Engine tips needed on potential purchase
03-04-12, 04:12 PM
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Engine tips needed on potential purchase
Greetings all
A couple friends and I have decided to build a ChumpCar racer and are looking for a car. We haven't decided on anything firm yet, but are leaning towards an RX-7. I went to look at one being offered quite cheap today and would like some input.
First off, it doesn't run. I'm not too bothered by this as I have engine troubleshooting experience, but am new to rotaries. I did a bit of research before looking at the car, and brought along my compression tester. It's just a regular piston tester, not the Mazda one, so I held the pressure release while the seller cranked the engine with the throttle open; because of this, and the fact that it was a cold engine reading, I'm not completely sure how to interpret the results. For both rotors, the pressure peaks were consistent, leading me to believe that the apex seals are intact. However, they seemed low - 60psi in the rear and 40psi in the front. I've read that a warm engine should read over 100psi; would the cold account for that much of a difference?
When I pulled the spark plugs, they were very fouled - thick black carbon deposits all over. I'm not sure if this is indicative of shoddy maintenance, as these cars do burn oil, or some more serious issue.
Finally, the shifter is very loose and I had trouble finding third gear. Is this common, and easily repairable or is it a sign of transmission issues?
Thanks in advance for the help.
A couple friends and I have decided to build a ChumpCar racer and are looking for a car. We haven't decided on anything firm yet, but are leaning towards an RX-7. I went to look at one being offered quite cheap today and would like some input.
First off, it doesn't run. I'm not too bothered by this as I have engine troubleshooting experience, but am new to rotaries. I did a bit of research before looking at the car, and brought along my compression tester. It's just a regular piston tester, not the Mazda one, so I held the pressure release while the seller cranked the engine with the throttle open; because of this, and the fact that it was a cold engine reading, I'm not completely sure how to interpret the results. For both rotors, the pressure peaks were consistent, leading me to believe that the apex seals are intact. However, they seemed low - 60psi in the rear and 40psi in the front. I've read that a warm engine should read over 100psi; would the cold account for that much of a difference?
When I pulled the spark plugs, they were very fouled - thick black carbon deposits all over. I'm not sure if this is indicative of shoddy maintenance, as these cars do burn oil, or some more serious issue.
Finally, the shifter is very loose and I had trouble finding third gear. Is this common, and easily repairable or is it a sign of transmission issues?
Thanks in advance for the help.
Last edited by gracer7-rx7; 03-05-12 at 11:43 PM. Reason: better title
03-05-12, 11:42 PM
#2
Piston tester should give you 3 even pulses front and rear. Check the FAQ threads for specifics on PSI. There is also a decent video how to somewhere. I think I saw it on youtube once.
Thick carbon on the plugs? Got a pic?
Shifter bushings need to be replaced.
Thick carbon on the plugs? Got a pic?
Shifter bushings need to be replaced.
03-06-12, 12:08 AM
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Okay, from what I've been reading the compression should still be pretty good with a cold engine; seems there's a chance that adding some oil to the combustion chambers would give decent numbers, but I don't think I want to risk it. Going to pass on this one and keep my eyes open for another.