Queston about honing a cylinder

[bertsmobile1]

I am going to chime in with a little bit of (possibly incomplete) information that I am aware of (or believe to be true and pertinent)

You must cross hatch or hone your cylinders when you replace the piston rings. I was told (informally) that two fold, the newly roughened surface aids in the new rings being seated to the cylinder mating surface. [side bar]
Yes the bore is not perfect round and neither are the rings so they wear into each other.
If you just replace the brake pads without resurfacing (or glaze breaking) the rotors, the pads will not seat on the rotors and you will only have partial contact, thus less braking ability]
No wrong a myth circulated by owners and makers of disc grinding machines. The amount of clamping pressure applied by the brake piston is orders of magnitude higher than the force applied by rings to a bore.
Piston rings also remove a significant amount of heat from the piston to the cylinder wall
So in that sense, if you just install new rings on a glazed and polished cylinder bore, there is not any microscopic rough surface to aid in the wear and break in of the new rings. You may have been better off leaving the old rings in there as they have already been shaped and polished to the current cylinder profile.
Sort of true , if the rings have worn too thin, then they are too thin and you run the risk of them breaking up
Basically, your break in period, is a period of all the parts being worn and polished to perfect the microscopic fit of all the components to one another. If you were to monitor everything that is going on, you would note that compression increases over time of correctly breaking in period, and temperature will slowly decrease as the parts polish and friction decreases.
Correct
Remember it is called cross hatching, so while you are spinning the hone, you need to be always moving in and out of the bore. Don't just put a hone stone in there and rotate it quickly without aggressively moving in and out of the bore. Slow to moderate rotation and a balanced in/out movement all the while lubricating to remove particle matter. Think wet sanding a paint surface with fine grit sandpaper. You use the water to keep the cutting surface of the sandpaper from clogging with the dust...

Also, the cross hatching will hold more lubricating oil for the break in period, and assist in carrying the wear metals away (well, this is true in crankcase engines with oil bath and I can imagine somewhat similar in two stroke also)
No, you don't want any oil in there which is why you install rings dry. Initial wear in particles are sent to the crank by blow by and you run a new engine rich to help wash the bores.
Which inspires another comment for discussion, in two stroke, use additional oil in fuel for initial break in?
No same reason, actually I break in two strokes with a very lean mix. Fuel alone will provide sufficient lube for the big & little ends for a long while and a little squirt of strait oil directly into the crank will keep the mains happy.
And we are air cooled, I know with aircraft engines, we do not run them much on the ground, (especially with the cowling removed) they need to be flown a certain way that puts the most cooling air across the cylinder fins for cooling (shallow climbs), and shallow descents (powered) descents to avoid shock cooling the cylinders.
If you overheat the cylinders during that break in period of high friction, you run the risk of galling the pistons.
Galling is the wrong term but you do get metal to metal contact which will abrade the piston and deposit aluminium on the bore
So maybe, we should start a freshly honed cylinder with new rings, run it for an initial period (in tall grass like someone previously posted) but for a limited period and then let it cool off. Then an little longer run with a heavier load, but keeping in mind not to run it too long and getting too hot.
Not allowing the engine to overheat is a good idea however, heavy loading to develope maximum pressure on the rings is the go then back off to reduce the load allowing the debris to be removed then heavy contact again.
After 5 minutes the rings have seated & worn in, after that you are worried about everything else setteling down
I was told one time to drive it like I stole it,
This is to bed in the rings
and other said to baby it during break in.
This is for fully rebuilt engines where bearing and bushes have to stettle into place thrust washers have to position themselves, crankcases have to heat up, expand then contract to align itself in its bearing / bushings, cam followers have to break in etc etc etc.
I know with aircraft engines during breaking, it is common practice to continually change the power settings so as to not "groove" the engine to being used to just running at one particular power setting...
yes proper run in technique for any piston engine
I apologize for being so long in the finger. I like to learn and teach what I have learned. If I openly run my keyboard, maybe someone will point out where I am thinking wrong...

Not far off, not meaning to sound patronising

 

[jp1961]

Thanks Bertsmobile1,

Yeah, two old countries separated buy the same language and a very large pond,,,lol. Your input is appreciated.

Jeff

 

[timw128]

... I seriously doubt there would be any casting voids in a modern pressure die cast cylinder...

Highly incorrect statement. A simple look at Mercury Marine V6 2 cycle engine blocks from the 1980's forward will clearly remove any of your doubt.

