1/3 Scale Ford 289 Hi-Po

[petertha]

Thanks for your detailed writeup, Terry. Even though I've bookmarked your prior builds regarding rings, I always learn another tidbit or two.


Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall.
- I always assumed the lapping was more related to dealing with the parting off operation, specifically more variation in thickness dimension & higher potential for edge burr. I didn't consider the seal aspect. So dumb question, now you have a nicely lapped flat ring face. So how does one ensure the quality of the mating ring groove face in typically aluminum is of similar quality? Do you have a preferred tool or treatment for that?


I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult...

- maybe you mentioned elsewhere, but do you make your fixture & expansion pin from same type of CI

- what kind of oven do you use yourself & what is your recipe for minimum heat/soak duration time? I've seen some documentation specifying time per volume on Durabar grey CI equivalent post #27 https://www.homemodelenginemachinist.com/threads/piston-rings.36318/page-2#post-415318 )


- you mentioned using uncoated inserts steel/CI alloys before(which I assume are the ones engineered for aluminum type alloys) on certain. I have used them myself in steel for similar reasons. The only downside seems to be a bit more fragile (sharper nose radius) & they wear faster (lack of coating?). But my question is more why do they work? I noticed I could actually order coated/steel inserts with the same sharp nose radius as my aluminum ones. In fact it made me look at some 'for stainless' ones I bought out of curiosity which cut better than the regular ones in more typical steel. But another parameter is I think aluminum inserts have a higher rake angle. This is not always easy information to quantify (at least on my tooling back alley locations). One would think this would not be conducive to a better finish or dimensional control in a tougher material. Anyways, any thoughts on this subject as to WHY the uncoated work as they do or you prefer them?

 

[mayhugh1]

Thanks for your detailed writeup, Terry. Even though I've bookmarked your prior builds regarding rings, I always learn another tidbit or two.


Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall.
- I always assumed the lapping was more related to dealing with the parting off operation, specifically more variation in thickness dimension & higher potential for edge burr. I didn't consider the seal aspect. So dumb question, now you have a nicely lapped flat ring face. So how does one ensure the quality of the mating ring groove face in typically aluminum is of similar quality? Do you have a preferred tool or treatment for that?


I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult...

- maybe you mentioned elsewhere, but do you make your fixture & expansion pin from same type of CI

- what kind of oven do you use yourself & what is your recipe for minimum heat/soak duration time? I've seen some documentation specifying time per volume on Durabar grey CI equivalent post #27 https://www.homemodelenginemachinist.com/threads/piston-rings.36318/page-2#post-415318 )


- you mentioned using uncoated inserts steel/CI alloys before(which I assume are the ones engineered for aluminum type alloys) on certain. I have used them myself in steel for similar reasons. The only downside seems to be a bit more fragile (sharper nose radius) & they wear faster (lack of coating?). But my question is more why do they work? I noticed I could actually order coated/steel inserts with the same sharp nose radius as my aluminum ones. In fact it made me look at some 'for stainless' ones I bought out of curiosity which cut better than the regular ones in more typical steel. But another parameter is I think aluminum inserts have a higher rake angle. This is not always easy information to quantify (at least on my tooling back alley locations). One would think this would not be conducive to a better finish or dimensional control in a tougher material. Anyways, any thoughts on this subject as to WHY the uncoated work as they do or you prefer them?

Peter,
When I cut ring grooves, I use a sharp insert with back clearance, and I practice on the end of a piece of scrap to get the feed and speed for the best surface finish. The insert also needs to be perfectly perpendicular to the axis of the piston. If the measured width of the groove doesn't perfectly match the width of the insert, the insert isn't mounted correctly and the surface finish will suffer.

I've never made the fixture from CI, but I think I'll try it this time. I've typically used 12L14 and 303 stainless. Matching the coefficients of expansion is probably a good idea.

My oven is a Ney Vulcan dental oven. My particular model isn't manufactured any more, but similar ones can be found on ebay.

I like using the high rake inserts on cast iron because they give a good surface finish even though they don't last very long. I'll some times use them for finishing passes on steel and stainless steel as well. On lathes without a lot of rigidity their peeling action seem to give great surface finishes without the chatter.

Terry

 

[mayhugh1]

I needed a break from lapping and started work on the normalization fixture before the second lot of rings was finished. The components of the fixture were machined from some 1144 left over from the crankshaft, and the critical dimensions were taken from the worksheet in a previous post. The machining was straightforward lathe work, and the finished parts are laid out in one of the photos. A spacer was included so the fixture could handle both large and small batches.

All traces of grinding grease were removed from the rings with solvent before they were gapped. Many simply snap their rings over a small drill, but Trimble's math assumes the dowel pin separator will contact the faces of a true radial break. Several years ago I built a cleaver to make these breaks, but when the gaps were opened up with a file and without some sort of alignment tool they tended to wander off course.

A two-sided diamond file was used to open up minimum .004" gaps that were verified inside a spare cylinder liner. The purpose of a ring gap is to allow circumferential expansion of the ring due to the high temperatures in the combustion chambers, and .004" provides a comfortable margin. Risking a broken ring by trying to minimize this gap is penny foolish because the leak it adds is negligibly small. For comparison, a ring that's just a half thousandth undersize can create a leak that's 200 times greater than that from a .004" ring gap.

