richard_rip said:[post]360556[/post] I've just had a look through all the bits I've bought, the rings I use are indeed NPR :?
I'll see how they go with this engine given it's not the original engine. I get a lot of nitriding done through work, I wonder if I could get the chrome removed and then nitrided. Or I could look at getting the cylinders relined in steel?
The thing with material pairing is that you by design want to make one material softer and one harder to be able to predict the behaviour in advance. Chrome is very hard and so is nikasil so you don't know which one will let go and obviously you don't want the nikasil to let go.
Here you can download the NPR catalogue: http://www.npr-europe.com/index.php?article_id=3&clang=1 and then browse through it. There you will find the finish of the rings and some explanations about them. Since there is no set meant for puma 1.7 engine (factory designation is MHA/MHB) I advise to go and have a look at sets for Porsche 911 from say 1987-2000. Those engines are nikasiled as well as puma engine and have a look at finish of those piston rings to see about the material pairing.
Regarding the sleeving: if you do that, you have removed one big hurdle out of equation: then you can use the honda set without problems as that set is designed for cast iron block and that is what you will efectively have if you resleeve the engine. However, you may have noticed that there is really no space between cylinders and I am affraid the sleeving might warp the engine block.
I would just like to stress one thing out: the rings being NPR means nothing bad, as NPR is very good company and their products are top class (on par with Goetze or Mahle): the problem is that particular set is not designed for puma engine.
Since you are thinking about removng chrome and nitriting of rings, I really do believe it is easier to order that other set for Nissan engine (I gave the cat. number in previous post) and use it's 1st compresion ring as it is already nitrited. The second being phospated in Honda engine is quite OK to be used.
Regarding the 3rd (oil scraper): In Nissan set it is nitrated but the stated height is 2.5 mm and I believe it is somehow to low. It is a 3 piece design so I guess you could use the rings form the Nissan set (again, they are nitrited) and the spring element either from existing puma or from Honda set to bring the rings to desired height.
IMHO that would be much easier and cheaper route than either sleeving or modifying the rings from Honda set (the chromed ones)