Another "Rods-only" engine thread
 

*calling patsmx5*

My plan is to stick manley rods in my stock 99 block that has 42k on it. Buy FMs "big flex fuel kit," use e85, ID1000s, and max out my little gt2560.

While I have the bottom end apart, my brain is thinking, "NEW RINGS? HONE WALLS? MIGHT AS WELL DO MAIN STUDS. WHILE IM AT IT BETTER STICK NEW BEARINGS IN THERE. HEAD STUDS...etc"

Is any of that really necessary for an engine that really isn't worn? It has 42k on it. I bought it from an old guy who babied it every Sunday to get ice cream. And I average 1000 miles a summer.
(This car will be used on the street 99% of the time. 1% at 1/4 mile)

I think I can truly do rods only and the engine will still last another 40k at least. Thoughts?

I would never ever re-use rings and not hone walls. Ever
Everything else is fine if you really want to keep it to the bare minimum.

Since rings are about the only thing I could confidently clearance at home..I'll bite the bullet for Mr.18psi. As for honing...are u just talking one of those gadgets that goes on a drill for diy home use? Wouldn't the crank have to come out then? I don't like all that stuff..more chance for me to install incorrectly

yes drill hone
no crank doesn't need to come out

Honing is not a simple or easy thing to do correctly. You need to put a specific surface finish into the cylinder at a specific angle, while keeping the cylinder perfectly cylindrical to within ~0.0003" or so. If you do it wrong, the engine will either burn oil or have a huge amount of blowby because the rings never sealed up. If you think you can do that with a bottle hone on a cordless drill, go for it. I would never attempt that in a million years, because paying a professional to do it on a machine designed for the job will only cost you ~$100 or so, and then you know it's done correctly.

Which is why I emailed you the other day about the cost of a built engine. I completely understand price vs done right and reliability. If I were to send the block to a machine shop for a hone, I'd do an over bore for bigger pistons as well. Which would lead me to an "allofit" bottom end. Which is not what im going for right now.
"If it ain't broke, don't fix it"
if the rings and cross hatching are in the condition that im guessing theyre in, they should have no problem sealing for another 40k....right?

Wait, reusing bearings is kosher? That might tempt my scope-creep to flare up again...

I would do main studs and head studs as a "while I'm in there" because they're easy bolt-ons, but then I probably wouldn't ever do a rods-only build.

--Ian

There's a difference between a low budget backyard/garage build and a full on built engine from a company/shop.

Many, and I mean MANY here have successfully honed their shortblocks with no issues. But this obviously assumes you know what you're doing. If you don't, you gotta pay.

I still stand by my statement of not re-using rings if you attempt this

Doesn't using stronger main studs change the main to crank clearance?

I know on our LS motors rod bolts are not the best. Apr bolts are a nice upgrade but they change the tolerances.

Would arp bolts on the rod caps change the clearance between the crank and rod bearings?
The reason I dont want to change anything besides rods is the fact that there are too many clearances, tolerances, variables, etc that can and will be out of spec if I attempt

You've done a comp/ld test and know for a fact your rings are flawless?

I have heard people claim that you need to line bore the main caps to use main studs, OTOH many people have installed them without doing that and I've never seen anyone say it was a problem. I've done it on two engines now, no problems.

I also don't know that I buy the theoretical argument. I'm a software guy, not an ME, but I would think a main stud can be stronger without necessarily giving more clamping force. If the clamping force is the same, then I don't see how the clearances change.

--Ian

I like to do "everything or nothing" so i would never just put rods in. Fully built, or unopened engine, but that's just me.

No. But it would be a must if I decided to re use the rings. Im sure they are not "flawless" bc they have 42k on them. My argument is that I've seen plenty of boosted engines that have never been opened up make it above say 150k miles. So if I have no reason to believe my engine in its current state couldn't do the same, then why replace things that don't need to be replaced and risk have wrong clearances. I guess an argument against that could be that bearings wear faster at 300whp than 250whp? Idk though

My main concern would be doing all that work and spending quite a bit of money (since all the gaskets won't be exactly free), and then having one of the rings not re-seal or find out you have to rip apart everything and do it all over.

I guess that's where the slippery slope really comes into play.

I'm scratching my head.. You don't need an overbore. Get a proper hone (if it even needs it, cross-hatching on these blocks lasts damn near forever), new rings, new gaskets, re-assemble. And your rods of course.

Don't over think it, 42K is very low mileage.

"Slippery slope." If I ever take this block to a machine shop, I'm doing everything

Of course it would, that's why caps are line-bored and line-honed with the caps torqued to spec, blocks are bore/honed with deck plates, etc. Sometimes the idea of "fixing" or "upgrading" something sounds great, but understanding the right way to do it escapes them.

OP, at a bare minimum you're going to need rods, a set of rings, and a bottle hone. I tried doing rods only, reuse rings and not hone, and it burned tons of oil. Redid it with new rings and honed it, and it worked very well. Most shops will hone a bock for 10-20 bucks/hole, it's really cheap if you don't want to do it yourself. I've done it myself, and paid others to do it.

If the clamping force is the same, then it's fine. Nobody using ARP mains torques them substantially less than stock though to achieve this (doing so negates the benefit of installing them in the first place...), so they will have a much higher clamping force when installed due to finer thread pitch and low friction lubricant supplied by ARP.

