06 Piston Ring Gap Clearances

[jjefferson]

Started to install my new piston rings (57 Belvedere 230 engine) into my 54 M37 Plow Truck .060 rings with .060 pistons and just realized that I don’t know what the required gap clearance in the rings should be. All my books just reference the standard piston and ring gap clearances.

Would it be to the same as a standard set of rings -
.007 to .017 for the upper rings
.007 to .015 for the remaining lower 3 rings

How about the groove clearance – should that be the same as a standard piston / ring combo.


The first 3 pistons all had broken top rings, with #2 being the worst. So the #2 won prize and gets a new piston plus the rings. Everything else is a hone job and some rings, new conn rod bearings, and some quick valve work. I know that's bad - but this is a budget job and just the plow truck. Drives me crazy to skimp and take shortcuts but that's the way this job is going.



Also wish I had finished this project back in October when I started it – awfully cold under the barn these days.

Thanks

Jim

[MoparFreak69]

Yes, all clearances will remain the same as standard sizing, the only thing that changes is how big the bore is.

While I agree with your point of view that the work you are doing is just a bandaid, I have to say that I have done the same sort of repairs myself. My first car, a 77 Datsun got an in-frame rebuild that really only consisted of pulling it apart, cleaning, replacing rings (guessed they were standard and threw them in without checking) and crank bearings (also didnt measure, just threw standards in). I did not even go so far as to hone the cylinders. Very far from ideal, but that thing ran so good afterwards it wasnt funny. It had more power, and ran smoother than my brothers truck (79 Datsun) that had been rebuilt in a professional manner.
My only point is that as long as everything else is good, you should be ok with getting away with just replacing rings. Triple check everything before you go back together though. I dont know about you but I hate taking things back apart shortly after assembling it because I didnt check anything over well enough the first time. If in doubt, its best to go ahead and replace it.

[Kaiser2boy]

Did you happen to check and see how much taper there is inside the cylinder?
Most older engines have the cylinders wide at the top and narow at the bottom.
If you gap them at the top they just may bind up solid at the bottom. And thats with a cold engine.
If you gap them at the bottom they will be wide open at the top and give up compression where you most need it.
I may be a bit off but I heard that .003 of gap per inch of bore is about right.
Just for the fun of it gap one at the top then press it down with the head of the piston and see what you get at the bottom . Heck you may be lucky and there is not much taper.

[jjefferson]

I just started with #6 cylinder. I put the rings down the bottom of the cylinder - like 2 inches from the bottom and gapped them from there (5 inches down from the top or so). The rings were within the spec range - the "loosest" was .016 which seems to be on the edge and the "tightest" was the top ring and that was .009. The old rings had a ring gap like 1/4 to 3/8 of an inch - it was huge. Like the whole set of feeler gauge huge.

At this point just trying to get it all back together. Way behind in this project and its snow season.

Just managed to snap the bottom ring - which raises the level of frustration about 509 %. And that was just barely massaging the ring over the rest of the piston with the piston ring pliers. I must have tweeked it just right. The best part is it took a month to get those rings in stock. Which then raises the level another 345%. So that's it for tonight. Otherwise I might throw something across the barn and that would be bad.

Jim

[MoparFreak69]

I have actually had more bad luck with those stupid pliers than I have with just using my fingers. They place too much stress on the rings, stress they are not designed to handle. The best idea is to just walk them down the piston one by one with your fingers and you are set.

[MoparNorm]

I have actually had more bad luck with those stupid pliers than I have with just using my fingers. They place too much stress on the rings, stress they are not designed to handle. The best idea is to just walk them down the piston one by one with your fingers and you are set.

That is true, just don't scratch the piston when installing them.
...and don't feel bad, I waited nearly 3 months for rings to a 400 BB, first ordered direct from Mopar and they discontinued them after I waited 6 weeks, then waited another 5 to get them from a second source, twice removed. The rings show in-stock, in everyone's catalog, until you place the order...duh.

