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Author Topic: blown head  (Read 5792 times)

March 22, 2011, 05:13:06 pm

dieselsmoke

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blown head
« on: March 22, 2011, 05:13:06 pm »
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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Reply #1March 22, 2011, 05:16:13 pm

Quantum TD

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Re: blown head
« Reply #1 on: March 22, 2011, 05:16:13 pm »
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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Reply #2March 22, 2011, 06:19:03 pm

RabbitJockey

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Re: blown head
« Reply #2 on: March 22, 2011, 06:19:03 pm »
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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Reply #3March 22, 2011, 07:24:03 pm

dieselsmoke

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Re: blown head
« Reply #3 on: March 22, 2011, 07:24:03 pm »
how do you post a pic? I took a picture with my camera and want to post it.
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Reply #4March 22, 2011, 07:30:26 pm

dieselsmoke

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Re: blown head
« Reply #4 on: March 22, 2011, 07:30:26 pm »
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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Reply #5March 22, 2011, 07:34:24 pm

dieselsmoke

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Re: blown head
« Reply #5 on: March 22, 2011, 07:34:24 pm »
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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Reply #6March 22, 2011, 07:44:37 pm

dieselsmoke

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Re: blown head
« Reply #6 on: March 22, 2011, 07:44:37 pm »
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Reply #7March 22, 2011, 07:47:56 pm

dieselsmoke

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Re: blown head
« Reply #7 on: March 22, 2011, 07:47:56 pm »
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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Reply #8March 22, 2011, 09:04:03 pm

Powered by Spearco

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Re: blown head
« Reply #8 on: March 22, 2011, 09:04:03 pm »
Probably the bad karma you deserve for the $200 you ripped me off for.

Sorry Vince.
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Reply #9March 24, 2011, 08:57:30 am

RabbitJockey

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Re: blown head
« Reply #9 on: March 24, 2011, 08:57:30 am »
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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Reply #10March 24, 2011, 04:28:59 pm

dieselsmoke

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Re: blown head
« Reply #10 on: March 24, 2011, 04:28:59 pm »
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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Reply #11March 24, 2011, 06:13:49 pm

rabbitman

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Re: blown head
« Reply #11 on: March 24, 2011, 06:13:49 pm »
Quote from: dieselsmoke on March 24, 2011, 04:28:59 pm
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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Reply #12March 24, 2011, 09:56:23 pm

R.O.R-2.0

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Re: blown head
« Reply #12 on: March 24, 2011, 09:56:23 pm »
Quote from: dieselsmoke on March 24, 2011, 04:28:59 pm
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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Reply #13March 25, 2011, 10:48:38 am

blackdogvan

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Re: blown head
« Reply #13 on: March 25, 2011, 10:48:38 am »
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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Reply #14March 25, 2011, 11:31:07 am

rodpaslow

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Re: blown head
« Reply #14 on: March 25, 2011, 11:31:07 am »
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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