Pistons won't fit back in my 3.1

[abob]

Ok so i started to put together my 3.1 and everything was going great until I went to put the pistons back in with new rings. I bought Hastings Piston rings (part # 4456). I figured the were just being a little stubborn at first so I try tapping a little hard but that did work.
Well for kicks I grabbed an old piston ( old rings and all) and decided to put it in. Surprisingly it went right in without much force. I need to know what the hell is going on. I'd like to get my 91 Cavy on the road again.

Thanks in advance for the help

[asylummotorsports]

Do you have new pistons and new rings or just new rings.

Did you check actual piston size? (Will the piston fit without rings installed?)

Did you check end gap on the rings to make sure they aren't butting together?

[3400-95-Modified]

You are using a piston ring compressor right? and torquing that sucker down tight right?

[95Grand-Am]

Did you clean the ring grooves in the pistons? The new rings may not be able to push into the grooves because of carbon build up.

[abob]

Yah I'm using the piston ring compressor to put them in. I'm not really sure what's going on. I can take 1 of the pistons with the old rings on it and it goes right in, but when I take the same piston with new rings on it the piston gets stuck right after the last ring goes into the cylinder.
I'm just running new rings. I tried putting one of the rings in by itself and it seemed fine.
I used a strange looking tool to clean the ring grooves. (the one ment for it).
I'm going to see if I can warranty them out and get a different set just to see if I got the wrong rings in the right box. That's been happening to me a lot lately

[TiredGXP]

did you check ring end gap?

[55trucker]

By the last ring....do you mean the top compression ring?.....if you take one of the new rings and one of the old rings and then insert them together squarely down into a cylinder (with the top of a piston) do they both go in?...and does the new ring have the same end gap as the old one?

[60dgrzbelow0]

Its been said that "If you are Nearly Correct... then you are Precisely Wrong...". This idea was never more in evidence than when trying to match hollow engine cylinders with pistons and rings for an accurate match without being too loose and sloppy or too tight and binding or seizing. You don't say what the mileage on your engine was or the reason you decided to do the re-build...but after a considerable amount of up and down motion, with the rings either expanding to fill the areas in your cylinders that are worn wide (mostly near TDC) or contracting as they approach BDC where the transition forces are at their least, they lose a lot of the 'springiness' as this would explain why they would more readily go back into the block. This does not apply to freshly machined cylinders that are straight and true from top to bottom. Did you machine or "freshen" up the block at all with a cylinder hone? If so... you would be surprised how many re-ring jobs end in disaster because after honing the cylinder walls...an enormous amount of removed metal and grit gets lodged inside the fine hash lines and when not properly cleaned and removed, it acts like an abrasive on the new parts. This is not a trivial matter. The care and caution you take in this regard will reward you later when you mash that gas pedal and the motor delivers exactly what you asked for...smooth, potent horsepower. But you will have to pay the price of patience and diligence to deserve this kind of performance and longevity before you put the parts and pieces together. The best way to clean the cylinder walls is with soapy water and paper towels, followed immediately (I mean RIGHT NOW) up with a liberal spray down of water-displacing WD-40 and then by a careful cleaning of each cylinder wall with paper towels soaked in automatic transmission fluid. When you don't see any more dirt or "gray" metal on the towel...then its finally clean enough to install the pistons and rings. Don't use cloth or cotton hand towels, as the fine fibers will strip off and get lodged inside the engine.

I suspect that your pistons/rings vendor/seller may have sold you some that are over sized... even if the invoice says they gave you exactly what you wanted. It is so possible to get a set of mismatches in either pistons or rings...or both on occasion. You have to remember that the people who handle warehouse stocking and shipping did not have to know differential calculus to get hired...and often mistakes in boxing and storing parts happens. My suggestion is that you get your hands on a 4" outside micrometer and a 4" snap gauge and take a closer look at the actual dimensions to find where the variances are. As for rings...it is rare that you can put in a complete set of '2 groove-3 oil sealing' piston rings and not have to do some trimming of the rings to get them to behave within there limits. Measure the width of your pistons 90 degrees from the wrist pin boss and be careful not to score them with the hardened steel tool when doing so. Measure the cylinder walls in two directions, about an inch or so from the top of the engine block using a good locking snap gauge. (Don't actually allow the gauge to "snap" open inside the cylinder or you'll dent the cast iron walls with the tool) Try to get the snap gauge as close to a right angle and at the widest portion of the cylinder walls when taking the measure of each one. Then just slip the snap gauge inside the 4" outside micrometer and measure it to determine the bore dimension.

If you insist on pounding the piston rings into the block just because of the label on the box...your engine will last about ten seconds when you crank it up the first time and the excessive friction melts them into the cylinder walls. To avoid this catastrophe, take one ring at a time, turn them on end and guide it into one cylinder at a time until they compress enough to rotate into a normal position, then take your one new piston and after inverting it...push the rings down inside the cylinders about one inch so they square up with each cylinder wall. Then take a feeler gauge and measure the ring gap on each ring for each cylinder to determine if they are all within specs...or require trimming with a ring file. If they do, get a ring file and mount the rings to be reduced in a vice so that one end sticks up just enough for it not to vibrate when you file from the outside inward. File only in that one direction..inward.. and use steady, flat strokes. Be careful not to take off too much from each ring or you'll have the rings too loose and find yourself buying another set. File just little at a time on each one.. and remember to clean the rings and re-measure. (Don't forget to...Wash, Rinse... Repeat)