[Gordon Maney]

An old time standard was .003 to .004 end gap per inch of cylinder diameter. So, a 4 in. diameter cylinder would have been .012 to .016 in. end gap.

[MoparNorm]

Modern engines have much closer end gaps than that, and if rebuilding with the new alloys you can match the ring manufacturers recommendations, but as long as it isn't too tight and they are indexed, it's fine.

Bottom line, go by the book!
That being said, in your case and since you did not re-bore, err on the safe side, as you have already done by measuring the gap vs. bore, all the way through the stroke range.

[Gordon Maney]

As I said, it was an old time standard. I agree; always use specifications if you have them available.

Also, in a used cylinder, always measure the gap at the bottom of the cylinder, as that will be the small end of the taper. Be sure to remove the ridge at the top of the cylinders with a ridge reamer. Do that before you remove the pistons during disassembly. If you do not remove the ridge, and it is a situation where you are hoping you can reuse the pistons, pushing a piston out of a cylinder with an existing ridge can not only break a ring [which we don't care about], it can also break a ring land in the piston, rendering it unuseable.

The new rings should have had some paperwork with them covering installation procedures and end gap specifications.

[jjefferson]

I have ended up using the .004 gap per inch of cylinder for the top ring and a hair over the other rings. So basically nothing less then .013 for any of the rings. For curiosity sake I gapped a few of the old rings that I pulled out – 0.175 and better. I basically stopped measuring the gap when I was sticking half the feeler gauge in the gap.

I kind of wonder if they put the wrong rings in the engine when they put the 06 pistons in. Seems like that gap (huge) is awfully large given there was still plenty of meat on the rings.

So in any event rings are all fitted - except for the broken one. Need to look for a set on Monday and continue onward. Might check the #3 piston – engine seemed to get a whole lot tougher to spin when I put that one back in. I was on a roll and didn’t feel like stopping so have to go back and check on it.

Jim

[jjefferson]

There wasn't a word on proper fitting the rings from the manufacturer. They spent a whole page discussing how to fit the oil ring but that was it.

Jim

[jjefferson]

I take the last comment back they did cover ring gap clearance - .003 to .004 per inch. I must have been sidetracked by the pictures.

Its amazing what goes in one ear and out the other sometimes.

Jim

[gusbratz]

As the rings wear the end gap gets bigger. In my opinion more is better if you are initially going to error, error a little large with your fileing. since 1 as the ring heats up it will expand and the end gap will become tighter as the engine is running (this is why the top ring sometimes has a larger clearnce than the rest of the power rings) and 2 the fireing pressure after combustion takes place actually flows through the end gap on the rings and into the cavity behind the ring flareing it outward and into the cyl wall makeing a very tight seal. without enough end clearnce the high pressure gases can not flow into the area behind the ring to push it out. Also improtant to understand that the ring has 2 seating surfaces. one being the cyl wall the second being the bottom of the ring grove. eventually this will wear and can be measured by putting a new ring into the groove and measuring the side clearnce. cast iron pistons usually give a very long service life compared to aluminium pistons. don't mean to talk down to anybody you probobly allready know this stuff but I figured I would put it on here in case it is of benifit to somebody.

[Gordon Maney]

Checking is the main thing. As I think back to all the engines I have assembled, I know I recall one where I had to file the end gaps, and maybe two, but virtually all I have done had sufficient gap, and that includes bored cylinders.

[Kaiser2boy]

I remember when I looked at the ring gap on my engine I was amazed. I gave up on the feeler gauge and checked them with drill bits they were so open.

What really amazed me was it ran!. It was a bit cranky to start . It was sort of like the engine on the airplane on the movie FLIGHT OF THE PHOENIX. But it ran smoothly. It did not have much power but it ran. I had it rebuilt. Its better but not a whole lot, it still is wimpy on any kind of hill and on flat ground it will get up to 45 MPH but anything after that is hard won.