Pwillyp

Hello, I wan to buy a rx7 it is a 82 that doesnt have compression in one of the chambers. He just put in a new rotor, wires, cap, and spark plugs. Do you know what the issue is and should i buy it. It’s 750

madhat1111

Wrong area champ. This section is 93+ (FD/3rd Gen) build threads. Check out the 1st Gen section.

Narfle

iTrader: (16)

thread moved

Banzai

iTrader: (13)

Although regular piston engine testers can be used to get a close general reading, It's best to use a Rotary specific compression tester. You'll get three pulse's from each housing. Normally the pulse's should be fairly even. Pressures around 100 - 110 PSI are average / good. Below 90 and it might need a rebuild. If you don't get anything the apex seals may be stuck in the rotor. Some have had luck unsticking the seals, depending on the severity of situation. Do a search on stuck apex seals.

Has the car been on the road lately or has it been awhile?

mazdaverx713b

iTrader: (91)

Given RX-7 prices these days, if the car itself is clean and straight, $750 seems like a fair buy, even with an engine in need of a rebuild. Plan for the worst but hope for the best.

As stated above, a proper compression test with a rotary compression tester is a good idea. The compression numbers will not be entirely accurate as the engine is not at normal operating temperature, but will still give you an idea if one rotor has a faulty seal.

Carl

iTrader: (2)

Rotary compression testers are pretty hard to come by. I agree they are the best tho.

A friend of mine who works for Mazda and has lots of experience with rotaries gave me a method for testing the rotary compression with a standard (more or less) piston engine compression tester. First test compression with the tester set to let the pressure "pump" up. That will tell the maximum compression. Then open the valve that lets the pressure out. My compression tester has a little button on the side that I hold depressed with a zip tie. Then set your smart phone to take a slow motion video of the compression tester. Crank the engine and record. If the pulses are all the same (and the max compression was fine) then you should be good. If one or more of the pulses is lower than the others, that indicates a compression problem. When measuring the individual pulses, the peak pressures will be lower, because you have to fill the gauge and hose every pulse, in addition to having the vent open continuously bleeding off pressure.

This method may already be described somewhere else on the forum, I am not trying to steal anyone else's idea. Since I am just giving a recommendation I didn't want to go through the pain of trying to find another post describing the technique.

Carl

Pwillyp

It’s been 15 years

Banzai

iTrader: (13)

Yea, the apex seals could be corroded / stuck in their grooves enough that the springs underneath cannot overcome it. You can try some marvel mystery oil in the chambers or squirted in through the exhaust ports. Again, search stuck apex seals to find threads about working them loose. Might be worth a try, otherwise it's teardown time. Should you buy it? $750 is pretty cheap in todays market, but it could be a lot of work and /or additional money to get it roadworthy again. You also have brakes, hydraulics and electrical components that have degraded over time. Need to consider all that into the final equation along with your mechanical abilities.