It would definitely make a difference and be good to know for sure which it is. If it was Bar the engine is healthier.

In the US both systems are used. In schools it is mostly SI units but in everyday life it depends on the context or industry. The UK not only uses both systems they also have other units such as "stone" and larger imperial gallons and bigger pints in the pubs, which is the real benefit.

 

Ok mine is 85.3 lb/in2 on both rotors.....is that good or bad?