98 2.5L piston/wrist pin replacement opinions?

[StuMpy77]

I'm currently working on a 1998 Legacy Outback with the EJ25D(152k) and auto trans. I have the engine out originally to replace the separator plate which has snowballed into just about everything besides the bottom end of it. I found out you can remove the pistons without having to separate the block so of course I had to go messing around. Would it have run fine re-gasketing the engine and cleaning up the valves? Yeah, I'm sure it would have but I personally don't care to drive a car that sounds like it wants to be a diesel without the torque to back it up :) I popped 3 of 4 pistons out today in search of it's piston slap issue (need to go buy/borrow an impact driver for the 2 screws on the #4 cylinder access hole plate...stuck in there pretty good!). That's a nice trick putting the wrist pins back in and using the crank to press the pistons out, was almost a fun job I hesitate to say. They all showed a fair amount of wear to the piston skirts, #2 was the worst so far showing some vertical scoring and light pitting. All of them had more carbon built up than I'd like to see. I'm going to borrow a bore gauge to verify but the cylinder bores looked fantastic, nice cross hatching from top to bottom 360 degrees around and virtually no cylinder wear ridge on any of them. My plan(when everything checks out) is to get a set of pistons w/rings, check clearances(piston to bore, ring end gap etc) and finish up the head gasket/valve job/use up the OEM gasket set job.

Has anyone used this cheap Mizumo piston set off ebay? ( http://www.ebay.com/itm/97-99-Subaru-Fo ... 51&vxp=mtr (http://www.ebay.com/itm/97-99-Subaru-Forester-Impreza-Legacy-2-5L-EJ25-DOHC-Pistons-w-Rings-/261035255633?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1998|Make%3ASubaru|Model%3ALegacy|Submodel%3AOutback|Engine+-+Liter_Display%3A2.5L&hash=item3cc6e9e751&vxp=mtr) )

A friend of mine swears the Nippon pistons which come in this set are made by the same people who cast the stock pistons for the Japanese OEMs. His mother drives a long rural mail route with a pair of rhd 2.2L legacy's and was blown away to find out our car didn't have a spin on transmission filter(which I do WISH it did, hard to convert to anyone?). Besides the point, he backed up his claim with an I want to say 1991 Mazda MX-6 he owns. He used this brand of piston(NPR) when he rebuild the 2.2L motor a few years back, runs 18-20psi of boost regularly and drives like a kid most of the time. 50k miles and still putting you back in the seats no problem! (keep in mind it's not a Mizumo brand piston, it's actually NPR, I already know Mizumo's suck from personal experience and why I want an opinion haha). Sounds like a good enough endorsement to me considering I'm not running any forced induction of any kind, plus I've driven the Mazda :) Can't beat the price on em either, $140 for pistons, rings and wrist pins.

I'm concerned about the wrist pins in this NPR set though, the OEM one's have a much thicker wall thickness than the NPR pins pictured in the link above. Am I potentially building a grenade with these cheap parts or is this a legitimate way to go? I do understand made in Japan doesn't mean ALL parts made in Japan are the same quality after all. I should mention, I need to double check tomorrow, but one of the stock wrist pins seemed to show visible wear in the connecting rod section. Machinist wise I've always been taught if you can see it with your eyes, it's probably fubar. If the stock pins are showing wear after 152k miles(wtf?....j/k) how are the thinner wall units going to hold up? Or are the stock pins just thicker because they're a softer metal, something along those lines? My vote is still thicker pins because OEM is better.

I appreciate your opinions and once again thanks for reading my long post!

[Grafton]

I'm using NPR rings and not having any trouble, but I'm just one guy so take that for whatever.

I went OEM when I replaced the pistons in my 2.5 just seemed like the right thing so I could assure I was getting the right sizes ( A, B or over sized) that I needed.

If they are the OE piston maker, I'd go for it but I'd need more than one guy going "those are oem" to make me believe it.

