Thread: ring gap questions

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I read that most prefit piston ring sets are undersized by up to +.030. I am
guilty on just slippin the rings on in the past, thinking they were right for the application from the factory. I know now that .016 to .018 is a correct gap to use. Is it true that you can give away 20-30 hp by not checking end gap?
Does any brand offer correct prefit sizeing or is it file fit from now on? Thanks.

I don't know about the rest of these guys, but I never assume anything when it comes to building a motor. I measure everything and in the case of pistons and rings, I talk to the manufacturer and get the recommended gaps for the application I'm building. Leave nothing to chance and you'll have no bad encounters.

Just like with cams. NEVER, NEVER purchase a cam based on the information you get on this or any other forum. Many of us can get you close and you can compare cams from grinder to grinder based on the knowledge gained here, but before you lay down your hard-earned green, talk with a tech at the cam grinder, not a tech at summit or jegs.

Originally Posted by techinspector1

I don't know about the rest of these guys, but I never assume anything when it comes to building a motor. I measure everything and in the case of pistons and rings, I talk to the manufacturer and get the recommended gaps for the application I'm building. Leave nothing to chance and you'll have no bad encounters.

Just like with cams. NEVER, NEVER purchase a cam based on the information you get on this or any other forum. Many of us can get you close and you can compare cams from grinder to grinder based on the knowledge gained here, but before you lay down your hard-earned green, talk with a tech at the cam grinder, not a tech at summit or jegs.

Words of wisdom, Read and Heed!!!!

Assuming anything out of the box is correct can be a very costly assumption. Using Denny's method, it doesnt' take a whole lot of time to verify the ring gap. Same goes for the rest of the engine parts, verify the correct fit before you do the final assembly!!!!

I was reading a book on how to balance and blueprint a chevy sb, by Rick Voegelin, but it was a 1988 edition.. so I guess some things never change.
TRW and Sealed Power are stated as the only two who make oversize, .005, file fit sets. I know this still isnt the case. Would anyone like to make a recommendation on who makes quality sets that are affordable. I imagine C & A make them, but I bet they are expensive.

This is real elementary stuff and you probably know it already. I sure don't mean to insult you, but make certain that your rings are properly "clocked" (the gaps are properly spaced around the piston and not neatly lined up in a row), and the oil ring spacer gap should be lined up with the piston pin toward the rear of the engine.

Also, make sure your oil rings are installed correctly with the spacer stopper pins facing in.

Take it from somebody who has done it wrong despite having a piece of paper from the navy saying that he is an engine mechanic.

Jim

Good stuff guys. I'm printing it and putting it in my home-made assembly manual. I hope thats all right with you guys.

Posted by Denny:
"Some racers believe that opening up the 2nd end gap even more (say an additional 10%) can improve overall ring sealing by allowing trapped gases to escape before they blow past the top ring and cause ring flutter at high rpm (say above 5000 to 6000 rpm)."

What's alluded to here is that the rings seal on the bottom of the ring against the flat shelf of the ring land. Blow-by past the cylinder wall/ring face junction of the top ring can cause a pressure build-up between the first and second ring and can apply enough pressure to unseat the top ring off the ring land and eliminate the seal. By allowing a little extra room for these gases to exit past the second ring and into the crankcase, the integrity of the top ring seal at the ring land is assured.

You know you guys are gonna make me tear my 440 apart again, don't ya!

I run a gapless compression ring, love em. Probably not recomended for daily driver type engines, but it sure works great on the go-fast stuff....

Dave how does that work, just curious.

Running wide ring gaps has negligeable effect on blow-by and oil consumption. When I built my 350, I ran .030" on top and .018" for the mid and oil control rings. I don't burn any noticeable amount of oil within my 5000 mile change interval.

Hey Dave , I was just being lazy on ya. I went to Total Seal and read up on the gapless setup, works great I suppose, but MAN! they are expensive!

As in, I see no difference on the stick when I change the oil. I'm not paranoid enough to actually measure the amount of oil that goes in and what comes out. I run my motor full throttle all of the time, it's too fun not to. I built it 2 summers ago and it's got 20k miles on it now. I've been running a fairly light oil, 10w30. I switched to 15w40 on the last change because I like the extra EP additives like zinc and phosphate. I almost a quart within the first 1200 by my first oil change. Afterwards, I haven't burned anything.

Originally Posted by techinspector1

Posted by Denny:
"Some racers believe that opening up the 2nd end gap even more (say an additional 10%) can improve overall ring sealing by allowing trapped gases to escape before they blow past the top ring and cause ring flutter at high rpm (say above 5000 to 6000 rpm)."

What's alluded to here is that the rings seal on the bottom of the ring against the flat shelf of the ring land. Blow-by past the cylinder wall/ring face junction of the top ring can cause a pressure build-up between the first and second ring and can apply enough pressure to unseat the top ring off the ring land and eliminate the seal. By allowing a little extra room for these gases to exit past the second ring and into the crankcase, the integrity of the top ring seal at the ring land is assured.

ok i was not going to post and tell anyone how i do it. but ths is how i do all the HP engines i build i have used the gapless rings ? there to much money and not really like the way they are made? think your are better with some blow down the walls helps keep the pressure from working the rings off the walls

Interesting. Well at this point I'm in favor of testing each bore for taper, trying to nail the .016-.018 for the top ring, adjusting the 2nd ring and run a standard oil (vs. low tension). Unless someone sways me from here, thats how I'll work it for now. I wonder how Eric does his???