Of further note, your statement regarding Nikasil is also questionable- https://en.wikipedia.org/wiki/Nikasil

 

[bertsmobile1]

Sorry Tim,
But an entry in Wickipedia does not cut the mustard.
Google "Heat Resistant Cast Irons" and you should come up with foundries casting,
Nickasil ( Ni-Al- Si )
Nicrosil ( Ni-Cr-Si )
Nimosil ( Ni-Mo-Si )
particularly in the UK
BSA held the patient for some of the alloys back in the 60's before they were asset stripped by Manganeese Bronze Ltd.

And a trade name for an alloy can also be used as a trade name for a plated coating as they are not the same thing.

You will find their chemical compositions and mechanical properties on pages 404-406 of the American Society of Metals Handbook volume 1 Properties & Selection of Metals
Also in Volume 7 Atlas of Microstructures

AS for mercury V 6 blocks you have me at a dissadvantage here I have never seen one,
OTOH I have cast around 1000 tons of finished Al castings and made about 60 tons of secondary foundry ingot per week for 5 years.

There is virtually no way to create micro pores in a casting without making a substantially inferriour casting.
Hydrogen is extreamly soluible in molten aluminium and almost all gas porosity will be due to hydrogen.
Because hydrogen atoms are so small they travel quite easily through the solid metal lattice and when 2 hydrogen atoms come together they immediately for a hydrogen molecule.
The hydrogen molecule is substantially bigger and forces the layers of aluminium atoms apart,
the net result of this is the item grows, gets physically bigger and was the chief reason for a lot of engines using heavy cast iron pistons because the aluminium ones expanded and siezed in the bores.
This expansion is perminant and untill a method of scouring the hydrogen out was found limited the developement of alloy pistoned engines till chlorohexamine was found to be efective and it is still used today, although chlorine gas delivered through a titanium lance is a lot more effective.
The only other way to have pores is to super heat the alloy then short poor so there is not enough molten metal to accomodate for the volume contraction from liquid to solid but this would not happen at a core because the melt solidifies from the outside in, not the inside out although with dendritic modification by innoculation combined with ultrasonic disruptions you can get almost equal rates of grain growth inside out & outside in but as far as I know this was only used to facilitate the pouring of larger cross section rolling & extrusion billets.
To get a consistant and equally dispersed surface porosity on the face of the bore it would have to be done chemically after casting.

You do get porosity in castings when using metal moulds, and that is a defect that happens till the surface temperature of the mould gets up to working temperature due to excess chilling at the mould surface.
You also get massive chill grains so the first few casting usually go back into the pot.

If you can explain how you get micro pores only on the bore , controlled so they are uniformly distributed and do not extend all the way through to the water jacket then I am all ears.

 

[fabricgator]

Not far off, not meaning to sound patronising

Thank you, I pick up some of this (previously posted beliefs) stuff through osmosis and contact in industry and some of it I draw my own conclusions. This is why I threw this out there so I could be either corrected or confirmed. Thank you for taking the time to straighten these belief's out. Your input only enhances my knowledge base.

I am also learning quite a lot from you and Tim's discussion on metallurgy, casting and plating. This is why I love the internet. I am continually growing and enhancing my knowledge base.

Thank you all.

 

[jp1961]

Hi All,

Nikasil plated cylinders may be more common than you think. The Zenoah G-20 model airplane engine has a Nikasil plated cylinder.http://www.horizonhobby.com/product...e-engines-15042--1/zp-20cc-gas-engine-zenep20

Click the 'specs' tab once the screen comes up.

Jeff

 

[motoman]

An interesting thread. I would like to hear more from the 2 stroke guys who (?had) hinted extra hard bores are used. Also ,like so many threads here, there is an opportunity for forum people to educate. There are many who read this stuff who wished they knew more about the unstated assumptions in many statements.

So maybe start with a primer on how piston rings work....

How many think sealing depends upon the spring affect of the compression rings? Like, dude, your have to compress them to get them into the bore?

How do oil rings work and what are they supposed to do?

What is a piston land?

Are there basic clearances and dimensions which must be met when installing rings?

Should bores be perfect or is taper , out-of-round ok? How about top ridges?

This can all be dug out of basic literature, but maybe some discussion is worthwhile?

 

[javjacob]

Out of curiosity is it possible to Nikisil plate a lawn boy cylinder?

 

[jp1961]

You could probably have any cylinder plated, but then you'd need a smaller piston and rings. Were Lawn-Boy cylinders ever available oversized? Some manufacturers offered oversized pistons to allow for boring to remove scoring, out of round, etc.

I have a Bridgeport with a boring head and could accurately oversize the bore, but I would need to know how thick the Nikasil plating would end up to return the bore to factory specs.

Jeff

 

[robinb66]

Also it may be worthy to note that when honing a cylinder or at least making the decision too cast iron cylinders are pretty much ok but if it is a aluminum cylinder with no iron sleeve then at most just run a deglazer a couple of times and don't hone it!