[StuMpy77]

Yeah unfortunately I didn't notice the whole A,B issue before I had her parents order the piston set. Never heard of such a thing, I know Ford does different oversized "service pistons" but why have 2 different sized bores entirely from the factory? Seems a little goofy to me but there must be a reason, be it good or not haha. Hell I don't know why I'm surprised after I went to purchase the valve cover gaskets and needed the vin number because there were 3 choices based on production number. Guess we'll just have to see what show's up, fyi I have the grade A pistons/bores which if i'm not mistaken are the 0.0004in larger of the 2 choices so odd's aren't real good I get something I can even use. Mine have one dimple in the piston face marking the front of the piston in the block, the one's we ordered show 2 dimples. Might be stuck paying $90 a piece for the stock units after all!

Glad to hear your having good luck with the NPR rings Grafton, my buddy beats the hell out of that Mazda and it never complains so I think they're probably decent. They are holding up to his aftermarket turbo and higher than stock boost levels quite nicely. He did mention today that he had the pistons cryo treated...thanks for leavin that out jackass! I doubt the NPR pistons are indeed OEM but they seem to hold up pretty well so I suppose it doesn't matter in the end. Either way the Ebay piston set is on its way, can let everyone know what happens if your interested?

[Huffer]

Piston slap is caused because the piston itself doesn't expand enough to fill the cylinder when it's hot.

Techworks Engineering makes a cylinder sleeve that is inserted into the bore that allows the piston to expand normally, but once expanded fills the cylinder better.

TWE also make pistons in different compression ratios also, in the event that you want to turbo, or go high comp.

[Crowboy]

I'm also running the NPR rings in my build and they have sealed up well.

I used DNJ pistons from Rock Auto, which was one of my regrets on this build. I had to order 2 sets to get the weights of 4 within a reasonable spec which eliminated any money savings. My pistons were similar with the plastic cast in to the skirts, but without the coating on the top. I have more piston slap than before, though it could be a function of the machining rather than the pistons since I had the bores oversized. (yes, I oversized the pistons, too, and gave them to the machinist to match the bores.)

OEM pistons from Subaru are actually not that expensive and I wish I had gone that route. NPR may get their raw castings from the same place as Subaru, but then the castings are machined by separate houses which may not have the same quality control when machining or assembling sets.

It sounds like you've already ordered the pistons, so I'd recommend when you get them in have them accurately measured for diameter and make sure you're within factory tolerances for the chosen cylinder (0.0004" to 0.0012" clearance). Also, make sure the piston/wrist pin combos are within 1.0g of eachother. I can't remember where I got that number so you may want to match weights closer than that. I was able to balance rotating assemblies to 0.1g, but you'd have to split your block to balance the rods. If anything is out of factory spec, I'd send the pistons back and go with OEM from the dealer.

Lastly, you probably still want to put a light hone on the cylinder walls so the new rings will seat properly. It's all about the micro-structure of the walls, not just a visible hatch pattern. This is tough with the block together because you want to keep any particles out of the bottom end. I'm a fan of the full teardown to replace bearings as well (they're pretty cheap and splitting the block is easy) but it's your car and your budget so its your choice.

Good luck!
Zack

[StuMpy77]

Well I suppose it's update time. I ended up sending one of the Nippon pistons back because the top compression ring clearance was pretty much nothing, the ring was physically tight in the ring land so I didn't even need to measure it to know it was bad. I called Mizumo about it and they were very willing to send a replacement asap, and were incredibly sorry about the whole matter. This should have been my first sign to turn back while I had the chance. I took it as good customer service as the "new" piston actually showed up the next afternoon to my surprise. Now I'm wondering if they are just that used to doing returns perhaps? I got the car all back together and after priming it by cranking with the cam+crank sensor's unplugged until the oil pressure light on the dash went out it fired right up to a perfectly normal cold idle. The piston slap is now worse than with the 152k stock pistons and during cold(1200 rpm-ish) idle it has an odd what could either be a light random misfire or what I can only estimate would be indeed a multiple cylinder imbalance. This is also more noticeable from 3000-3500rpm. Almost like it has a heartbeat, 4 individual pulses followed by a pulse length pause and then it repeats very predictably. It's probably still there when it idles down to normal but it's harder to pick up on, I did not check for it under load but from what I remember it's there.

