I am under the belief that a dead/thrown apex seal can only be discovered with a bad compression check. Am I correct or is there other ways of determining this? I have searched the forum and it seems compression keeps coming up as a symptom.

Also, if the seal is bad, is the engine even rebuildable without buying irons housings rotors? If an apex breaks do the pieces or whole apex seal beat up the nikasil chrome coating on the housing, break rotors or hurt irons? Just want to know because many for sale rx7's state dead engine for apex seal and I would like to pick up one of these cheap fc's to rebuild without spending big money on hard parts.

Thanks!

 

On every blown apex seal engine I've ever seen, it takes out the rotor and rotor housing.

Broken apex seals are fairly obvious...the engine has half the power it used to, and is difficult/impossible to start, with a weird galloping sound while cranking.

You can do a quick and dirty poor man's compression test by simply removing the lower spark plugs, unplugging the crank angle sensor, having someone spin the engine over with the key, put your fingers beside the open plug holes, and compare the sound and air volume of the pulses coming out. A zero compression blown apex seal is easy to spot this way, completely obvious. You want 6 even pulses of air with no discernable changes in sound or volume, front-back-front-back-front-back. Any skips or voids means you've broken at least one seal, but most likely all 3.

 

^+1
Just to add a little to the above test. It's easier to listen to each rotor individually. Listen for 3 even pulses. One strong pulse and two weak ones indicates an apex seal failure.

It is impossible to tell what an engine will need before opening it up. Typically an apex seal failure will take out the housing. Rotors often get damaged and result in hot spots and can lead to detonation.

An engine with coolant seal failure will typically be a better rebuild candidate, but it's always a gamble.

 

If the engine just has lower-than-normal compression on 2 faces, it indicates a worn seal rather than a completely broken or missing one. This would not typically damage the housing or rotor, which would greatly increase the chances of reusing parts. You really have to do an actual compression test to know for sure. 60 psi compression sounds essentially the same as 100 psi.

With engines that need coolant seals replaced, you've also got to be sure the owner hasn't just let it sit for months/years. Water inside the combustion chamber will turn everything into a pile of rust.

 

Im looking to do a compression test on my 12a.
Does anybody know what it is supposed to read?
Thanks

 

It depends on the state of the engine. A flooded engine can show zero compression, even though it is fine.

A tip-top engine in perfect running condition will show around 120 I believe...




.

 

Thanks thats a big help!

 

An experienced ear can pick out a blown apex seal from 20 feet away, but most people will have to do a compression test to be sure. It's fairly obvious at that point, though, unless you have one of those oddball scenarios where only one seal is cracked/broken and the other 2 are still intact...those (rare) failures are much harder to pick out by ear/feel and require an accurate compression test.

 

hey guys, i just recently bought an rx7 (last friday to be exact). now the engine was fine, test drove it and everything. and it still runs great. there were 2 scenarios however (today and last saturday) that after driving to my destination, turning the car off to run some errands, and turning the car back on, i noticed that the car rev low on idle and then the car couldnt keep it self alive. i managed to to get the car running with no problem at all (following the instruction of the manual bc i thought the engine flooded) and the car ran fine. now this was only twice, the previous owner said it could have been a sparkplug which he told me to change, but i am waiting for the wires to come in as well. the engine runs smooth, no clanking, no excessive smoke out the tail pipe. can anyone help me out or lead me to the right direction? i really hope its not the apex seal.

 

You might need new spark plugs, if they're old it'll affect performance, if they're all black they're probably very much needing replacement.

Id get ngk make sure u get 2 trailing 2 leading and not 4 of one.

 

@wthdidusay82 Thanks man!! I ran it again for the last couple of days, and I believe its the sparkplugs as well. The spark plugs came in. They are NGKs and i made sure I had 2 trailing adn 2 lead, and the wires came in again. BTW, if at all any of my post seemed to be noob-ish, its because I'm on my big bro's account. I will be starting my own soon so yeah. I just had to get an answer or a lead to this. Thanks for the respond!

 

@AvoDaesu, It sounds like it may also be a vacuum hose problem. I had a similar problem a couple years ago and it ended up that one of the hoses that had been capped of had blown the cap off, it kept it from idling high enough on its own to stay running, but if I kept my foot on the gas even just a little, it would run normal. The vacuum hose systems on these things are way more complicated then they need to be due to emissions regulations, etc etc, I'm told. You might have someone who knows about these to do a vacuum test on it and find out, it fixed my problem. Just a thought.

 

doesn't sound like a blow apex seal to me. That experience is just as "volrotary" has described.