How to replace piston on cylinder six?

Hi,

That requires the engine to be removed, taken apart, and basically rebuilt. Why do you feel a new piston is needed? If that is what is needed, there is likely other damage, so let me know. Note: This is a big undertaking and shouldn't be done if you are not experienced.

Let me know.

Joe

As Joe alluded to, it is very likely that if you have a damaged piston, it's very likely you have more damage than that. If you dropped something in the engine and it got into the cylinder and damaged it, then there is likely damage to the valves, cylinder head and possibly the engine block as well. My first step would be to use a bore scope and look inside that cylinder and inspect it for damage first. Look at the piston, bore and cylinder head surfaces for damage. If there is any, I would consider replacing the engine over the alternative of rebuilding it, unless there is no choice. Please let us know what you find and why you feel it is bad. Thank you.

Thank you, I will.

How can I manually verify if my head cylinder is not damaged?

Only two ways, use a camera to look inside the cylinder and inspect things, or remove the head and inspect it. The second option is the better one but the question is still, what makes you think the piston is damaged? That is also something that you would need to inspect in the same manner.

I can manually shake the piston, and I see it moving, while the other pistons are firmly in place.

How are you able to shake the piston? You have the engine out and apart or ?? That sounds like it could be more than just a bad piston. Can you take a video of it and post it here?

Sure, I had taken the head cylinder out, because I was replacing the head gasket and I noticed. But the engine runs well.

Okay, that's normal. The pistons start a bit loose in the bores and as soon as the engine starts they heat up and expand. If there were no room they would expand and lock in the bore. If the others don't move a bit in the bore the rings are likely carboned up and stuck in the grooves. As you have it that far apart I'd suggest doing a refresh on it. Pull the engine out the rest of the way. Pull the oil pan and remove the crankshaft and inspect all those bearings (or just replace them. While it's apart remove the old piston rings, install new rings and use a simple hone it each bore just to break the finish on the cylinder walls. Clean up the residue and put it back together. Reseal the cylinder heads and lap in the valves and you would have a better engine. Because of the lack of any damage the cylinder head shouldn't be a problem. Now if you wanted to you could actually go the full rebuild route and not just a refresh. That would involve removing the engine, stripping the block and sending it and the crankshaft to a machine shop and having the cylinders bored to the first oversize that has pistons available, line honing the crankshaft saddles and having the connecting rods resized and all new pistons, rings and bearings fitted. Now do the heads and you would have a "new" engine.

Okay, thank you my friend. So actually, it’s normal for that piston to move like that. Actually, the engine has been running very smoothly and quietly, only the top cylinder head gasket caused water to mix with oil.

So, do I need to resurface the top cylinder which had the blown gasket? Or how can I manually test to know if it’s right to fit in a new gasket. I bought lashers from the manufacturer Audi, not from a third party. So, they are original. What can you advise me?

Use a scraper to clean the surface real well, then get a straight edge and some feeler gauges to verify that the flock and head are actually flat. When a head gasket fails it's commonly because the surfaces are not flat, and the gasket isn't clamped evenly. There are a couple engine build series on this sites YouTube channel that show some of the measurements. That works for most engines. More videos of the various items you do at https://www.youtube.com/@JAMSIONLINE as well.

Thank you, this started with a leakage on the water-cooling system, then resulted in overheating and a blown gasket on cylinder 4 and 5, Can I use also a sand paper with a flat table surface for cleaning and aligning any bends on the top?

I will send you an image of the blown gasket position.

I wouldn't try to surface a block with sandpaper. Far to easy to cause problems.

https://youtu.be/a8ctywVmzK0?si=_p4CIwNiY254WRG0

Can I use this method to resurface my cylinder head?

That works for old iron heads if you are not really worried about introducing other errors. Aluminum is different because it is very easy to ruin a head that way.

Got it. Thanks!

Aluminum is fussy about the surface finish as well so it's really better to check it for flat first using a straightedge and feeler gauges and if it needs work have a machine shop true it up. It really depends on how long you plan to keep the car. You could have the machine work done and go through the engine and it would last another 100 thousand or more miles, but is the rest of the car in good enough shape to justify the cost? If yes, then do a full rebuild and enjoy it. If the rest of the car is questionable then maybe use that technique with some 400 grit paper just to see if the head is bad or use the straight edge, and if it's not really bad just bolt it back together with new gaskets and bolts and call it close enough and drive it. Those become a judgement call that you would need to make based on the actual conditions you have.

Thank you very much for this information. Is it possible to get the specifications for resurfacing this block. I actually checked using a straightedge and a feeler gauge, both head cylinders are all flat, using the 5 steps method. But rather the block is sung in between cylinder 4 and 5. So rather it’s the block which needs resurfacing. I will send you an image.

That black spot right there is the block where I had the failed gasket, using a feeler gauge and a straightedge, I noticed it’s sunk in just about half a millimeter, I think. This blade could go through it with very little resistance.

That isn't a good thing. A good machine shop would be able to machine it a bit, then weld up the low areas and then machine it back flat. Or it might be possible to deck the block and get it flat but that would take measuring the pistons to see how close they are to hitting the cylinder head. If they are too close material removal could cause problems.
The other option would be a different block.

That explanation makes a whole lot of sense. I think feeling and resurfacing it flat would be the best option. If the block is ducked, that might cause a permanent problem and would require a new block. It’s an option I would not want to take.

This German cars are quite complicated, the feeling the low spot is the ideal option to work on. After feeling flatting the surface.

Thank you very much, you have been very helpful.

Good luck with it, there are a lot of shops out there that can do the repair. Just need to find one that isn't booked for the next 2 years.

Hahahahahahahaha, thanks!

One last question for now. Please advise me on this valves on the head cylinder, I got two which looks a little bit oily. Let me upload the image.

Hahahahahahahaha, thanks!

One last question for now. Please advise me on this valves on the head cylinder, I got two which looks a little bit oily. Let me upload the image.

I noticed it looking that way when I took out the top, but I have turn the camshafts to inspect its opening and closing, it opens well and closing needly.I am truly not a professional mechanic, but I am a professional in cars electronics and electrical, maybe about 60% in mechanics, but I am a fast learner..

I would just clean them up. That could be oil or coolant hard to tell which. But if you go through the heads and refresh them it shouldn't be an issue when you put the engine back together.

Ok, thank you.