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UK 98 3000GT TT
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550 Posts
Discussion Starter #1 (Edited)
Well I installed my new back turbo yesterday that took way to long to do.
Started the car and she was running ok, then I note that the car seems to be missing so I did a compression test on the car.

Back 3
1 155psi
2 155psi
3 155psi

front

1 155psi
2 155psi
3 1psi!

Looks like I need new pistons guys :(

I can see piston 3 going up and down but no compression at all.
The cars not making any knocking sounds at all or ticking sounds so would it just be that piston that’s the problem?

What other damage might of happened with the car?

how easy would it be the change the piston myself?

Also where would the best place be to get some good pistons that wouldn’t do this again?

I know where there are some GTO twin turbo engines laying around, so could I just get a piston from one of them and put it in?
 

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Registered
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8,762 Posts
Dat's not good! :( That was a warm compression test, right? You might want to try putting a teaspoon of oil in the offending cylinder and trying it again...you never know...

What other damage? Well...your cylinder wall may be scarred. A piece of the piston may have went through the front turbine (or wastegate if you're lucky like I was). That piece of piston may have messed up a valve on its way out of the engine too. As far as changing the piston yourself it depends on your mechanical ability. I fix jet engines for living and I don't trust myself to do stuff like that. I don't have the hands on experience and I don't feel like practicing open heart surgery on my baby. Where to get pistons? Providing there's no valve damage then I would just yank the old one, inspect the cylinder walls, and install a new stock piston with new rings on the original rod. If you're planning on running 420+HP everyday then I might consider forged pistons.
 

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UK 98 3000GT TT
Joined
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550 Posts
Discussion Starter #3
Man I just hope that it didn’t mess anything else up on the way out :/
I’m going to pull the head off next week and have a look at what happened.

And yep the car was worm when I did the compression test.

So just replacing one would be ok?
 

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Retired
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12,235 Posts
It all depends on what you want to do. You can either go the cheap route or expensive route.

Luckily it is on the front, so it will not be 'that' difficult. If you installed the rear turbo, then you can do this job. Remember though, it will not be a walk in the park.

Cheap route: I have my old pistons and rings. I will sell you one of them for $25 plus shipping. Then you will need a new head gasket $35, oil pan gasket, etc...

Or you could go the expensive route: all new forged pistons, all new rod bearings etc...

This is assuming that your cylinder wall is in good condition. If it is not, then you are kinda screwed. I think your first step will be to pull off the front head and see what the damage is. You must feel confident about setting time too. Do not attempt this if you are scared to set time. We are all here to help you out.

I would do the little oil trick that trevor said and try it again. If it is bad, then you need to determine WHY it went bad (eg. overboost, bad injector, etc...)

good luck.
 

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UK 98 3000GT TT
Joined
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550 Posts
Discussion Starter #5
Ok guys here the update.

I just did that thing where I put some oil in the piston and did a compression test again on the piston.

And I got 75psi on it.

So I’m thinking that I may not have a hole after all.

So what I’m I looking at now?
 

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Lovbyts
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3,618 Posts
By putting oil in it and the pressure going up you just confirmed that it is your rings. If the pressure did not go up you would either have a hole in your piston or a bad valve.

I have to replace my back #1 piston due to meltdown. It was melted down to the rings on the outside of the piston but the walls are in good shape.
 
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