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Author Topic: Tell me how to fit a convential ring to anengine.  (Read 564 times)

Offline frank mccune

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Tell me how to fit a convential ring to anengine.
« on: November 05, 2018, 04:11:28 PM »
          Hello All:
 
          Kindly tell me how I can correctly fit a ring to a cylinder.  What I have in mind for an OS SF.46 engine is to purchase an aftermarket ungapped ring, cut a relief for the locating pin, Dremel Tool with cutoff disk and a Swiss File for adjusting the end gap, .001". Where may I purchase feeler gage stock that measures .001"? If you have successfully done this, kindly share your knowledge and knowledge.

        There are a few reasons that I want to do this myself but since I have never attempted this task, I need help!!!

                                                                                                                                               Tia,

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Offline Dave Hull

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Re: Tell me how to fit a convential ring to anengine.
« Reply #1 on: November 05, 2018, 06:13:37 PM »
You should be able to buy feeler gauges and shim stock at any industrial tooling store. If there isn't one near you, you might consider McMaster Carr.

     https://www.mcmaster.com/feeler-gauges

I often cut a feeler gauge down to suit a specific purpose, or, if you use shim stock you have even more options in regard to shapes. For ring fitting, this is not really needed. If you cut a gauge, be aware that you may have changed the edge thickness. I keep a plastic gauge set on hand, but these are much softer, so depending on what you are doing, they may be less suitable. In the smaller sizes, they are floppy, which is not an asset for ring fitting.

Fitting a ring properly has a lot of "feel" to it, so it can be hard to describe. Here are a few of the steps:

Take the ring and compress it until you can slide it into the liner, which has been removed from the engine. Square up the ring in the bore using the piston. Remove the piston. Backlight the liner so you can look for fit and gapping. Carefully tilt the liner around in front of your light source until you are observing the gaps (if any) at their largest. You may be surprised at how big they appear, but know that using light gaps is a very sensitive method.

For a conventional ring you can estimate the fit of the thickness before attempting to install the ring. Just put the outer edge into the gap. If the piston has carbon built up in the gap, you must remove this before you start. Most guys will tell you that you should use a broken ring to do this. If you want to try this, I suggest that after you break the old ring, grind the end flat, and at 90 degrees to the local curvature. Don't break the edges after grinding. I would cook the piston in antifreeze first to remove as much carbon without likelihood of damage as possible. It also softens any remaining carbon. I have also used thin basswood strips and baking soda to work on the bottom of the groove. Get the stick wet and dip it in the baking soda.Work the stick back and forth in the groove. The overriding concern is not to bugger up the ring groove unless you want to buy a new piston.

Once the piston is clean, and assuming the groove is still nice and square and not gouged on the bottom, you can think about lapping the ring height if it is needed. If it is already too loose, then go get another ring. If you have not done a lot of lapping before, go research the do's and don'ts. A lapping plate is not mandatory, but something very flat, cleanable and chargeable is. I would make a cylindrical ring holder that has a shoulder and fits your ring. Otherwise, you are just winging it. If you don't have a micrometer to measure the ring as you go, you are also winging it. A good way to measure the piston ring groove width is with a set of gauge pins, but those are expensive and most people won't have any around. I don't. With a full set of shims/feeler gauges, you can stack them to measure the gap. Be aware that the accuracy is less because of the stackup. Don't force steel shims into the groove and bugger it up. This is where plastic shims are an advantage. Don't just trust the cited thickness of the shim stack, adding them all up. Measure the stack with the micrometer.

If you are planning on cutting a pin relief with the Dremel, then you are going to need to be an artist. I have not done this, but suggest you consider clamping the Dremel tool down above a table saw miter groove. Make a sliding plate that you can clamp the ring to. Set the heights and position. You might only get one shot at this. I would use a full clamping pad above the ring. Be sure the ring is undeformed before and after you clamp it. If your saw's miter slot is loose, tighten it up first. Another similar problem is going to be the (very) large endplay of a Dremel. The position may or may not be repeatable at speed. Depending on the size of the pin, you are likely going to have to use the smaller, unreinforced wheel due to its thinner kerf. However it may not be wide enough to do this on one pass. I would practice and fine tune the whole setup using a surrogate ring made out of similar diameter piano wire.

