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Engine Specific Info and Questions => IDI Engine => Topic started by: dieselsmoke on March 22, 2011, 05:13:06 pm
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I have a 94 jetta 1.9 TD aaz engine that was totally rebuilt 10,000 km ago. I go the over sized pistons put in and have a giles performance pump with matched injectors to it. I started my car up this morning and heard a loud banging from the engine so I turned it off. I checked the timing and it appears the timing some how went out. I had to pull the head and I found that the pre cup on the head for cylinder number 4 somehow got blown out and a piece of it fell ontop of the piston. I have to get a new head now ($700) but I am wondering if I can still use the piston. The cylinder wall is fine but the top of the piston got a nice imprint of part of the precup. Can this piston still be used or is it no good now?
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If it's not punctured, maybe. I'd be worried about a bent rod. Bending valves is bearable, but a whole prechamber?
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i wanna see pictures, what is the history of the head? and how were you running the car? extra boost and fueling? if the indent isn't too bad i would still run the piston, i had an engine with valve indents in all the pistons, it ran like a top and got awesome mileage and was an automatic
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how do you post a pic? I took a picture with my camera and want to post it.
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the head was brand new and I am running a giles performance pump with max boost at 15 psi. I have been running it like this for just over a year with no issues.
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I was suprised that the pre chamber let go. The only thing preventing the whole prechamber from falling onto the piston was the head gasket. Unfortunatly about 1/4 of the pre chamber fell through and the piston hit it. I don't think the rod is bent or damaged as I turned the car off right away and the piston comes up to the same height as the other piston.
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(http://i1221.photobucket.com/albums/dd474/jdepiero/engine.jpg)
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as you can see in the pic it took a little bit of a pounding. you can compare what it is supposed to look like on piston #3. Even though the top of the piston got a bit beat up there doesn't appear to be a crack in the piston and the cylinder walls didn't get touched. I just want to make sure if I put a new $700 head onto this that it will still run properly.
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Probably the bad karma you deserve for the $200 you ripped me off for.
Sorry Vince.
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i'd check the ring grooves out, and it will probabaly run fine, honestly tho i would replace, that area is pretty important to the combustion process
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I was going to replace it untill I found out that it is close to $450 for one oversized piston from VW and $700 for a set of 4 aftermarket ones. Plus I would have to get the rod pressed out of the old one and into the new one. I still have to finish cleaning the top of the piston off, I have to sand any edges down. Will the car run crappy because the original indents are messed up? what is the purpose of those indents on the top of the piston anyways?
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I was going to replace it untill I found out that it is close to $450 for one oversized piston from VW and $700 for a set of 4 aftermarket ones. Plus I would have to get the rod pressed out of the old one and into the new one. I still have to finish cleaning the top of the piston off, I have to sand any edges down. Will the car run crappy because the original indents are messed up? what is the purpose of those indents on the top of the piston anyways?
I think to guide the flame front...........
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I was going to replace it untill I found out that it is close to $450 for one oversized piston from VW and $700 for a set of 4 aftermarket ones. Plus I would have to get the rod pressed out of the old one and into the new one. I still have to finish cleaning the top of the piston off, I have to sand any edges down. Will the car run crappy because the original indents are messed up? what is the purpose of those indents on the top of the piston anyways?
dude, myke_w offers GOOD pistons for like 85 bucks a piece.. hes a vendor on this forum.
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If you have the indent of the prechamber on the top of your piston doesn't that point to the wrong thickness headgasket? Did you swap one rod at some point?
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Just another thing, you don't have to have the piston pin pressed out. Circlips hold them in place so changing the piston is easy.
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update
I got a new cylinder head ( had to reuse my camshaft and lifters) made sure the piston wasnt damaged on the sides and cleaned up the top of the piston. I put it all back together and fired it up. For the first little bit it runs really rough and smokes like crazy. Once it warms up it runs fine. I checked the timing and it is set at .91 ( I have a giles performance pump and rebuilt injectors from him) I figured I would advance the timing to .97 since I have read that alot of people like to run the pumps at .95-1.0 but that didn't make a difference. Anyone have any ideas as to why it would run rough and smoke like crazy when cold but when it warms up it is fine? It almost seems like it has a miss in the engine until it warms up. The smoke looks like a whiteish grey i believe. Is it possible that the lifters need to settle in after being pulled and re-seated into the new head??
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Sounds like an injector to me. Whiteish grey smoke sugests unburnt fuel.
Start it up cold, crack open each injection line/injector union in turn.
If one of the injectors is not working properly there will be no change in the way the motor is running when that union is cracked.
If cracking every union does not effect the running then you can at least rule out the injectors
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no. I did not pull the piston as just the top of the piston got a little banged up from the piece of the precup that fell ontop of it. I checked the walls and they are fine. This engine was rebuilt 10,000 km ago with new oversized pistons and rings.
I will try the injectors and see what happens. the injectors are new from giles with 10,000km on them. It just seems weird that it has a miss and smokes like crazy then as it warms up it goes away.
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i will check the injector this weekend. is there anything special I need to do to check them besides cracking the nut on the top of the injector while the car is running.
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I'll test them for the $200 you ripped me off for! >:(
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so i checked the injectors and found that when i cracked the fuel line to #4 it made no difference. i swapped injector 3 and 4 around to see if that would help and it made no difference. looks like the piston itself may have an issue. is there a vendor on here that sells oversized pistons for the aaz engine?
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so i checked the injectors and found that when i cracked the fuel line to #4 it made no difference. i swapped injector 3 and 4 around to see if that would help and it made no difference. looks like the piston itself may have an issue. is there a vendor on here that sells oversized pistons for the aaz engine?
or else it has a bent valve, or a badly blown head gasket..
those are the culprits i would be looking at, not pistons.
(might just be some bad karma tho)
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i have a new head and head gasket I put on so it won't be that. I'll have to pull the head again. Shouldnt take as long now that I have already done it once.
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Maybe if you didn't get HHHHHHHIIIIIIIIIIGGGGGGGGGGGGHHHHHHHHHHHH before you work on it or make any deals on here, you'ld have it figured out the first time.
But seriously, its probably a bad transmission. ::) ;D
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Maybe if you didn't get HHHHHHHIIIIIIIIIIGGGGGGGGGGGGHHHHHHHHHHHH before you work on it or make any deals on here, you'ld have it figured out the first time.
But seriously, its probably a bad transmission. ::) ;D
ROTFLMFAO!!! ;D
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changed piston out and all seems good now. Thanks for all the help.
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Wow, just over six hours sence your last post and you changed out the one bad piston and its fixed now!
Hows the compression ballance between the other cylinders, piston to cylider wall clearance, piston wrist pin clearance and such? Post up a video?
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well Josh, you successfully scared him away!