black piston
 

The top of my piton is black and so is the bottom of my plug. Motor might have 1 1/2 gallons threw it. What does this mean? Seems to be running fine but I'm worried about damaging the motor. Also is there a way of removing the build up?

that is normal, and actually a good sign your fuel has caster oil in it......

I'm now using werks 30% if that makes a difference. The same thing happened to a motor last year and it seemed like it lost compression rather quickly. Both motors were orion crf 21 wasps.

if it lost compression fast it is likely you ingested dirt.......carbon buildup on the piston has nothing at all to do with it, in fact because it has a carbon buildup it means you weren't running lean......so the only reason to lose compresion fast is you ingested dirt and wore the piston down

here is how to tell if you ingested dirt....take the crank out and inspect for these markings..

http://i107.photobucket.com/albums/m...h172006032.jpg

Was your plug dry? Seems like its running too lean. Post a pic of what you are talking about.

if you get the erge to clean it....dont! send it to Maximo or someone who knows what their doing. ive run nitro for a few years now and hate taking them apart. i would rather sent them in and pay a couple bucks to have them looked over, then take them apart and waste a 250+ engine.

Heavy black carbon buildup is usually a super rich bottom and super lean top... the fuel builds up in the engine during low RPMs and gets burnt at a very high rate when the lean condition begins at near or wide open throttle, before it can be exhausted from the engine, same thing when you come back to an idle... the fuel will burn at a high rate while cooling the piston. Hence the run-on associated with that tuneup.

A lean HSN will shorten the life of an engine almost as fast as ingesting dirt. The piston is sent through a series of expansions and cooling cycles it prematurely wears the seal portion of the piston away.

If your engine has a crank that looks anything like Maximo's pic... your rear bearing is toast and the crank to block seal is most likely damaged to some degree. Dont even check the bearing, just replace it and hope the block seal is good enough for a decent idle.

some of the best performing fuels I have used have always left a heavy black carbon buildup on the piston......I actually feel safe when I see that as i know the fuel has a good amount of caster oil...the fuels that leave no residue are the ones that scare me ! Now of course I am into screaming the jeebus out of my engines, so I tend to stay away from all synthetic mixtures.... to me black residue means caster oil...clean piston means synthetic oils....caster protects better at high RPM's so thats why I prefer it........... However seeing a black buildup with synthetic mixture means it needs some tuning LOL !

I'll post pic tomorrow but as far as dirt I'm anal about keeping a clean filter on. I even use horse wrap. I'm just getting mixed signals on this whole deal and I have a reedy in my buggy and the plugs and piston seem in tip top. Not sure if this (2nd) orion is giving me a hard time.

So true
 

I like the way you think buddy.

It gets old hearing guys talk about how clean their engines are after 4 gallons. So silly. Take it apart and gently clean the engine. No big deal, but I usually wait until 5 gallons or so to change the rod and pinch it, inspect the bearings and so on. I woul not take the engine apart just to get the carbon off...Especially from 1-4 gallons. Let er rip :lol:

Caster is a love hate for engines... it doesnt combust to its a hate, but it does offer uncomprimising protection so its a love....

Its all in the tuneup. The little amount of caster in fuel these days doesnt result in carbon buildup, it results in a "sticky" residue inside the engine, its the rich LSN and lean HSN that creats carbon. A "lean and clean" LSN and slightly rich HSN rarely has any carbon buildup after many gallons. Not to mention caster retains heat and will add a few degrees to your temp gun and reduces runtime.... those are not things that are all the rage these days.

These are all my opinions, not to be taken as the "bible" lol

Now as far as taking temps...... I maintain the spec temps during breakin and keep an eye during the next few weekends but as far as that I just go by if it's producing smoke or not. I know I still have alot to learn on this engine deal and don't get me started on the suspension.