Just a few of the steps. See what other guys do.

Decide from what you see when you look at your parts what needs to be done. Don't expect miracles from old parts. Certainly not from damaged parts....

Good luck,

Dave  PS--I forgot to mention that I would measure the gap with the ring at or near TDC. It is hottest up there, and if your liner has taper you need to account for that as well.
« Last Edit: November 05, 2018, 06:36:27 PM by Dave Hull »

Offline Motorman

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Re: Tell me how to fit a convential ring to anengine.
« Reply #2 on: November 06, 2018, 07:33:08 AM »
Frank, where are you getting the aftermarket ring? I got some rings from  Bjorn Baal and they were horrible and unusable. 
There will be a sunny day and we will fly our airplanes.

Offline frank mccune

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Re: Tell me how to fit a convential ring to anengine.
« Reply #3 on: November 06, 2018, 01:34:13 PM »
         Hi Walt:

         Yes, that is where I plan to source my ring.  Is there a better source?

         What was it that made you dislike his rings? Did you contact him about your concerns? I spoke to him via telephone and he instructed me to return the entire engine to him for follow up work.  He also said that there would be no charge for his help.  This was an offer that I could not refuse! Sounds like he stands behind his work and product.  We will see.
 
          Got a ring for my HP .40 from a bloke in  England that worked perfectly.  It took about 2 weeks to get the ring and the to9fral cost was less than $20.00.  Perhaps I got lucky. Anybody know who the bloke in England was? I think that I found him on the BAY.


                                                                                                                                         Be well,

                                                                                                                                         Frank McCune

Offline frank mccune

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Re: Tell me how to fit a convential ring to anengine.
« Reply #4 on: November 06, 2018, 01:41:41 PM »
        Hi Dave:

        Thanks for taking the time and effort to answer my post!  It was very informative.

        In the past, I have installed rings on many engines of all types but this one was real challenge.  I now know why.  It was made very differently than any ring that I have ever seen.  It crumbled into many small pieces when I turned the engine over by hand.  Must have "hooked" on a port. In any case, I have a ring coming from Bjorn Ball.  It is made differently which may solve my problems.


                                                                                                                                                      Be well,

                                                                                                                                                       Frank McCune

Online Lauri Malila

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Re: Tell me how to fit a convential ring to anengine.
« Reply #5 on: November 06, 2018, 02:13:40 PM »
I must partially agree with MM. So far the best rings I've had are the ones that I turned, heat treated and fitted by myself (As per Frank Bowman's instructions which I then improved). Second best was when I sent my piston/cylinder groups to Frank for fitting the ring. Worst was when I bought his stock rings. I could not use them because of geometry & surface issues.
But it's not really a quality problem, in my opinion the only way to go is to fit rings individually to each piston/cylinder group. At least with my AAC's, maybe steel cylinders are easier on that. L

Offline Dave Hull

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Re: Tell me how to fit a convential ring to anengine.
« Reply #6 on: November 06, 2018, 09:14:04 PM »
Frank,

Considering your follow-up comments (which I hope I understood correctly):

1. If the ring gap is too small and goes away when installed, or if the bore is tapered, and the gap goes away up top, then the ring may seize and shatter. Did you check the gap at TDC before you installed it on the piston?

2. If the ring is distorted during installation and takes a permanent twist, then it is more likely to hook a port. Did you install the ring by spiraling it on, or did you open it and lay it over the piston?

3. Was the inside of the ring deburred before you installed it? If it was not deburred, and you spiraled on the ring, there is the possibility that you dragged a burr off the top corner of the piston groove into the groove and the clearance and float went away. Also, was the split in the ring clean, or did it have any burrs?

4. Did the ring float on the piston before it was installed? If it won't float (even a pinned ring) then it wouldn't surprise me that it would jam and shatter.

5. I'm continuing to assume that no other pre-existing problems are your cause--but really have no idea without seeing the parts.

6. If you broke a ring in an assembled engine while turning it over, I would be very suspicious that the liner is still in usable condition. Similarly, that the ring groove shoulders in the piston are not damaged as well. Check carefully before giving it another try.

