j_corso

OK, OK I know that we're susposed to get a mazda tester- but $$$, so I used the getto method. I tested the top hole of each housing(correct?). So , long story short, I got +/- 123 psi after 4 tries on each rotor. I have an 82 GS with 112k. Is this good and what are factory specs. BTW I looked on this and other sites and couldn't find it.
Thanks
Josh

mar3

iTrader: (8)

It still doesn't sound like you got real readings...let's see what the engine builders in the house have to say...

Mario III

Go48

iTrader: (7)

The factory specs are in the factiry service manual that you can acquire free from the link in the FAQ.

Since you reported only one reading per rotor, I assume used a conventional tester and let the pressure build. That really doesn't tell you much of anything since you could have a failed apex seal and the one "good" rotor face will pump the number up by itself. Try it again like so.

Remove the schaeder valve (or hold in the pressure release button on the side of the tester) and as someone cranks the engine, watch the needle to see what the numbers you get with each bounce. You should see 3 evenly-spaced bounces for each rotor. That will give you a better idea of the health of your engine. Anything above 85 psi at 250 rpm is good.

Edit: Oh, and make sure that the person cranking the engine over holds the gas pedal to the floor. Very important.

j_corso

The reading I got from the front rotor was about average 120 psi w/ a hand , rubber-tip type tester(I pushed VERY HARD and had someone else bump the ignition for me)- tested each rotor 4X. Cleared results after each cycle. Back rotor was slightly higher at an average of 125 psi- same process. This is a one owner RX7 that my Godfather gave me with all the mazda dealers service and factory records. He, I'm sure, naver did dougnuts etc. He is a very gentle guy with his cars. can you post the link to the site You are refering to? Also didn't know about holding pedal to floor.
Thanks for your help
Josh

Go48

iTrader: (7)

Get the factory manual at: http://foxed.ca/foxed/index.php?page=rx7manual
Click on First Generation

Go here for compression test specifics: http://mazdarx7.iougs.com/myfaq.shtml
Compresssion test: Did you "see" three regularly-spaced bounces for each rotor? If so, the compression is very good. However, it sounds to me like you didn't understand what I said about holding in the "clearing" button, or removing the schraeder valve from the tester, when cranking the engine. Otherwise there would be nothing to clear when you stopped cranking the engine.

1st Generation FAQ at: https://www.rx7club.com/1st-generation-specific-1979-1985-18/1st-gen-rx-7-faq-page-237777/
Read the FAQ at the above link.

You should be hanging in the 1st Generation Specific section of the forum to learn more about your car. Read, read, read and search if you have specific questions. Most questions you will have were answered long ago and usually many times over. Only then should you start a thread with a question. You will gain a wealth of information by just reading some of the posts. You will get good and not so good information from members on the forum, but in time you will recognize those members who know what they're talking about.

Enjoy your car. It is a unique vehicle that you will learn to love and hate at the same time.

*TOUCH*

iTrader: (29)

120 psi??! you gotta be doing something wrong

well i shouldnt say that, but with 112k miles, the motor SHOULD have lower compression

His&HerFC3

so you can use a standard compression tester but you have to hold the release valve on it so it doesnt build up pressure on the guage and i should se the guage jump 3 times for the 3 sides of the rotor correct ? and what should the comppression be for an engine that has 150000 k miles on it im new to the rotary family

Go48

iTrader: (7)

Yes, you can get a general idea of engine compression with that technique.

Check the factory service manual for the specification for your particular generation. The difficulty in using a standard compression tester is that there is no way to determine the engine cranking speed during the test. And the compression readings will vary quite considerably with the engine cranking speed. Mazda specs the compression at 250 rpm. See the correction chart in the factory service manual to see what I mean.

Go to the first two links in post #5 for more information.

j_corso

Thanks all
I got it figured out now. Its actually more like 75-80 psi. Very helpful!

Go48

iTrader: (7)

That's a little low assuming the engine cranking speed was 250 rpm. But, if the numbers are fairly even across all faces, your engine is just a bit tired. No reason to rebuild right now if the car runs good. Start saving your money for a rebuild or replacement.

Now, if your battery was low, the cranking speed may have been slower than 250 rpm in which case your numbers would normalize to something a bit higher and probably very close to the 85 psi specification.

fcs3l0ve

3 even bounces per one full rotation of the engine at 250 rpm is good compression. anything less is a tired engine or shot seals meaning you need a rebuild. i never have tested my engines compression but im very sure it's low and i need a rebuild with 122,000k.

Go48

iTrader: (7)

Oh my. Without knowing the compression for each bounce, you cannot determine the health of the engine. For example, you could have 50-60 psi compression at each of the three faces of the rotor, but that does not indicate "good compression". BTW, one full revolution of the rotor (i.e., three compression pulses) results in three revolutions of the engines eccentric shaft.

j_corso

I have a brand spakin' new batt. - if that matters- right before the test

Go48

iTrader: (7)

New or old, the key is if it was fully charged. In your case, I suspect it was essentially fully charged. And so, with spark plugs removed from both rotor housing when cranking the engine, the cranking speed would likely be more than 250 rpm. That would "translate" to normalized compression numbers a bit lower than what you saw. See the rpm correction chart in the factory service manual to see what I mean.

j_corso

thanks for all the great info

fcs3l0ve

so around 85 psi on each rotor face is good? i want to get a compression test done on my engine. i need to seriously get on that.

Go48

iTrader: (7)

Acceptible is a better word I think. That's at 250 rpm engine cranking speed, of course.

For a proper compression test, head on down to KDR Performance. Tell Dave that Larry at RDS sent you.

*TOUCH*

iTrader: (29)

i think "still working" is a better phrase haha. especially on NA rotors (going by your heading). but seriously, thats getting dangerously close to not starting. i think one guy on here said he couldnt get his s5 NA to start with ~80psi all around. dont know how reliable that "guy" is...

j_corso

Well, let me just say that the car starts and runs great, idles great (right at 750) and if I could get a damn oil cooler and lines for the thing, I wouldn't hesitate to drive it halfway across the country. It sat for two years almost without being started. It was just serviced before that at a very good Mazda dealership, and always has been. So I'll go look at the service records and check out what they have done. I'll post later
BTW- I'm probally not getting the test done correctly with my getto gauge still!

*TOUCH*

iTrader: (29)

that is awesome. i never had a car with that low compression (except when it first blew and then when it was first rebuilt haha) but i was just saying that i have heard of fcs w/~75 to 80psi compression starting hard. maybe 12As hold up better?

Selonari

iTrader: (4)

always wondered how to do a cheap compression test haha

fcs3l0ve

i recently just talked to my friend who is a mechanic and he told me he can and will do a compression test on my engine if i drive it to his shop. i do have a hard time starting the car sometimes but i think it has something to do with fuel. im almost positive i have low compression but it'd be killer if i didn't.