I usually tune for performance and sound....smoke is something that can be inconsistent depending on weather conditions and ambient temperature....Some days you wont see much smoke at all, other you will see a thick trail of smoke.... As a rule the exhaust note doesn't lie, if the engine is out of tune it will sound out of tune, if a engine is tuned correctly it will sound like it is tuned correctly........A properly tuned engine has certain performance characteristics that Ialso look for. Same applies to an improperly tuned engine.........Now of course when your racing at a indoor event, and even outdoor for that matter it can be very difficult to to hear your own engine run...which can make it a little difficult to tune by sound.........This is why I feel it pays to take time with a new engine away from the track, so you can learn its tuning characteristics in a environment where you can hear it exclusively.....learning to tune a new engine at the track is definitely much more challenging then learning to tune it on its own away from the noise of other engines....

so if you gonna be lean on one of the needles it better to be lean on the low end?

lean is a relative term.... its not good to be lean on any needle.

what I mean by a lean LSN would be it can idle till the cows come home with no change in RPM and revs up without needing to be "cleaned out" BUT the HSN will need to be ran on the rich side (another relative term) to prevent overheating and or flaming. This tuneup gives the best runtime and "touch" power in my experience. But some engines dont like this tuneup, so there's more variables than can be typed here. Anytime someone brings their engine to me locally to tune I always start with the clean and lean bottom ad see how the engine likes it.... if it doesnt ill go the other direction. Rich LSN's can easily be spotted by a varying idle speed after full temp is reached. I run my engines with both tunes depending on the track etc etc

I plan on doing a few vids on youtube to clearly show the differences, its very easy to spot the differences once you see them.

I don't know how you guys do it by tone. I do kinda know by sound when its running to rich but as far as which needle you got me. Cuz when it's gurgling it's too rich right?

On a side note. When I ask the pros at the tracks for a little advice they tell me " I don't run a orion I run a werks or I don't drive a associated I rock losi" so it's kind of a turn off to ask guys that are actually there and now I have to try and have a conversation with some one in cali or australia. I do appreciate the help guys just alittle agro with the local pros.

Better get these out before you all loose interest. Thanks for all input

Im sticking to my original diagnosis... see how the coil of the plug is grey/white and dull not shiny? That is too lean on the HSN. Ive never seen an engine turn color like that from a LSN thats too lean.

I recommend starting with a new plug then richen the HSN til it sounds like it swimming in fuel.... then lean your bottom and lower the idle until you get 3-4 seconds doing the pinch test 1" from the nipple at idle fully warmed up. Get the bottom stable then start bringing in the HSN slowly. It may take a full turn on both by the time your done.... no telling. You can get the bottom in the ballpark faster if you want to set your idle gap to around 1mm or slightly less, find a paperclip or something thats about the right size. If it fires and wont idle, start leaning the LSN until it will. When you rev it cold it should rev and then sound super rich, if it does your in the neighborhood, it should immediately drop to a nice low idle.... if it sits up high then drops after a few seconds, keep leaning the bottom and lowering the idle.

That sucks your locals are too busy being rockstars to take 5 mins to help someone.

Thanks man. I appreciate the help. I'll give it a go after I clean and rebuild. And that plug might have 15min on it to.

What kind of fuel are you running?

I started with byrons 30-11. But now I'm running werks 30

This thread couldn't have come at a better time. I found this thread by chance via a random google search. I have a
Xtech EB Mods Pro engine and pipe in my truggy. It was running absurdly crazy fast when the temps decided to drop. My tune was lost and i became confused. I asked the guys at my track why my engine sounded funny coming off the straight... Basically i would let off the throttle amd it seemed like there were three levels to my low end tune. It would drop a pitch until the engine would sputter and die. So i searched all over the net trying to figure out and learn what was going on. I found my answer on youtube via a horizon hobby engine tuning video. Turns out my engine finally broke in at 2 gallons and when it did this my lsn became super rich. So far i have turnes my lsn 3 full turns back (one turn mean a full 360 degree rotation of the needle). My engine now idles well again and can make my truggy wheelie. Temps are a nice 220 at empty tank, and the top end sounds like i have room to grow. Sadly my air filrter came off so i shut down my engine amd took her apart. I found tons of black carbon at the top of the piston. So i did a search of what this meant and thats how i found this thread... Awsome!!!!

So whats the purpose of removing the extra head shim after break in??

There would be no purpose, not unless you wanted to run a lower % of nitro and a different plug.

There is a purpose.....
At maximum pinch there is also a maximum compression. When the engine is broken in and the pinch is (almost) gone the piston is actually floating on an oil layer in the sleeve. The huge pressure of the combustion can push some along the side of the piston so there is a tiny compression loss. That can be compensated by removing one shim.

But it is all about how the engine is configured at the start, some engines have that extra shimm from the start, some do add an extra shim in the box, some do advise to use an extra shim and others do not anything.

