Using Alusil pistons in Nikasil cylinders

[daytona1]

Hi Newbie with a question, I am getting conflicting info from various sources (all specialists). I've had my Alusil Cylinders recoated and honed to size with Nikasil. I have been told that i can reuse my original Alusil pistons so long as i run them with the correct Nikasil rings, however in Waynes book it's stated that you can't use Alusil pistons with Nikasil cylinders but it doesn't specify if this is meant as not to use with alusil pistons AND rings or not even with the correct Nikasil rings?

Any help or opinions would be much appreciated

[Steve@Rennsport]

Alusil pistons are iron-coated and incompatible with a Nikasil bore. Using them can ruin the Nikasil plating.

[SCadaddle]

I'd suggest using the "advanced search" function of this forum and using my username SCadaddle as the user name if for nothing more than reading "My" story. NOTE: I'm certainly no engine builder but rather an end user that can only offer 1 data point.

[daytona1]

Thanks for the replies, as in my first post i was advised that using the original pistons but with the correct rings for Nikasil bores should prove okay, i've had the bores re Nikasiled with the correct piston to cylinder clearance (as the pistons are in perfect condition). Obviously if i change my pistons as well as the cost of these, i will have to have the Cylinders recoated at a large cost to match the new pistons
I'm at a bit of a loss as what to do, i phoned my specialist this morning and they are adamant that they have done this on many occasions with no issues, anyone with first hand info on the above? As i don't know which way to jump.

[TibetanT]

I think you should pay attention to what STEVE said above. No matter what anyone else says, Steve is speaking with many years of experience.


There is a very good reason why Wayne mentions this information in his book on engine building. In fact, if you have the Porsche Factory manuals take a look at what they say about "replacement" pistons and cylinder if you don't want to listen to STEVE above.

Just my two cents. And, Good Luck.

[evan9eleven]

Originally Posted by TibetanT

I think you should pay attention to what STEVE said above. No matter what anyone else says, Steve is speaking with many years of experience.

^^^ +1, Steve is the man and will save you from outcomes that only end in tears.

[Henry Schmidt]

Although I don't always agree with Steve, in this case he is 100% correct.
Iron coated pistons are incompatible with Nikasil cylinders.

[daytona1]

Thanks for all your replies, i'm going the JE piston route

[Walt Fricke]

Daytona - among other things, it appears (from all the authorities, not that I am one, but I remember what I read) that it is not possible to "coat" or "recoat" Alusil cylinders. Nikasil is a coating (a machinist corrected me on that once, because technically it is a plating, not a coating). Alusil, on the other hand, is something inherent to casting the cylinder in the first place.

While I don't entirely understand why the iron coating would damage the Nikasil (silica is pretty tough stuff), when enough guys with enough experience say something, it should go to the top of the list. A machinist told me he had tried it, and it didn't work. Enough for me to decide I didn't need to do my own testing.

[SCadaddle]

It's interesting to read what Bruce Anderson' take is on the Alusil/Nikasil topic, check out Page 68 of the "911 Performance Handbook" preview linked here where he states "ferrocoat piston to prevent galling during break-in".


https://books.google.com/books?id=rOKlQ0ZzL6cC&pg=PA2&lpg=PA2&dq=bruce+anderson+911+performance+handbook&source=bl&ots=IChlMFcnkh&sig=2FbbWM6MvysyXL5a75JCxytN_is&hl=en&sa=X&ei=WnH3VLbXB8WdNuGXg9gL&ved=0CEgQ6AEwAjgK#v=onepage&q=bruce%20anderson%20911%20performance%20handbook&f=false

That makes me wonder just how much of the "coating" is left on say a KS Piston from an Alusil set that has 150k miles. Maybe rub it with a magnet and drop it in a bucket of metal filings?

[chris_seven]

Originally Posted by Steve@Rennsport

Alusil pistons are iron-coated and incompatible with a Nikasil bore. Using them can ruin the Nikasil plating.

Steve,

I would be interested to know more about the wear and what happens.

Is the problem with the Nikasil or does the piston have issues.

I understood that EBS sold ring packs for Alusil pistons to run in Nikasil plated cylinders and that this was a relatively common practice but clearly have no direct experience.