You can begin to see why working on engines can be tedious and expensive. And why the guys that repair engines for pay really have their hands full---they never know what they are going to receive. If the piston or the liner are not good, then you can't expect a new ring to fix that.

Best wishes getting this one running again,

Dave

Offline frank mccune

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Re: Tell me how to fit a convential ring to anengine.
« Reply #7 on: November 07, 2018, 06:04:19 AM »
       Hello Dave:
 
       Thanks again for taking the time and effort to guide me in my quest for compression in my O.S.!

        I will attempt to answer your questions:

        1. The fit at the top and all through the cylinder remained .003" which i thought was excessive.

        2. I spiraled the ring on from the top.  Is this correct? On larger engines, I have used a ring expander for installation.

        3. Were there any burrs onthe ring or the groove? I did not see or feel any. Nex time, I will check with a piece of silk plus fingers.

        4. The ring appeared to float in the groove and was easy to turn in the grove.

        I regard ruined parts as  the price of tution for learning a task! Lol There is a large tution cost incurred while making life's journey!

        I will be taking a holiday for three days to contemplate my next move.  I will look for damage to the cylinder as the ring shattered in many small pieces and one large piece.


                                                                                                                                                     Be well my friend,

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Offline Motorman

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Re: Tell me how to fit a convential ring to anengine.
« Reply #8 on: November 08, 2018, 09:56:12 AM »
         Hi Walt:

         Yes, that is where I plan to source my ring.  Is there a better source?         

I would contact Bob Whitney in FL.
There will be a sunny day and we will fly our airplanes.

Offline John Eyer

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Offline frank mccune

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Re: Tell me how to fit a convential ring to anengine.
« Reply #10 on: November 15, 2018, 01:02:38 PM »
       Thanks to all who replied:

       John, that is the way that I installed the ring but I must have made a mistake as the ring shattered prior to be run.  I would say that the ring hooked on a port.

       The piston on the OS SF .46 has a pin to prevent the ring from turning.  However, the ring  had no cut on the inside to match the pin.  I was informed that I should place the ends of the ring up to the pin.  This produced a ring gap of at least .003" which was excessive.  The ends of the ring on the inside had a long bevel for some reason.  The new ring is supposed to have a notch milled into it to locate it on the pin in the piston.  I do not know if the new ring gap will be beveled on the inside or will the gap have square ends.  In any case, I hope that new ring solves my problem.

                                                                                                                                           Be well,


                                                                                                                                           Frank McCune


Offline Motorman

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Re: Tell me how to fit a convential ring to anengine.
« Reply #11 on: November 15, 2018, 01:20:13 PM »
If there's any way you can get rid of that pin you would have much more success. There is a formula for max port width that should be easy to find. If your ports are less than max, pull the pin out, it causes so many problems.

Motorman 8)
There will be a sunny day and we will fly our airplanes.

Online Brett Buck

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Re: Tell me how to fit a convential ring to anengine.
« Reply #12 on: November 15, 2018, 01:31:29 PM »
If there's any way you can get rid of that pin you would have much more success. There is a formula for max port width that should be easy to find. If your ports are less than max, pull the pin out, it causes so many problems.

   You don't want to remove the pin! Even if you can prevent it breaking off in the port, holding the ring in one place maximizes the chances of running consistently. If the ring moves around, it can run almost randomly.

    Brett

Offline Motorman

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Re: Tell me how to fit a convential ring to anengine.
« Reply #13 on: November 15, 2018, 03:21:39 PM »
From my experience with the Webra Silverline 40 the ends of the ring ride up on the pin and cause the tips of the ring to wear out in short order. Even if you have a zero end gap the ring seals on the bottom too and it's pretty hard to cut the ring perfectly around the pin. It's all academic if the ports are too wide. The K&B 4011 had it right.

Motorman 8)
There will be a sunny day and we will fly our airplanes.

Offline Dave Hull

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Re: Tell me how to fit a convential ring to anengine.
« Reply #14 on: November 15, 2018, 04:06:28 PM »
A square-ended pin needs a squared cut in the ring, not a radius. If the ring pin relief is cut radiused, then the pin better get rounded. From Frank's evolving description, it would seem that his prior attempt was going to bind up for sure. A chamfered ring?

