Tech Tip "Cylinder prep before instalation"

[RM_guy]

Originally posted by motometal
...but the rings are now riding on peaks of metal (which will protrude thru said oil film) unstead of a nice smooth "bearing" type surface...

The rings (and piston) ride on a film of oil, not metal. That's why the oil is there. If there was metal to metal contact it would wear out very quickly. With out the hatching, to retain oil, your engine will not last as long.

There is also a surface roughness on your fork tubes to lubricate the fork seals. It isn't much but if you polish the inner tubes too much it will ruin the seals.

 

[motometal]

uhhh, I follow what you are saying, but the inner tubes are chrome plated induction hardened chrome-moly steel tubing, which has about the finest polish you can possibly have! If you don't believe me, run your profilometer over your fork tube and tell me what reading you get! :debil:

let's not forget that the piston also has machine marks which would help retain oil. Does this mean that if these marks weren't there the engine would be doomed to impending failure? I realize that unlike the cross hatching, the marks in the piston have no effect on ring seating.

(I love these techie debates...so much more interesting than the weather!)

 

[RM_guy]

I’m just going to ramble on with some thoughts. This is usually a misunderstood topic and I’m glad to see it being discussed.

Just because the plating and base material of the inner tubes are hard materials doesn’t mean that the surface finish is smooth. And you don’t have to be able to see or feel the roughness for it to be there. The fact is, there has to be some surface roughness that retains oil to lubricate the seals. As the seal slides along the inner tube it wipes oil from it. The nooks and crannies of a rougher finish will trap oil to allow the seal to slide and extend it’s life. There will be stiction if there isn’t any oil. The best surface finish for a dynamic seal is 10 to 20 micro-inches. Of course too rough of a finish and you’ll tear the seals apart. If you want I can email you some information on seal life vs. surface finish.

As far as the piston is concerned, not all pistons have machining marks on them. If you look at a cast piston you won’t see as many machining marks as on a forged piston. Since the process for making a cast piston leaves small voids, they are enough to trap some oil, plus a cast piston usually has some friction reducing materials that are added to the aluminum. A forged piston doesn’t have the voids so there are small machined grooves that help with oil retention. The piston and the rings both wear against the cylinder wall so they both need lubrication. If a forged piston was smooth it would wear faster than one that had machining marks on it but the cross hatching on the cylinder wall has some oil so that helps.

When ever two materials wear against one another there must be some form of lubrication or galling will take place and the softer of the two materials will be the looser. The lubricity can be from the material itself as in Teflon or from constituents in the material like silicates in a cast piston but the most effective lubricant is oil. The oil forms a boundary layer that separates the two materials so there is never any metal to metal contact. Since a fresh batch of clean oil is brought in with every cycle, there is always good lubrication. The oil can only do it’s job if it can “stick” to the moving components long enough to protect them. That’s why the cross hatching is needed.

I’m not sure if ring seating has much to do with surface finish. Honestly, I’m not sure what even happens when a rings “seats”. There was an earlier post about engine break in with a new top end and if I remember, Rich said that tolerance’s were more important than anything. That’s why the pros can race an engine with little or no break in. The mechanics make sure that all the clearances and fits are perfect when the engine is assembled.

 

[dale williams]

I don't think there is a requirement for the cylinder wall to retain oil on a 2 stroke because there is oil everywhere. The oil vapor is constantly condensing on the cylinder walls provided you don't run the coolant temperature above something like 400 degrees F. 4 strokes tend to wipe the oil clean on the down stroke and if the mixture is rich it condenses on the walls and dilutes the oil film that was left behind. More oil in the X hatching would require more gas to reach the same dilution point. Modern car gas has a little oil in it. I'm not sure it is for the injectors or to increase cylinder life but I think it is a big contributor to the increased miles we are getting on cars between overhauls today.

 

[RM_guy]

This link discussed the need for accurate honing of the cylinder wall in order to properly retain oil for lubrication of the rings. Although it refers to automotive (4 stroke) engines, the concept is transferable to 2 strokes.
http://www.automotiverebuilder.com/ar/ar49852.htm

Here is another article that is actually better…
http://www.babcox.com/editorial/ar/ar90058.htm

If anything these help me to understand ring seating. When the rings seat they are actually knocking off the high spots that remain after honing. It leaves a “plateau” at the peaks of the honed surface that an oil film can develop for the rings and piston to ride on. The film is replenished by the oil that is trapped in the valleys. The interesting thing is that the “plateau” can be pre-established to reduce break in time. Of course the trick is to not “plateau” it too much.

Dale,
There is a lot of oil in a 2 stroke engine but unless it’s getting to the right spot it really doesn’t help much. As the rings slide up and down, they are constantly scraping away and oil that may be there. If the cylinder wall was perfectly smooth, all lubrication would be lost and there would be metal to metal contact. Some oil may not be scraped off but most of it would. A properly honed cylinder leave valleys that trap oil, that can’t be scraped off, therefore maintaining the oil film.