Another "Rods-only" engine thread
 

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?

factory pistons = factory ring specs

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.

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?

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).

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?

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.

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

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.

No hone? No removal of crank?

Correct.

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

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.

Now we are gettng somewhere.

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

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!

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?

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

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

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

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!

Im going through with this as we speak. I think its a tough call on using pistons that weren't originally in that bore from the factory. But i think jafromobile did it with his kia 4g63 build. And imo if he did it, its acceptable. That dude is crazy.

https://cimg5.ibsrv.net/gimg/www.mia...5ffca178d6.jpg

my "rods only" engine.

AIUI, if all you change is rings and everything is in good shape, then a simple hone is fine. if you change out any piston and don't rebore, then you're playing with fire.

--ian

Thanks! That's what I figured.

The difference in compression between the NA8 and NB1 seems to only be ~.5 so going through all that hassle doesn't seem to be worth it. I.e. if you're going to rebore...might as well just get the pistons that would make the most use of it.

Another bigger issue is using "used" pistons to get the lower 1/2 point vs buying new OEM. And, if you buy new OEM pistons you're within a couple hundred of forged anyway. But the forged force the bore + hone vs just hone.

Personally, I'd never go with used OEM pistons in an engine I was putting money into.

Hi OP! Heh.

What all did you end up doing finally?

I have a build thread that needs its title changed.

-Cleaned stock pistons/rings very well
-opened up top ring end gaps to .016"
-Manley rods w arp rod bolts
-acl main, rod, trust bearings. (All plastiguaged within factory specs)
-arp main studs
-arp head studs
-BE stage 2 oil pump
-ATI super damper

re-doing all fuel system components
-dw300
-fuelab inline filter
-fm fuel rail
-ID1000s
-fuelab mini fpr
-gm flex fuel sensor
-all -6an vibrant braided nylon hose

-gen2 gtx3071 w/ tial .82 housing

Nice!

Did you have a machine shop do any of the work?

Yeah, I probablyyyyyy wouldn't be looking at used ones. Looks like oem is about 250-300 for pistons, aftermarket is like 100-150, but I'm not sure have been vetted here like the rods have been since folks don't usually half ass things if they're going through the trouble of swapping over the pistons.

You will want to hone the block. I think I paid a local machine shop $150-200 to cleab the bottom end, check specs, and hone.

This was for your rods only build right?

If the used piston don't have a bunch of scuffing on the sides, use them, the diff between OEM pistons as manufactured isn't enough to matter. Just hone the block so the new rings well seat. You should check the bores for taper.

Referring to the pistons that are mated to the engine already or other used ones if one were to try to switch compression ratios?

No problem interchanging the used pistons as long as they are in good shape.

Pistons don't mate or wear into an engine. I would want to measure the new and old to make sure they are the same within a few ten-thousandths. If they are, swap away.

Rover has been running a rods-only BP05 longblock for ~8mos now with good results. Reused OEM pistons, OEM rings, Manley rods, ACL bearings, ARP mains, and an OE VVT oil pump. No plans to run past 250whp on gas and 300whp on E85, so stock pistons were fine.

I'm nowhere near close to doing this, but I was just reading a billion different things that people had done so I figured this thread was a great place to keep the information going since it already had a tone of great stuff.

That's awesome info though. My goals are modest, but I want things to be reliable. Seems like rods (manley/ebay) with a few other supporting things like you outlined and potentially NA8 pistons will be pretty solid for a daily pump 93 bewsted setup. I think I'll be more than content with the 2560 setup with the 2.5 exhaust that I have waiting to go in. I just want to be able to enjoy it at a level that the setup can offer safely without worrying about a rod deciding that it wants a rumspringa.

Thanks a bunch for the info Andrew.

I read a few ancient threads on here about 8.8 NA8 pistons. Do those actually exist or is it just part of fabled miata kitty and unicorn lore?

They were around in the earlier engines and you used to be able to buy them but for now just 9.0's are available new in OEM pistons I think. 2 tenths ain't go to make alot of diff.

I was thinking of picking up used pistons and having them cleaned up. So figured I might keep an eye out for them.

If I had to buy new oem pistons, I'd likely just go forged (which likely wouldn't happen). I'd be reticent to buy no-name oem style pistons because I haven't seen them described, tried, or written about here. I was going by what you guys had said about just dropping in cleaned up pistons. I think the drop from 9.5 to 9 is worth it for pump gas, no? If the .2 doesn't matter thennn what's the point of .5 haha.

Lower comp helps on pump gas. If you had E85 I would run the highest comp oem piston you can get your hands on though. I have run 10.5:1 on pump gas and 20 PSI boost, it can be done with conservative timing. Low AITs are really important for that combo to work though and not knock.

.5 well allow you to run more timing. If you are needing pistons because yours are bad every little bit helps. To be honest with a 2560 turbo I wouldn't worry about running the 9.5's. I ran the FMII kit for several years with 9.5's. If you keep it around 12 psi max you well have no issues. The draw back to running stock pistons is the ring glands well wear out faster then with forged. The 2560 max efficiency is about 14 psi but running that much with stock pistons well probably wear stock piston ring glands out in 2 years, to where if you keep it around 12 they well probably last 4 years of doing track days, mine did.. So a .5 difference is not as important as say running a built high horse big psi motor.

Pat mx5 Doing 1/8 mile drag racing is alot diff then running on a track for 20 to 30 mins.