The Stovebolt Site Forums The Shop Area Engine Shop measuring piston rings

Hello.
On the piston rings, do I measure the gap between the two ends of the ring where they come together in the cylinder
AND
do you also measure the distance between the ring and the groove of the piston?
Thanks
Judson

Yes, and yes. There will be specifications for minimum ring end gap, but the maximum gap can be much larger without a problem. The clearance between the ring and the piston is pretty critical, as worn ring lands will allow the rings to flop up and down and possibly break. Specifications for both ring gap and groove clearance will be in any good service manual.
Jerry

Hy Judson, yes you should check both specifications, if your working with a freshly bored cylinder and new pistons the job is a little easier. Use a piston inverted to position the piston ring square in the bore to measure the end gap, measuring the ring groove clearance involves holding a ring in the appropriate groove and measuring the clearance with a feeler gauge. Should you find your end gap to be too tight they can be "filed" to increase the gap, a word of caution if you happen to have "moly" filled rings I would take the rings to an automotive machine shop to have the pros make the needed adjustments, hope that helps.

Thanks, guys. That helps.

Ive taken the pistons and rings out...ordered new ones from NAPA. Ill go tomorrow and see if they are the correct ones.

I was suprised when I took the rings off, my #1 compression ring on top had only one ring, but the #2 compression ring had the compression ring (fatter), a small thin ring on the bottom, and then some type of hexagonal looking ring behind them. The #3 ring (oil) also had that same hexagonal looking ring behind.

When I measure distance from the piston groove to the ring, I assume you measure it with all of the ring in the groove?

Im not doing anything fancy like re boring the cylinders, just trying to replace the rings for compression.

Thanks,

Judson

Do you have a ball hone to take the glaze off the cylinder walls?

Once you hone the cylinders, be sure to wash them really good, you can use cleaner of your choice, but then you are done you should be able to wipe each cylinder wall with a clean white towel and still have a clean towel. If you get a dirty towel, you didn't clean enough. The grit must be removed so the rings do not wear to quickly. The pattern from the hone will seat the rings. Use quick up and down motion while spinning at a medium speed, not to fast. I use a heavy duty 1/2" drill, full speed is just right. Smaller 3/8" drills go to fast. I spray thin oil in the holes as I am honing, you need enough to wash away some of the grit and some to lube the hone, not sure you can get to much. When done right, you should need to wash the whole block. Don't try it with crank in place, and don't try to bore the holes out. A hone is just for taking the shine off.

Joe

What rings are you using? I don't know of any multiple piece compression rings in the second groove. Don't take that too seriously it just means I have not seen them. Lots of things I have never seen. Just curious. To me it sounds like 2 sets of oil control rings and only 1 compression ring in the top groove. Like I said I can be wrong and have been many times.

Thanks, Joe. will do. Judson

Steve,

Your question is a good one, and I am kind of wondering if someone before me did it differently and/or wrong before-because when I look in the manual it does not really say how many rings are in each groove.

I know the bottom ring is an oil ring because it has the oil grooves in it, and I think the second ring is a compression ring because its a thicker, fatter ring-but those hexagonal looking rings that sit behind the rings threw me off.Its almost like a backup ring to push the outer rings out more.

Has anyone any experience with these rings on a 41 engine-216? Are there three rings on both the second and third grooves?

Thanks,

Judson

Do you have iron pistons? I have never worked on that style engine so like I said it might be something I have never seen before. You are at about the right time in Chevy's history to have either kind. I don't know just when and for what models the change occurred. But I would bet that the rings would be different for cast iron pistons and aluminum pistons. Some one on here will know and that is what is so great about this site. Iron pistons might very well have had rings like you describe. Oil control would be very different with each type of piston.

....I may not remember correctly so this is an opinion. Back years ago when I worked at the Chevy dealer as a kid it seems I remember a couple of the mechanics rebuilding and old engine and talked about the ring groove being to wide....or the ring was to thin.... so they used a spacer to "tighten up" the ring so there would be no "slop" in the ring/ring groove.
Someone correct me if I'm wrong and I'll delete this. Don't want to lead anyone astray.

You remember right, Alvin- - - -it was not uncommon to repair a piston with a worn ring land by using a special cutter to square it up and putting a spacer under the ring to get the clearance right. The middle ring is called a "scraper" ring, and it seals compression on the upstroke and twists to scrape any oil the oil control ring missed on the downstroke. It's not uncommon to find a tensioner ring behind the scraper on some ring sets, especially on heavy duty truck applications.
Jerry

I think you guys are right on.

When I went to NAPA to pick up the new rings, they gave me the standard compression rings (1 for the top two groves each) and the oil scraper ring with the two smaller rings that line the top and bottom.

I think that ring that was in the back of the setup I pulled out(the hexagonal ring) must have been what Lincoln was referring too-a ring that improves tension.

The second, thinner ring on the second groove must have been to make up the distance in the groove because it was much smaller in width than the new compression ring. The new compression ring fits snug. The old one jumped around alot it there.

Perhaps there was more to not having compression on the engine than a simple valve job. Perhaps the rings were bad as well.

