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Hi @Danuzzo
I used the steel grades I had on hand for the cylinder
Piston: aluminum 6061, 7075, brass, cast iron
If I use cast iron rings, I don't worry too much about the inner diameter of the cylinder, if I use O-rings, I have to bring the inner diameter of the cylinder to the outer size of the O-ring
If I don't use rings, I just need to make the piston smaller than the cylinder diameter by about 0.03 or 0.04 mm

Danuzzo said:
Also, many questions on lapping/honing the cylinder bore. 1. What is the difference between the lapping and honing?
2. Is the purpose to make the bore very smooth? My bore came out smooth with the lathe, at least to the naked eye and feel.
3. Is it necessary to hone or lap if rings are used, or is it dependent on the material of the piston?
Click to expand...
--lapping/honing the cylinder bore : No difference , depends on cylinder diameter and tool selection
2. and 3. : Simple way: make a piston and test compression, if compression is good - suction is good then you don't need to worry about the cylinder

This will give you more confidence ..
the young guy did this engine and it runs well !

4.jpeg
6.jpeg
8.jpeg
 
Last edited:
Danuzzo said:
Thanks for all the responses. Good points by all. Nerd1000, thanks for pointing out the typo. I do have time, but not that much patience ;). Also, the more I measure the bore for taper, the more I am getting either no taper at all, as far as I am capable of measuring or no more than .0001". I will measure again today once I complete the head end of the cylinder and get it off the chuck.

It appears that it has been aptly pointed out that the piston material and/or ring choice is an important consideration. As pointed out a few posts ago, the cylinder is made of some mild steel. It looks like many of you opine that an aluminum piston is the way to go. Is that with or without rings. I do note that Awake used a cast iron piston for his steel webster. I have suggested a 12L14 piston and am also wondering how a bearing bronze piston would work. I have plenty of 12L14, bearing bronze, and aluminum for the piston size. Further detail on material with or without rings and fitment would be greatly appreciated.

Also, many questions on lapping/honing the cylinder bore. 1. What is the difference between the lapping and honing?
2. Is the purpose to make the bore very smooth? My bore came out smooth with the lathe, at least to the naked eye and feel.
3. Is it necessary to hone or lap if rings are used, or is it dependent on the material of the piston?
Click to expand...
There are basically 3 ways to get a seal around the piston:

1. Metal piston rings
2. Viton rubber O-ring
3. Make the gap between the piston and the cylinder so small that the oil itself will form a seal.

If you use metal rings the purpose of honing or lapping is to create a slightly rough crosshatch texture on the cylinder wall. When the engine first runs the piston rings will abrade the 'peaks' of the crosshatch and make a smooth surface with valleys through it to hold oil, at the same time any imperfections in the rings are worn down to make them smooth.

If you use a viton rubber ring, you instead want the cylinder wall to be lapped smooth to avoid damaging the soft O-ring.

For method 3 a smooth surface is also desired, however you also need to make the piston and cylinder out of materials that have similar coefficient of thermal expansion. Usually a cast iron piston and cylinder would be used. The piston is made slightly oversized, and lapped down until it fits in the cylinder with a very light press (finger pressure).
 
Danuzzo said:
Also, many questions on lapping/honing the cylinder bore. 1. What is the difference between the lapping and honing?
2. Is the purpose to make the bore very smooth? My bore came out smooth with the lathe, at least to the naked eye and feel.
3. Is it necessary to hone or lap if rings are used, or is it dependent on the material of the piston?
Click to expand...
The length of the cylinder is like two inches long. You are having an inordinate concern for a tapered bore here and your gauge readings seem to stall you out on the progress. Continue the build with whatever choice of material and get a hands on experience with the cutting properties and develop some instinct on matching up the piston to bore interface. 👍
 
Cylinder is done with all but the holes to be drilled and lapping the bore.
 
on rings, if your buying the ones from otto engine works as plans give a part number for (which is what i used on mine) then you do need to be as per plans call for. i later learned to make my own rings. i bore the cylinder with hopes of getting it spot on size but usually a tad over by mistake. i then cut the piston to match the bore and the ring grove in it. i then cut the ring stock to outer size match the bore and inner size to match ring groove with just a little bit of wiggle room because the corners of the grove in the piston usually keep you from compressing all the way into the piston ring grove. and honestly i feel that the engine would have ran without the piston rings due to the good fit of the bare piston in the cylinder to begin with. but this is just my experience. i only have to 4 strokes under my belt. the webster and the upshur vertical single. the rest were vacume flame eater, steam and a partially running 2 stroke diesel
 