Carbon build up on the top of the piston could also be "compensation" for more compression. That dosent mean if you dont want to clean the build up off the top of the piston, you have to ADD a shim either. If you have to remove a head shim to make up for power loss due to a worn sleeve, (in the end thats what your saying to do) then you would HAVE to run a lower % of nitro and change to a lower heat plug. If you dont you could have some pre-det happening. You dont want the top of the piston to start to pit. Not to mention the unnecessary stress and wear you will be putting on the rod and wrist pin. In the end it's beter to have the sleeve pinched, not remove a shim on the same plug and fuel.

Now, if there is a engine out there that requires you to remove a head shim after break in, thats a first to me. I have never used one.

almost all engines are over shimmed from factory....

Maximo, I respect your opinion but that could be considered a blanket statment. That could be a "how long does one want a engine to last, how much power do you want out of it and how much money do you have" thing. All the big name engines I have personally seen the internals of all only came with one or 2 shims to begin with.

a resize works as well but for quick and easy the "removing a shim" method works just fine , sticking with the same percentage nitro which in most of our cases is 30% :nod:

To each their own. If I see any kind of decrease in power and the "quick and easy head shim removal" could possibly need to be done, I'm just pulling the sleeve out for a $10 pinch from my local guy. $20 tops if you have to ship it to a guy you dont know. Not worth risking a $160 dollar matched piston and sleeve for me to yank out a shim. Like I said, To each their own.:nod::cool:

out of curiousity what makes you think removing a head shim will cause the p/s set to become "unmatched" :confused::D

I never under stood sleeve pinching, trying to compress hard as glass chrome doesn't seem a good solution. lap honing a new piston to fit is the best solution, I have personally done that. but manufacturers won't sell us just a piston...:flaming:

But I would have to agree with the other guys who say just drop a shim. I doubt pre-ignition is going to happen if the overall amount of compression at TDC is going to be about the same. I guess the way to really find out is a compression test between a freshly broken in motor vs a worn motor with removed shims. houston, done this? would you have a suitable subjects to do such a test?

A thing I have noticed in regards to carbon buildup, don't clean it off! especially the little carbon ring that develops around the cylinder. every motor where I cleaned that stuff off always ran weaker than if I left it alone. It does no harm, in fact probably aids a compression seal. and the carbon on the piston head retain heat for better ignition.

Thanks Newland for the insight on tuning. I think myself have been running the top too lean since we have come back outside. I always had the impression (told by others) you needed to run the low end richer. eager to try a different approach.

Since we are doing the opinion thing I will give mine. All of my motors run a tighter clearance then factory and have more compression and power. From what I can tell compression ratio has nothing to do with engine life. Improper tuning and dirt is the enemy!

I do not think the carbon layer does reach 0.1mm thickness but the carbon layer has a more important function, it act as an heatshield for the piston. Overheating pistons do get weak, the carbon layer does alow the engine adjusted to more performance without overheating the piston.

Expansion is the word why manufacturers do not sell sepperate pistons. Manufacturers do change materials which can have different expansion rates. With that you want a sleeve that folows the piston best. It is impossible to tell which piston does fit the sleeve and if you do combine different specs piston and sleeve you can notice that right away in several ways but not an perfect running engine

it maybe just me ... but i would think the carbon buildup will get soft when up to operating temps... do a test yourself.. take you carbon coated button and just put a little heat on it with some nitro... so i don't see ho what can help with proper tuning because the piston and button will have an inconsistent surface... maybe i'm wrong.. just like the carbon build up in tune pipes... if its not clean you loose performance...

but i maybe wrong... either way i use to clean the carbon off my engine parts if needed when i inspect my engine.. which is like every half gallon to a gallon ( depending on the conditions i was running in prior).. now that i switch fuels, carbon buildup is very negligible...

I clean everything except the sides of the piston/rings and the seal at the top of the sleeve

I'm not over heating anything, I was making a point. What's this have to do with the price of tea in china?:lol:

I was talking about pulling the shim and running the same nitro %. I can drive a couple miles and have it pinched. Even If It took a while for me to send it out and have the work done I still would. I would know before that though if it was losing power and would nip that in the bud long before there would be a shim removal option going through my head.

When the engine is near its end of life you could remove one shim to compensate the compression with the compression loss/leak. Another trick is to use a cooling head with more cooling capacity.