burnt pistons!
 

what causes pistons to be burnt on the only on the intake side of the pistons? a little on to top, most on the top of the first compression ring. could it be timing? fuel? or ring did not seal properly?

Re: burnt pistons!
 

thats where the detonation started

Re: burnt pistons!
 

yeah but not always detonation - it could simply be over heating. But yeah if its wrapping around the ring land area thats knock potential and thats when you start breaking ----

Re: burnt pistons!
 

Most of the time when you melt a piston, it starts on the intake side. usually you have had high EGTs and prolonged detonation. High speed highway runs + lean condition + high EGT's = Fail. Turbo Mr2's are the worst for it. They have shitty intercoolers and poor engine management to begin with, toss in a half dead knock sensor and there you go.

Re: burnt pistons!
 

no pings what so ever. egt is around 1500f fullboost. afr is 11 at fullboost. its a toyota 4agze turbocharged with greddy emanage ultimate, walbro and 750cc. could it be over rich mixture or oil goes to the side of the piston and heats up?

Re: burnt pistons!
 

By chance, did you put the engine together yourself? If so, what sort of piston-to-wall clearance did you have?

I ASSume this is in an FX by your screen name. ------- sweet. At this moment I own an 87 MR2 and an 89 Supra thats in the process of a 2JZ-GE swap.

Re: burnt pistons!
 

i'm not the mad scientinst, but i don't think you can burn pistions up with a rich a/f ratio and no detonation.

and usually the hottest part of the combustion chamber is the exhaust valve. intake valves have the air charge to cool them off as air enters the cyl. exhaust don't have ---- to help cool them. i've always read that the exhaust valves are a good place for the preignition to start at, but never heard about the intake.

do you have any pictures of said pistons?

Re: burnt pistons!
 

yes i did build the engine. as far as i could remember piston to wall clearance is at 0.004in with the stock 4agze pistons.

its an fx 16 front on a sedan. still tyring to find out what happened. to make the story short. it was on the dyno. made 291whp 240tq lb. on like the 12th run. sunddenly stop. the sleeves gave. ok. no bent con rod. only the number 3 cyclinder gave. but i cant understand why all four piston are burnt on the intake side part.


picture will follow soon.

any inputs.

Re: burnt pistons!
 

burnt, or just carbon build up?

Re: burnt pistons!
 

Ugh. Thats too tight for that kind of power. Factory wants quiet, smooth engines. We want loud, reliable ones. 0.004" is too tight. Thermal expansion owned your piston. That sucks. Bet the skirts are gauled up pretty bad huh? Id say you might have had a tuning issue, but im willing to bet the lack of clearance was the real problem. You see it all the time in the 2jz-ge N/A-Turbo cars, they bust around 350hp and the pistons are done. The piston-to-wall wear spec on a 2jz-ge is where the tolerances start on a GTE. 4A-GZE is the same 7rib block as the GE, with dished pistons. Get the idea?

Nice power though, get some pics up here.

Valve temp has little to do with the piston's ability to transfer heat from itself. Every engine Ive torn apart that melted a piston, started on the intake side.

Re: burnt pistons!
 

hence, why i noted that the information was read. i have yet to tear down a motor that's had a melted piston. i plan to keep it that way while tuning my z6 turbo setup

Re: burnt pistons!
 

If your not breaking stuff, you arent going fast enough. Gotta crack some eggs to make an omelet. ;)

Re: burnt pistons!
 

CP Pistons, I mean Honda motors with forged pistons that have melted, usually start on the intake side because there's the least amount of material there around the intake reliefs. That area then heats up quicker (less material to x-fer heat), which fucks the ring area right there first, which lets oil past it. Then that leaked oil self-ignites, which puts the engine into a death spiral as it starts to reach the melting point. FYI the rich mixture cools the intake charge and the surface of the internal parts (preventing detonation). 1500F gasses will heat much farther than just the surface, which cause heat failure in parts.

BTW I don't know about Toyota engines, but .004" is more than enough for most engines near 100hp/L. The generic Wiseco answer to a Honda @20psi is a .0035" clearance. Usually .004" is for weekend cars, larger is for race-only.

Re: burnt pistons!
 

Correct. Most Toyota engines (pre 1997) are iron blocks, honda has run aluminum alloy in the civics since 88'. Aluminum transfers heat faster. Open deck doesnt hurt either.

Re: burnt pistons!
 

really .004 is to tight? its a daily driver. still cant get my pc to load my pics.

Re: burnt pistons!
 

taken with a crappy camera phone!

Re: burnt pistons!
 

http://img381.imageshack.us/img381/5880/image124tw4.jpg
http://img360.imageshack.us/img360/9293/image125pv0.jpg
http://img49.imageshack.us/img49/6659/image126xe9.jpg
http://img207.imageshack.us/img207/4623/image127un7.jpg
http://img207.imageshack.us/img207/3286/image128zk6.jpg

Re: burnt pistons!
 

What kinda of piston clearance would be good for this application? I'm building a 4agte and was just thinking about it.

Re: burnt pistons!
 

ran a .004 on the clearance.

Re: burnt pistons!
 

that's what I was planning on. But if yours turned out like that... I don't know.

Re: burnt pistons!
 

ran your a little wider

Re: burnt pistons!
 

After thinking about it for a minute, keep the ring gap the same, hone your cylinders out to around 0.005" or .127mm. Basically, you want to run at or a bit more than the factory wear as possible. Most factory toyota turbo cars run about that. Doesnt sound like alot, but it makes a difference.

Scorch, what did the cyl walls look like? Can you catch you fingernail on the marks? Basically, can you hone it out?

Re: burnt pistons!
 

i have new block now. not sleeved like the last time. just honed it. my old block didnt have any scratch on it. the resleeved block gave. dont know why. still dont know why my pistons are burnt on the intake side only.

Re: burnt pistons!
 

Pre-ignition/lean mixture started and heats up the piston beyond the knock threshold. First thing the air/fuel mixture hits when it enters the chamber is the intake side of the piston, from there its just a domino effect of the piston being kept hot, and burning itself from continuous pre-igniton of the mixture, until you lose compression in the chamber. By that time its too late.

I would also consider having your injectors cleaned. All it takes is one sticky injector to help it on its way out.

EDIT: BTW, Honda-tech doesnt have tech. They cant build hondas much less a 'yota. ;)

Re: burnt pistons!
 

hitchhikkr,

thanks man,
maybe the the old 450cc dsm is the culprit. i just changed my injector to 750cc. ill check the new 750cc for spray and flow pattern also.
but really i never had detonations before. 11afr at fullbost.

Re: burnt pistons!
 

Detonation and pre-ignition both have disasterous results, but you rarely get burnt pistions from detonation, usually it looks like it got beat with a hammer. The lack of pock-marks on the piston is a dead giveaway.

You can have a lean mixture and not detonate, pre-ignition leaves no fuel left for the detonation to occur after the plug fires.

Re: burnt pistons!
 

You suck dude, you didn't take pictures of the piston skirt, etc, so I can't be 100% sure.

Looks like there's pitting around the sides of the piston crown, right above the first ring. Might be some oil coming across causing pre-ignition, might be a bore that's too tight causing heat to linger in that area, bunch of stuff really.

Re: burnt pistons!
 

that was my first reaction. some oil going to the pistons. ill try to take a better picture. ill get som shots of the block also

Re: burnt pistons!
 

what do you guys think of bore fuel wash?

Re: burnt pistons!
 

I finally found the piston clearance spec. On a GZE it should be 0.0047" - 0.0055".