candlelit

iTrader: (21)

Hey everyone. I have myself a little situation with pistons and wall clearances. First off, I bought some used Wiseco dished pistons that are '402' pistons and recommends a "4.005" finished bore/hone. So here's my problem, my block is honed to 4.005", but the machine shop I had the pistons sent to called me today and said the pistons are too small and that if installed I would have moderate piston slap. He said that they think the piston is meant for a stock bore (4.000).

If what I'm thinking of what the machine shop guy said, then if they will work in a stock bored block then wouldn't the piston be measured at like 3.995-3.997? And that would still be a 402 right? (6.0 iron block). So lets say if the piston measures at 3.997 with a 4.005" hone that would be .008" clearance, or .010" clearance if the piston measures at 3.995. If that's the case, then taking a piston with that much clearance, would it be problematic for the 4.005" finished hone? I'm not sure of the clearance specs that these pistons need. I read somewhere that a Diamond 2618 piston spec sheet says .007" clearance. I will call the shop in the morning and have them give me the exact measurement of the piston.

1CAMWNDR

iTrader: (21)

If the machine shop is not smart enough to call Wiseco and give them the part number on the piston to find details you need to find another machine shop. I prefer tighter clearance for piston to bore.....something like .004".

KCS

iTrader: (20)

I agree. I'd be wary of a shop that doesn't bother to look up the piston specs from the manufacturer, especially used pistons.

Usually ~.004" is the norm for a 2618 alloy piston in a streetcar type engine. If you have too much piston-wall clearance, you can send the pistons out to get coated. The coating will take up that extra clearance, but by then, you might as well have bought new pistons.

Sales2@Texas-speed

iTrader: (5)

And it's worth asking if he is measuring the pistons correctly. You'd be amzed at how many machine shops don't have the tools or know-how to properly setup measure piston to wall clearance!

candlelit

iTrader: (21)

thanks guys. and actually they did look up in their catalog and didn't find this piston. it was a custom ordered piston and doesn't have a part number (16cc, 4.00 stroke, 402 piston). they are supposed to measure below the grooves right, where the skirt is the widest? I'll be sure to mention that as well. as for their reputation, the best LSx mechanic/tuner in our state recommended me to them, as they've done pretty much all of his customer's machine work. I actually decided the 80 miles distance from here to there would be worth it just because I trust his recommendation.

KCS

iTrader: (20)

A new set of pistons should come with a spec card, including the manufacturer's recommended clearance, as well as where to measure the diameter. Given that it's a used custom piston, I think it would be a very good idea to call Wiseco and get the spec card.

However, if the pistons are too small, then the pistons are too small.

candlelit

iTrader: (21)

I called Wiseco today and they said the standard for 2618 alloy forged pistons is .004, but with my iron block & 12-13 lbs of boost he mentioned .0045 to .005. So, with this information I called the machine shop and they said the guy who has been working with me on my stuff is out of town and won't be back til Monday. If these pistons really are smaller than 4.000 then how much will getting them coated cost me? I guess they (who?) charge per piston? If it's not expensive it may be worthwhile because I got a good deal on this set. Or I can just sell them, get a new piston with new rings, and I'd literally save $300 by going stock stroke 365ci instead of 403ci assuming my pistons wouldn't need coated. If the seller told me it was a "402 piston" & "requires a 4.005 finished bore" I'm unsure if it'd be ethically right to debate the problem with the seller if these pistons turn out to measure around 3.995 to 3.998 and really would only properly work with a 4.000-4.003 finished bore

KCS

iTrader: (20)

Yeah, the more power the engine makes, and therefore more heat, the more that piston will want to expand. I've seen as much as .007" in a 2000hp turbo car, and then click off 188MPH at the track.

Polydyne here in Houston coats piston skirts, bearings, etc., but from my experience, they seem to always have little bumps in the coatings. I don't know if it's dirt or coating clumps, but it doesn't seem very high quality. Calico, however, seems to be a lot nicer. I've seen 2-3 sets of pistons and bearings from them, and they looked flawless. I think each company will charge about $20-40 per piston, depending on the coatings.

That's the problems with buying used stuff, you never really know what you get until you've bought it. If you can save money by going with 365ci, I'd do that. I know, I know, "no replacement for displacement", but with the stock stroke you can get a super strong piston (lasts longer) that doesn't have the oil ring intersect the pin, and best of all, it's a brand new piston that you know hasn't been abused.

helicoil

iTrader: (104)

I have never seen an instance where a skirt coating was used to compensate for an undersize piston. A coating is just that a coating, it is sacrificial.

DSRE

iTrader: (7)

I'm running X-seriers wiseco's in my iron 383 "5.3 Block" and i had my local coaters coat just the tops since wiseco did the sides already and it ran me 200$, i'm running a high DCR in a big truck so i wanted extra insurance, FWIW ring seal is critical in these short cyl wall blocks and i have an excellent machinest and since the coatings are anywhere from .0005-.001 thick both sides and it will wear we run .0035 p-wall with awesome ring seal, he does machining for a lot of C6 twin Turbo LS7 alluminum blocks as well, i honestly wouldn't go past .004 if it were my own and that will still make a lill noise fwiw

KCS

iTrader: (20)

Just because you haven't seen it, doesn't mean it doesn't happen. There are all types of coatings, not all of them are necessarily sacrificial either. Take Nikasil for example. It's a coating, used by Katech among others, and serves as the friction surface between the aluminum piston/rings and aluminum block where an iron liner would typically be used. Same with Casidiam, another type of coating, except it's normally used on lifters, valves, and piston pins.

Nabdrill

iTrader: (19)

My flat top 408 was set up to .003 on each side, so .006 total. NA motor, per manufactures specifications.

candlelit

iTrader: (21)

update: couple of random pistons were measured and they said they were at or slightly below 4.000, like 3.999, making clearance .005 to .006 rather than the recommended .0045 to .005. How bad will piston slap be at that amount of clearance? Guess the rule of thumb is a little more clearance with an increase in boost, so how about adding more boost to compensate only problem with that is breaking more crap, and that it'll be NA until next year.

ring grooves were measured 1/16, 1/16, & 3mm with spacer rail. 1/16 is equivalent to 1.58mm. any ring recommendations out there?

candlelit

iTrader: (21)

bump for this thread lol.

current topic is, opinions on .006" piston-wall clearance with the older Wiseco pistons. Will piston slap be annoying? and would you all recommend Hellfire or Total Seal AP rings? Will be ran NA as a daily driver for about 5k miles before the switch to boost (11-14psi). I'm just kinda worried about getting them seated.

BgBoost1

iTrader: (2)

I would consider using a new machine shop. If they really knew what they were doing they would have measured the pistons BEFORE honing the block so the pistons would fit. Calling you afterwords and saying your "Pistons are too big" seems like a fly by night shop to me.

Good Machine shops individually hone each bore to each piston and refuse to hone the engine without the pistons sitting right there being measured.

My .02.

candlelit

iTrader: (21)

guess I didn't mention it anywhere, I bought the block separately & it was already honed. machine shop didn't touch it.