84transamdude

ok so i have a 383 stroker with flat top pistons. The last time I parked it was running great. please bear with me as i'm going to list my day so it may better help someone point out my problem.

Lets see i started off by changing plugs to accel shorty header style and msd 8.5 wires that you have to assemble. had to move diss. cap to put back wire on. got the timing back good enough to start had it set at 8 deg. advanced. went to gas station and got some plus normaly run premium but i figuredd i would try it to see how it ran car was preaty much empty. got about 5 gal or so. i think the car was loosing power at about 4 grand but not sure didnt drive it a whole lot today. when i got to my buddies house i shut it off and it like tried to start again. guy there said it was my timing. he said with upgraded motors cant be adjusted by light. he said we should advanced it and turn it off to see if it was hard to start or not. so we did that and it started up no trouble. then i left my friends house was sitting at a stop sign and figured i would get on it. put it in first and floored it got to 5 grand and shifted into second tire chirped and motor started vibrating realy bad. Shut it down right away. got it back down to my garage and took off the valve cover and turned the motor with the started and all rockers seemed to be moving like normal. turned the timing down some and started it up which was a little harder than normal but as soon as it was running the whole car vibrated like crazy. Did nothing after that.

so please post what i should be looking at. spent 4grand on this motor and only have like 2,000 miles on it.

camaronewbie

Sounds like maybe you have a plug wire ran incorrectly - since that's the only thing you've messed with.

You need to get TDC on #1 cylinder on the COMPRESSION stroke, then wherever rotor points make sure that is #1 plug wire, and refollow firing order.

To get TDC #1, remove spark #1 plug, remove coil wire, hold finger over #1 plug hole and have someone bump starter over until you feel air presure against your finger. Then manually turn engine over until balancer mark is at zero on timing tab. Then, where rotor points, is #1 plug wire on dist cap, then follow firing order clockwise around cap.

I assume this is an aftermarket non-computer carbed car? If so ...

After you get the plug wires right, then you can set timing - you need probably at least 10* BTDC, probably more. Set timing, take light with you, make a WOT run. If no spark knock/pinging, then set timing up 2 degrees and go again. When you get spark knock, reduce timing 2 degrees and lock it down. Then adjust carb to compensate for idle changes.

cuisinartvette

Use a damn timing light on it, you cant time that by ear or "wait til it gets hard to start". Your friend doesnt have a clue. Cant use timing lights, guess GM put the timing marks on for fun lol.


Start over and do it right, one step at a time.

84transamdude

ok guys thanks i'll start with that tomorrow.

torque_is_good

I'd just like to pint out a few curiosities

You spent $4,000 on the engine

you aren't using a timing light to time the car so ti sounds to me like you've paid someone to previously do the work because experienced people know to use a timing light

and, after the $4,000 expense you are trying to save 10 cents a gallon on gas and for your 5 gallons you saved a whopping 50 cents. 12,000 mile sper year at 15mpg you'll save about $1.50 per week not running premium.

and then, you go on to write how you "got on it" so that means that you want performance too.

do you understand what the octane ratings mean?????

Do you see any conflciting statements? I do?

please get a timing light and a person who knows how to use it as well as how to time a vehicle. Also, I assume that you have a mechanical fuel pump? But, FYI, when you have vehicles with electric fuel pumps don't let your tank get low. The fuel actually cools the fuel pump and "lubricates it" vs sucking air and burning out the pump. In other words, putting off that wallet harming stop at the gas station could actually hit your wallet harder.

84transamdude

ok guys so i went down to look at car today and heres what i got for ya.

Started of by checking TDC which was still on. went to start and it was backfiring out of carb and making a tapping/knocking noise. Put old plug wires on and found two wires that got crossed somehow. stoped back firing but still making the noise sound like passenger side of motor. car will not stay at idle without help with staying on gas some. with not even 5min of running time all at different times like a min her 30sec there. I have coolant mixing with oil. stopped right away when i seen it on top of heads (had valve covers off) pulled the plug and let the oil drain. havent done anything since. a couple people i talked to said more than likely its in the top end ie. blown head gasket or messed up head. for me i hate to say this but i'm wishing a head more than a gasket. what do you guys think. and also if i tear this down and its a head whats the better thing for my block to get that coolant out. I was reading about after its fixed to put in some oil and run for 2 min and drain and repeat that step a couple times.

84transamdude

anyone??

camaronewbie

Not sure what you want to hear. You've been told ... timing. Got to get it timed. Do you have any idea what timing is? You HAVE to get a timing light, you HAVE to find TDC on the COMPRESSION stroke.

