A new attempt at making piston rings

[Brian Rupnow]

The news is positive. With new cast iron cylinder, piston, and rings, the engine has high (to coin a new word) Suckability!!! It fired, it ran for three short blasts, but I'm having head gasket issues. The aluminum head has a ring of material that fits down into the top of the cylinder about 0.060". Or, let me rephrase that--It is supposed to extend down into the cylinder about 0.060" minus the 0.030" thickness of the head gasket. A close examination of the cylinder head shows that that ring of material is "hanging up" on the inside of the bore and not letting the head bolts tighten the cylinder down evenly all the way around. I'm going to set the cylinder head up on the lathe and trim a tiny bit off that diameter that is giving me problems.

 

[Brian Rupnow]

I'm having a no work Sunday---I need it. But the old brain cells keep clicking away. Every thing I read about rings recommends that the ring thickness should be 1/30 to 1/25 of the cylinder bore (and the depth of the ring can match the width so your ring actually has a square cross section). On a 1" bore, that gives a ring width of 0.033" to 0.040". The width of the groove in the piston should be 0.001" greater than the width of the ring itself. So---If I made my rings 0.038" wide, then the groove in the piston should be 0.039"---And 1 millimeter is .0394". Okay, cool!!! Now, where do I buy a 1 mm wide grooving tool? I have googled this and still have no clear answer. I can turn a lathe tool for general purpose turning from HSS, but I don't trust myself to be able to make a 1 mm wide grooving tool. I don't want to spend a zillion bucks on this either. My lathe has a 12" swing, and it has a quick change toolpost on it. I prefer 3/8" square tooling, but in a pinch I can mount 1/2" square tooling. I'm not averse to using inserted carbide if the price for the carbide and the appropriate holder don't break the bank. Since the piston groove will be in cast iron or aluminum, I could even work with 1mm wide HSS and a 3/8" square shank.---Thanks.---Brian

 

[Gordon]

I'm having a no work Sunday---I need it. But the old brain cells keep clicking away. Every thing I read about rings recommends that the ring thickness should be 1/30 to 1/25 of the cylinder bore (and the depth of the ring can match the width so your ring actually has a square cross section). On a 1" bore, that gives a ring width of 0.033" to 0.040". The width of the groove in the piston should be 0.001" greater than the width of the ring itself. So---If I made my rings 0.038" wide, then the groove in the piston should be 0.039"---And 1 millimeter is .0394". Okay, cool!!! Now, where do I buy a 1 mm wide grooving tool? I have googled this and still have no clear answer. I can turn a lathe tool for general purpose turning from HSS, but I don't trust myself to be able to make a 1 mm wide grooving tool. I don't want to spend a zillion bucks on this either. My lathe has a 12" swing, and it has a quick change toolpost on it. I prefer 3/8" square tooling, but in a pinch I can mount 1/2" square tooling. I'm not averse to using inserted carbide if the price for the carbide and the appropriate holder don't break the bank. Since the piston groove will be in cast iron or aluminum, I could even work with 1mm wide HSS and a 3/8" square shank.---Thanks.---Brian

>.040 cut off blades are fairly common. Another alternative is to use your new tool post grinder to grind down a wider blade like grind 1/16 wide blade to .040 on the end. You only need a short piece on the end ground down.

https://smile.amazon.com/HHIP-2000-...cut+off+blade+.040+wide&qid=1622410048&sr=8-3

 

[kuhncw]

Brian,

AR Warner sell high speed steel 0.031 inch grooving inserts, along with 0.015 and 0.062 widths. You can buy a kit with holder or individual inserts.

Chuck

Kit #21 3/8 inch Cutoff Groover Right Hand

 

[Ghosty]

Brian, This is what I use, 1mm groove cutter for circlips, will go to a depth of 2mm(80 thou)
Cheers
Andrew

 

[Nerd1000]

Just grind one from a HSS blank, it's easier than you'd think. I started my 0.8mm grooving tool by hacking a chunk out of the side of a 1/4" HSS blank using an angle grinder with a cutoff disc. Then I ground the sides, you don't have to keep them parallel so long as they get narrower as you move back from the point and are relieved towards the bottom. You can leave the end of the HSS blank alone as it is already square and relieved. Once I got close I got my micrometer and started doing very light touches on each side, followed by a check with the mic across the tip. Finally once it was on size I honed the tip sharp. No need for rake or anything, just leave it flat.

Alternatively, as you have a toolpost grinder and are using cast iron pistons, why not mount a 1mm cutoff wheel for a 5" grinder and grind your grooves in?

 

[Harglo]

Brian
Ive run into this piston grove cutting tool think. I hand grind it as close as can than cut the piston grove FIRST then make the ring height to fit even if its a thou or two on way or another. Its just seems easer to adjust the ring height than changing the piston grove
Harvey

 

[Gordon]

I have always had a problem getting the groove to the correct depth. I have used the dial on the cross feed and when I put the ring in the groove and try to put the piston in the cylinder it will not go in because the groove is not deep enough. When the groove is only .030 to .040 wide it is hard to measure. The only thing I have which will fit in that narrow groove is the depth end of my dial calipers and I cannot get the same reading twice. I do have a depth mic and I may have to sacrifice that by grinding down the end so that it will fit in the groove.

What do others use?

Gordon

 

[L98fiero]

I have always had a problem getting the groove to the correct depth. I have used the dial on the cross feed and when I put the ring in the groove and try to put the piston in the cylinder it will not go in because the groove is not deep enough. When the groove is only .030 to .040 wide it is hard to measure. The only thing I have which will fit in that narrow groove is the depth end of my dial calipers and I cannot get the same reading twice. I do have a depth mic and I may have to sacrifice that by grinding down the end so that it will fit in the groove.

