cracked pistons

[souren]

can any one tell me why the hell or how do pistons 2 and 3 crack, this is the second time i have come accross this problem. they crack around the grove for the rings. i am looking to replace them what would be a decent type of piston to get for a reasonable price. i have already got copper head gasget. now i need a set of pistons and rings.

[Junkers]

Pistons 2 & 3 crack because of the throttle body setup/single point injection, they lean out and crack.. the only way to solve this is to convert to multipoint. How much boost are you running?

[souren]

its all standard nothing touched. this motor is out of an caar driven by some old guy.

[redzone]

use galant vr4 pistons & rings. they go STRAIGHT in, cost fk all and are a shiteload stronger than stocky`s. have thinner rings and thicker ring lands(the parts u describe that have cracked).as an added benifit they allow u 2 run more boost without pinging and it`ll spool up quicker as the piston crown is a better shape and creates a better burn in the chamber.

i`m using cheapo taiwanese brand vr4 style pistons with 20psi boost for over 20000 k`s (and 16 psi for 30000 k`s before that) and havn`t had a problem. they cost me $180 trade, though i`d recommend you use hypatec brand pistons as they`re much better quality and only cost $350ish. or just spend $750 on a set of cp forgies..

and the main reason they crack like that is from pinging not lean outs, lean outs will melt aswell as crack whereas pinging will crack without melting. pinging is caused by too much boost for the tune, or shit fuel, or too much ign timing.

[flav]

Its quite a common thing....but we use Endurotec over the Hypertec. The Hypertec fail alot earlier and use the thicker piston ring which means the smaller ring land. This is not good. Save the dollars and use CP or JE.
Or the Vr4 stuff if you can get it to suit your bore size.

[mrb1]

and the main reason they crack like that is from pinging not lean outs, lean outs will melt aswell as crack whereas pinging will crack without melting. pinging is caused by too much boost for the tune, or shit fuel, or too much ign timing.

Lean outs can cause pinging for sure.

[redzone]

errr..... thats why i said lean outs will melt aswell as crack....... :D

you can create pinging from a lean out sometimes, obviously when cylinder temps rise 2 a critical level, but if the piston has failed by cracking a ring land without melting the ring and/or land (which sounds like the case here) then its a DETONATION problem (pinging) as i said caused by shit fuel 2 much timing etc etc etc. believe me i learnt this the hard way in my younger days experimenting with turbo gemini`s and then with my first starion..

i won`t use hypatec or endurotec or ANY other brand (including genuine mitsubishi) standard starion pattern pistons in a starion ever again as i truly believe they`re a bad design from the factory thats why i use pistons meant for an australian delivered MITSUBISHI GALANT VR4 (turbo 4wd) that have a better dish for a better burn in the cylinder, thinner rings (1.2mm 1.5mm and 4mm if my memory serves me-compared to 2mm 2mm 4mm for the starion-i`ll dig it out and post it up if u like)with better ring spacing and thicker lands which aren`t nearly as fragile as the standard stuff.. i`ve never ever had a prob with vr4 pattern hypatec`s. but i agree wholeheartedly with flavva flav, go for the vr4 pattern c.p. forgies if u can at all afford it as they are excellent quality and will give u the least probs..

[quest]

hmmm. I wonder how bad or what combination of things occur for this to be a common problem - poor fuel/ metering/ wack ignition dizzy operation, etc.
We've heard how -bad- oe pistons are then..... how good are they ?
Whats the most power seen from them.
Several stock piston 2.6 starions done 400+ whp. Some on pump! I'm thinking, how much weaker can the 2L staz pistons be

[JD_Stazza_Brendan]

power isnt the biggest killer of pistons,, Detonation is.
a motor can make 300hp all day..
Same pistons in a 200hp car with detonation will kill pistons quicker

[quest]

Nothing will tolerate sustained detonation. Not even forgies.
A pistons tolerance may show how 'bad' it is, but that depends heavily on too many other variables... most, we have control over.
On a good tune, out of curiosity, compared to oe 2.6 turbo piston...
same question;
"Whats the most power seen from 2L staz oe pistons ?"

[JD_Stazza_Brendan]

Ive "heard" they can handle 15psi.. and can make 300hp (not sure if thats wheels or flywheel).

just from what ive heard

[redzone]

i`m not saying that the material used in the standard pistons is shit, just that they behave like they`re made out of glass when subjected to ANY detonation at all, comparatively speaking. and how many starions out there havn`t been subjected to a 17 yr old pulling the wastegate line off or cranking the timing to `make it go harder`.. u just have to be SOOOOOO careful tuning an engine fitted with em.

and the reason certain number cylinders tend to crack before others is in my opinion more due to differing cylinder head chamber volumes making certain cylinders have higher comp ratio than others, also the well known fact that cylinders 2&3 run hotter than 1&4 as the centre 2 are copping heat from either side whereas 1&4 get slightly cooler water circulating around them.

of course mixture distribution can also be a contributing factor, but i dont have that problem with my ja running 20 psi and standard single point injection, standard manifold computer etc so i dont think it`d be a worry on a stock motor with up to say 12-13 psi (ie before the fuel cut)