AFN Pistons: Weight Difference Up to 60g!

Hello.

I have a Volkswagen Golf 3 Jubi GTI with an AFN engine (manufactured in 07/1996).

Unfortunately, last week the second piston (in the second cylinder) failed in this engine, cracking completely across to the pin. I've been trying to find a replacement piston, but so far I haven't been successful... and who wants to be without their car for a long time?
So, it turned out that I initially received a piston from Nüral as an accessory. I immediately weighed it at the dealer to compare it to the original. It was noted that the Nüral piston was 20g heavier than the original, whose manufacturer is not indicated on the piston itself. Since I didn't want to install this piston, I tried to order a piston from Mahle, which I received this morning. Unfortunately, this piston is now 40g lighter than the original. This is an interesting situation for tuning purposes, but I don't really want to buy and replace a whole set of pistons, being a poor student. Well, the engine mechanic nearby suggested that I replace another piston to compensate, meaning he would also install a new piston in the fourth cylinder. That's ridiculous, isn't it? Does anyone have any ideas or perhaps even a used piston for the second cylinder that weighs 556g without the pin? I need it urgently!

Best regards from g-lad.
Maik.

Can you rule out the possibility that some material was also lost due to the crack? And just between us, take the other pistons out and I suspect they also have some variation in their tolerances. 40g is a lot, but I think you'll have to live with 20g if you don't want to completely disassemble the engine. After all, there's also the crankshaft, and it's probably not perfectly balanced either. That's always been something the tuners have taken care of.
What does your cylinder look like, and did it survive the process without any problems?

Okay, I hope you get more answers here from people who know more than I do. However, I think that replacing all four pistons is probably the most elegant (and expensive) solution. What's the cause of the crack... was it due to chip tuning or excessive mileage?

Well, I'm not taking it personally. The chip from Tuneline, which supposedly adds 146 horsepower, is just for fun, and it probably puts a lot of stress on the pistons all the time.
The car has 118,000 km on the odometer. I bought it with 70,000 km about 15 months ago, and the last 50,000 km have almost all been long-distance driving. There's nothing wrong with the cylinder itself. The piston also isn't damaged; there's no material missing, it's just cracked. And the variation in weight among the pistons from the factory is certainly no more than 10 grams.

What if you were to go directly to Audi and take a look at a piston?
Because that would then be original merchandise, and it would certainly be exactly the same weight.

Did you flush your engine with cold water because it cracked, or was it due to the injector?
If you don't know, I would definitely recommend checking or having someone check the beam pattern.

And I think that the tolerance should not be more than 10g, and a maximum of 15g is acceptable.

However, I would recommend checking with a reputable manufacturer of mortar tubes, as they can provide you with more precise information. It's possible that a 40g difference is insignificant, especially since the peak pressures in all cylinders are likely to vary by around 50 bar anyway.
Good luck!

Okay, I would also have the injector checked by Bosch... something is definitely not right with it.

To my knowledge, there are only 3 manufacturers for these pistons (and only 3 suppliers for VW).

That would be.
KS, Mahle, and Nüral...
The KS piston cannot be the correct one because it has a size of 79.45mm.

I'm already in contact with a tuner and engine rebuilder who would replace all 4 pistons in my case.

'VW also doesn't have any in stock either; they would have to order it from Kassel, apparently. It would also be a piston from a newer series, and its weight isn't specified anywhere.'

Well, it looks like I might be able to get a set of used pistons right now, hopefully they'll be okay.

What are your thoughts on honing the cylinders?

Okay, so the four pistons will be fitted with new rings. The engine has 118,000 kilometers (approximately 73,000 miles) on it, and there are no signs of any dead spots in the cylinders. The honing marks are still clearly visible.

Should I have the cylinders honed?

Hello,

If the tire treads have honing marks and no shiny or noticeable spots at the top dead center (TDC) points, then re-honing won't make much difference. Everything should still be within specifications. You should break in the engine again with new rings. Personally, I would have used the 20g heavier piston and lightened it by 20g. Since you're taking out all the pistons, you can weigh them all. Then weigh the connecting rods on both sides, and everything will be perfect. Since diesel engines don't rev much above 4000 RPM, it's not as big of a deal as it would be in an F1 car with 18,000 RPM. If you've already taken the engine apart this far, I would also replace the connecting rod bearings along with the rings.

Best regards,
Christian.

It is not recommended, and also almost impossible, to reduce the weight of the piston by more than 10 grams.

statement

From Twistern Motorsport http://www.vontwistern.de.

If I start replacing the connecting rod bearings, and possibly even the crankshaft bearings now... hmm, then I might as well buy a new engine soon. No, no, I'll replace those only when they're broken. The way my engine is running, everything else will fail before that anyway...

That's actually my everyday car, if I didn't need to use it every day... otherwise, the entire crankshaft mechanism would certainly be perfectly balanced and fine-tuned to the gram.

Hello,

Of course, that's your car. Pleullager (connecting rod bearings) aren't really expensive. You've already exposed them, I see. If you can hear them, it's already too late, and the crankshaft is almost always irreparably damaged.

Best regards,
Christian.

Well, actually, this car has already driven quite a few kilometers. Maybe it would be better to buy a brand new car instead.

Please, people, this is about the piston... thank you.

You want to install 4 used pistons (??) with completely new rings and are asking if you should have the block honed.

Make as much money as you want, but you clearly aren't interested in any advice.

No further comment.
Christian.

noxinu wrote:

Well, it looks like I might be able to get a set of used pistons right now, hopefully they'll be okay. What are your thoughts on honing the cylinders? Okay, so the four pistons will be fitted with new rings. The engine has 118,000 kilometers (approximately 73,000 miles) on it, and there are no signs of any dead spots in the cylinders. The honing marks are still clearly visible. Should I have the cylinders honed?

noxinu wrote:

Well, actually, this entire car has already been driven for so many kilometers. Maybe you should consider buying a brand new car instead. Please, people, this is about the piston... thank you.

Hi,

I hope you are aware that the four pistons in a TDI are not all the same!
As far as I remember, the pistons are always paired together (i.e., 1 and 2 are a pair, and 3 and 4 are a pair).
Weight differences between couples can be normal and even important.

If that's the case, it should be listed in the AKTE system, and then you should inquire about it.
because you need one.
But you might be right with that statement.

Quote:

I hope you are aware that the four pistons in a TDI engine are not all the same! As far as I remember, the pistons are always paired together (i.e., 1 and 2 together, and 3 and 4 together). Weight differences between partners can be normal and even important.

Steffarn wrote:

if that is the case, then it should be in the FILE

.
It's true!
The document indicates a separate number for cylinders 1 and 2, and another number for cylinders 3 and 4. Please ask the friendly staff for clarification.

For AFN 96, this corresponds to 028 107 065 AL (pistons 1+2) and ... AM (pistons 3+4).