My old four port 13b has even, but low compression 75psi pretty sure it's time for a rebuild. I have auto experience just not much with a rotary.
Any advice?

 

Your 13B is a vintage 74-75 "3B" engine. The housings have the early chrome. You need to take it apart to see how good it is. Then depending on condition, either purchase new OEM apex seals if chrome is good (little bit of chrome flaking) or purchase Atkins seals if not as good (more chrome flaking perhaps beyond spec but is a cheap way to reuse old "dead" housings for 1 to 5 years as you save up your moneys to build an amazing engine*).

The other option is to look for good used 85 and older 13B housings. *Or get brand new GSL-SE housings. Then you should get some OEM apex seals so the engine will last for a good long time (10, 15 years years).

I suspect your oil seals are done as well, due to the early non-nitrided irons having an abrasive effect on the oil seals. Might look at side seals and corner seals too.

Or better yet, look for a set of R5 or Y irons from an RX-7 12A for your build. The nitrided surface lasts virtually forever and is very easy on oil seals etc (can last 15, 20+ years easily).

Stay away from any irons that have been lapped/resurfaced. These have had their nitrided surface removed and will kill an engine in 20k miles or less with smoking issues, hard starts etc.

Lapping/resurfacing is obsolete, and became obsolete when Mazda started nitriding their irons in 1979. Only crooked shops still recommend lapping/resurfacing on any modern 79 and later nitrided irons.

I don't give a rat's *** what any of those shops tell you about the benefits of lapping/resurfacing. Any way you look at it, it costs (you) more and ruins perfectly good irons, thus creating a repeat customer (you) as you will be back when you experience engine problems related to the resultant damage caused by lapping/resurfacing.

You see, the base iron under the nitrided surface is actually softer and more abrasive than the early irons like your 3B ones. You can tell just by porting them, and in other ways if you know what to look for (softness along edges, porosity etc). Lapping/resurfacing must be eliminated from our rotary culture just as ATF also has no place in our engines. Use MMO instead for carbon lock etc.

I've given you my warning about it. You of course are free to spend your money any way you choose. Good luck.

 

75 psi is low and will need a rebuild at some stage, if it's 75psi even across all 3 faces like you said then it's good signs. But at the end of the day you won't know what condition the motors in till you tear it down.

 

How are you measuring the compression? Using the real deal mazda tester or some homegrown
method?

What made you even think to see what the compression was? Was it running poor?

Just make sure you really, really need to get it rebuilt before tearing into it.

 

TG is right. We don't want to see your car in a scrap yard because you couldn't fix the engine and gave up on the whole car.

 

buy.a.rebuild.how.2.video
BEST $30 you will spend.
I used the mazdatrix one, but there are several (Atkins) out there. Easy to rebuild but need to know some of the basic tricks, tools and "gotchas"...

Stu Aull
80GS
Alasks

 

Ya know what? I tried the 'ATF trick' and the car is a new beast! Runs smoother, better power, it even now requires choke to start cold, where's before it didnt.
It does not leak or smoke anymore than normal. Haven't checked the compression again, but pretty happy for now.

 

At least your oil seals aren't completely shot after the ATF crap. Should have used MMO. Oh well, glad it runs good again.

 

You must have had some carbon build up. Your not redlining enough!

 

Nah, he has a weber or dellorto. It explains everything.

 

Yeah, your both right! But I love my Dell and I'm gaining more understanding of these wonderful little mazda motors thanks in part to you all.