Author Topic: A new attempt at making piston rings  (Read 16261 times)

Offline Don1966

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Re: A new attempt at making piston rings
« Reply #150 on: June 04, 2021, 05:35:18 AM »
This may sound like a stupid question, but if you have compression and you did a leak test and the timing is right, all cab adjustments tried . What about the ignition plug, plug wire and coil. I have seen engines run with poor rings and bad cylinders. Just my two cents….


 :cheers
Don

Offline Jo

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Re: A new attempt at making piston rings
« Reply #151 on: June 04, 2021, 08:54:10 AM »
This is a good time to ask a theoretical question. If I had a Viton ring on a piston, and shoved the piston half was down a length of cylinder, there would be no leakage at all past the Viton ring. A Viton ring seals perfectly around it's full circumference. If I stood the cylinder on end and filled the top half with Varsol or any other fluid, none of it would leak past the Viton ring---ever. That is a given.

I have done that.---Now, if I take a piston with two cast iron rings on it, each ring having a 0.004" gap between the ends, and the gaps set at 180 degrees to each other, it will leak. If placed half way down a cylinder and stood on end, and if I fill the top half of the cylinder up with Varsol or some similar fluid and left overnight, some of the Varsol would leak past the rings and be puddled in the bottom half of the cylinder. Iron rings are not a perfect seal.

---Any comments???

An observation on using oil to do a sealing test: Piston rings are designed to provide a seal when running in a hot engine, when hot the rings will expand which is why we leave the gap in the rings. While cold there is a gap in the rings so yes the oil will leak through. With an O ring there is no gap so you will get a good hydraulic seal

I have not been following along on this thread so far but looking on the first page there is a single figure for ring gaps  :headscratch: Hepolite recommend different values based on bore diameter and application:

Air Cooled Engines:                     Not less than 0.005" per inch of bore (0.127mm per 25mm of bore)
All other engines:                        Not Less than 0.003" per inch of bore (0.7mm per 25mm of bore)
Air compressors and refrigerators: not less than 0.001 per inch of bore. (0.025mm per 25mm of bore)

As you can see applications with different working temperatures require different gaps and that gap is adjusted for the diameter of the cylinder bore - all this is to do with thermal expansion of the cast iron.


If your gap is a bit big your model engine will still run but be a bit Smokey and you may get blow through the crankcase.  ::). If the gap is too small then when the rings expand the rings have no where to go but into the wall of the cylinder and engine will make a horrible noise as it seizes  :toilet_claw:

Jo
« Last Edit: June 04, 2021, 09:16:32 AM by Jo »
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Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #152 on: June 04, 2021, 04:51:46 PM »
Question Jo--When you make rings, do you machine the outside diameter of the rings after they have been heat treated? I'm trying to get a handle on this. The Trimble method does have a final "Skimming" step where the o.d. of the rings is turned after the ring is heat treated.  I believe that many people make rings quite successfully without this final machining operation.---Brian

Offline Dave Otto

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Re: A new attempt at making piston rings
« Reply #153 on: June 04, 2021, 06:34:10 PM »
If memory serves the Trimble method does not require that the rings be skimmed after heat treat. Have you read the entire article?
If not maybe you should obtain a copy, lots of good information contained within.



Dave

Offline Jasonb

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Re: A new attempt at making piston rings
« Reply #154 on: June 04, 2021, 07:30:18 PM »
As Dave says Trimble goes to great lengths to get a good finish on the OD of the "tube" before parting off the rings so no further work is needed on the OD. I don't skim them either.

I think you are getting muddled up with rings that are sawn, where some methods close these up after sawing on a mandrel and turn the ring to the correct OD

Offline Jo

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Re: A new attempt at making piston rings
« Reply #155 on: June 04, 2021, 07:45:07 PM »
Question Jo--When you make rings, do you machine the outside diameter of the rings after they have been heat treated?

No. I turn the rings the same diameter as the bore.

My heating technique is to spread them round a piece of scrap sheet or bar steel of an appropriate thickness. They hang from this while being heated and they will hold on until they take the set when they just fall off. Then just leave them to fully cool naturally. I don't clean up the outside not even to remove the scale which comes off quickly first time they rub up and down the bore.

I "crack" my rings by scoring the inside surface with the boring tool and then holding the ring in side of the vice on the line and just gently twisting the ring with pliers. You get a lovely straight edge which can then be gaped by hand with a needle file.

Jo
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Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #156 on: June 04, 2021, 08:39:23 PM »
Thanks Jo!!

