Hello. I owned an rx7 years ago and wasnt able to hold on to it. I'm looking at an s5 convertible to return to now that I'm a little older and was sent a picture of a compression test done at a dealer. I wondered why it was written for 225 rpm or is that 275? Figured a dealer would get it at 250? Also the one drop down to 88 caught my eye. I'm not sure if that's a concerning difference between rotor faces or not. It seems like a lot to me. Would I be ok with this engine for at least a couple years? Or would it need a rebuild sooner rather than later?



Edit: I found links to manual and see that it might technically be within an acceptable range. What's thoughts / experience on those numbers from the forum?

 

The readings from your compression test are somewhat consistent and typical of a high mileage motor, with the exception of one of the faces on rotor #2. The low reading of 83-88 psi is probably due to a sticky side seal on either side of that one rotor face. As others have suggested on the forum, it may help to squirt some ATF into the housing of rotor #2, cranking it around to make sure that all faces of that rotor are coated with the ATF. After letting it sit for awhile, the ATF should free up the side seal. I would even suggest using Marvel Mystery Oil as well. You may even want to perform two treatments for good measure. Many people neglect the need for rotary engines to be de-carbonized every 50,000 miles to prevent seal lock-up from excessive carbon, as well as a buildup of deposits on the rotor face, which could lead to a damaging ping from a detonation event. I own a 1990 RX-7 convertible that I bought in 2016 with 128,800 miles on it. One of the first maintenance operations I performed was decarbonization using two cans of Sea-Foam. The last thing I wanted was a hard ping from detonation which would break an apex seal, which would then ricochet around in the housing, damaging everything, and requiring a complete rebuild with a lot of new parts.

As for these readings, I would say that you are getting close to an engine overhaul, since the acceptable compression range is 90-120 psi for a well used motor. If you are in a position to start collecting new engine and rebuild parts, go ahead and buy the car; I'm sure you could get a couple more years if you dedicate to the maintenance.

 

Thank you. I was thinking and hoping this might be the most likely answer from everything I'd been able to find. My experience is limited though so it was great to have a second opinion.

I guess there's no way to truly know for sure but I took the plunge and purchased it. Have a couple day's worth of cleaning and maintenance planned with the longer labor day weekend. Can't wait to spend all my money! Hah

 

You're welcome...Happy to help! I have another idea that you may want to think of when it comes to decarbonizing the rotors. You could also use Chevron's Techron additive, assuming that it is still available in stores. What you would want to do is run the car so that the fuel tank is nearly empty. Then, obtain 3 bottles of Techron, pour each of them into the fuel tank, and then add 5 gallons of fresh gasoline. Immediately drive the car and use up as much of that 5 gallons as possible, and then fill the tank with more fresh gas, and then drive it for at least 10 miles.Techron is highly effective at removing carbon, but it is also powerful enough that you don't want it remaining for long in your fuel delivery/fuel injection system in that strong concentration.

This, of course, would be one of the next steps to take after you treat rotor #2 with either ATF or Marvel Mystery Oil to loosen that sticky side seal.