You say "I have coolant mixing with antifreeze." Antifreeze is coolant, I'm lost. Do you have coolant in the oil? Could just be an intake gasket.

Again - a $4000 motor deserves some real attention to detail. If it was built by someone else, from pan to carb, then I'd make them figure out the coolant in the oil issue, b/c THEY did something wrong.

84transamdude

fitst off *** I know what im doing. And yes I meant coolant in oil. The car is TDC and that is not causing the noise.

dellman83Z

iTrader: (9)

Can you better describe the noise its making. Knocking, ticking, .... Have you checked to make sure your rocker arms are adjusted properly? A loose one or two will cause the motor to run very badly because its not opening the valve, just watching the rockers move is not good enough. As far as timing, you do have the vacuum advance plugged off on both ends to set the base timing right, then plugged it back to make sure total timing is good. The reason I say this is because most stock HEI dizzy's (assuming you are using one) need to be recurved for a 383 or beyond, mine did. My base timing was good, but the vacuum advanced it wayyy to far causing detonation and that can cause some serious issues.

84transamdude

its more of a high pitch then a low knock leaving me tobelieve its top end. the noise and vibration was first. oil was good after a couple times of running the coolant started to mix with the oil. when i did the plug wires i didnt pull the dizzy out so it is good in that sense. before it started the noise it was loosing power around 4grand so when i took it to 5 i think what ever the problem was, was just to much for it. ran great 3 weeks ago. I do not drive this car every day. motor only has 3,000 miles or less.

dellman83Z

iTrader: (9)

When you drained the oil, how much antifreeze was in it?

84transamdude

hard to say since it was mixed. my overflow bottle was empty and you couldn't see any in rad. it was also way up the stick. 5 to 6 qt maybe thats just a guesst thou. couldnt have taken it long to get in there

and also to CAMARONEWBIE when i picked up the motor the told me there is not gaurente on there part because they built it to my specs. I bought all the parts for them. They did the machine work and put it together. I did call them and let them know. The guy said to take motor out and take it to them. 1st reason i don't want to Is if its a head gasket, or something happened to the head thats just more work for me to take it out. 2nd is he didnt say they were going to cover labor and at 67 dollars an hr I dont know if I can afford that again. And if its a deffect in one of the parts i bought they realy not going to cover it.

torque_is_good

using parts that you bought is not building it to "your specs"

a good shop will inspect any used part that is trying to be used and they will also verify new parts. Now if you gave them standard size pistons and the engine was bored .030 over then that's an issue

Sorry, something doesn't pass the sniff test here. $4,000 to rebuild an engine and you provided all of the parts is a bit high (unless your parts are in that calculation)

If your story is true, yank that darn engine, stop messing with it and have warranty work performed at the shop. If you have coolant in your oil, and you keep running it, it's going to be new bearings and a tear down/clean to get all that coolant out of every nook and cranny

something just smells fishy here

84transamdude

yes when i first seen the oil and coolant together I jacked it up and drained it right away. I will call them monday and see what they will do money wise.

And the 4grand thats parts included.

dellman83Z

iTrader: (9)

I have to agree with torque. Something with the shop sounds really wrong. The coolant leak is more than likely from the intake gaskets, and after a couple thousand miles to start sounds like they may have not been torqued down properly in the first place, which is not your fault because they assembled it. Generally, if the head gasket was bad, you would see white smoke when its running and a little oil in the coolant, not the other way around. Once the leak is fixed, then report back to try to solve the other issues. It really sounds to me like the mains are wiped due to the coolant in the oil and causing the low knock, which does mean a total teardown to fix it.

torque_is_good

the shop I now use gives a 12 month warranty. If a part is defective then it's defective. But, if tyey didn't use RTV when putting on the intake man, or re-used head bolts then it's their issue. A good shop will insist upon doing things a certain way to avoid issues like you are now experiencing.

They have no clue if you are a mickey mouse or know what you are doing.
They don't know if you are going to torque down bolts correctly so if they didn't do the assembly, there probably isn't any warranty.

Now, if you had the machine work done and then assembled the engine yourself then you probably are S.O.L.

84transamdude

yes and intake gasket would be great but the wiped out bearing not so great. As I stated before and dont no if i'm missing something here. the noise started before the antifreeze leak. As soon as the motor started to act funny I shut it off going down the road at 60+. Towed it to my garage and first thing i checked was the oil and it was normal color. It wasn't till after I started it a couple time that I seen the coolant and oil mix.

