[RichardGoller]

It looks like I will have to replace the rings on piston 4 in my N52 and I'm wondering, the materials to replace all 6 is not that expensive, so I might as well while I'm in there. I'm just wondering if it's something that you should only replace the one that is worn, in case you replace an otherwise healthy one to be safe just to mess it up. Rod bearings aswell.

[lowrydr310]

Replace them all. If you've done the labor to access the rings on a single cylinder, it's not much more to replace them all.

[E92_William]

Why are you doing it in the first place? Have you tried to clean and free up the rings first? Either way I'd prefer to do all of them unless you're super tight money wise but got loads of free time and your other cylinders are by some witchcraft all perfect

[rjahl]

Originally Posted by E92_William

Why are you doing it in the first place? Have you tried to clean and free up the rings first? Either way I'd prefer to do all of them unless you're super tight money wise but got loads of free time and your other cylinders are by some witchcraft all perfect

There must be some backstory to this and a reason why one cylinder is dead.

Probably far better to find a lower mileage second hand motor and swapping the whole running block.

[hassmaschine]

He's in London, so it's probably the N52B25, which has piston ring issues.

Definitely replace them all. You need to deglaze the cylinder walls as well, N52s have alusil liners, it doesn't take the same honing process as a steel block. If you just stick new rings in there without properly honing for alusil, it's not going to work.

[E92_William]

If so then I think it's a better idea to swap in a B30 like guys have done here previously which would probably be less time consuming than this and you end up with an overall better engine.

[hassmaschine]

I agree, the only issue is in the UK I think they pay taxes by engine size, so it's sort of illegal, although I doubt anyone would notice or that the emissions are really much different..

[RichardGoller]

Originally Posted by hassmaschine

I agree, the only issue is in the UK I think they pay taxes by engine size, so it's sort of illegal, although I doubt anyone would notice or that the emissions are really much different..

I already have a B30 in. But there is something dodgy with the compression rings in cylinder 4.

[RichardGoller]

Originally Posted by rjahl

There must be some backstory to this and a reason why one cylinder is dead.

Probably far better to find a lower mileage second hand motor and swapping the whole running block.

Might be better, but then I do have to think about what makes sense financially, the whole engine costs about 4 times more than the parts to do this job, including replacing timing chain, engine mounts, etc while I'm in there

[RichardGoller]

Originally Posted by E92_William

Why are you doing it in the first place? Have you tried to clean and free up the rings first? Either way I'd prefer to do all of them unless you're super tight money wise but got loads of free time and your other cylinders are by some witchcraft all perfect

I have tried pouring seafoam in the cylinder and leave it for a day, but didn't help, but I'm open to other suggestions.

[desertman123]

It's wayyy easier to drop a used, good motor in. Are you planning on honing the cylinder?

How'd you come to the conclusion you need rings?

[RichardGoller]

Originally Posted by desertman123

It's wayyy easier to drop a used, good motor in. Are you planning on honing the cylinder?

How'd you come to the conclusion you need rings?

Low compression, high leak down. Put oil in cylinder, compression back to normal. I'm not after whats easier, I'm after what makes sense financially. Also, if nothing else in there is bad, I will end up with a better engine than the one I could just have dropped in.

[F31B48]

Originally Posted by RichardGoller

Low compression, high leak down. Put oil in cylinder, compression back to normal. I'm not after whats easier, I'm after what makes sense financially. Also, if nothing else in there is bad, I will end up with a better engine than the one I could just have dropped in.

Are you sure its not a valve or valve seat causing the compression loss?

The only issue with the rings on these engines was oil consumtion. ie, the oil control rings, the compression rings were fine.

[RichardGoller]

Originally Posted by EvaBmw

Are you sure its not a valve or valve seat causing the compression loss?

The only issue with the rings on these engines was oil consumtion. ie, the oil control rings, the compression rings were fine.

To be honest, I'm not sure of that, but from what I gathered if wet compression test shows normal compression and dry compression doesn't it's definitely the piston rings. Could it be the case that the oil seals the not seating valve or valve stem?

[F31B48]

Originally Posted by RichardGoller

To be honest, I'm not sure of that, but from what I gathered if wet compression test shows normal compression and dry compression doesn't it's definitely the piston rings. Could it be the case that the oil seals the not seating valve or valve stem?

I would say it's far more likely that something is stuck under the valve seat or the valve/valve seat has been damaged by something. It's a pretty unusual failure though for an n52. Has the engine had a DISA failure at some stage?

Have you had an endoscope in the cylinder and had a look for any scoring on the cylinder walls?