GCV190 Piston Ring Question

[JBtoro]

Opened up a GCV190 that was smoking badly. Surprisingly, the insides looked good, cylinder, piston, crankshaft, etc. However, there was excessive carbon build-up on the exhaust valve such that it wouldn't close all the way. Thinking that this may have been the cause of the smoking, I replaced it and now the valves are sealing good. But since I already had it apart, I also removed the piston to check end gap which I believe is acceptable according to spec. However, several days went by & I didn't pay enough attention to which was the top ring & which was the second ring because I figured that I could refer to the spec sheet when reassembling. But to my surprise, both rings look identical color-wise & there is no "dot" marking the top. Anybody run into this? Does this mean that this particular set of rings in essentially interchangeable?

 

[bertsmobile1]

If they are identical then it does not matter which way they go
Have a good look at the ends of the rings
If they are identical then as above
If one has a double champhur it goes on the top as per the curve shown in the diagram
If one has a single champher then that is the 2nd ring and the champher goes down.

 

[JBtoro]

With a magnifying glass, I examined the ends as you recommended. Did not detect a champhur. However, on closer inspection, I did see that one ring (bottom ring below) has a thin copper colored coating around it's circumference. That ring is also ever so slightly narrower (less wide) than the other.

 

[JBtoro]

If they are identical then it does not matter which way they go
Have a good look at the ends of the rings
If they are identical then as above
If one has a double champhur it goes on the top as per the curve shown in the diagram
If one has a single champher then that is the 2nd ring and the champher goes down.

I decided to use the ring with the copper-colored rim/edge as the 2nd ring. Honda for some reason differentiated it from the other ring and typically Honda colors the 2nd ring black vs chrome for the top ring for identification purposes. So, I reasoned that the copper ring is another way of letting the user know which is which. Otherwise, they appear to be the same; that is, no chamfer nor dot mark & very close in other dimensions. If you get a chance to see my reply yesterday, you can see what I'm talking about & I would be most grateful for you more experienced opinion. Thanks.

 

[Born2Mow]

Your question and answer have 2 parts...

1. Back in the 60's you might have seen a difference in #1 and #2 ring, but since about 1990 both top-most rings (on a 3 ring gasoline engine piston) are most always the same ring. If there is not a visual difference in the rings, then I wouldn't really worry if #2 got put on top by mistake. That part is not a big deal, unless there's a visual difference.

Honda sometimes supplies a shiny chrome ring for Top, and a black cast iron for Middle. Each ring material offers the engine a special capability. And so to have the best engine results in all circumstances, Honda includes one of each. Obviously it's more trouble and cost to do this, but Honda can demand a higher price.

2. However, look closely at the cross-section of the ring. If the ring is a perfect rectangle then you're OK. (Such as the Top ring in the graphic below.) But a lot of piston ring brands have a small notch cut off one of the inside corners. The notch usually goes to the bottom. (As shown in the Middle ring in the graphic below.)



That notch (whatever shape it happens to be) helps the ring expand and seal to the cylinder wall. If it's present, it must go down.

Hope this helps.

 

[JBtoro]

Your question and answer have 2 parts...

1. Back in the 60's you might have seen a difference in #1 and #2 ring, but since about 1990 both top-most rings (on a 3 ring gasoline engine piston) are most always the same ring. If there is not a visual difference in the rings, then I wouldn't really worry if #2 got put on top by mistake. That part is not a big deal, unless there's a visual difference.

Honda sometimes supplies a shiny chrome ring for Top, and a black cast iron for Middle. Each ring material offers the engine a special capability. And so to have the best engine results in all circumstances, Honda includes one of each. Obviously it's more trouble and cost to do this, but Honda can demand a higher price.

2. However, look closely at the cross-section of the ring. If the ring is a perfect rectangle then you're OK. (Such as the Top ring in the graphic below.) But a lot of piston ring brands have a small notch cut off one of the inside corners. The notch usually goes to the bottom. (As shown in the Middle ring in the graphic below.)

View attachment 56522

That notch (whatever shape it happens to be) helps the ring expand and seal to the cylinder wall. If it's present, it must go down.

Hope this helps.

It sure does help. thank you. Under a mag. glass there isn't a notch on either ring; the only real difference is that thin circumference of copper-coloring visible in the picture I posted previously. I got this engine in a trade & the original owner told me he hasn't performed a lot of maintenance, much less major surgery like putting in new rings. Thus, the rings I removed were the rings that came on the mower from Home Depot where he bought it new. Therefore, just as you explained, it appears that Honda saw fit to install undifferentiated 1 & 2 rings at the factory even though it supplies chrome/black rings as a replacement part.

I put the "copper" ring as # 2 but haven't tested things yet because I am still cleaning & reassembling the rest of the engine. Will post my results.