Should I replace my pistons?
 

Hi, I am rebuilding my 1.8 stock engine on a 95 Miata for the first time. I just removed the pistons to inspect what I have. I am for sure replacing rings bearings and I have already decided on going forged rods. Based on what I've read on the forum and my goals I planned on keeping stock pistons. However, after quick inspection I'm not sure if I should just opt in for new pistons, opinions? I am definitely a noob. Thanks!

https://www.miataturbo.net/attachmen...ine=1466041084
https://www.miataturbo.net/attachmen...ine=1466041084

Post photos of all 4 pistons.

For rebuild purposes, there is nothing wrong with oem pistons on a rebuild. Just do your homework.

But... If you have the monies :burncash: no reason not too grab supertech+wiseco xx rings.

OEM Pistons can probably go up to 300whp if tuned correctly.

I think I may be able to afford the supertech/wiseco combo if I need them. The thing is though I was setting my goal for around 300whp so I was thinking I could get away with OEM. But if I did wanna bite there bullet would 949 be the place to go for about $550? Here's what all 4 look like.
https://www.miataturbo.net/attachmen...ine=1466054579
https://www.miataturbo.net/attachmen...ine=1466054579
https://www.miataturbo.net/attachmen...ine=1466054579

They look fine, I'd inspect closely around the tops. Do note if you grab the supertechs you'll likely have to bore out the block so that they fit. Extra costs...

fwiw, I'm pretty much satisfied with my manley forged rods. Snag some ACL bearings if you can... I had to settle with cleavite due to ACL shortages.

Replace the pistons for fun!

:burncash: :yippee: :burncash:

Most of the forum vendors sell the supertech/wiseco combo in a variety of diameters and compression ratios. If you get them, you want the 8.6:1 compression ratio. I would want the extra security of running e85 at 300whp on stock pistons, but I tend to be a bit more conservative about such things. Just be careful with your tune if you're on pump gas.

:eek5: I can't stop. Instead of doing a timing belt on my 1.6, I swapped and turboed. Such a slippery slope

needed a new crank pulley for my 1.6. ended up with a vvt motor with manley rods.

very slippery slope! lol

Fab9 has the supertech/wiseco combo for $474

Boring the block to fit the new pistons will run you about $100, so that isnt bad. At least thats the cost around here where i am.

Pistons would give some extra security but your stocks should be fine with a good tune.

Also, it doesnt matter what pistons you run, tune is the absolute most important thing!

I'd hate for him to want to satisfy an itch later down the road, and realize that the effort and work of pulling the motor and then doing what he should have done in the first place is just more of a burden.

I want thank everyone for the help . I ordered acl race rod and main bearings. I'm still up in the air about the pistons. Can someone tell me why I shouldn't do this?

Supertech P4 MA8350 N4 4 Piston for Turbo Nitrous Applications for Use with Pi | eBay

It's literally the same model number as listed on 949 for a 5th of the cost. Am I missing something? Besides rings

That price is per piston. There is no reason you shouldn't do this unless you are really super strapped for cash, at which point, i'm surprised you're rebuilding a motor rather than buying a running one

Wow I'm actually embarrassed for myself. I can't believe I didn't read or realize that was per piston lol. So basically going through a forum vendor is probably the best option? And based on what was said above I'm probably looking at around $575 for a set of pistons, rings, and a hone. Worth it for the peace of mind even if I'm not planning on making crazy numbers right now?

It never hurts to know that there are no weak points in your bottom end. Even if the tune is perfect, you know the engine is built enough to handle whatever you want to throw at it.

I'm on Supertech/Eagle rods.

A $600 investment means you will be able to change your setup around in the future if you so desire without having to blink twice about the motor. Aside from an upgraded oil pump and a harmonic damper.


I am happy to send my money to 949. The slight increase in price compared to other vendors is made up by fantastic customer service and great communication. There are cheaper places, but if there's ever an issue with your order, you may never get it rectified and end up spending more to get the correct parts you weren't sent.

You're right, I think I'm gonna go for it then! Thanks again!

Do you have a build thread?

