piston gaps as big as my front teeth gaps

lt4ever · 10-26-2005, 12:49 PM

Alright... for all you seasoned engine builders or for that matter anyone who's ever filed a set of piston rings... how dead nutz do you have to be on setting the appropriate gaps?

I just got my LT1 383 block back from the machinist who did all the necessary work (ie. internal balancing of rotating assembly, clearanced block, magnafluxed, blah-blah-blah). Well, I'm trying to achieve 0.018 clearance for the top ring and 0.020 for the bottom ring. I've never file fit a set of rings before... so I'm a little new to this process. I might be a smidge over on a few rings and one bottom ring is way over... at 0.027!! I'm not sure if I need to buy a new set of rings or if I'm being way to anal about this...

**ncbandit75** · 11-02-2005, 01:17 PM

should be aight , 351 my dad and his buddy done , they filed the rings down like crazy he had like 215 pounds on each cylinder.

**ncbandit75** · 11-02-2005, 01:21 PM

compression!!

lt4ever · 11-03-2005, 05:07 AM

Yeah, i've heard that besides a hefty oil blow-by that will leave huge amounts of burnt carbon deposits on the top of the piston from the oil, that the cylinder may not hold compression as well. But I guess that's better than getting them to small and not filing enough, b/c too small of piston ring gaps will increase the piston temperature which could lead to detenation. But with too big of ring gaps it will lead to an increase in carbon deposit on top of the piston and can eventually lead to a decrease in combustion chamber size, thereby increasing your compression ratio. As it turns out, you can buy individual rings from JE Pistons rather than buying a whole new set. So, I bought a top and bottom ring, but it also comes with the oil rings and oil ring rails for $25.00 which I don't really need. Guess I'll refile fit that ring that's way over and be gentle with it this time.

LS1ROC · 11-11-2005, 01:25 PM

You really need to follow the GM specs on this one. Or contact the ring company.....i meann its do it right or take the engine out later when it has no compression . And whatever you do .........be careful and space the ring gaps out right.......I have screwed it up before....YOU DONT WANT THAT......

**5.0THIS** · 11-11-2005, 11:47 PM

Well, typically you're not doing anything with the oil control ring(s).... You havent done any of those have you? I have filed several sets of file fit PM rings for our race motors. It is just a time consuming process. It's a matter of taking a little at a time and rechecking so you dont go over

Anyway... THere probably wont be too much difference on that one cylinder as long as you have the rings clocked correctly. If you're a few thousanths or less over on a couple of them I wouldnt worry about it, but more than 5 thousanths and I wouldnt leave it in there on a high mileage street motor. Get the ring manufacturers opinion on it.. they will know best... Also, make sure after you've got a ring to the correct gap that you dress up the edges of where the ring grinds against the cutting surface, because you are leaving a small ridge.

lt4ever · 11-14-2005, 05:15 AM

appreciate the insight. Thanks! No, no... I"m only gringing the top and second compression oil rings. I'm not grinding the oil ring rails. Well, after I got a new couple of individual rings in, I grinded them with about 3-5 strokes on the file between each test fit. Takes a long ass time, your right! But now they're spec on. The biggest gap on one of my top rings is only +0.003 over and about +0.002 over on a bottom ring. I'm confortable with those. I didn't deburr the edge of the ring that I filed, b/c I didn't want to take chips out of the chromoloy. Someone told me that would be bad. (any truth to that!?) However, I wonder if I even created I ridge when I filed, b/c I only filed from the outside towards the center of the ring and only went in that one direction with each pass over the file. Do you think there's still a ridge that could cause scrapping on the cylinder walls???

**5.0THIS** · 11-14-2005, 10:33 PM

Originally Posted by lt4ever

appreciate the insight. Thanks! No, no... I"m only gringing the top and second compression oil rings. I'm not grinding the oil ring rails. Well, after I got a new couple of individual rings in, I grinded them with about 3-5 strokes on the file between each test fit. Takes a long ass time, your right! But now they're spec on. The biggest gap on one of my top rings is only +0.003 over and about +0.002 over on a bottom ring. I'm confortable with those. I didn't deburr the edge of the ring that I filed, b/c I didn't want to take chips out of the chromoloy. Someone told me that would be bad. (any truth to that!?) However, I wonder if I even created I ridge when I filed, b/c I only filed from the outside towards the center of the ring and only went in that one direction with each pass over the file. Do you think there's still a ridge that could cause scrapping on the cylinder walls???

It's just one of those little things you can do to help the rings seat properly. It may not make a big difference in a street motor... For me it's just something I have picked up after listening to some of the pros in my area that also build racing motors. Typically to do rings you use a tool that is specifically made to grind rings. It is a small abrasive wheel, either hand turned or driven by a motor, with a small platform around it to ensure you keep the ring flat, and the grinding straight. Not sure if you used one of these, but what tool you used to file the rings will determine how much of a possible ridge you have left. Even when I've only taken a light pass on a ring, sometimes you can feel the small ridge with your finger.... Your call though... maybe they dont need it. If you clean them up properly, you wont damage the ring material.

lt4ever · 11-15-2005, 05:40 AM

I just used a standard shop flat metal file that I put in my bench vise. I was careful to try and keep the filed edge as straight as possible as well. I thought about buying one of those ring grinders, but since I don't build engines for a living, I figured my need for one didn't outweigh the cost. But now I've got a whole new set of issues. I'm driving myself nutz trying to remember if I installed the bottom oil ring rail support ring in the right direction (anti-rotational dimple facing down). I'm thinking I'd better take the pistons out and check and side with caution, just in case. I'd hate to melt a piston for something that could've been easily prevented.