I think it’s a moot point whether it’s a 2 or 4 stroke engine. Both designs need crosshatching to retain oil for lubrication. The difference is that in a 2 stroke, the oil is part of the fuel mixture and pretty much slathers everything in oil and a 4 stroke has an oil sump that splashes oil up onto the cylinder and the oil rings catch and hold it to replenish the oil on the cylinder wall.

 

[motometal]

Certainly the amount of ring seating needed would vary widely depending on the mismatch in profile between the rings and the cylinder. For example, I just changed out the original top end in my CR250. It had about 1 1/2 seasons on it. I'm not going to guess at the hours, because you guys will yell at me. The compression was at 190, and measuring the old and new pistons side by side I had trouble finding any wear on the old piston (using a good digital micrometer).

The ring gap on the old rings was about .002" wider than the new ones. Certainly most of this is normal wear rather than seating, but let's say for argument's sake 1/2 of this wear took place before the ring conformed to the cylinder, which puts us at .001" difference in circumference. Mathematically, since circumference = dia. x pi, this would equate to a difference in diameter of only 1/3.14 (about one third) of the difference in circumference, or about .00035". This puts us at .00017" per side. I would venture a guess that this amount of gap, or mismatch would not result in any significant loss in compression...in fact the film of oil would effectively seal a gap larger than that.

My point? I think machining and quality control practices have produced engines that require minimal ring seating. Certainly, there are engines out there on the loose end of the tolerance that would require more break in and seating, thus furthering the need for carefull break in and good cross hatch on the cylinder.




Regarding the finish on chrome fork tubes...if these imperfections or scratches carry oil, why doesn't the fork tube act like a dust magnet?I would think that some of these dust particles would then be carried back into the fork, then washed off by the oil. The oil would become dirty very quickly.

 

[RM_guy]

Originally posted by motometal
…My point? I think machining and quality control practices have produced engines that require minimal ring seating. Certainly, there are engines out there on the loose end of the tolerance that would require more break in and seating, thus furthering the need for careful break in and good cross hatch on the cylinder.. .

Very true.

Nice analysis of your engine wear. It sounds like you take good care of it and you don’t wind it out all the time.

Regarding the finish on chrome fork tubes...if these imperfections or scratches carry oil, why doesn't the fork tube act like a dust magnet?I would think that some of these dust particles would then be carried back into the fork, then washed off by the oil. The oil would become dirty very quickly.

I’m sure it does to some extent but we’re not talking about deep scratches that hold a ton of oil.

 

[DEANSFASTWAY]

Nice observations on thew Top End , What kind of mixing oil do you use ? do you ride in dust and do you ever follow anyone or are you always out in front .You must take good care of it and never really beat it .On the forks I have seen where mud cakes up the seals but not really dust but when a fork seal gets weeping it seems to attract anything that will stick in the oil . I find it amazing how long this thread has gone.

 

[motometal]

I run 32:1, and have used mostly plain old Suzuki two stroke oil ($3.75/qt) with the exception that I went thru a gallon of Klotz R50 last year. No real preference between these two other than the R50 smells more interesting. People tend to be afraid of the Suzuki oil because they figure they need synthetic, or that it's too cheap to be good. It rocks!

My engine sees the powerband on a regular basis, but it's not like I ride in sand with a paddle tire tapped in 4th all the time. I don't ride in too much dust, I either lead or back way off.

The air filter is only cleaned when it starts to look really dirty. I try not to let it go until it gets caked, but occasionally this happens. With changing the filter every ride, there is more chance of dropping dirt in the boot than really doing any good. As long as the oil is still doing it's job in the filter, dirt shouldn't make it's way through. When I clean my filter, there is never any visible dirt on the inside. I use Silcolene filter oil, with grease smeared inside the boot. Greasing the sealing surface isn't needed unless the metal ring is really warped (it shouldn't be).

My methods may not be the best, this is what has worked for me in the long run.

 

[IRISHCOFFEE]

as a 57 year old i have been thru many brands of oil. Motometal has found a great secret. for some reason few would even think of using suzuki cci. i was put on this oil 20 years by an ACE mechanic. i still feel it burn as clean as anything out there and lubricates excellently. now i can admit that i go the similar time period on top ends. i have been on cr 250s since 86. i ride 6 to 10 harescrambles and at least 5 enduros each year. this is mixed with at least 20 good trail rides. with good filter oil (bel-ray) i have NO problems with excessive wear.

 

[mhardee]

I rode for ten years (10 years ago!) and rode Maicos.. (440 and 490).. back then we'd bore and hone the cylinders for new pistons.

Now, I hear about plated cylinders.. with, what I expect to be, less cylinder wear than in the past.. I have just purchased a 2003 KX-500 and wanted to know where to find out what plating is used on it and normal top-end practices.. hone and replace standard piston or if it's wore what do you do about boring?

Thannks for helping an old-timer out!

 

[DEANSFASTWAY]

CCi is good stuff I remember when it came in a can!KX 500 are plated , you canhone them very carefully once or twice but after that you must replate.

