For what it’s worth, Nikasil lined air cooled aluminum cylinders used on motorcycle engines regularly go 100,000 miles with no visible wear and hone marks intact. These run at maybe 4,000 rpm on the motorway. Steel cylinders on older (pre-1980s typically) motorcycle engines do wear visibly in the same service.
People replace worn pistons in those Nikasil cylinders without touching the bore.
I have this from one engine shop:
So, the short answer is: it varies highly.
I looked up Nikasil. Why aren’t these coatings used in GA engines?
Peter wrote:
Why aren’t these coatings used in GA engines?
I remember having seen some companies which have this, might be thirdth party companies.
Peter wrote:
I looked up Nikasil. Why aren’t these coatings used in GA engines?
Rotax 912 has never had anything but Nikasil coated aluminium cylinders. I believe ULPower also has it, but im not sure, probably something similar, but not Nikasil as such, which is a trade name. Continental delivers engines with Nikasil (or same stuff, but different name). Their Titan Lycoming clones can be bought with Nikasil coated aluminium cylinders. The Carbon Cub EX come with this option as default.
Peter wrote:
I looked up Nikasil. Why aren’t these coatings used in GA engines?
Nikasil a coating for aluminum cylinders, deposited directly on the aluminum. I think all aluminum cylinders (no steel cylinder) would be a good direction for development on Lycomings, both from the point of view of potential wear resistance and reduced running clearance. The AX50 cylinders now available appear to have high silicon alloy replaceable liners, i.e. not Nikasil coating, but apparently can regardless be made to produce a lot of power.
Incidentally although I’ve never seen or heard of an issue with Nikasil on motorcycle engines, it was phased off a number of European car engines after problems with erosion by high sulfur auto fuels.
A little more info and discussion on the AX50 aluminum cylinder liners (or sleeves) here.
Apparently the design utilizes replaceable Nikasil coated aluminum sleeves in aluminum cylinders, versus directly Nikasil coating the bore of the cylinder as per automotive or Rotax practice. That seems like overkill to me, given that Nikasil coating can be redone commercially. Whether liner replacement would make sense at TBO (in other words overhauling and running the cylinders themselves for 4000 hrs or whatever, 2X TBO) would depend I suppose on the crack resistance and fatigue life that is demonstrated by these cylinders in service.
If I had need or opportunity and if they aren’t causing trouble in service, I’d like to try a set of these cylinders.