No I don't, and not to sound like a super huge noob but I'm not exactly sure where I would even start with one.

Also might be worthwhile calling your machine shop first to get an actual quote on machine work. Factor that into your budget to see if it's worthwhile.

You're in the right sub forum. Just create a thread (or ask mods to modify this one) to include some clever name and state your intentions, post photos of the process, of your cats, of your failures, and successes. Just keep it updated and when you have problems or need guidance we can chime in and follow your work.

That would be awesome! And I'm sure that would really help me out and it would be cool to see the progress! I have read a lot on the forums before I even posted anything. And it seems like the thing that irritates people the most is whenever a dumb question is asked that's already been answered 500 times. I'm not trying to be like that but at the same time it is nice to have help on your specific build (in my case piston wear.) Maybe I should start a new thread so it's fresh.

As far as the machine shop goes I probably should call considering I've never even been to one before lol.

Expect to spend $500-1000 at the machine shop depending on how much work you have them do. At a minimum you will need them to bore and hone the block. Since you sound like you have never been in a motor before, I would highly suggest you have them put together the complete bottom end.

Yea it goes up if they magneflux, linebore, or do ring filing etc. If you weren't already going to do the reassembly yourself, the automotive machinists do this for a living, and may be worth the piece of mind.

I'd say you look pretty handy for a novice, but there are some particulars that come with experience.

Any suggestions on how best to acquire the experience? I've also never opened up a motor, although I've always done all the work on my cars. A compression test appears to indicate my rings are going south so I've been contemplating doing a rebuild. It's something I've always wanted to learn to do, and I would likely grab a spare block to build, or a good engine to swap and build my current one, so I could take my time and not stress about getting the car back on the road. Thoughts? Sorry for the slight threadjack!

If you have time, space and funds:

Option 1: Replace your current motor with a running one for a couple hundred bux. Tear down your old motor and slowly build it up

Option 2: If your engine is fine but you want to replace it eventually, start sourcing parts and piece together a new motor so when yours does fail, you have a backup.

Option 3: Run your motor blissfully into the ground, when shit hits the fan, rebuild your existing motor and get a second car

I did a combination option 2 and 3 as my car catastrophically failed and had to rebuild a completely different motor.

https://www.miataturbo.net/attachmen...ine=1466172229

:giggle:

There are a lot of little things that will trip you up on building a motor yourself. Things a competent machinist will know, but you being a newb will not. Unless you know someone who has built a few motors I would highly suggest just paying a machine shop to put together the bottom end. Destroying a motor because you did something stupid sucks and is not really a path you want to go down.

For an example on my first motor build a friend and I built it. I installed an oil pump, but did not install the relief valve. So when I got the motor running I had zero oil pressure. I then had to pull the motor again to install it. A machine shop would have caught that and installed the relief valve at the start.

Girz0r, I think we should be friends.

You're telling me. I have progressed like this: initial goals of a nice reasonable 220whp on stock bottom end/5 speed -> engine's bad, need to rebuild, have e85 nearby, why not shoot for 275-300 -> well if I'm gonna have to buy a 6 speed and 3.9 rear anyway might as well buy a whole new low mileage car that already has those pieces attached and build my current motor while I drive that...

All this while I've been waiting for months to install my turbo cause I have 3 little kids and only have time to buy parts and talk about it on the internet, not actually work on my car.

Given the aforementioned lack of time this makes a loooot of sense.

Hey guys, I'm 100% set on doing the work myself. Even though this is my first time in a Miata engine I have done a lot of research. I've been in smaller engines before and I have also watched a lot of videos on the YouTube's. I have kept all my hardware in order based on the order it was disassembled. I also have taken pictures to help me reference things.
However, $500-1000 sounds like a lot to me. I was pretty set on only doing a bore/hone. Based what I've seen in my engine I don't think it needs a line bore, crank polished, ect. But I could be wrong. The only real thing I'm confused about is assuming I go with 83.5mm supertech's do I get the cylinder's bored to the piston+the ring?

:likecat:

https://www.miataturbo.net/attachmen...ine=1466189625

Yes, have the pistons in hand to give to the machinist first