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #157 on: June 04, 2021, 08:42:24 PM »
I've just sent off for the three magazine articles that cover Trimble's method of making rings in strictly I. C. Magazine in the USA.

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #158 on: June 05, 2021, 06:47:20 PM »
I have just received and read thru the Trimble method of making piston rings. It is very well done, and a bit "long haired" so it will require a bit of concentration to re-read and fully understand exactly what Trimble is saying. He treats the subject "in depth" and does provide very good guidelines for making compression and oil rings for small engines. I would recommend it to anyone who has had trouble making their own rings.---Brian

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #159 on: June 05, 2021, 06:53:23 PM »
WOO-HOOOO---I just got my second covid shot this morning. Wife and I drove to a nearby town and after they confirmed that we had our first shot in early march and that we were "essential caregivers" to my 100 year old mother they went ahead and injected both of us. Arm is not sore, no hives, no sick feeling (at least so far).

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #160 on: June 05, 2021, 09:27:18 PM »
I have read thru the Trimble method about three times now, and I probably can get my head around about 80% of it. Only four things really jump out at me. #1---He uses a calculated diameter of round pin on the neutral axis of the ring as his "gag" when spreading the rings for heat treat. #2--He clamps the rings flat in a fixture for heat treating, which makes sense, because that keeps the two ends of the ring in perfect alignment whereas spreading the rings on a "gag" but not clamped flat does allow the rings to "squirm" a little bit and become misaligned. #3--He uses an expanding collet style fixture to mount the rings on one at a time to deburr the inner and outer diameter of the rings on the "blind side" which couldn't be deburred when parting off from the original parent stock. and #4--He is quite adamant about not trying to do any further work on the o.d nor on the i.d. of the ring before mounting it on the piston. To me, his rings look awful damned thin at 0.022" on a 1" piston. I could not make the 1/16" wide rings as purchased from Debolt work for me. That is probably my fault, not Debolt's.  I am buying a 1 mm (0.039") wide grooving tool to put the ring grooves into my piston, I'm going to make my new piston from aluminum, not cast iron, and my compression rings will be made 0.038" wide x 0.038" radial thickness.----Brian

Offline crueby

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Re: A new attempt at making piston rings
« Reply #161 on: June 05, 2021, 10:13:07 PM »
WOO-HOOOO---I just got my second covid shot this morning. Wife and I drove to a nearby town and after they confirmed that we had our first shot in early march and that we were "essential caregivers" to my 100 year old mother they went ahead and injected both of us. Arm is not sore, no hives, no sick feeling (at least so far).
Terrific, glad you were able to get it!

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #162 on: June 07, 2021, 01:13:08 AM »
After finally getting the complete Trimble method of ring making, I see that I have been misinformed. Trimble does not call for a final "cut" on the outer diameter of the rings. In fact, he strongly recommends against it. He strongly suggests that the o.d. of the rings be brought to a very high degree of finish in the initial sizing before being parted off. He suggests that the rings be machined to about 0.0015" to 0.002" oversize, then using a "fine India stone" to remove all tooling marks, then brought to final size with 400 grit paper on a flat strip of metal. He recommends a "mirror finish" on the o.d. of the rings, and that the o.d. of the rings is the same as the bore of the cylinder.. He also disagrees with breaking the ring manually in a vice, and provides design for a "cleaver" which cuts the ring much more cleanly than breaking them.

Revised 07-june---I misread the tolerance.
« Last Edit: June 07, 2021, 08:22:06 PM by Brian Rupnow »

Offline Jasonb

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Re: A new attempt at making piston rings
« Reply #163 on: June 07, 2021, 07:11:31 AM »
Good luck taking 0.010" off with an india stone :'(

Try reading it again, he roughs the OD to +0.010" then bores.

He then turns with his finest feed the OD to + 0.0015 to 0.002"

Then get out the stone and take it down to +0002 to 0.0005"

Then polishes it down to finished size with abrasive paper.

To be able to do this you really need to know the exact size of your bore, don't just assume all yours are 1" as your reamer may be cutting oversize and any honing or lapping will increase the bore and an old digi calliper is not the most accurate tool to measure it with.

Offline Brian Rupnow

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Re: A new attempt at making piston rings
« Reply #164 on: June 08, 2021, 12:05:32 AM »
Today I had one of those wonderful, drop in, 8 hour jobs from an old customer. Design fixtures in the morning, send off to customer for approval, get immediate approval, make detail drawings, then machine like a fiend until suppertime. I don't want any "big" jobs, but I love those one day deals. I'm having a grooving tool ground for me at a local shop to make piston grooves, and todays work will pay for that with money left over.