 

[steve.emma]

I agree that on a 2 stroke there is not a lot of point in bore honing as the oil for lubrication is carried in the air mixture, not splashed up as in a 4 stroke. Also many well meaning owners will probably cause more harm than good honing their cylinders for little or no benefit. Cylinders that have worn plated bores are at risk of being worn right through by excess ball honing. Cylinder cross hatch is important on 4 strokes to retain a tiny amount of oil on the cylinder wall for ring lubrication, this obvouisly dosen't apply to 2 strokes.

 

[RM_guy]

Steve,
Re-read the thread. Cross hatching is important on a 2 stroke.

 

[WoodsRider]

Originally posted by steve.emma
Cylinder cross hatch is important on 4 strokes to retain a tiny amount of oil on the cylinder wall for ring lubrication, this obvouisly dosen't apply to 2 strokes.

How do you think the rings are lubricated on a 2-stroke?

If the depth of the cross-hatch is deep enough to go through the plating then the cylinder is either oversize or the plating is too thin.

 

[LEE BAXTER]

The way I hone in my cylinder is to first get a Scotchbrite cloth (nylon pan cleaner)and give it a light rubbing all around the cylinder so it is slightly shaded but not dull (if it is dull then you are too heavy handed) . and spray with WD-40 around the cylinder and rebuild. This is what I use and it works. I own a kx and it works.

 

[Fark]

Still waiting to hear about the nylon hone. I don't think I'e ever seen one.

 

[dbrace]

Ring seating? ring break in? are u guys serious? new bikes dont even need to be run in. as long as your jetting is ballpark and u warm it up get out there and hold it on. You guys carry on like a bunch of old ladies who should take up knitting!

 

[Pete Payne]

guess what?A new bike has a cylinder on it that the bike manufacturer just finish honed before assembly!!!!
After a bike has been ran a bit, the unburnt oil will fill the crosshatchor some of the crosshatch will be worn off . So it is important to renew the crosshatch at each rebuild.

 

[motometal]

Regarding the KX500; unless it has a problem with the cylinder plating from the factory, you shouldn't even need to look at it for at least a season if not longer (depending on riding conditions, etc)

500s don't wear like 125s...low piston speed, and the piston and rings have a HUGE surface area over which the forces (wear) are dispursed.

I once had an air cooled 495 KTM with several hard seasons on it, was going to freshen up the engine but it looked like new when I inspected the innards!

The engine was the last thing that needed attention on that (very heavy) bike!

 

[Jeffack1]

Just rebuilt my GP800 Waverunner. One cyclinder was rehoned and the other cylinder had to be re-nacasiled. Got them back from the shop and put them in the dishwasher (potscubber cycle) when the wife was no where to be found.

Nice clean cylinders. Hope the wife doesn't find out.

 

[holeshot]

Originally posted by mhardee
I. I have just purchased a 2003 KX-500 and wanted to know where to find out what plating is used on it

Kawasaki changd their plating process for '03 to a more durable chrome-type plating (not sure what they call it).

 

[HeavyExpress]

Honing a plated cylinder is chancey at best.You dont want a bunch of people ruining the plating.In itself,the plating has microscopic pores wich have the properties for oil retetion.It does not take a whole lot.If honing is to be considered more important for crosshatching for oil retention,then manufacturers would shurely have a honing tool that exagerrated the crosshating depth.Honing would only be used for breaking the glaze in a cylinder,maybe to smooth a scratch in the wall.Never to put crosshatching in a plated cyclinder.Castiron bores on the other hand need the crosshatching to help seat the rings and the bore,also to hold some oil for this process.
To take a chance on chipping the plating around the port area's of a 2 stroke cylinder are costly.Modern 2 stroke are desinged with this coating to provide better heat transfer and longer lasting cylinder geometry.The pistons and rings are desinged to be put in this type of cylinder combo.I would suggest removing the glaze,and put a good cleaning on the everything(hot soapy water is the best)then assemble everything as clean as possible,keeping your hands clean.It goes a long way to keep it clean.
Really we have a strong debate wether to hone or not to hone...!I dont.In the last ten years i have not seen engine failure or excellerated wear from not having a maincured crosshatching!If you intend to hone the cylinder make shure you know what speed to hone at,and the proper up and down stroke.Also use a good lubricant...ATF is excellent...and by all means dont overhone,more is not better.
most importantly have fun and enjoy your skills.
L8TR

 

[Wilson-1]

With todays hard ultra hard plated cylinders being the norm, I've been under the impression the much softer piston is the item that takes the wear. This make scence as it's cost may be a fraction of what a new cylinder will run.

 

[KM Burgess]

Remember to ball hone at a relativley low speed as the balls on a ball hone can impact the the areas where the Nikasil is bonded to the edges of the ports. I have seen small chips and the Nikasil coating compromised by a ball hone that was too big and/or done too fast. Some times a ridgid hone is safer but requires a bit more skill to use ay home so too much material is not removed. Food for thought?

Cheers