I am surprised to hear that there is an incompatibility between Iron and Nikasil as , of course, piston rings are made from Iron based alloys.

Brand new Alusil pistons used to have a very thin 'boundary' layer of Tin over the Iron to prevent initial pick up in a brand new cylinder and this may not be great.

[Walt Fricke]

Chris - aren't the current pistons for the Lokasil bores similarly coated? I have heard that a shop which tried using one of the standard anti-friction coatings on bores which had been resleeved with Nikasil plating for repair or to resolve wear issues didn't work. I think there are others who think this will work. Have you heard anything about this kind of thing? Applying a coating to the piston, and then having the Nikasil plated Alusil cylinder machined for the right tolerances might be the same approach?

[chris_seven]

I believe that although there are differences in casting technology between Alusil and Lokasil the finish of then bore following machining and etching is identical and that Iron plated pistons are still needed.

If you re-finish either Alusil or Lokasil with an Nikasil plated finish then a conventional piston, with or without coating should be OK.

If you try to coat an 'Alusil' piston there may be adhesion problems with the coating but I would be surprised if a simple Xylan coating would be an issue as it should stick to iron reasonably well. I am not sure how long Xylan will last as it is probably the lowest cost coating currently available.

I am not sure if MolyKote will work but Omega use this system and have their own plant so I will ask.

When the 928 was first introduced I thought that the piston had a very thin layer of Tin on top of the Iron to aid running in and this could cause an issue with the adhesion of coatings.

I am still trying to figure out why an Iron coating would be a problem with Nikasil.

The standard Goetze ring used with a Nikasil cylinder is basically Iron. I believe that it removes the surface Nickel from the liner quite quickly and the ring then effectively runs on the silicon carbide that is left.

I can't understand why Iron should pick up on this surface.

I can accept that the unusual shape of an Alusil piston ring could be an issue but Goetze do make a Nikasil compatible ring for the Alusil piston.

I have discussed this issue with Langcourt but they have never tried this so were unable to comment.

There is another thread running where Alusil pistons in Nikasil plated barrel and this motor seems to have run without issue for about 7000 miles.

If you run an Alusil bore then an uncoated piston will clearly be a problem.

Woessner make piston with a coating which they claim is Alusil/Lokasil compatible but that isn't iron.

I have asked them for more information.

[SCadaddle]

Originally Posted by chris_seven

I believe that although there are differences in casting technology between Alusil and Lokasil the finish of then bore following machining and etching is identical and that Iron plated pistons are still needed.

If you re-finish either Alusil or Lokasil with an Nikasil plated finish then a conventional piston, with or without coating should be OK.

If you try to coat an 'Alusil' piston there may be adhesion problems with the coating but I would be surprised if a simple Xylan coating would be an issue as it should stick to iron reasonably well. I am not sure how long Xylan will last as it is probably the lowest cost coating currently available.

I am not sure if MolyKote will work but Omega use this system and have their own plant so I will ask.

When the 928 was first introduced I thought that the piston had a very thin layer of Tin on top of the Iron to aid running in and this could cause an issue with the adhesion of coatings.

I am still trying to figure out why an Iron coating would be a problem with Nikasil.

The standard Goetze ring used with a Nikasil cylinder is basically Iron. I believe that it removes the surface Nickel from the liner quite quickly and the ring then effectively runs on the silicon carbide that is left.

I can't understand why Iron should pick up on this surface.

I can accept that the unusual shape of an Alusil piston ring could be an issue but Goetze do make a Nikasil compatible ring for the Alusil piston.

I have discussed this issue with Langcourt but they have never tried this so were unable to comment.

There is another thread running where Alusil pistons in Nikasil plated barrel and this motor seems to have run without issue for about 7000 miles.

If you run an Alusil bore then an uncoated piston will clearly be a problem.

Woessner make piston with a coating which they claim is Alusil/Lokasil compatible but that isn't iron.

I have asked them for more information.

Er, that would be me. 7,345 miles to date. 1 year and 3,775 miles since last oil change Brad Penn 20/50. I might have used a bit more than 1 quart in that 3,775 miles. Typical smoke on cold start up but no detectable smoke afterwards. I sent the KS Alusil pistons and cylinders to EBS. EBS had them Nikasil plated and supplied the Goetze rings.