The rings from the first lot were normalized in two separate batches. After being loaded into the fixture and sealed in argon gas inside a crimped stainless steel 'bag', each batch was held at 1050F for two hours and allowed to slowly cool. An early indicator that all went well is that after cooling the dowel should slide freely through the fixture while the rings hold their shape.

I don't know about others' experiences, but my rings and fixtures invariably wind up covered with ugly black deposits. They're easily burnished off the o.d. of the ring stack using a white scotch brite pad, but the rings also wind up stuck together and have to be carefully separated with an X-acto knife. These deposits appear on every set of rings I've made. Everything that gets sealed in that stainless bag has been ultrasonically cleaned with either naphtha, lacquer thinner, or acetone, and the results are always the same. My next attempt to eliminate these deposits will be to do a low temperature bake-out of the rings and fixture before they're sealed for the actual normalization.
In any event the side faces of the normalized rings were lightly re-lapped with 800g grease to insure they're clean and smooth, and their o.d.'s had to be gripped with yet another shop made tool. - Terry

 

[mayhugh1]

The final step in my ring-making process is to light test the rings. A shop tool made up of a 2000 lumen flashlight, a spare cylinder liner, and some turned bits of Delrin were used to sort the rings into subjective A, B, and C fit categories. One of the Delrin pieces is a dummy piston with a diameter turned .020" smaller than the liner i.d. This piston supports the ring while in contact with the wall of the liner and normal to it. Light from the flashlight passes around the piston but is totally blocked by a perfectly fitting ring except at its gap. Depending upon any additional light that gets past the ring, it's classified as A (no additional light), B (usable with just a tiny wisp of excess light), or C (two wisps of light and usable if necessary). Anything worse is discarded.

After finding a couple A and B rings, I realized a large number were going into the discard pile. Microscopic examination uncovered burrs on the outside corners of a number of rings that were most likely raised up during parting. These burrs hadn't been accessible by lapping and could actually be felt with a finger run around the outside corners. A folded postage stamp size piece of 1000g paper carefully rubbed on the rings' o.d.'s removed the burrs without otherwise disturbing their machined surfaces.

When completed, I had 14 A rings, 13 B rings, and 9 C rings. Only 2 rings were scrapped. - Terry

 

[Sparky_SC]

Very interesting. If we call the ring gap 12 o'clock it appears the light leakage is always around the 7 o'clock position. Wonder why that is????

Have you ever tried inserting a piece of paper in the stainless bag to consume oxygen ? (as it burns). I have seen many who do that to lower any residue.

I always admire your work.

 

[petertha]

Terry, what are you using to take those highly magnified pictures? Its a different visual world at that scale!

 

[mayhugh1]

Terry, what are you using to take those highly magnified pictures? Its a different visual world at that scale!

Peter,
It's just a cheap USB microscope for a computer:

https://www.amazon.com/Microscope-M...gital+microscope+for+computer,aps,141&sr=8-30

Terry

 

[mayhugh1]

Very interesting. If we call the ring gap 12 o'clock it appears the light leakage is always around the 7 o'clock position. Wonder why that is????

Have you ever tried inserting a piece of paper in the stainless bag to consume oxygen ? (as it burns). I have seen many who do that to lower any residue.

I always admire your work.

Sparky,
The 7:00 o'clock thing may be a coincidence due to a too small sample size. I checked another dozen rings and can't say I saw a pattern.

I tried the paper trick when I first started making rings. I was getting some yellowish brown deposits when it occurred to me the brown paper I was using probably had a high sulphur content. I remember trying different papers, but I can't remember what my final conclusion was. I'm guessing I was still having some problem since I switched to a more complex solution with the argon gas. My best results seem to sometimes be a thin black sooty layer, and my worst result is similar to the the thicker nastier deposits shown in my second batch photo. I have to say I don't see any of this stuff when I'm hardening drill rod in the same argon filled stainless bags. It seems specific to the rings and must be related to the lapping grease of the solvent used to remove it. - Terry

 

[Steamchick]

Mayhugh, this is excellent work and description of your process. Thankyou. Maybe you should write a book?
I saw cast iron rings made in the Hepolite factory in Sunderland back in the 1980s. The only difference to your process (as I remember) was a lapping of rings in bores using a set-up that simulated piston motion in the bore, but while rotating the cylinder as well as oscillating the piston axially up and down the bore. During this process the whole pack of around 100 rings was washed with a fluid that had the lapping medium in suspension. A pity I never got a photo/video of that process!
All my notes remained (company confidential) with my Company - archived for 30 years - so long gone by now. so all I have is memory to rely upon.
Just an idea about the "staining" of cast iron when normalising: Cast Iron contains lots of carbon - with traces of other impurities - so could that be "leaching out" of the metal? A blacksmith (had a traditional country forge and worked on Farmers' equipment mostly) once explained to me that they were "black" smiths from the carbon they beat out of the cast iron during forging, to make steel. He also told me his cheapest source of steel (by tonnage) was reinforcing bar for concrete... reckoned it was stronger than "mild" steel and cleaner than cast iron for forging horse shoes, frames for everything, etc. that he made from steel stock. But not having a scientific understanding at the time I didn't understand it was carbon from within the cast iron that he reckoned they beat out of the metal... I had assumed it was just forge coke and black oxide from the surface..
Thanks for your excellent work. A MODEL lesson in Engineering in itself.
K2