I am attempting to rebuild my first 12A motor right now and have noticed that on my center iron and on my back iron, there is some decent stepwear in the same spots on the side. I can catch them both with my finger nail pretty easy but my nail doesn't get stuck which gives me some hope, but I can still feel them with my bare finger going over the bump so I'm pretty sure they are toast.

Like the title says, I am wanting to try and get them lapped if it'll possibly help. I will be trying to get an actual gauge measurement this week if I can.

I'm unsure of how many miles the engine has on it, last owner messed with the gauge annoyingly, but any ideas to why the rear rotor side seal would be causing so much stepwear in the irons on same exact spot? What smoking gun should I be looking for?

Thanks,
- Adam O

 

Step wear is normal at the side seal track near the spark plugs. The side seals get forced hard against the side housings by combustion pressure, and the rotor motion makes the side seal move in a slashing/cutting motion rather than a scraping/sweeping motion.

Not running an air filter, or having a vacuum leak, will increase side housing wear, sometimes dramatically.

All may not be lost, though. A practical tell is to check if there is a step that the oil seals have to ride across. If that exists, they need to be lapped. If the whole oil seal track is smooth, you can use the side housings as-is.

 

Can you further explain what you mean by checking if there is a step that the oil seals have to ride across? Are you referring to the rotor side seals?

Thanks again!

 

The side seals sweep up into the area where the oil rings go (the oil ring track is circular, the side seal track is not). The oil rings are a fairly soft metal and depend on having a sharpish edge to function, they will be ruined if they have to cross over a lip.

So, as long as the side seal wear marks don't travel up into where the oil rings go, you are fine.

 

Gotcha, I understand. I'll go check if the oil control rings pass over the area and make a good step or not. Thank you so much!

 

made quite a few passes over the step with the control ring in my hand. The back iron took a lot of angle before it started to step while the center didn't need much of an angle. Didn't feel the step with the control ring level with the chrome.

I'm still assuming that that would mean lapping is the best course of action. Did it once it'll keep doing it overtime.

 

You'll need a dial indicator and base to check it, I've attached the page from the factory manual that shows how.
The full manual can be downloaded at foxed.ca

 

I do have the book printed out actually, I'm going to get the dial gauge measurement hopefully later this week. For now I'm shopping around for lapping options if it comes to it

 

No connection to and no experience with this particular tool, but it is a recent new option for lapping irons.

https://www.rx7club.com/market/1172280

 

good luck with the build. here's the source for those manuals

https://foxed.ca/index.php?page=rx7manual

 

An aside, now that Chip's is apparently out of business, I have been low key looking into what it would take to properly grind *and reharden* side housings. His rates were $650 for an engine's worth, that is four grinding operations, three rehardenings, and removing/replacing all coolant and oil plugs. I don't foresee being able to match that even at a loss. He did everything in house, I would have to farm a lot of it out.

I have about ten engines' worth of 12A parts to run through, I only had him do two engines, both of which came out beautifully.

 

According to this thread Chip outsourced the nitriding. It may have been affordable if done in large batches.
I have also read that there were quite a few failures from the last batches of irons from Chip . Either the re-nitriding or the post-treatment surfacing was done wrong.