And to tq I took the block and pats to the machine shop and said this is what i want and they took it from there. when i got it all I had to do to motor was but on carb and drop in the dizzy.

torque_is_good

well, that sounds strightforward to me. You need to engage in a cool/calm/collected discussion with the shop. If it ends up being a failed part then the shop has a legitimate point because they probably warranted the labor.

This may end up costing you some money if that's the case but any decent shop will want you to be happy and will help with rediuced rates. And, this time, let them buy the parts.

84transamdude

Yeah I agree they should I called them today and told him I didn't have the money to bring it up there for there labor rate and he didn't say anything. So I might just tear it down my self cause if it ends up being a failed part I won't be able to pay again. So frustrating

84transamdude

ok so i've decided. Tomarrow I'm going to be taking everything down. I'm going to get everything ready like taking off headers, alt, power steering and carb. then a buddy is coming over and we are going to tear down from top to bottom till we find what went wrong.

I will post back with what we find and hopefully some pics. (praying for something in the top end)

david chambers

do tell the name of the shop you used,as for no warranty,you went for that!!?? sometimes a conversation with mr colt or mr remington helps a whole lot

84transamdude

well here is what i found

now please not the two inner cylinders are cleaner than the outer 2. What do you guys think happened


oh and by the way the motor has 1,020 miles on it

izcain

Well there was DEFINITELY something foreign in the cylinder banging around in there. Need more pics of the damage as well as better plan on pulling the engine out and getting a more complete assessment.

I would have many questions for the coolant but would need more information on the build before I started asking.

84transamdude

yeah thats just it the only thing that was in there banging around was the broken piston. what questions do you have about the build. going to try and pull the other head off tomarrow. No smashed spark plugs on that side thou.

InfernalVortex

iTrader: (4)

Are those hypereutectic or cast pistons? What are the odds detonation got it it and ripped the ring land off that piston? You ever hear any knocking/pinging out of it? Maybe they didnt gap it properly. Some hypereutectic piston manufacturers are real picky about their ring gap specs. Re-reading the original post, Im thinking your timing/compression ratio was too radical for mid grade fuel and detonation set in and ripped the piston apart and caused the damage you see. You set the timing at 8 Deg advanced, but you said it dieseled when you turned it off, that's usually caused hot cylinder temperatures, one cause of that is timing that's too advanced or a lean fuel mixture, etc, basically anything that causes pinging.

Either way I speculate that for whatever reason your ignition, compression, and fuel grade caused the piston to overheat, the rings expanded and seized against the cylinder wall and ripped the ring land off your piston there.

I'd look REAL close at that cylinder bore to see if the bore is damaged/cracked. The head looks okay, but there's coolant leaking somewhere, and I would bet that damaged piston is the cause, but I dont see the source yet which worries me. Youll want to pressure test the head and get a valve job done on that cylinder. You'll want to look over the block REAL REAL REAL close, but it may be salvagable too. But the coolant mixing with oil didnt start til AFTER it ran bad, so clearly the broken piston caused damage somewhere that allowed the coolant to get into the oil. To me that says that piston damaged the block, the head, or maybe just the head gasket. Maybe it lifted the head off the block and cracked the deck around the head bolts. Pressure test the heads, magnaflux the block, and you'll know what you can save.

By the way, dont get too discouraged, we've all been there at some point, this was mine:



The rusty water in there is from a crack in the cylinder wall that showed up the first time I took it around the block. Notice the rusty spot in the bore?

84transamdude

they are hypereutectic. I just got off the phone with the machine shop and they to were also saying about timeing. Earlier in the day when i noticed it was loosing power at 4grand I had 93 octane in it and time at 8. then i put the plus in cause the machine shop had told me i could try it and see how it ran. if the block is screwed I dont think I will do another 383 just cause thats alot of machine work. I do have another 350 block 2 bolt main in my garage. going to go down and pull the other head today to see what those pistons look like.

btw i heard slight knock out of it sometimes but I would have to be under the hood. and when driving down the road if the car was under a load say at 2grand it would make a weird noise like a rattle. People told me it was from the flex fan I put on. Now im wondering

84transamdude

ok got the other side off. and have a closer picture of the cylinder wall that has the broken piston. Looks to me like a cracked wall.

