Ok, today I picked up a lightweight steel flywheel and clutch from forum member Terrh (great guy to deal with BTW), but I need a counterweight for it. I'm having trouble finding out what counterweight I need for my engine. I was told it was a NA 13B that was originally from a 88. Well, I got the old flywheel off today and it says differently. Actually, according to the number on the back of the flywheel, its a 83-85 12A.

To clarify things, the number on the back of the flywheel I took off the "S4 NA 13B" is 31. According to a mazdatrix FAQ page, thats the flywheel from a 83-85 12A engine. Now, I know for a fact my engine is a 13B, but now I have no clue what series it is, S3, S4 or S5. If someone could tell me any way of telling what series the engine is just by looking at the shortblock, that would be great. Frankly, I'm not even sure how this engine ran smoothly with a 12A flywheel.

Here is the mazdatrix page I got the info from http://www.mazdatrix.com/faq/flywheel.htm

 

Nobody have any ideas?

I have done a little research and I think it would be possible to have a 83-85 12A flywheel with an S5 NA motor without any serious side effects. If you compare the two rotors, the 83-85 12A weigh in at 4353 grams. The S5 NA rotors are only 25 grams less at 4328 grams. Now, unless there are other forces at work here, I would think that this small amount of weight difference is hardly enough to create a problem, unless of course you are running up to 10K rpm all the time. The engine did seem to run perfectly fine with this flywheel, no severe vibrations or anything, just the fact the motor wouldn't run right at all with the stock FI.

 

I took a flywheel off a GSL-SE the other day that had the numbers 326. According to that web page, it's for an '86-'88. The front and rear stationary bearings were well into the copper, but there wasn't any noticeable vibration. The rotors were obviously the 3mm '74-'85 type, not the 2mm apex '86-'88.

Is there any way for you to look inside your engine? Can you tell what size the apex seals are?

 

Hmm, the exhaust ports are very big on this engine (sleeves removed) so I can try to shine a flashlight in there. I'll let ya know what I find out.

 

Ok, after feeling up my engine for a good 5 min, I believe the apex seals are about the same size as the 12A ones I have here. That would be 2mm right?

Anyway, I'll have to check out the E-Shaft for any play. Supposedly the engine was run like this for 60K km, about 35K miles. Hope there is no problem. Hope I can even feel for play if there is a problem. There may not be enough to feel for a problem.

 

Pre-86 are 3mm seals SEs and 12As. I doubt if you will be able to feel any play. If you could, the rotors would have been banging on the housings long ago.

 

Ya, this ain't good. I NEED to find out if that flywheel was the right one for the engine or not. Chances are that if it wasn't then the engine is pretty much toast as the bearings would most likely be severely worn. 60K is a long way to drive with the incorrect flywheel, especially since it seemed to me like the past owner of the engine really ran it hard.

 

Ok, I have spent WAY too much time today figuring this out. At this point, it is safe to assume the WRONG flywheel was on this engine. There is no combination of rotors in a 13B that would make it "safe" to use a 12A flywheel on it. So, my main concern right now is to figure out a way to check the bearings for excessive wear and figure out what counterweight I need.

So, new question. Is there any way to check the rear main bearing for wear without dissassembling the whole engine?

 

Ok, the rear bearing proves it. The flywheel was definately the wrong one. I came across my answer searching for something else, that I can remove the rear stationary gear without any side effects. I wasn't sure about that so thats why I asked. Anyway, there is copper showing on the bearing, so its no good. I think I'm just going to replace the front and rear bearings together.

But this still doesn't solve my problem of what engine I have.

 

You will probably need to replace all 4 bearings. At least you will know what you have when you tear it down.

 

So your saying I should replace the main bearings and rotor bearings? That would mean taking the engine totally apart. I was figuring just the front and rear main bearings would do fine, but would the rotor bearings wear out because of an incorrec flywheel?

 

Well, the engine is out and a gasket kit is less than 200 bucks. Is that worth knowing the bearings are good or not? You also might wish to spec the clearances between the e-shaft and new bearings, just in case.

Can I say for sure the rotor bearings will have the same wear, no, I can't. But you also have no Idea what parts from what years were used to build this engine, this is one way to find out. I would, for the peace of mind.

 

You do have a good point there. I was thinking about just rebuilding the engine with all new hard seals as well since the engine is going to be out. Hmm, mabey I will half-bridgeport it at the same time. I figure I might as well put the money I was going to use for a body kit into rebuilding this engine. Anyway, I think I will at least tear the engine down to inspect the e-shaft and rotor bearings. I'll need a little time to decide if I will completely rebuild it, but like you said, at least I will know what parts were used to build this engine. Thanks for the help trochoid. I appreciate it.

 

Ok, I've decided I'm going to just rebuild this motor. I had plans of this in the future anyway, but I figure I'll just do it now. I'll also know for sure what I have inside this thing.

Anyway, I'm going to leave the ports alone, mabey just clean them up a little if needed. But I have a question about lapping. Do the irons HAVE to be lapped? If so, I've read somewhere that you can use a piston engine valve lapping compound on two of the irons and just rub them together in a figure 8 pattern to get the right results. Will this work? This would be my first rebuild, so I'm just looking from answers from someone that isn't looking for my money and therefore wouldn't give me a biased answer.

 

When you get the engine torn down, measure the step wear on the irons, there is a spec limit. If you are within the limit, don't worry about it. Hand lapping should only take a week or so to do by hand and you will have a nice set of arms when done. lol Hand lapping is not really a viable option as far as I know. Imho it's too hard to get the faces perfectly smooth, lapping by hand. Either send them out or locate better set of irons if they are worn beyond the limits.

 

Ok, I'll have to check them out then. Chances are they are fine as this engine only has about 60K KM on it, but I will check them out anyway. I really hope they are fine anyway. I don't know of anywhere around here that does any kind of lapping. I would have to send them away to somewhere like mazdatrix or something, which would be quite expensive for me.

 

https://www.rx7club.com/general-rotary-tech-support-11/hows-engine-look-547992/

Here is a link to the thread I started in General Rotary Tech. Basically shows what I found when I took apart my engine. Anyone looking to help me just post there.