This is trial and error work that when done right, will guarantee your engine will seal and develop compression in each cylinder for a very long time to come. Don't manhandle these new rings...they are brittle and can break like pretzels if you get too enthusiastic and impatient while working on them. You will have to do this for the entire piston and rings set...and they must be kept separate and marked after sizing for each unique cylinder position (zip-lock baggies marked 1-6, etc.) And make certain to clean the rings you worked on to prevent contaminating each cylinder with ultra hard metal filings and grit that will cause problems later. When it comes to asking much from any motor, Cleanliness really is next to Godliness. When you have done all this and are ready for assembly, check each set of rings for placement orientation on each piston (proper angled sides up) and the spacing needed to make sure they will work. We all understand that this is a job that even seasoned mechanics rarely have to do...so it is an area that is easy to make mistakes with while doing the work. Some mechanics go so far as to organize their ring sets on an inexpensive wooden "Pin Board" that allows them to be methodical and careful, laying out the rings for each unique cylinder...without having to wake up at three AM. in a pop-eyed sweat, fearing they may have installed the rings on cylinder #4 ..upside down and now the engine is back in the car. I've included some images for positional depth reference and for the conversions to use when calculating SAE piston and rings sizes for an engine that is otherwise, entirely Metric.

Good Luck with this repair...

--==Bob==-

[abob]

WOW... That's alot of info. Thank you.
Yah all the rings would enter the cylinder and then the piston would seize up. I'm going to have to take a set of the old rings and compare them the new ones just to see if they mistakingly gave me over sized rings.

I will be carefully working everything over again this weekend to see what is going on. Beleive me soap, water and Paper towels have become my best friend when working on this motor. I plan on this motor running for a long time

[60dgrzbelow0]

One last thought...Why not take one old piston with the old rings and your new pistons/rings sets back to the store you bought them from and ask the counter staff to check everything over for you? They'll have the tools on hand to make the necessary measurements and if they find out they made a mistake, they can rectify the problem for you on the spot (assuming you still have a receipt/proof of purchase). It would also be very interesting for us to see some comparison photos of these parts and the engine, too.

[pocket-rocket]

Unless it is Autozone. I was recently forced to use an Autozone when away from home while working on a friends car. I almost couldn't believe it when the dude asked me who made a Lumina. Really, man.... my gramma could answer that question...

[abob]

Okay so I think I found my problem... I took all the rings and set them on a table and matched up the one side with a peice of cardboard, and this is what I got. I feel stupid for not doing this before but I guess that's how you learn. I've got new rings on order and they will be here tomorrow. Autozone actually took them back for me.
I will post up how everything goes when I get the new rings. (using old pistons with new rings)

[3400-95-Modified]

All the new rings were different sizes?

The correct way to check this is to insert a ring in the cylinder NOT on a piston, but use the top of the piston to push it in a little to make it level, you then check the gap between the two ends of the ring. And well obviously if you cant get the ring in, or the gap is nada, then the rings are probably too tight, or oversized.

You didn't compare rings one and two in that stack did you? Because I know they are slightly different.

[60dgrzbelow0]

I feel stupid for not doing this before but I guess that's how you learn.

We're glad you took the time to investigate the problem and got to the bottom of things with the rings. If you follow the methods and procedures I went over in my last (all too long-winded) post... you'll be okay. We're looking forward to seeing your new images and finding out that things went back together properly, but there are still a few other important considerations you have to deal with before that can happen.

You might want to show us some close up images of the lands and grooves on your pistons and examine them for any possible hidden build-up of carbon; easily cleaned by using a pair of leather work gloves to keep you from shredding your fingers with the razor sharp edges of the rings and then carefully dragging some pieces of old, broken compression rings around the grooves to gradually scrape out all that black carbon crap from deep inside each groove (watch the aluminum though!) You should also be inspecting each piston for any new damage sustained when you first tried to forcefully insert them in the block. The cast aluminum lands can break off and fracture fairly easily when butted up against the hard steel rings stuck on top of or inside the block... so look them all over very carefully before installing your 'newest' set of rings on them.

You still have not mentioned whether you used a hone on the cylinder walls to sort of "cut the glaze". If you overlook doing this, all those new rings you put on the old pistons will slip and slide over the well-worn, polished surfaces of each cylinder like your grandmother taking a header on an icy sidewalk. In order for the rings to seat properly, they require a particular angle of honing to encourage the new rings to wear in correctly and achieve the proper amount of compression.

The other important reason for doing this involves lubrication. Without having these surfaces renewed with all those myriad new hash lines available to hold enough oil on the cylinder walls being slung there from the motion of the crankshaft as the pistons move up and down, an insufficient amount of oil will remain. With such close tolerances between the pistons/rings/cylinders, without a durable coating of motor oil for protection from friction, these components will soon heat up, expand and and wear the hell out of all these mating surfaces very quickly. It goes without saying that the six, freshly honed cylinders will have to be made spanking clean before re-assembly, too (see prior post for details). Don't you just love the idea that "All Solutions... Breed New Problems!"?...LOL

By the way...what is all that Alien organic stuff coming down from the ceiling of your garage? It looks like an H.R.Giger rendition of innards of the Alien spacecraft that crashed on LV-426 (Alien 1979 Ridley Scott) I'd love to see what kind of intake and exhaust manifolds Giger could come with for the 60* engines... He'd probably give John (Forced Firebird) a real run for his money!

[abob]

Yah I honed out the cylinders. (The weird looking tool that attaches to a drill.)
I'm slowly going over everything again just to check to make sure nothing got damaged or is out of place. That way I won't have to worry about it later lol.
The garage ceil is just insulation hanging down. We haven't had a chance to finish it yet. The only thing that garage gets used for is to store my moms motorcycle and 1975 MG Midget.