InfernalVortex

iTrader: (4)

http://www.google.com/images?um=1&hl...&aqi=&aql=&oq=

Very common. Hyper pistons are harder than forged pistons, they are lighter, and they can be sized much tighter in the bore because their thermal expansion is much more manageable. The problem is that because they're harder they're more brittle and when they get hot from detonation they just cant handle the heat that forged pistons can. A forged piston would fail in the same scenario, but it would take much longer. They get hot and expand, the rings expand and seize to the bore because the ring gaps close all the way up and there's no more room to expand, so the ring seizes to the wall, and the piston get a chunk ripped off of it. Something has to give.

Thats a crack and that's your source for coolant in the oil. Sucks.

http://i232.photobucket.com/albums/e...x/100_6812.jpg

Been there done that.

I'd stay with a 383. You have all the parts. You need new bearings and a new piston. Have the new piston balanced to the old ones and get the same brand of bearings, and then just find a block to clearance to a 383 and rebuild it. Check for damage on the cylinder head, get a valve job done on that cylinder, and get ready to put it back together. If you've got good heads anyway...

If you need to take some time off do it. Recharge your batteries, I know I was pretty upset when it happened to me. My beloved RS sat in the garage in hovercraft mode for about a year before I got serious about putting it together again... I just needed time off and time to regenerate my money so I could afford to get it together without stressing the whole time about my car being broken.

84transamdude

thanks for all your input guys. I had e-mailed all the pics to the machine shop. He call me with his thought. He told me that there is no sign of that piston or any other of denation from timing. He said it looks like it just failed. I asked him if the company would back up there parts and pay for some of the damaged. He told me sometimes its hard but if its a manufacture they usualy deal with he would give them a call. I told him and he is going to get back with me on monday.

InfernalVortex

iTrader: (4)

Thats awesome... good to hear.

And he's right, it doesnt really have that overheated look most detonation failures come with. I wouldnt rule it out, but it does seem possible that it's just a failure. Could it be that the block had a crack and the crack in the block ripped off the corner of the piston? Can you pull the piston out and see if there's an excessive amount of damage on the side that had the corner broken off? Is the damage on the piston in the same part of the cylinder as the crack? Could be the pressure of combustion caused it to crack and the piston/ring caught the lip of teh crack.

But that would mean the manufacturers arent at fault...

Sounds like you're dealing with a decent machine shop. At this point they have your money they could just tell you go bother someone else about it, and that it isnt their problem. My machien shop is similar, you can tell they're focussed on trying to get repeat business, and that means good, courteous customer service even after the sale of services/parts. If they're even talking about trying to help you out with the parts suppliers that's well beyond what they're expected to do. When you do your next build I'd go back to them.

DT1987RS

What cyl. head casting is that. It is hard to tell from the photo but it looks like a 601 H.O. 305 casting which on a 383 your comp. ratio would be a bit high for pump gas and would def. give you detonation no matter what you do aside from running 110 octane. Did you calculate your comp. ratio?

84transamdude

its a 350 block. the comp is about 10.5 to 1.

Infernelvortec
the crack is on the other side of the crack piston

DT1987RS

What is the chamber volume on your cyl. head ? A .030 over 350 block with 3.750 stroke and a 64 cc chamber volume would give you aprox. 10.1:1 with the piston .020 in the hole. Your combustion chamber looks smaller than 64cc. Did you have the head chamber vol. checked? It may be some of your problems. If it has 55cc your comp. would be 11.2:1 which would be to much on 93 octane with a carb. you could get away with it on a well tuned efi system.

84transamdude

I just re-read your other post and yes they are 601. I bought them as a reman and supposed to be 64cc i think and the motor was bored 60 over.

InfernalVortex

iTrader: (4)

In order to keep 64cc heads doable on a 383 you gotta have pretty deep-dish pistons. I think to get 9.5-10:1 you have to have around +15cc pistons. Yours look like +5cc flattops. I dont see how your compression ratio would have been anythig less that 11:1 and with iron heads and pump gas that's just too much. Do you have a HUGE cam that can bleed off excess pressure? Being bored over raises the compression ratio also.

1969RSSS

I see the cracked piston but it doesnt look like it broke all the way off and wasnt bouncing around, I would suspect that something else was bouncing around in that cyl and the one next to it ( regergitated through the intake valve and into another cyl). Did your old plugs all come out in one piece or did one crack and drop the center elctrode off while you were braking it loose ? Was the air cleaner off and something was dropped down the carb? Make sure you check the intake manifold for objects before reinstalling (lots of new engines are destroyed from objects in the manifold not cleaned out)
The other thing that may have happend and is evidanced by the run-on that you mentioned is too low octane fuel with exesive timing for that fuel causing pre ignition (ping). Cyl pressure can go sky high with run-on causing massive damage. Then the WOT hit (with cheap fuel ?) may have just finnished it all off.
Either way i would say this, Do your researh before building as that piston is a flat top not dished in conjuction with a 64cc iron head and pump fuel is asking for dissaster as noted in almost every iron head artical on the net. Not checking total timing and then adding lower octane fuel and a WOT to 5k= DISSASTER

izcain

I think your on to something here.

