Piston Rings Vs Cylinder Surface

[Samal Yb]

Dear Guy Croft, I have rebored my Honda D16Z6 engine. Now the cylinder diameter is 75,5mm (used to be 75mm). Right, so, for doing that I put Akuro new pistons, set the clearance to 0.025mm (0.01mm to 0.04mm which is recommended by Honda), the pistons fit perfectly and the job was very well done (the hone pattern too). Then I noticed that my new piston groves are more tight! I opened the NPR piston rings set SWH30363ZZ, and there are NOT like the old ones. Now I have 1mm, 1.2mm, and 2.8mm and the old rings where 1.25, 1.5 and 2.8mm. The compose is obviously not the same, but the dealer assure me the rings are OK and will break in a correct way in my steel cylinders (not nikasil, not chrome, not nitriding compose). The rings fit and have the wanted clearance in the piston grooves, but the compose of the rings is so different looking the olds one, that's why I'm holding the assembling. The first ring, in place of have chrome and steel, has got a red steel and no chrome (cast iron look like in the contact surface), the second one, in place of Cast iron have nitriding compose (all black)
I need to confirm that this kind of rings will break-in properly in the steel cylinder. I have spended a lot of money on it and don't want to wast it out again.






I will really appreciate your response.


Here some photos of the entire work of the engine. (Now is laying in my dining room).





















Thanks!


Samal.

[Guy Croft]

Ivan, hi

first thing I want to say is no-one uses uncoated steel liners. Steel has no oil retention at all. If they are not coated with some chrome-carbide-cobalt or Nicasil - or are not plain cast iron you cannot use them at all. If you hone steel liners that were originally coated - they have to be, well, recoated...

As for the rings:

Now I have 1mm, 1.2mm, and 2.8mm and the old rings where 1.25, 1.5 and 2.8mm.

Now - if this is correct you are going to have way too much side clearance, on rings 1 and 2 you've got 10 thou" and 12 thou" (0.009", 0.012!) which is 4 times or more what you should run. That will cause very severe ring and groove wear as they fly up and down in the grooves.

For the record: The honing finish is based on the compression ring (the top one) and for ductile iron top rings (which is what they most likely are from NPR, maybe with molybdenum inlay) it's 240 grade, for chrome faced/plated it's 180 grade. Silicon carbide Flexhone should be used, that is the optimum way to control the finish. If you go too fine on chrome they will never bed in.

Those issues of ring thickness and bore material need to be urgently addressed. The dealer is wrong, to put it politely.

GC

[Samal Yb]

Dear Guy Croft:

My Cylinders were steel finish (same honing pattern that I have now). Now I'm 100% sure that I must find the NPR Chrome rings.

The Groves in the piston are 1mm, 1.2mm and 2.8mm, the clearance of the rings in the desired for Honda's shop manual.


I really appreciate your response.




Iván.

[Guy Croft]

I think you may be confusing cast-iron and steel. Sure, they look similar. If your liners are really steel, you're in trouble.


GC

PS _edited your post slightly, be careful what you say here please..

[Samal Yb]

The Engine's manual just describe the process of re-bore and honing. It doesn't say anything about any coat.


I Think by putting chrome rings, it will break-in properly.


Thanks!


Ivan.