Mixing different types of piston rings

[badeaslava]

SO this is a question for the engine builders that know their way around piston rings. I have a gs650 that i'm doing an engine rebuild including replacing piston rings. As far as i can tell from the suzuki manual they have 2 types of piston ring sets "R" and "N" and those differ only by the shape of the oil ring spacer (the 3rd ring). The difference in the shape of the ring is illustrated in the attachment, taken from the manual. The manual says strictly "do not mix the "N" and "R" type rings".

Now here's my problem, during my installation of new piston rings I broke one new middle ring (also known as the "oil scraper ring"), this is due to my own mistake and does not reflect the quality of the rings in any way. So i figured I would use one of my old middle rings instead of the broken one, it wasn't really worn down as the bike only has 17K miles on it. However it seems that my old piston rings are "N" type and the new ones are "R" type. Thus it seems like I am mixing the different types of rings together on 1 piston (type "R" compression ring, type "N" scraper ring, and type "R" oil ring). The manual says not to do it, anyone know why? Any problems i'll get down the line with this mixing these rings on 1 piston ( the other 3 have all new ring sets)?

Thanks in advance!

 

[Datsa Noydb]

I am not the "expert" that some of the other guys are, but I would guess that they are meaning to not mix the different components of the oil rings. The two types of rings look similar, but the spreader is different, meaning that the "N" rings can not be used with "R" spreaders and vice versa.

I could be wrong (again) but that is my guess.

 

[GregT]

The oil scraper (2nd ring) and the oil ring below are designed to work as a set. From memory the 2nd rings differ in that one type has a taper face and the other doesn't. Again from memory the top ring in both types is a plain parallel chrome face ring so both types should be similar there.
At this end of the world we do occasionally have to mix things up due to poor supply lines etc so I'm prepared to go out on a limb and say that a "N" 2nd ring and oil ring set used with an "R" set top ring should be OK.

 

[badeaslava]

The oil scraper (2nd ring) and the oil ring below are designed to work as a set. From memory the 2nd rings differ in that one type has a taper face and the other doesn't. Again from memory the top ring in both types is a plain parallel chrome face ring so both types should be similar there.
At this end of the world we do occasionally have to mix things up due to poor supply lines etc so I'm prepared to go out on a limb and say that a "N" 2nd ring and oil ring set used with an "R" set top ring should be OK.

Greg I actually have an oil ring and top rings that are "R" and the scraper being "N". I suspect that would not be ok? i checked the old scraper rings type "N" under a microscope and they don't seem to have any taper either, just like the new "R" type. Maybe the taper got ground down after years of use...

If i leave it the way it is, will just eat tons of oil? or the bore will not be oiled properly?

 

[gearhead13]

I would think of it this way: are you prepared to tear the top end apart again if it does burn oil? Or would you be ok if it did burn oil? How much is one set of rings? Is it a time problem?

 

[badeaslava]

I guess it's a matter of curiosity for me at this point. New set of piston rings go for about $40, and i would rather not pay that if i could. Burning a bit of oil in one cylinder due to the scraper ring being not of the same type is not a big deal, on the other hand if the bore is not lubricated well and causes excessive wear on the rings and piston that's a bigger deal. So I suppose i'm just trying to make sense of how it all works together, because as I mentioned when i looked at the profile of an old scraper ring from my bike, it looked very much square just like the new one that i broke.

So the bottom line is that I know that the rule is use the same type of rings, but i'm questioning the underlying cause of that rule. I thought maybe some of you guys on the forum might have insight into that.

 

[JJ]

Just spend the $40 and do it right...

I can't believe you'd rather have an oil-burner than to do it right.

 

[storm 64]

Just spend the $40 and do it right...

Heck, I'll give you the 40 bucks to do it right!

 

[badeaslava]

Hello everyone, thanks for all the input on the thread, it's been quite informative. I don't mean any disrespect, but I am a firm believer of doing things "right" but not necessarily by the book, but by the underlying principles behind the "book". This is why i was asking all these questions regarding different piston rings/shapes etc. So again i checked the old "scraper" rings on the microscope yesterday and i can definitely see that they had a taper a long time ago, probably during install, but 18k miles (on the bike) later the tapers are completely ground down to a rectangular profile on the scraper ring. This is why they looked identical to my new type "R" rings in cross section. So I believe at this point in their life the old "N" type scraper rings are for all intents and purposes functionally the same as the new "R" types, thus installed with an "R" type oil ring "should" function exactly the same.

So I will take the risk and keep 1 old "scraper" ring in there. I'll keep checking the compression once I start riding the bike after a proper "break in" cycle and if this particular cylinder behaves worse than the other 3, I'll update this thread with my results.

Thanks to everyone for their input!