Dave

Online Brett Buck

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Re: Tell me how to fit a convential ring to anengine.
« Reply #15 on: November 15, 2018, 05:19:15 PM »
From my experience with the Webra Silverline 40 the ends of the ring ride up on the pin and cause the tips of the ring to wear out in short order. Even if you have a zero end gap the ring seals on the bottom too and it's pretty hard to cut the ring perfectly around the pin. It's all academic if the ports are too wide. The K&B 4011 had it right.

       Certainly you must not have a situation where it can ride up over the pin, however, that's doesn't mean you want to let the ring rotate freely.

     Brett

Offline frank mccune

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Re: Tell me how to fit a convential ring to anengine.
« Reply #16 on: November 15, 2018, 06:23:21 PM »
      Hi Dave:

      The ends of the ring had long tapers.  I called them beveled, as  they came to a near point at the ring gap.  This is where I was told to butt the ends against the pin. ???? The pin must have been at least.003" in diameter as this was what the gap was. After talking to the ring manufacturer. he assured that there will be a notch on the inside of the ring that was cut via an end mill.  The pin is round.

      I hope that this helps.  Perhaps the ring will arrive soon to enable me to get this thing out of my life! Lol

                                                                                                                                         Be well,

                                                                                                                                        Frank McCune

Offline Dave Hull

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Re: Tell me how to fit a convential ring to anengine.
« Reply #17 on: November 15, 2018, 07:20:02 PM »
What I was trying to say, and didn't do a good job, is that the diameter of the pin in the piston is likely to be half the width of the ring groove or more. I can't believe it is only .003" diameter. (Or, I'm about to learn something new....)  The pin should be pressed in until it is exposed only about half the depth of the groove. Enough so that the ring can enclose it--except for about .0015 to .003" which is needed to keep things from locking up. So if the pin has a squared off end, then the ring needs to have a step in it at the split. If the pin has a radiused end (like one end of a standard dowel pin) then the ring step can have a radius up to the same size, but no larger. If the radius is larger--or if there is a long taper that comes almost to a point--then it will ride up over the pin and jam in the bore.

If the prior ring had a long taper on the inside diameter at each end, and the tip was thin enough to ride up over the end of the pin, it is going to jam and break. This is what it sounds like happened to you based on your descriptions.

Of course, not being able to see your actual parts makes diagnostics uncertain..... A picture would be worth 500 words.

Dave

Offline RandySmith

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Re: Tell me how to fit a convential ring to anengine.
« Reply #18 on: November 16, 2018, 09:33:52 PM »
If there's any way you can get rid of that pin you would have much more success. There is a formula for max port width that should be easy to find. If your ports are less than max, pull the pin out, it causes so many problems.

Motorman 8)

You cannot get rid of the pin, in that OS engines  and  most all of the OS Loop Charged engines, the ports are way too big and the end gaps  WILL get caught in the ports, trouble  will then follow

Randy

Online Lauri Malila

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Re: Tell me how to fit a convential ring to anengine.
« Reply #19 on: Yesterday at 12:11:17 AM »
Randy,

So far I have used a pin that is pressed in from top of piston, a dia. 1mm spring pin.
I can see that a radial pin would be better, but with my Dykes ring it would get quite thin, about 0,6mm and I'm worried of its strenght.
What would you recommend for pin material? In real engines they seem to use roller bearing pins, but they are not available in this size. Spring steel wire?
Workwise it's not a problem, I think I can manage it. L

Offline RandySmith

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Re: Tell me how to fit a convential ring to anengine.
« Reply #20 on: Yesterday at 10:09:33 AM »
Randy,

So far I have used a pin that is pressed in from top of piston, a dia. 1mm spring pin.
I can see that a radial pin would be better, but with my Dykes ring it would get quite thin, about 0,6mm and I'm worried of its strenght.
What would you recommend for pin material? In real engines they seem to use roller bearing pins, but they are not available in this size. Spring steel wire?
Workwise it's not a problem, I think I can manage it. L

Hi Lauri

I use  either piano wire  or I have used  01 tool steel that i hardened , either one will work well, I have not seen the  need for anything tougher, as there does not seem to be that much force put on the pins

Randy


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