Hi, im rebuilding a B18C6 (EDM type-r) because of burning oil and low compression. Stock rebuild not all motor, boost...
-Cylinders look really nice when disassembled, it was cylinders honed and resurfaced in a Honda specialist in my country.
-Oem 81mm pistons de-carbonized
-Npr piston rings 81mm std.

I checked gap with new npr and old oem rings.

1st npr ring is 0.5 mm ring gap, oem is 0.4mm; service manual say it will be (0.2/0.35 new ring and 0.6 service limit)
2nd npr ring is 1.04 mm ring gap, oem is 0.65mm; service manual say it will be (0.4/0.55 new ring and 0.7 service limit)
3rd npr ring is 0.45 mm ring gap, oem is 0.4 mm service manual say it will be (0.2/0.5 new ring and 0.7 service limit)

Are normal this widths with npr rings? I sent a message to my dealer, because of this, 2nd ring is completly out of specs.

Many thanks.

 

Not sure about npr rings but they should not in general be that off, sounds to me like it is for a different bore.

 

Cylinder bores are:
1-81,04mm
2-81,04mm
3-81,05mm
4-81,04mm

​​​​​​Service manual std new is 81,00-81,02. Service limit 81,07.

I checked ring gap in different depths with same numbers in all cylinders.

 

sounds like you got a bad ring since the bores are all within spec. Just have them send you a new ring pack and you should be set.

 

 

It sounds to me like the motor is not together and this is actual measurements while building. I'm not sure how your post about a running motor symptoms applies to a motor in the process of being assembled.

 

I send some e-mails to my dealer here in europe and to npr-japan:

My dealer:
Hi, in our opinion, NPR rings seem to be designed for “fit and forget” rather than “file and fit”. If you wish, we can also contact NPR’s support team but I will warn you not to expect a fast reply. Alternatively, you can send them back for a refund as they do not meet your requirements (we cannot do much about NPR’s tolerances, we are a reseller not the manufacturer in this case), thanks.

NPR-Japan:
Thank you very much for your e-mail.

We would like to investigate this NPR piston ring Part No. SWH30373ZZ that you
bought.
Could you courier us this ring with packages (box and label), please?
We are willing to cover the shipping charge.
We look forward to hearing from you.

Im going to buy OEM Honda and send back to my dealer, anyway i send meassurements to NPR-Japan.

 

You should send the ring package to NPR and let them investigate. Your dealer likely won't do that and NPR will not get a chance to improve their products. They are willing to cover the freight, and NPR will quite likely send you another set on their dime so you will be out nothing and get a good set of rings.

 

I ran into this issue when buying oversized NPR for B18C1. Nearly all the rings were beyond service limit, my limited research showed that people didn't seem to care and just used them. I never returned the rings or installed them.

 

send them back and get a new set, simple or take a chance and run these, since the gap is much wider expect more oil burning and white smoke at least from that cylinder.

 

I had ordered hastings/manning rings, these were way out of spec for 81mm - too loose. Mannings rings folks said that is how they are meant to be - ordered npr they were perfect. I think you got a bad batch.

 

Finally received new oem rings, gaps are fine with these.