Cylinder bore surface help

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Joump5

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I’ve bored my 2” cylinder and honed it to the
point where it doesn’t seem to be getting any
smoother. It is very smooth to the fingertip, but
I can see rather coarse looking hone markings,
that can barely be felt with a fingernail, I was using a 220 grit, 2-7” hone. I am thinking bore needs to be smoother,but I’m not sure if I
should look for a finer grit hone or cast and
turn an aluminum lap.
Is a crosshatch pattern needed on the bore
of an experimental /hobby engine?
Can anyone describe how smooth bore
needs to be?
 

Hopper

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IC engines will usually have a clearly discernible cross hatch pattern honed onto the bore. If you are using conventional cast iron rings, it will wear in to a smooth surface with remaining fine cross hatching for oil retention. 2" bore is same size as a small motorcycle engine so normal automotive practice should be appropriate. I wouldn't lap the bore of an IC engine that size. Depends too on what rpm you are looking at. Model aero racing two stroke engine is a different beast from a vintage hit and miss model.
 

Joump5

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Thanks for the replies.
I haven’t made piston or rings yet but I was
thinking three solid cast iron rings. I have
no idea what RPM to expect but would like
to try to keep it as low as possible for heat/
wear/ stress reasons.
 

XD351

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If you want a finer finish wrap some wet and dry paper of a finer grit than your hone around the hone and give it a few passes . This is something many engine builders did when pre lapped rings hit the market as they didn’t need as much bedding in .
Why 3 rings ? For a 2 inch bore i would stick with the two for a two stroke and two + an oil ring for a four stroke unless it is a diesel .
I had to lap the cylinder on my hit and miss engine because the cast iron bar i machined it from relieved itself and the cylinder went oval as i bored it
 

Joump5

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XD- I was thinking about trying to use some
fine wet and dry with the hone, but I thought
the paper might stick to the bore,with the
hone running over the back of the paper.
I will give it a try. As for the three rings-My
plan was to drill a hole down through the side of the cylinder,into the bore,so that with the piston all the way back, the space between
the second and third rings could be filled
with oil to lubricate cylinder enough for a
short run. Does this sound like it would work?
As you may have guessed, this is my first
experience designing and building an engine.
Edit- this will be a four stroke engine with
homemade cast iron rings. No actual oil
control ring.
 

lohring

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In experiments with a 26 cc racing engine, it was found that the hone pattern made a small power difference. The bore was 34 mm diameter. The cylinder at that time was nitrided steel with a single commercial steel ring. The best power was with a course hone with the peaks smoothed off leaving a smooth bore that had a course groove pattern. Later it was found that a very smooth chromed bore was even better. Commercial cylinders run a chromed aluminum bore that is very smooth.

Lohring Miller
 

XD351

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To stop the paper slipping i cut a notch in one end so i end up with two tags which are wrapped around one stone and glued back onto the back of the wet and dry sheet - i forms two hoops that hold onto the stone and the notch gives clearance for the pivot point on the back of the stone .
My hit and miss engine uses the same system for lubrication but i run two stroke oil in the fuel as well .
 

Joump5

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On the advise of XD351,I used wet/dry paper
with my hone, which worked very well. I then tried putting crosshatch in using 220 hone, and am not really thrilled with the results. Angle of crosshatch is shallow and irregular because
drill speed and in-out motion were hard to
regulate. I’m going to go back in with the wet/dry and then try putting in crosshatch again. Any advise on getting something close
to a good 45 degree pattern? Will my 220
grit hone provide proper depth for holding
oil?
 

XD351

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I wouldn’t go back to a 220 grit i would hone to size with it then use a finer grit wet and dry of 400 or 600 grit to smoothen it up and the last few passes i would be concentrating on getting the cross hatch near enough to 45 deg but you should already be getting a cross hatch with the 220 grit ,the cross hatch will be irregular while honing to size as you often have to pause for a few extra rotations of the hone where the bore measures a little tight or you may short stroke it to keep it down at the tight spot a little longer . It sounds like you are trying to polish the 220 grit finish out completely then put it back in . One trick i have used a lot is to get a reasonable cross hatch finish is to rotate the hone by hand for the last dozen or so strokes and this will put all the cross hatch you will ever need and don’t panic if the pattern isn’t perfect - the engine will run just fine and a round and parallel bore is more important than a perfect cross hatch . The cross hatch does more than hold oil it causes some controlled wear when the engine first fires up which helps the rings bed in to the shape of the cylinder better that is why you de glaze a cylinder when fitting new rings into a used bore and once that happens the effect of the cross hatch is ever diminishing as the engine is used to the point of needing a rebuild .
 

doc1955

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You really don't want it real smooth a 63 finish is plenty good enough if you are using cast iron rings if you are using rubber rings (which I personally will never use) then you would want a 16 or better. The smoother you get it beyond a 63 the longer it will take the rings to seat.
 

Joump5

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Yes,my latest plan was to polish out the first 220 crosshatch attempts with 400 wet/dry and then go back and try again to put in crosshatch with 220 hone.I’m not really trying to get to a certain size,as piston and rings haven’t been made yet. I was assuming crosshatch should be relatively deep to hold oil.
What is 63 or 13 finish? I’m
Milllicrons ?
Is there a way that I would measure or eyeballasize that?
 

XD351

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https://www.cnccookbook.com/surface-finish-chart-symbols-measure-calculators/
This explains what doc1955 is talking about although you won’t be able to measure it as you don’t have the scale .
If you are making your own rings the 240 finish will help your rings to bed in better if they were commercially made i would go finer , home made rings can be cantankerous especially if you are new to making them .
 

doc1955

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Here is a link to charts if you are not familiar with surface finish call outs. With a 63 you can still feel the boring bar marks in the cylinder with your fingernail which is what you want for cast iron rings. Scratches in the cylinder are ok as long as they go around the bore and not straight up and down. As the rings seat these will be taken out by the rings.

https://www.engineersedge.com/manufacturing/surface-roughness-conversion.htm
 

Rocket Man

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I use to work in a factory that made cylinders they never honed any of the cylinders they used steel ball bearings to roll in the bore surface to make the metal smooth. It worked like a hone but instead of having a 600 grit stone it had 6 rows or .250" diameter steel ball bearings. Once the devise was inside the cylinder bore there was an adjustment that pushes the roller balls out very tight against the cylinder surface. Turn on the oil lube then turn on the spinning roller ball tool let it spin about 30 seconds to 60 seconds cylinder bore was smooth as glass with a mirror finish. They always left bore diameter about .0005" extra metal the tool device would push the metal down to .0000" The tool room at work invented this tool I have never seen one for sale but that was 50 years ago. Maybe someone makes and sells them now if not your all machinist make one.
 
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holmes_ca

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I used a Flex-Hone on the four cylinders of my Sealion 1-inch bores got a beautiful crosshatch, placed oil in a large Coffee container and used slow speed hand drill worked a treat,

Edmund
 

holmes_ca

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Sorry made mistake 7/8 bores and Flex-Hone was 7/8 180 grit Meinhite cast iron liners

Edmund
 
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