werowance said:
on rings, if your buying the ones from otto engine works as plans give a part number for (which is what i used on mine) then you do need to be as per plans call for. i later learned to make my own rings. i bore the cylinder with hopes of getting it spot on size but usually a tad over by mistake. i then cut the piston to match the bore and the ring grove in it. i then cut the ring stock to outer size match the bore and inner size to match ring groove with just a little bit of wiggle room because the corners of the grove in the piston usually keep you from compressing all the way into the piston ring grove. and honestly i feel that the engine would have ran without the piston rings due to the good fit of the bare piston in the cylinder to begin with. but this is just my experience. i only have to 4 strokes under my belt. the webster and the upshur vertical single. the rest were vacume flame eater, steam and a partially running 2 stroke diesel
Click to expand...
I don't think I will use rings. I like the idea of a close fit of an aluminum or cast iron (if I can find some cast iron stock) piston. That is how I have made my steam engines.

Still don't know enough about honing/ lapping to decide what tool to use to do so, particularly with a mild steel cylinder to close fit aluminum piston combo.
 
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That is not a good combo on an IC with no rings as the heat will likely make th episton expand and sieze the engine. Cast iron will be better in your steel liner.

You will need to use a lap to smooth the bore and this also helps ensure it is parallel. Then lap the piston into the bore
 
Jasonb said:
That is not a good combo on an IC with no rings as the heat will likely make th episton expand and sieze the engine. Cast iron will be better in your steel liner.

You will need to use a lap to smooth the bore and this also helps ensure it is parallel. Then lap the piston into the bore
Click to expand...
Excellent point. I think I can scrounge up some C.I. for piston size.

As to lapping, what should be used? A cylinder hone? Or some other appropriate tool?
 
You use a hone for honing and a lap for lapping.

Quite a few choices such a scommercial laps as linked to above, you can make your own expanding lap from aluminium or copper and charge it with various grades of silicon carbide powder mixed with oil to form a thin paste. Don't use automotive valve lapping paste a sit is too coarse. For small bores even a piece of hardwood turned to size can be used with the abrasive.

Steel liner on homemade ali lap


IMAG0627.jpg




Iron Piston being lapped into the same liner

IMAG0647.jpg
Or the good old emery cloth wrapped around a wooden dowel, metal trod or tube can give a good result working down through a couple of grits and adjusting the diameter by slipping in a piece or two of copy paper between the Emery.

Photo 26.jpg


This is another engine CI on CI that was just done with emery, no rings, gasgets or even valve springs but you can see by the way the engine bounces back on compression that there is no problem with that.



Runs OK too, valve springs and head gasket in place but no rings

 
Thanks, Jasonb; you have come through again with an excellent post. Need to study this for the next few hours.

Thanks, Chuck. Price is certainly reasonable. Just so I understand how they work. I would think I want the 7/8" size (.875") if I were to go that route. Would it go down in size to .872" to start and then adjust up to .875", is that how they work?
 
Have you considered the cylinder liner material that has no need for honing, lapping or boring? There for no tooling for these operations needed and just fit the piston to its bore?
 
Longboy said:
Have you considered the cylinder liner material that has no need for honing, lapping or boring? There for no tooling for these operations needed and just fit the piston to its bore?
Click to expand...
I have already made the cylinder out of mild steel. I don't want to buy more materials. If I understand correctly, my current cylinder bore type that was bored on the lathe needs lapping?
 
Last edited:
i lapped mine. i made my own crude lap out of a piece of aluminum round stock. drilled and tapped it 1/4 x 20 with a taper tap then sliced it on the band saw long ways twice. then when i start in a 1/4 x 20 bolt in the end it makes it expand as the bolt starts hitting the tapered bottom. i used diamond lapping past i got on ebay. the result was a near mirror finish
 
minh-thanh said:
You have to measure several places along the length of the cylinder, if the dimensions are close together it should be fine.
Can you take a picture of the inside surface of the cylinder ?
Click to expand...
I have done so, and it looks like no taper. I will try a photo but doubt it will show adequately.
 
Longboy said:
You should test fit your piston after the boring. If it slides and turns uniformly in the bore full stroke....leave it at that.
Click to expand...
I made an aluminum "piston" and it seems like a good fit. (just checking for fit and working toward making a lap; I will not be using aluminum for the piston.)
 
minh-thanh said:
You have to measure several places along the length of the cylinder, if the dimensions are close together it should be fine.
Can you take a picture of the inside surface of the cylinder ?
Click to expand...
Here are a couple of pictures. You will note some tool marks; but, I cannot feel them. Very smooth.
 

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