LownSlow616

Did you just use factory clearances on the rings? Maybe on the loose end for expansion? And would you recommend head studs, BE oil pump, or harmonic Balancer? Those are just some "while im in there bolt ons" that I'm considering.
Also, what seals cannot be reused?

18psi

iTrader: (76)

factory pistons = factory ring specs

patsmx5

iTrader: (16)

Yeah more or less. Mine were within specs, I checked and the new rings were within stock spec after honing so I just installed them.

I would do this:

ebay Rods, aftermarket moly rings, hone block with a bottle brush hone and a drill, clean the crap out of the cylinder walls WITH SOAP AND WATER to remove the abrasive left in the walls from honing, clean block, oil cylinders so they don't rust. Look up plateau hone if you want to do this just right.
Check clearances with plastigauge on bearings. If ok, reuse bearings.
New mazda gaskets/seals throughout.
That's it. If I didn't list it, you don't NEED it. I've run the above described motor to 28 PSI myself. Sure you can tripple the cost of what I described with new stuff here and there. If that's what you want, do that. If you want cheap, this is IMO the minimum for it to run reliably and not leak, not break.

LownSlow616

Did you use the rock auto chromoly rings? I read a thread that you started about this type of engine and your hopes of it lasting "3 years or 30k," how'd that work out for you?
In that same thread someone mentioned the chromoly rings needing a special kind of hone. Should I have that done at a machine shop or will a bottle brush hone from a drill be fine with the moly rings?

Savington

iTrader: (31)

It's not that chromoly rings need a "special" hone. It's that chromoly needs a different type of hone than what iron rings want. This is why I suggested having a machine shop do it - they'll ask what kind of rings you're using and then hone appropriately.

The "slippery slope" argument is fine, but it's a personal choice to resist it. You could absolutely drop the block off and just have them hot tank and hone it. There's no need to go "slippery slope" and bore it if you don't expect to need the strength of a forged piston. I have done exactly that before (disassemble, hone, replace rods, new OEM rings on old pistons, new bearings, reassemble).

LownSlow616

Can I just get oem rings then? Stock bore, stock pistons, might as well use oem rings? Or are aftermarket chromoly rings actually superior/necessary?

Savington

iTrader: (31)

On the one I built, I ordered new rings from Mazda. Rings are just about the single most difficult (read: labor intensive, $$$) component on the entire car to replace, so my customer and I weren't willing to risk a potentially sub-par aftermarket part. That motor ran 50+ enduro hours after the rebuild with no loss in power (and is still running today AFAIK), so while we could have saved some money by going aftermarket, there were no regrets.

LownSlow616

great! looks like im going with oem rings, and manley rods. would you recommend having the rods and pistons balanced? are the oem pistons balanced by themselves or with the stock rod? Maybe BogusSVO could handle that for me

pdexta

iTrader: (17)

I've had great luck with rods only motors. Two motors, both have run great with no issues at all (one car was totaled and insurance took the motor, the other is waiting to get swapped into my current car). Every time I've tried to build a motor the "right" way, either by building it myself or paying to have it built, I've had issues shortly after.

On the motors I've had success with I've pulled the head, pulled the oilpan, removed pistons/rods, swapped fordged rods on my stock pistons, reinstalled everything. The only thing I replaced was the rods and the headgasket (reused rings, reused bearings). It's worked for me and the motors have held significantly more power than a stock motor could hold.

Not discounting a proper build by any means (I've just had crappy luck apparently), but it can be done cheap and it can work well.

DNMakinson

iTrader: (3)

No hone? No removal of crank?

pdexta

iTrader: (17)

Correct.

hi_im_sean

iTrader: (3)

No. If a given screw is any stronger (via material tensile strength or diameter), then it will require more preload to avoid cyclical fatigue failure.


Bolt science isn't very intuitive.
Why bolt preload is important

jmann

You can replace the rods only as you want to do with no issues and staying at around 14 psi or lower if you are going to track the car as heat is the issue with iron rings, they well loose their tension after awhile. I tracked one with a 2560 turbo for 3 yrs without any issues with oem pistons and rings, but you need to install new rings and hone the cyls.. The rings and cyl. walls well get a glaze and that is what honing removes and keeps the rings from sealing if reused. I'm sure you well have cross hatching left in a 42k motor but it is the glaze that you are after removing not seeing pretty cross hatches. I suppose you could take and hone the cyls. and scotch brite each and every ring but that is alot of work when new rings aren't that costly. With [oem] iron rings use a medium grit ball hone, where with a chromemoly ring you want to use a fine one. The cross hatch needs to be approx. 40 to 45* and is not so critical with iron rings as it is with cm rings. I see no reason for arp main studs, but if you do install them I see no reason to have to line bore it if you are torquing to mazda specs. I have run stock main bolts over and over at 350 whp for several years with no problems and on the track. If you are going to turbo the car and run on the track at 20 to 30 min sessions I would gap the tings slightly wider then stock, if you are just running it on the street or drags then standard gaps are fine. You should be able to reuse the brgs in that motor. Unless you are going to run the car in long races the stock oil pump should be fine with a ATI or super miata dampner if you are going to be winding it above 7K.

nitrodann

Now we are gettng somewhere.

Ive done a bunch of rod/pump only 330+whp cars. never had a failure.

vitamin j

iTrader: (5)

Come ride along with me...
https://www.miataturbo.net/build-thr...6/#post1338239

Hand-drill honed, ebay rodded, ARP studded, OEM gasketed, new OEM rings, OEM bearings build. The last time I did this to a 100k BP and it lasted another 100k burining minimal oil and taking 14psi til I increased timing and put a rod through the side. Hoping for better results this time!

pdexta

iTrader: (17)

I find it interesting that you put a forged rod through the block before melting a stock piston. Any idea what kind of power you were making? Or what timing you were running at the time?

vitamin j

iTrader: (5)

The one that went through the block was a stock rod.

gtred

One thing that you might consider if re-using the oem pistons in a low mileage rods only + refresh race motor is to do what I had tried before:
1) Be sure to have your machine shop check the pin bores, especially if you've previously boosted or run the car hard.
2) Have the machine shop shot peen the piston skirts and then stiff-hone to the proper finish (depending on the requirements of your rings). The shot peening does slightly build up the piston diameter; and this will allow you to hone out some of the shallow scratches you might find in your cyld walls and still maintain piston to wall clearances. However, this build-up goes away quickly... leaving a reasonably loose fit (OK for a race motor). Mostly, the peening is to help prevent future galling, as it allows the piston to hold onto lubrication.
3) Now is the time to refresh your rod/main bearings.

this is the shop I've previously used: Hatch Engine Inc | Precision Engine Machine Shop

icantlearn

This should be a Sticky. Tons of good info here.

ridethecliche

iTrader: (2)

Sorry to bump an old thread, but I figured this was a good place to ask.

I've read a bunch of these threads where folks have reused their pistons and 'gotten away' without having the engine worked over by a machine shop because the clearances didn't change. I'm guessing this all goes out the window even if you change to OEM pistons right? I read some old threads about folks swapping their NB pistons for NA8 pistons to go to slightly lower compression to ward of det that extra little bit and I was curious if using different pistons, even if they're oem, means that the bare bones 'rods only' build is no longer applicable. Guessing the answer is yes, but figured I'd ask!