[Pouria]

Hi;
I need help about my 2008 E93 335i I purchased 3 months ago out of which 2.5 was spend in the garage And last week, exactly when I went to take it from garage after some rear end repair, oil change and head unit upgrade to android Multi Media, with a lot of hope and happiness, I started the engine and put to D and pushed the pedal, engine died immediately and didn't start again!!! We could realize from the engine sound when cranking that there was no compression at all so we guessed that the timing failed and we are about to see some bent valves! After opening the valve cover, we saw the exhaust cam aluminum cover broken from the tips gone into the head (all of them broken!!!) And after opening the head, we saw 12 bent exhaust valves while surprisingly the intake valves are in good shape and weren't touched by pistons. I am sure you could guess that I am already broken and need to rob a bank to bear the costs. Having the engine out of the hood on the repair stand, I decided to check the pistons, rings and cylinder walls too. On the pistons is written 83.967 that seems to be the piston diameter and says the cylinder size is standard and never saw the machine shop. We took out the pistons and measured the bores sizes shown in the attached picture.

The pistons also decreased in size a couple of hundredth of millimeter that caused the piston to wall clearance higher. Now, the thing I need help for:

1- The engine is standard and I want to keep it standard to the most possible extent.
2- It is expensive to send the block to the machine shop for over bore.
3- I am not sure about the quality of boring and honing that is gonna happen.
4- The ring gap in all the cylinders is 0.25mm except cylinder 5 that is 0.3mm that is still in good range.
5- The hones on the cylinder walls are still there.

So, I am thinking to buy new OEM standard pistons and rings and throw them in the motor without having the block machined and over bored. As I had no experience on N54 before and this is my first Bimmer ever, I need to know your opinions and recommendations to choose the right way. I am very limited in budget and will touch my savings to do an entire engine overhaul ONLY IF it is really necessary from the technical point of view.

Thanks in advance for your inputs.

BR - Pouria

[iqraceworks]

I just went through an engine rebuild, so I hope I can help you out.

The first thing I would do if I were you is to look at a set of Mahle forged pistons in standard 84mm size...much cheaper (and stronger) than oem cast pistons.

CSP Racing has them on sale right now for $908.....and they are in stock. I got mine in a couple of days.

OEM pistons from FCP Euro will cost you $2,100. And the rings are another $800. So $2,900 for stock cast oem pistons and rings, or $908 for a set of coated Mahle forged pistons and rings. Kind of a no-brainer. They will work with the oem connecting rods.

The Mahle pistons come sized so that they will fit in the stock 84mm cylinder mores, and have the proper .0025"-.003" clearance...which mine did. They fit perfect, no machining required.

I used a Flex-Hone to brake the glaze on the cylinder walls and get the rings a good surface to seal against.

While you are in there, I would also replace the rod bearings. You can get a set of standard sized King rod bearings from FCP Euro for a good price.

Here is the link to the pistons....cheapest place online that I could find them.

Let me know if you have any more questions.

https://www.cspracing.com/mahle-1978...gjh-197832209/

[Pouria]

Originally Posted by iqraceworks

I just went through an engine rebuild, so I hope I can help you out.

The first thing I would do if I were you is to look at a set of Mahle forged pistons in standard 84mm size...much cheaper (and stronger) than oem cast pistons.

CSP Racing has them on sale right now for $908.....and they are in stock. I got mine in a couple of days.

OEM pistons from FCP Euro will cost you $2,100. And the rings are another $800. So $2,900 for stock cast oem pistons and rings, or $908 for a set of coated Mahle forged pistons and rings. Kind of a no-brainer. They will work with the oem connecting rods.

The Mahle pistons come sized so that they will fit in the stock 84mm cylinder mores, and have the proper .0025"-.003" clearance...which mine did. They fit perfect, no machining required.

I used a Flex-Hone to brake the glaze on the cylinder walls and get the rings a good surface to seal against.

While you are in there, I would also replace the rod bearings. You can get a set of standard sized King rod bearings from FCP Euro for a good price.

Here is the link to the pistons....cheapest place online that I could find them.

Let me know if you have any more questions.

https://www.cspracing.com/mahle-1978...gjh-197832209/

Thanks a lot for your reply. I thought that N54 pistons are forged, aren't they?
Did you check the actual bore sizes of mine attached to my previous post? My main concern is to make sure I don't need to increase the bore sizes by one step.

[iqraceworks]

Originally Posted by Pouria

Thanks a lot for your reply. I thought that N54 pistons are forged, aren't they?
Did you check the actual bore sizes of mine attached to my previous post? My main concern is to make sure I don't need to increase the bore sizes by one step.

No, the oem N54 pistons are a cast "hyperutetic" material.

How did you measure your bore dimensions? Dial bore gauge and a micrometer? Something else?

Your bore dimension all looks fine.....84mm = 3.3079". Your largest dimension is 84.15mm = 3.3129" and your smallest is 84.00mm = 3.3079". So you have a .005" variance. And that's at the bottom of the cylinder where it's not going to matter much.

If you look at the variance in your "middle of cylinder" measurements, the largest is 84.03mm = it's 3.3082" ....so only .0003" variance.....that's great.

I would just order the stock size 84mm Mahle pistons, and go from there.

[Pouria]

Originally Posted by iqraceworks

No, the oem N54 pistons are a cast "hyperutetic" material.

How did you measure your bore dimensions? Dial bore gauge and a micrometer? Something else?

Your bore dimension all looks fine.....84mm = 3.3079". Your largest dimension is 84.15mm = 3.3129" and your smallest is 84.00mm = 3.3079". So you have a .005" variance. And that's at the bottom of the cylinder where it's not going to matter much.

If you look at the variance in your "middle of cylinder" measurements, the largest is 84.03mm = it's 3.3082" ....so only .0003" variance.....that's great.

I would just order the stock size 84mm Mahle pistons, and go from there.

Thanks for the info about the N54 pistons. Yes I did measure very precisely with dial bore gauge and micrometer. My largest bore diameter is 84.05mm not 84.15. So, you mean my cylinders are just fine and ready to go, that's what I really loved to hear! Thanks again. Let me see how I can get to those Mahle pistons. I live in Iran, not easy to order parts! I need to find them in Dubai or Turkey.