The piston slap is coming from what seems to be the #3 cylinder though it's hard to track with a stethoscope as it transfers through the block pretty bad. So far I have only driven the car from my work shop to my house which is next door. As bad as it sounds we've been leary of transferring the license plates off the current driver which will be sold when this is done. I just can't live with the fact I put new parts in it and it sounds worse for the experience. The noise does get slightly better after the car warms up to normal temp but it is still very noticeable and much worse than previous. It goes away with some rpm in park so I'm pretty sure it isn't a bearing. It does get worse in gear(auto trans) at idle, only checked with light throttle and foot on the brake to load it up. It was louder under load. It's strange to me though as the driver side #2&#4 pistons showed moderate to heavy wear on the piston skirts yet it's the passenger side(which looked almost new by comparison) making the worst piston slap now. I'm really leaning towards these pistons being poorly made and I'm not real happy about it.

I had the machine shop measure my bores and replacement pistons along with the stock original pistons. I do not own a 3-4" micrometer capable of measuring down to 0.0001in. I should have had him write down actual measurements, he didn't and said only that the new pistons were all 0.001 larger than the used ones and that I would be just fine based on Haynes manual specs I brought with me. It should also be noted the replacement piston they sent out did NOT get measured and I am not sure where it ended up in the motor, in hind sight I should have kept track of it. I did measure the ring end gaps and everything was middle or very near middle range of the spec. I know this isn't by any means an accurate way of determining the cylinder bores are okay but I take it as a good sign not knowing the actual numbers bore diameter wise. Wishful thinking I guess. I really should have checked the piston to bore clearance as well, it seemed a little sloppy to me. I would have had to find and purchase a feeler gauge set capable of 0.0001in increments to do this accurately if I'm not mistaken. I also wish I would have weighed each piston, I don't know why but I totally miffed on this one. Any time I've replaced pistons in the past they were checked, Im pretty sure the kitchen scale measure's to the tenth of a gram. Girlfriend loves seeing kitchen tools disappear into the garage lol! I did put a light clean up hone on each cylinder, flex hone type and laid on my back with the engine on the stand to minimize metal bits getting into the bottom end. Gave it a good wash with soap & water followed by a thick coat of oil.

My questions are:
1. Is there any benefit to cracking the motor back open and replacing the 2 of the stock pistons which showed visible wear with new OEM pistons and using the other 2 stock pistons that looked good yet over? I'm coping with the waste of $100 bucks in head gaskets and be damned but I'm reusing the new head bolts we bought. Exhaust gaskets are going to be reused as well as the valve cover gaskets, cam seals etc if I do more than likely open it back up. This project was supposed to be a birthday gift for my girlfriend and it's turned out to be more of a pita and money pit than it's been good. I am currently trying very very hard not to hate this thing altogether and want to be rid of it.

2. What are the chances I have a tight or otherwise unhappy wrist pin? I was going to go drive the car around the block a few times and see if an attempt to seat the rings helped anything. I know it's not going to get any better leaving it the way it is and just driving it but considering I'd rather not pull the engine apart again I might just give it a shot. Dumb question time, what are the chance's this may improve with a break in period and after the switch back to 5W-30 after a couple hundred miles?

3. Based on layout of the Grade A vs B whole deal with these motors, the only difference I have found is 0.0004in in diameter between the two. Are there any differences between the two I'm missing? Bore shape, the size difference logically would alter weight a bit but a noticeable amount? I ask because they seemed to be balanced as in #1 is grade A, #2-B, #3-B, #4-A. Does it also have something to do with crankshaft harmonics?

4. Is there any way to isolate the noisy piston better without taking the motor back out? I was wondering about disabling one cylinder at a time in hopes of finding my slapper, or would that not work as the piston is still going to be knackering around in there?

5. Anything else I've missed which could be causing my issues? I ran a compression test on it today, 165-170psi with no leak down on all cylinders. It's not mixing anything fluid wise, doesn't leak or burn anything of note either. Spark plugs are new but they all looked even and normal.

Thanks for any ideas and opinions, I'm really sick of working on it at this point and still don't have the plow truck ironed out completely but that's unrelated. My options as I see them are limited and fairly expensive, I'm trying to cope but it's been rough haha. We moved where we live in the middle of this project as well, with everything else going on I need to come up with at least a plan on where to go now.