Why did I go this route you ask?


1) I bought an '82 SC at about 153,500 indicated miles. Cold compression right at 165 PSI on all 6 during brief PPI. We did not remove the lower valve covers.

2) At 154,890 indicated miles, a broken head stud was found during a valve adjustment and the engine was torn down to replace all lower Dilivar studs.

3) At tear down, the rings were discarded. Not actually thrown in the trash, but my engine builder thought it foolish to re-use the rings. I agreed. They all wound up in a stack on the table.

4) Engine Builder #2 as consultant to Engine Builder #1 and owner (that would be me) insisted the typical on the shelf set of Goetze rings for the Mahle sets would absolutely NOT work in the Alusil applications. We'll need part # XXXXX-XXXX and they'll have to come from Hans or Frans in Germany at about $650 for the set...IF we can get ahold of either Hans or Frans and IF they can get their hands on a set.

5) Faced with this dilemma, phone call placed to a well known engine builder contributing to this forum. "Call EBS, have them Nikasil plate them, get the rings from them and run them on your Alusil pistons. Makes for a nice tight engine. Talk to Don." I'm a bit amused this person has recently done a complete 180 on that statement. Maybe this is all Top Secret-Area 51-Racers Edge-confidential kind of stuff OR a bad sense of monetary humor. I'll suggest the former as 7,345 miles later indicates it hasn't been the latter. Regardless, I will NOT "out" this person to anyone ever in fear of a visit from a black helicopter. Or little green dudes. Perhaps subscribing to the Late Great Harry Pellow "keep the faith" with my 912 he's graduated me to the "inner circle" of the 911 world. But I've yet to receive my membership card.

6) Call Don at EBS. "Not a problem. Do them all the time. We've got the rings. Yes it will work."

7) Weigh the options: $650+ for a set of rings IF we can get them and re-use the Alusil set with NO guarantees that the rings will seat OR spend about $1,000 to ship, plate, set of rings and return shipping.

I spent the $1,000. I've still got an engine. It hasn't exploded yet. Perhaps as they say "time will tell". If and when it does all go wrong because I have an iron coated aluminum piston running in a Nikasil bore I will be the first person to report it didn't work to the 99.9% of others that say it wouldn't work in the first place, with nobody to blame but myself. And I can live with that. "Keep the faith".

[Henry Schmidt]

I am not an engineer so I shy away from the why in most of these questions.
"Why" is often a fools errand because without a full lab and years development work quite often the conclusions are wrong.

My comment on mismatched pistons and cylinders is based on actually trying it with poor results and opening engines where others tried the same. The result of this combination (Tin coated piston in a Nikasil cylinder) is scoring in the cylinder.

[chris_seven]

Henry,

I believe that the Tin coating on the early Alusil pistons was for 'boundary' lubrication during initial break in. The Iron layer was the substrate for the Tin coating and was the more important coating that prevented galling.

Tin, in this application, is extremely soft having a hardness of about 55 HB.

I would be surprised for this coating to be the cause of scoring.

I recently bought an interesting book entitled 'Pistons and Engine Testing' edited by Mahle GmbH and they make the following statement on Page 79:



The fact you have found scoring is undoubted but it isn't likely to be caused by the Tin and the Iron also seems an unlikely candidate.

[Henry Schmidt]

Originally Posted by chris_seven

Henry,

I believe that the Tin coating on the early Alusil pistons was for 'boundary' lubrication during initial break in. The Iron layer was the substrate for the Tin coating and was the more important coating that prevented galling.

Tin, in this application, is extremely soft having a hardness of about 55 HB.

I would be surprised for this coating to be the cause of scoring.

I recently bought an interesting book entitled 'Pistons and Engine Testing' edited by Mahle GmbH and they make the following statement on Page 79:



The fact you have found scoring is undoubted but it isn't likely to be caused by the Tin and the Iron also seems an unlikely candidate.

The pistons are designed differently (cast vs forged) so perhaps expansion rates play a role, who knows?
There could be a plethora of reasons why the piston/cylinder combination has failed in the past. If you have the time and inclination, take a shot and report your findings.
The fun part of DIY is that you can try anything you want and see what happens.
Cheers