I thinking about buying a 1st gen RX7 from someone nearby and he has told me that it has low compression. What are some of the most common (or uncommon) causes of low compression? This is a really nice looking car and I want to know if it is worth it to repair. So if anyone can help I would appreciate it. Thank you.

 

It needs a rebuild. less than a thousand bucks if you do it yourself. More than a thousand bucks if you have someone else do it.

The most common reasons for low compression are:

Blown apex seal

Stuck apex seal

And exessive chrome flaking on the rotor housings.

Stuck seal would be your best case scenario and it would be worth trying things like mmo and the atf trick before you pull the motor.

But, long story short. Be prepared to rebuild or replace the engine if you buy that car.

 

carbon buildup in the seal tracks
broken seals
broken housing(s)
dying or dead seal springs
compromised sealing surface

or any combination therein

what do you mean by worth it to repair? if the body is clean and you want the car (i mean REALLY want the car, not just think, "well, it might be cool if ..."), then it's worth repair.

 

This is key.

Car projects are a commitment.

If your gonna want a 240sx or a CRX next week don't even bother.

 

side seals.. corner seals.. blown gaskets.. cracked housings.. are also things that would loose some compression, i think.

 

Before you get too worried about it, there are a couple of things you can try. If the car was driven "conservatively" for most of its life, then there's a good chance that you are simply dealing with carbon buildup. Rotaries need to be thrashed on a regular basis to keep them happy, and easy driving can lead to issues.

If the car is driveable right now, then try this; add one can of Seafoam to the gastank when you are down to about 1/8 of a tank. Then take it out for some hard running. If you are dealing with a stuck apex seal (good possibility) then this should help to break it loose.

If the car cannot be started as is, then; use a 2X4 to hold the gas pedal to the floor, then slowly pour some Seafoam into the smaller barrels of the carb while turning the front pulley by hand (dump a little, turn a little, repeat). Rotate the pulley clockwise. This will get the Seafoam into all of the chambers and onto all of the apex seals. Let it sit overnight, or even for a couple of days. Then, remove the spark plugs and rotate the pulley counter clockwise (this will push most of the Seafoam out through the sparkplug holes). Replace the plugs and start her up.

With any luck, one of these two procedures will get you going again. How many miles are on the motor?

 

If you do this be prepared to change spark plugs after, its a good idea anyway and only use NGK or Denso.

Poor spark can effect the power so do plug wires also unless you know they're newer.

How did he come to the conclusion the compression was low, a rotary is different to a boinger.

 

Use NGK only. I tried the Denso plugs before and the engine ran like crap. Got NGKs the next day, problem solved...

 

Denso's are the oem plug the 7's came with from the factory.

 

lol kentetsu and his seafoam. I think hes reccomended that to everybody now

 

As aussie said. Rotary motors are low compression due to the larger chamber as compared to a boinger. Did whomever that concluded this was low compresion take this into consideration ?

 

Well, if you find something that works great for you and might help others with similar problems, you'd be a bastard if you didn't share that knowledge. Lucas is another name you'll see me endorsing, that stuff saved me a rebuild about 15,000 miles ago (due to leaking oil control rings).

 

Thanks for all the suggestions. I pretty sure I am going to buy the car. It is driveable now, he just says it smokes a lot and that the compression is low. I am prepared for a rebuild but I would like to avoid it if possible. I will keep you posted on what I find that works. Thanks again for the help.

 

chances are you need a rebuild and I would GET IT before it shoots apex seals out your tailpipe . so factor in teh rebuild as you buy the car because it will be alot cheaper not then if you have to replace more internals .

 

Don't do the atf trick..unless you want your soft seals (exposed to it) to start leaking. Like oil control rings. Seafoam or MMO only.

 

Don't forget AlumaSeal as well for those pesky coolant leaks. I'm a believer now!

 

Please do tell about the Lucas Oil save!

-David

 

I would like to hear this as well. I may be interested, I have a very minor smoke on startup if she sits for a few days.

 

It will swell your oil ring a little reducing the drip after sitting. It weakens it though over time though. Not a bad thing if your at 200,000 miles on a motor you should be saving up just in case anyways. I also had to use 10w30 when my oil rings were weak or I'd have a smoke trail. That was my old car. Not a bad motor by any means, doesn't mean the bearings are bad.

 

Good info, thanks!

 

don't forget seafoam. good ****.

 

lol, yes Seafoam is good stuff. But just put it in the gas tank and let the firefighters get a little rest!

The Lucas does not swell the seals. It does, however, drastically reduce the amount of oil sucked past work oil control rings. My car would leave a smoke trail when decellerating, which was bad enough to make the car undriveable. After using a quart of Lucas, it was reduced to almost nothing. I ran that motor for quite a while before it coughed up an apex seal at 213,000 miles...

 

I will recommend calling fire dept that you'll be smoking out your neighborhood.

 

Haha never tried lucas although I have a prme cantidate in my garage.. I HAVE tried seafoam and its great. Cleans everything up beautifully and makes a good smoke screen. My dad thought my car was going to explode the first time I used it lol

 

hi there. Quick question: how much cheaper would it make an RX7 if it’s not starting due to lack of compression?