commpresion test results?

[jon haines]

hi, i have done a compression test on my 1990 n/a 7 and am a bit confused by the result ,i got mid 80\'s on rotor 2 on all 3 chambers but got hi end 90\'s on rotor 1, the mazda workshop manual said i should only get 85 p.s.i. on either rotor can anyone explain why i got to much compresion. by the way the car has done 80K and i have no history to suggest a re-build.

[nikp]

You could always take some of the higher compression off the first rotor, and put it one the second rotor to even them about a bit! :p

[MikeLMR]

are you using a rotary compression tester ? you should have 3 readings for each rotor. A normal compression tester won\'t really tell you the whole picture. It would be better if you remove the one way valve and watch the needle move but theres no real substitute for a proper tester (Mazda or aftermarket or homemade ... )

[jon haines]

yes its a mazda w.d.s computer doing the work. tested my mates fd last night he\'s into it by 9 grand (looks beautiful though) and his second rotors only showing 57/56/57 - oops.
to mikelml - you seem like local bloke if you ever want yours testing give me a kick and i will borrow it again( unless you already have access).

[MikeLMR]

thanks for the offer, once I get my car running that\'d be great. Did you borrow it from Lincoln\'s Mazda dealer ? I know most of the people there

[jon haines]

yes but its obviously unofficial as the gears not allowed to leave the workshop.

[MikeLMR]

of course

[Carl]

It could arise from a couple of things,one is that the cranking rpm was high,also there could be some oil getting into the seals that may mask the reading.If you did the readings of the higher rotor first,then try the other way around next time.
The test must allways be done on a hot engine,and asap after shutdown.
Regards
Carl

[jon haines]

the test speed is 250 rpm and mine was on jump leads and turned over at 266 but the results were high even for that, i did the tests twice is there any way to tell if there is exessive oil, it doesn\'t smoke at all but i havent done enough miles to know if its useing more than it should yet. also you might be able to help me with an exhaust to manifold gasket, the local dealer wants two arms and one leg for one. i will ring sometime soon about it when the car comes back from the body shop,thanks jon