I have a 1997 XK8 that dropped a valve. Some slight scoring in the cylinder. Can a Nikasil cylinder be honed? What happens if you don't and just replace the piston?
Thanks,
JAY111

 

You can but I wouldn't recomend it. I am under the understanding that the pistons and cylinder linings in the 4.0 are both aluminium so the Nikasil lining on the cylinder lining prevents the aluminium pistons and lining wearing each other out. Without the coating they will wear each other much faster. If you have wearing already though you will need steel liners inserted I should think.

 

^^ Agreed, and it appears you would also need some specialised equipment. The coating is very thin (.0025" - .0003") apparently.

Can you post a pic of the damage? One of the gurus here could likely provide a steer.

 

no

 

^^^^^^ This !


your realistic choices are to leave it alone and drive it with the scratch or install a replacement block.

honing the cylinder will degrade the coating and cause you worse issues.

Z

 

There are companies which specialize in honing and replacing the Nikasil cylinder coating. It is costly, but can be done. They can also plate the pistons themselves.
Millennium Technologies

 

If you leave it then you should ensure you have the correct oil level as this was raised by 1 quart for early models. Gives more splash onto the cylinder walls. I have added molybdenum additive as I have piston slap on one cylinder and these two measures have largely eliminated the problem.

 

In the early 2000s I collected a few worn AJ27 engines with extreme blowby (failed nikasil) when I worked at the dealer.
Took a block to a machine shop I used for a few decades because the guy knew what he was doing.
He said he could 'sleeve' all the cylinders for about $60 per hole.
He installed steel sleeves and I bought a set of piston rings for the steel sleeves. (not the low tension nikasil rings)

I put the engine together and I still have 20 years later it but I never installed it into anything.

It turns over by hand but I should get it running. I just have too many projects.

 

My crazy idea is that if and when the time comes that the cylinder walls need to be honed on my engine, i will consider adding the Nikasil cylinder coating if possible. To my knowledge this is becoming common in performance builds.
Note that where the coating is already present, engines needing a mild refresh often do not have cylinder wear requiring honing and re plating. This material is that durable.

 

Do you still have the engine? Is it for sale?
If so how much?
Thanks, JAY111

 

will a 1999 AJ27engine block work in a 1997 AJ26?
Thanks, JAY111

 

I just wanted to add a few facts that I remember from engine plant. It may help answer your question.

The Nikasil coating was sprayed on as a molten metal alloy and the average thickness of application was 100 microns (0.1mm).
Some people may think this is very thin but it is way harder than any other engine block material or liner. It was state-of-the-art back then and, to be frank, it is still considered superior.
The bore face was so hard that conventional honing tools could not touch it and only expensive Diamond finishers with 10 radial stones were used.
Coating thickness was reduced by 8 microns (0.008mm) per cycle. The honing and gauging process was automatic and many bores required 2 cycles until gauge diameter was reached. The consensus was that finished coatings was circa 70-80 microns thick (same as human hair) but manufacturing variation introduces a big question mark.
I think with the right machine and diamond tool you can re-hone the bore perhaps a max of 10 micron removal. But this may not remove your visible scratches. Obviously, the risk of breaching the coat thickness gets higher with every hone cycle you take and it's possible that your scratches have already compromised the coating....