What do others use?

Gordon

Measure across the largest feeler gauge you can fit in the groove and piston with a caliper or mike and subtract the width of the blade and the piston should give the depth of the groove. Obviously the closer the feeler gauge is to perpendicular to the axis of the piston, the more accurate the result will be.

 

[Gordon]

Measure across the largest feeler gauge you can fit in the groove and piston with a caliper or mike and subtract the width of the blade and the piston should give the depth of the groove. Obviously the closer the feeler gauge is to perpendicular to the axis of the piston, the more accurate the result will be.

This got me to thinking and I looked online and found digital depth gage and I have a narrow probe that fits on the end of a dial indicator. If I make a sleeve to fit on the shoulder of the indicator I can just let the probe stick out of the end of the sleeve I can place it on a flat surface, zero it out and read the depth on the indicator. Just never really looked for a good alternative. Again "Too soon old and too late smart"

Gordon

 

[Steamchick]

Fair enough Brian. I haven’t tried lapping a big piston.



which confirms my thinking that the fit of the piston isn’t critical for a piston with rings. There are thousands of engines being mass produced every day without lapped pistons.

Hi Tim, the piston manufacturers work to 0.0002 mm when machining, but the maching of measured pistons to bores needs better than that so the pistons and bores are measured, given size grades, and matching grades are selected on the assembly line. This applies to bores, crank journals, gudgeon pins to pistons and con-rods, rings, bearing shells to cranks, con-rods and crank-case journal mounts. A big part of the longlevity of the engine, so it can be driven from new as if it has been run-in already. And then last 100 of thousands of miles before it needs a re-bore or crank re-grind.
In the mid-1960s cars needed a re-bore at 20, 000 miles (I did dozens!), and crank re-grind at 40,000miles. In the 1970s I had a well-tuned motorcycle that wore the rings so I had compression loss after 3 ~5000 miles! Nowadays, that would be quite a low performance engine! As standard I changed the rings at 10,000 miles, to regain good compression. Poor by today's standard, but that is the same technology and machining capability achieved by our model workshops...
It was a revolution in machining in the1970s that made engines to better tolerances, partly driven by the fuel crisis and public and national interest in economy, partly following the small wealth boom of industries that survived the 1960s, who invested in new machinery with better capability. Yet in the late 70s I worked with 4 other engineers, and we all had new Company cars, built in the same week, and with the "same" engine. Top speed varied fromantic about 90 mph indicated to nearly 110mph, and a clear difference in performance as driven, and fuel economy. - We compared then together over 12 months and 20 - 30,000 miles per car. As we were working on a job 350 miles from home we did the same commute and long trips. One was showing definite worn engine symptoms at 30,000 miles (losing some compression, and burning oil), one just seemed like new. Very variable quality! Not in the industry today.
Enjoy,
K2

 

[cwelkie]

Another overlooked way to cut a (ring) groove is with a saw blade. They come in many and various thickness of numerous tooth counts. An arbour that mounts in the toolpost is straight forward such that the cutting edge can be rotated into position at the correct height.
... or give grinding one a go; it's surprising how close one can be done by hand with care and patience.
Charlie

 

[cds4byu]

My lathe has a 12" swing, and it has a quick change toolpost on it. I prefer 3/8" square tooling, but in a pinch I can mount 1/2" square tooling. I'm not averse to using inserted carbide if the price for the carbide and the appropriate holder don't break the bank. Since the piston groove will be in cast iron or aluminum, I could even work with 1mm wide HSS and a 3/8" square shank.---Thanks.---Brian

I recently figured out a setup on my Sanford surface grinder that makes it trivial to grind grooving tools. Send me a blank, and I'll make the tool and send it back to you. PM if interested.

Carl

 

[Brian Rupnow]

Carl---I'm in Ontario, Canada. Where are you?--Brian

 

[Vixen]

Hi Ghosty

Do you have the maker and part number for those grooving inserts

Thanks

Mike

 

[Ghosty]

Hi Ghosty

Do you have the maker and part number for those grooving inserts

Thanks

Mike

Mike, I only have the holder # as I bought the cutters from a machine shop getting rid of new old stock, I bought 5 which gives me 15 cutters.

 

[L98fiero]

Hi Ghosty
Do you have the maker and part number for those grooving inserts

For one offs the Nickole inserts are probably the least expensive way, I think MSC has 1mm inserts for about $32 USD and the holders are easy to make from a piece of square stock.

 

[Vixen]

Thanks, I will have a look at each of those.

Mike

 

[jkimberln]

If you want Nickole inserts, buy them at Victornet.com. Cheapest vendor I've found at $19.50. I have a few of these and they are not cheap anywhere but are a good product. I used to use Thinbit but they are beyond my economic interest.

 

[petertha]

I used a Nickole for the ring grooves on my radial pistons, mostly because I already have the toolholder set. You could just as well use self made HSS parting type tool because the depth is so shallow. I didn't make the groove width in one go. Stepping over is no big deal especially with DRO or indicator. But it provides the opportunity to creep up on dimension using a feeler gauge stack so you hit your target dimension exactly. A blade micrometer is handy in these instances, or alternately mic off a pair of parallel feeler gages or gage blocks

What is important is the cutter should have a square, sharp corner. Or re-phrased, any tool corner radius should be less than the slight chamfer you have on the ID corners of the ring such that there is no chance the ring will hang up on what would become a micro fillet in the groove. These pistons (which dimensionally mimic the top end of an OS-56) also have a slightly reduced diameter crown from piston top to ring groove. I presume that's for easier ring installation & has no adverse effect on performance.