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Old 04-02-2010, 01:30 PM   #1
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Default maybe i should have just bought from FM

i just pulled my weisco pistons and am happy to see no real signs of detonation(aside from alil on #1 yeah tunning), however i am disheartened by the sight of what looks like latteral wear on the piston and the cylinder walls adjacent so i geus i was getting abit of piston slap. There is no evident damage but i can definetly see where the stuff had worn alil. So all you engine builders on here with real solutions what would you do? Keep in mind i am a cheap bastard and if i can get 50-60k miles out of the motor i will be more than happy with it. pics to come later
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Old 04-02-2010, 04:06 PM   #2
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These engines have crappy rod ratios so forged pistons will oval cylinders over time. How many miles did you get and was the comp still good?
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Old 04-02-2010, 05:24 PM   #3
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What sort of piston to cylinder clearances were you running with the Wisecos?? Are the Wiseco's a 2618 alloy or a 4032 alloy?? FM lists their pistons (custom made for them by Wiseco) as being a 2618 alloy. Forged 2618 pistons are generally accepted as being stronger than 4032 forged pistons but they have a higher coefficient of expansion and require more piston to cylinder clearance. You are going to get more cold piston slap with 2618 pistons than 4032 pistons but this shouldn't be a problem if they are properly clearanced and you are not beating on a cold engine. Did you actually mic the pistons and cylinders and verify that they are "oval"??
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Old 04-02-2010, 06:16 PM   #4
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Good point. I still have a block that shows some wear (no more visible cross-hatch) on the cylinder walls, but the cylinders are near-as-darn-it perfectly round still, and it had great compression when tested before removal. This was with Wisecos (not sure what alloy).
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Old 04-03-2010, 01:18 AM   #5
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Yeah, I doubt that the Wiseco pistons are the problem (I think most Wiseco's are 2618). What can be a problem is if someone uses stock Miata piston to cylinder bore clearances with 2618 pistons (2618s require more clearance than 4032s which require more clearance than stock cast pistons). Once the pistons warm-up (and fully expand), the piston to cylinder wall clearances become too tight and scuffing can result.

Edit:

Some piston slap is normal on a cold engine at startup with high coefficient of expansion forged pistons. It should not cause any abnormal wear if the clearances are "right" and the motor is not put under boost/strong load when cold. On a properly "clearanced" forged piston motor, there will be no piston slap once the engine is warmed up. Piston slap on a warmed up motor is sign of very loose piston to bore clearances.

Last edited by sn95; 04-03-2010 at 01:23 AM. Reason: Added piston slap
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Old 04-03-2010, 01:47 AM   #6
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Quote:
Originally Posted by sn95 View Post
Forged 2618 pistons are generally accepted as being stronger than 4032 forged pistons but they have a higher coefficient of expansion and require more piston to cylinder clearance. You are going to get more cold piston slap with 2618 pistons than 4032 pistons but this shouldn't be a problem if they are properly clearanced and you are not beating on a cold engine. Did you actually mic the pistons and cylinders and verify that they are "oval"??
2618 is stronger than 4032, not generally accepted, just look at the fatigue strength at elevated temperatures...I can also tell you that the pistons are oval, just measure at the same height up the skirt and you will find that the difference between the skirt axis and pin axis is probably .0125''.

Magna, take a pic of the wear, if you're seeing scratches up and down the bore, then it's most likely ring wear and tension. If you're just seeing darkened areas on the cylinder over the skirt face, that's typically just the peaks of your cylinder honing wearing slightly.
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Old 04-03-2010, 11:46 PM   #7
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Forged piston slap at cold and low speeds drove me crazy for a couple years. I don't waste emotions "hating" anything. With a firm hold on my lightening rod, I admit to fudging the truth; I do "hate" piston slap.

I cured the problem in every case in which I used forgings by the old/old/old knurlling of the piston thrust faces and then baking on a Dow Corning molycote bond on dry film lubricant in the knurl.

The piston will prove reluctant to push down the bore on assembly, but bash it soundly with something soft and it will shear off all the stuff that it needs to in order to slide down the bore. When the engine is cranked up it will establish the absolute minimum clearance that it can live with in the range of temperature induced expansions.

Presto, forged pistons, no cold slap, and no hot idle slap. Easy 60K durability. This procedure is right in there with the absolute best margarita formulas.

