Nickasil cylinder damage

[mike.smith]

A heads-up: my plane is grounded until I replace all my cylinders (AeroVee 2.1). When I ordered the engine I opted for the Nickasil cylinders to save weight, but like other Nickasil owners they came back to bite me. I got back an oil analysis that showed extremely high levels of nickel, and abnormal levels of iron and aluminum. Those are the materials that make up the cylinders (aluminum and nickel), and the rings (iron).

So I pulled off the head on one side of the engine today, and this is what I found:

https://www.flickr.com/photos/127253485 ... 8164690406

Both of the cylinders had mushroomed at the top edge, where they meet the head. I had a heck of a time getting the cylinders out of the head because the mushroomed area had jammed in there. I presume my other 2 cylinders will look similar. I know some others have had this same issue. It took 120 hours for this to show up. My heads were meticulously torqued to specs, and my CHTs usually run 290 to 340, with a temporary max of 380 (full gross, climb out, on a hot day) for a minute or so.

Sonex will sell me new steel cylinders at a discount.

Lesson learned (besides not getting Nickasil cylinders) is that OIL ANALYSIS WORKS! There were NO other indications that the engine was having issues. Compression was around 80/75 (tested cold) on all 4 cylinders. CHTs and EGTs have been nice and cool, and the engine was running well. So I would just offer that if you don't do oil analysis each time you change the oil, you are doing yourself a dis-service. It costs me $12 for the oil analysis, and I get the results just a few days after I send in the sample.

[GordonTurner]

Good write-up and good advice. Thanks

[kevinh]

Great post. Just curious, which oil analysis company did you use and how did you like their reporting?

[nwyooper]

Thanks for the report Mike. I didn't like what I was hearing about the Sonex supplied Nikasils so I changed mine out after 3 hours of operation when I had to disassemble engine to replace the circlips. Shortly after I went to cast iron, Sonex quit selling the niks. Not saying it is Sonex's fault but they obviously had a bad supplier and I am glad I made the change.

[mike.smith]

Lab One Inc
480-839-5221

You can buy the analysis kits from ACS: http://www.aircraftspruce.com/catalog/e ... ckkey=4932

[mike.smith]

After doing some research, this is my take on the Nickasil cylinders:

http://www.cwgsy.net/private/ramva/tech.htm#Cylinders : The AeroVee cylinders are 92mm inside diameter. More than one source (like the above) claim that the cylinder walls are just too thin. And that's with standard steel cylinders. Aluminum, as in the Nickasil cylinders, would be worse.

My opinion is that the aluminum cylinder walls are so thin that the combination of standard torque values and heat (even if running 'in the green') make the rims of the cylinders susceptible to crushing the top edges where they meet the heads. I saw none of this at my annual when I had a valve job done, when I had 80 hours on the engine. Having the valve job done meant I had to go through the head torquing process again, which I did. Each time I retorqued I was surprised how far some of the nuts had to go to reach the published torque values. I think the repeated torquing (original engine build and after the valve job), along with the normal metal fatigue of the thin aluminum through repeated heating and cooling cycles, made the tops of the cylinders finally give way. I might guess that if the torque values were set lower for the Nickasils, they may have lasted longer or even indefinitely. Though I'm not sure how that would affect the required pre-loads on the head studs. That's just a guess.

Here's what I've decided to do: I'm going to tear the engine down and install all new bearings. When I took the cylinders off I found lots of nickel/aluminum residue in the cylinders. More than likely that stuff is in my oil, and the oil screen is not fine enough to get it out. More than one VW guru over the weekend has suggested that the bearings have either been compromised, or will become so soon. My front hub has been leaking oil. It used to be a little; but it's been increasing. It may be coincidental, but there also could be a connection (I checked and I have no blockage of the breather). THAT bearing is a bitch, since replacing it requires removing the prop hub. It's been suggested I just try flushing out the front bearing instead of removing it. I'm not sure about that one yet.

[rizzz]

The AeroVee cylinders are 92mm inside diameter. More than one source (like the above) claim that the cylinder walls are just too thin. And that's with standard steel cylinders. Aluminum, as in the Nickasil cylinders, would be worse.

Yep,
My local VW guy told me this as well, he prefers to go with either 94's or 90.5's but avoids 92's for that exact reason.
Standard 92mm barrels are just 90.5's bored out to 92mm, hence the thin walls, the case is still left as it would be for a 90.5 set.
(with the Nickasils I assume this means they're just "made" this way to also fit a 90.5mm case)

As you're tearing down your engine and replacing the cylinders/pistons anyway, you could have your case & heads machined further to accept 94's if you're uncomfortable with the wall thickness of the standard 92's.
They sell "thick wall 92's" which are 92's with a wall thick enough to slip into a 94mm machined case,
or,
If you're doing that anyway you could just go with a 94mm set of barrels/pistons and have a bit more total displacement like the 2276cc Great Plains engine (94x82). Everything else should still be the same.

(the machining work above should not cost you more than $150-$200: http://www.brothersvwmachineshop.com/machine.htm)

[wlarson861]

Glad to hear you are tearing it down all the way. I had the circlips score the cylinder walls of 3 cylinders. If I hadn't decided to replace my bearings I never would have seen that the oil passages in the crankshaft were mostly plugged by the shavings created when the circlips gouged the cylinder walls. If the oil carried that into the oil passages I'm sure the tolerances for the bearings were way gone. You probably didn't shed as much metal as I did but probably enough to damage the bearings.

[mike.smith]

I replaced my clips, but fortunately no damage. However, on the advice of other VW race engine builders, I'm planning to use teflon buttons on the wrist pins this time, instead of the clips. http://www.cbperformance.com/ProductDet ... tCode=1040

[DCASonex]

Mike,

Your analysis of repeatedly taking up head bolts is very similar to what happens with Jabiru engines where steel cylinder meets aluminum head. Early soft aluminum heads in particular have been destroyed by cylinders bedding in too deep. CAMit, with somewhat better grade of aluminum in heads, suggests that if head bolts take up when checked, engine has been running too hot. Only one head bolt on mine has moved since installed, and that only a few degrees so hoping I never see that problem.

David A Sonex TD #1327 with CAMit 3300