Thanks all!

Judson

I think your getting the cart ahead of the horse with your project. Have you determined if the bore is straight? How about is it standard size? Checked the ring lands in the pistons to make sure they are not worn out? I have a link below with some basic information to read about piston rings that may give you some insight. I'm not trying to rain on your parade, just don't like to see someone put alot of time and money into a project to have it end up being a mess. Don



http://en.wikipedia.org/wiki/Piston_ring

Thanks, Don. No worries. Its good to learn all I can as I go through this process.

Im kind of at a stand still right now because I want to clear out those oil lines before putting the pistons back in and putting the head back on, but I guess to do that properly I need to pull the crank.I was told that if I blow compressed air through the lines as it is now (with the crank in)all the gunk will accumulate at the crank.

Ive been looking on youtube at the video riding the film to try and better understand the 216 oil flow. But if I pull the crank, I think I should pull the engine and I do not have a hoist or stand yet. Ive been working from underneath the car up to this point, so Im at a crossroads. I could put it together and hope the oil lines are not clogged, or I could wait until I have a stand and hoist and pull the engine and crank. If I pull the crank I could also do the plastigauge measurements....

You would probably do yourself a favor to take it out and follow through doing everything.

what are your thoughts on removing the oil distributor? Is that possible/helpful?

You will destroy the oil distributor tube trying to remove it. It's a one-time installation. There are kits with all the hardware necessary to replace the tube, however.
Jerry

oh. good to know and im glad i asked. sometimes it feel stupid asking questions like this one, but I had already taken off the cover so I will put it back on and not go any further. Thanks again! Judson

Asking questions beforehand is always better. If more people would do that, fewer mistakes would be made.
Jerry

so, today I took the piston rings I bought from NAPA and put them in the cylinder with the top of the piston 2in. down the cylinder like the manual says.

According to the manual, the gap should be from .005 to .015. My gap was at least .022-to big!

So I have a few questions now.

1. Is it possible someone rebored my engine already and the pistons are not stock size?

2. Do all cylinders and pistons have to be the same size-i.e. cylinder 6 would not be bigger than cylinder 1, correct?

3. On the first piston head there is a marking 030-do you think that is my piston size? Otherwise, how do I find the right rings for the pistons I have?

Thanks,

Judson

Your ring gap is exponentially proportional to the bore size. Even an increase/decrease of just .001" can change the gap significantly. If the piston to cylinder wall clearance is at or near the max, so will the ring gap. From what you mentioned was stamped on top of your piston, that would surely indicate the overbore size of the engine, so if your trying to install standard bore size rings in it, that is your problem. To remove all doubt, just mic the piston to verify its size.

030 stamped on top of the piston would tell me it's 30 thousands oversize...that cylinder has been bored. Check the others for the same markings...as 12 Port suggested, mic the piston to be sure what you have. If you don't have mic's take it to a machine shop and ask them to check them for you.

Mike B

not only is it possible, but extremely likely your engine has been rebuilt. The .030 stamped on the piston is pretty much proof of that. Yes you can have cylinders different sizes, I wouldn't recommend it, but yes it is possible. You should get a manual, which is available from nearly any of the normal vendors, or you can go to "OLD ONLINE CHEVY MANUALS" nearly all the manuals are available there. It is quite obvious you are new to this, you need to ask lots of questions. Keep in mind this hobby can get pretty expensive, and if you aren't absolutely sure of what you are doing, you can waste a lot of money really quick. I would also recommend that you take the engine out.

Take the piston marked .030 and try to insert it in the other cylinders. Upside down from the top is OK. If it fits all the other holes, go swap those standard-size rings for a .030" oversize set.

It sounds like you are in WAY over your head on this engine rebuild. Is it possible to find a mentor somewhere nearby to assist you with the basic measurements, cleanup, and assembly procedures? Just a few rookie mistakes along the way can torpedo an otherwise simple engine rebuild. Although the guys here are very good at answering questions, we might assume you're doing something we consider to be routine and fail to mention it to you.

Good luck, and keep asking about anything you don't fully understand!
Jerry

Yes, you have a .030" over sized bore. You will have .007" to .010" ring gaps with .030" rings.

Go back and get .030" rings and you should be fine.

Just to be sure, check all six holes or pistons, someone at some point might have bored just one hole.

Joe

Thanks, guys! I found over sized .030 rings at NAPA-simple exchange. Ill try them out. Thanks again. Judson

if the ring overlaps, is it too big? I know you can file them down, but if its already overlapping does it mean go down a size?

can u use .020/.010 oversize rings on pistons stamped .030?

In racing stuff where you have a true file fit ring that you custom fit to each cylinder, the overall ring diameter can't be more than about .005 larger/smaller than the bore of the cylinder, or the rings radius will be too large/small to seat all the way around the cylinder. If you have a .010" or .020" oversize ring and your cylinder is .030" overbore, those rings will have a radius too small to work, even if you get the gap where it needs to be.

At this point you should find someone with stuff to measure your cylinder bore diameter for you. Your guessing at things that should never be guessed. Also measure each piston, then see you will know what you have.

thanks, guys. will do.