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SLK32 AMG - Melted #2 piston

8K views 43 replies 19 participants last post by  chevvy 
#1 ·
Sad to say my SLK32 AMG, 37K engine melted the #2 piston and has severely scored the cylinder wall. I have completely stripped the engine to a bare block and was planning on getting it repaired. I heard one opinion that these blocks are not repairable, would like hear from others that may have experience on this subject?
Look forward to your replies, thanks.
 
#37 ·
Its time for a long overdue update!

First off, thanks Neil for your statement "good luck with the glue".
That really hit home - so glad to say that "Mickey Mouse" idea has left the building:laugh:

I've always had the mindset that if you put your mind to it, something can always be done to solve a problem. A never give up attitude, as more often than not something positive will come from it - call it brainstorming 101.

Desperately wanting to improve on my first idea, I spent a good day on the internet to gain some needed knowledge.

My initial goal was to confirm what material this engine block is made of and go from there.

I was originally told by other resources that the cylinders were coated with a silica material and was very thin (much like Nikasil plating). A scored cylinder that was deep enough to catch your finger nail was deemed not repairable turning a very expensive engine block into a boat anchor :frown:

Well the good news is the block is made out of Alusil which consists of 70% aluminum and 30% silicone. This means that the cylinders are not coated which opens up some potential repair options:grin:

This material make up requires a chemical etching (factory process) to remove some aluminum away from the silicone particles which allows two important functions - the raised silicone particles are very hard which creates a durable surface as well as pockets which trap the oil for lubricating the rings much like the cross hatching works on a normal cylinder wall.
Fortunately there is a company that has perfected the etching process using a honing process rather than a chemical etching process which supposedly can be difficult to control.

If anyone has further interest on the particulars of the above I will add a couple links which may help you out as it has me.

Honing Options for Hypereutectic Aluminum Cylinder Bores - Sunnen
https://goodson.com/products/an-30-silicon-compound

Stepping back, I should mention that the engine I purchased awhile back did not work out as the engine had issues which did not show up till after the engine was removed from the vehicle.
This was another motivation to see if I could repair my existing block. The idea being I would still be actively looking for another donor engine just in case my repairs did not work out as planned.
Due to the severity of the score on my cylinder I did not want to fork out too much cash to get my block done professionally so decided to do all the cylinder honing myself.
I contacted the flex hone company and explained to them the type of material I would be working with and they suggested what I should use for grit and hone material to accomplish this job.
Fast forward a few weeks and I have a cylinder that looks comparable to the other 5 less one slight score still visible on the damaged cylinder.

I have gone through a thorough cleaning of the block which is now ready to assemble.

I have ordered the required gaskets and one set of rings which will be going on the used piston I purchased on ebay.

Will post back - hopefully some positive results:wink:
Cheers
 
#40 ·
Wow! That's a tough one, the cylinders are lined with silicon/aluminum applied at the factory, lining the cylinder bore with anything else may lead to issues with differences in coefficient of expansion, for instance if you were to sleeve the bore with steel when the engine heats up the block would expand faster then the sleeve allowing it to become loose. I don't have any experience with that depth in the M112 Engine, hopefully someone who's been down this road before can help you, it would be a shame to go through a lot of work only to have the same cylinder fail again. Sorry to hear about your situation, I hope you find an economical solution that works.
 
#42 ·
Hi,

Just read the whole post, nice one ;)

Did you actually find the root cause of the melt down ??

BTW I have repaired (long term successfully), many exotic Road and Race Engines which have 'xyz' coated Bores, the trick is, when you have bored / honed and therefore removed that coating, get a set of rings the same size but of the correct material to suit running on the non plated bore ;)

Then run said engine in very carefully over the first 2000 miles ...................

Use Semi Synthetic Oil with no oil additives, which allows a tiny amount of wearing, (running in) to take place, next change the Oil at 500 miles then 2000 at which point you will use flush oil and return to the proper specced fully synthetic Oil :)

HTH,

Cheers Dave
 
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#44 ·
Hi Dave, I will say the root cause of the melt down was me - I should of never ran the engine as long as I did without stopping and checking things out further to prevent the melt down!
Not sure if you found my other post regarding the electrical issue I had after the rebuild but had to replace the ECU - when doing so I did not keep the custom ECU remapping. Coincidentally, my car has not coded once nor does it have any detonation knock issues with the stock ECU mapping. One could say that may have been the original cause but I will not be throwing anybody under the bus but myself.
Further to your statement - "removed that coating" - the block does not have a coating - the entire cylinder is made of alusil. After boring out the cylinder to 3.547 in. (repair max = 3.550 in) I had to condition the cylinder with a special silicone compound to remove the aluminum to expose the silicone particles to allow for proper oil retention in the bore.
My biggest concern after I did this work was having the conditioned cylinder with the proper amount of aluminum removed and silicone particles exposed. If not done properly, my engine would of been a mosquito flogger. I will say to this point it appears I was very lucky on how I conditioned the cylinder.
I did a lot of reading on what to do and not do regarding engine oil and break in - there seemed to be two schools of thought on this subject. I picked one and went with it.
I ended up using conventional oil with a break in additive - ran her for 50 miles mildly, then changed to Mobile One 0W40 and slowly started working the engine with varied RPM's and WOT shots.
Hopefully, the engine will continue to run as it has and this winter I will remove the head for a visual inspection of the bored cylinder or at the very least complete a compression and leak down test.
Cheers
 
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