Corky
On second thought, its just close.
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Old 04-04-2010, 02:11 AM   #8
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i feel stupid after reading your post Corky cause there is a lot of big words in there that i have no clue as to what they mean! lol damnit, i should of went to college or paid more attention in high school!


this thread is really making me 2nd guess using forged pistons in my engine build and just sticking with OEM pistons and having the Tri-coated like Rotornut did!
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Old 04-04-2010, 03:57 AM   #9
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The big question in deciding whether you want cast or forged comes down to tuning. How are you going to tune it? Keep in mind you can run 4032 forged pistons and keep piston to wall clearance at a minimum to prevent piston slap. Crack resistance due to detonation changes from the type of material too, so if you can get a good tune from the get go maybe cast pistons are down your alley...
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Old 04-04-2010, 09:30 PM   #10
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ok here is a pic of #1 for reference overall after not looking at it for a day it looks alot better than i was thinking. there is a interesting defect about an 1/8th of an inch or so wide going down the bore wich i suspect was from dirty assembly at the machine shop or something last time. 12k miles fwiw anyway what do you guys think? will i be ok to just slap in my new rods and bearings and pwn some face or what?
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Old 04-05-2010, 12:57 AM   #11
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Quote:
Originally Posted by magnamx-5 View Post
ok here is a pic of #1 for reference overall after not looking at it for a day it looks alot better than i was thinking. there is a interesting defect about an 1/8th of an inch or so wide going down the bore wich i suspect was from dirty assembly at the machine shop or something last time. 12k miles fwiw anyway what do you guys think? will i be ok to just slap in my new rods and bearings and pwn some face or what?
Those vertical scratches in #1 aren't good, do all your cylinders have vertical scratches?? Vertical scratches like that are usually caused by dirt/debris getting caught between the piston and cylinder wall. Do you remember what the piston to bore clearance was when the motor was built?? At a minimum, I think you are going to need to hone the cylinders and see if you can eliminate the vertical scratches (may be able to do this with a bottle brush style hone) to be able to get a good ring seal.

Assuming you don't have a dial bore gauge or inside micrometer to check the bores, it's probably a good idea to take the block to a machinist/machine shop that has one and get the bores checked for taper and out of round. You can also have the piston dimensions checked vs. new Wiseco specs and make sure that nothing is drastically worn (which seems unlikely given the picture of the #1 piston). Once you have piston and bore specs for each cylinder, you can calculate the piston-to-bore clearance and make sure if it is within Wiseco specs for 2618 pistons (you don't want clearances too tight with forged pistons).

Hopefully, a cylinder hone, some new rings (file fit to TURBO end-gap specs) and lot of meticulous cleaning (clean everything twice, keep clean parts in sealed ziplocks until you install them, assemble in a clean dust-free area and seal up the shortblock with plastic bag anytime you are not working on it) will be all you need.
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Old 04-05-2010, 03:17 AM   #12
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nah its just on that one cylinder and yeah i was gonna atleast brush those out cause they arent deep but ima take care of em.
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Old 04-05-2010, 10:14 AM   #13
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Quote:
Originally Posted by Corky Bell View Post
...I cured the problem in every case in which I used forgings by the old/old/old knurlling of the piston thrust faces and then baking on a Dow Corning molycote bond on dry film lubricant in the knurl.
...
The piston will prove reluctant to push down the bore on assembly, but bash it soundly with something soft and it will shear off all the stuff that it needs to in order to slide down the bore. When the engine is cranked up it will establish the absolute minimum clearance that it can live with in the range of temperature induced expansions.
...

Corky
For realz? Makes sense, but sounds brutal, and sounds like THIS will scratch the bores.
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Old 04-05-2010, 02:27 PM   #14
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well i dont geus it is a myth about our rods being weak atleast 2 of my stockers are bent i wondered where my hp was going. maybe i didnt need cops etc after all.
On a side note where the hell do you get new circlips i had a few spring on me on disasembly reasembly and they went pretty damn far and i am unable to refind them.
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Old 04-05-2010, 03:36 PM   #15
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[QUOTE=webby459;550653]For realz? Makes sense, but sounds brutal, and sounds like THIS will scratch the bores.[/QUOTE

Isn't this just shearing off molycote which should be softer than anything you have to worry about scratching?
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Old 04-05-2010, 03:42 PM   #16
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Quote:
Originally Posted by magnamx-5 View Post
On a side note where the hell do you get new circlips i had a few spring on me on disasembly reasembly and they went pretty damn far and i am unable to refind them.
Mazda Motorsports, p/n 0221-11-205, at least for '97. Prolly find them from Rosenthal for you dumbfucks that don't have a motorsports account.
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Old 04-08-2010, 12:39 AM   #17
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i ordered some from fastenal if this dont work i geus i will have to hit up rosenthal or some other random dealer
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Old 04-08-2010, 01:33 PM   #18
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ok fastenall=fail luckily rosenthal has em for 1$ apeice lol god i hate ky so much at times it nvr has what i want or need.
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Old 04-08-2010, 01:44 PM   #19
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ok fastenall=fail
Fastenall=always fail, in my experience.
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Old 04-20-2010, 02:39 PM   #20
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ok well i put the oilpan and head back on and proceeded to try and prime the oiling system only to find i had low flow and oil pressure. hmm. on a hunch i pulled my oil squirters and geus what i found on #2
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Yep so how much is this bad boy and where can i get one? Or should i just cap it off and be done with it pros cons anyone?
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