Also what was the total timing with this? 8 initial doesn't mean anything with a performance engine.... Need to pay attention to total timing.

84transamdude

Well as DT1987 pointed out that the casting are 601 so they might end up being 58cc heads is this true.

cam: hi rev from 2800-6000 int/exh duration 236 and lift 436 Not sure if i worded that right.

izcain how do I check total timing.


On another note we all no i'm screwed and even debated selling the car but I love to drive it even if its just once a week. What would you guys do get another 350 block and start over with the 383 or just replosih a cranck thats in it. I have a 2 bolt main with a crank in it. And do a bigger cam. most of my parts should still be good.

james.gould150

id just do stock 350 maybe cam ported/polished heads and a nice intake...youll get plenty of power out of it...wont be a 10 sec car but unless you run it at the strip why do you need the 383 power?

InfernalVortex

iTrader: (4)

Thats the most ridiculous post Ive ever read. "If you dont race it why do you need the power" .... LOL.... Power is fun, period. No one needs it.

If you go 350 unless you get an assembled, good condition shortblock you're going to need to get a new rotating assembly anyway, so the cost difference between a 350 and a 383 at this point wouldnt be that huge unless your machine shop charges a fortune to clearance the block. Depends on what length rods you have, if you have 5.7 or 6 inch rods you can get 350 or 383 pistons, so it's the cost of a new crank and new pistons vs just new pistons.

I'd get some new heads though. Be careful keeping your compression ratio managable though. For a street car you want it between 9 and 10:1. Closer to the middle the better. Your cam is big enough you could handle right around 10:1 pretty easily, especially with some good Vortec heads, but that's only for a 350. If you go 383 play with online compression ratio calculators and try to figure out how deep of a dish you need with your head gasket thickness. I remember it being between 20 and 15 cc, but I dont remember it was a while back. I was wanting to hypothetically use my Vortec heads with a 383 shortblock, and my vortec heads are 64cc chambers. If you want a 383 you need flat top pistons and 72cc chambers or 64cc chambers with a dish and if you want a 350 you want flat tops with 64cc chambers.

There's a whole lot more to it than that, but if you stay in that range you should be fine. We are all here and glad to lend assistance and a lot of these guys know WAY more about this stuff than I do.

84transamdude

yea i was talking to a machince shop today about rebuilding something and he was saying that if I do a 350 that I would want 11.5 comp and that it would be fine on pump gas like 89 octane. that is so false right?

Hopefuly i'm going to go talk to another guy this week about see what he charges and come up with.

torque_is_good

nah, just retard the heck out of your timing (lose performance) or run a water or methanol injection system. heck, you could run 87 octane with a methanol injection system..............of course premium gas is cheaper and discussing a performance build and worrying about the cost of gas at the pump don't belong in the same sentence.

InfernalVortex

iTrader: (4)

I would never go past 9.5:1 static compression ratio for a street car. If I had a nice, modern set of Vortec heads I'd get near 10:1 (I have them and I still stick to 9.5:!). The damage you have may or may not be from detonation, but that is exactly the type of damge that happens when you have a compression ratio that's way too high. Cylinder temps get too hot and you ping at high loads at wide open throttle and the engine WILL grenade itself just like that.

With aluminum heads you add a point to the safe compression ratio... So you'd go to 10.5-11:1. Aluminum heads absorb and lose heat faster than iron, so the combustion chamber temps actually drop and energy is lost, you make up for this by raising the compression ratio a point.

Giant cams are inefficient and you can go with a higher ration with a large duration cam because the dynamic compression ratio bleeds off so much pressure at low/medium RPMs. Yours is about average for hot street cars in my opinion. Stick to 10:1 or lower unless you get aluminum heads.

The GM ZZ4 350 crate engine uses aluminum heads, is an EXCELLENT example of a great street built fast 350. Its not the best or the most modern really at this point (it uses heads from the 80s, but so were you) , but it's very typical and its a great combination. And its compression ratio is only 10:1. The most powerful ZZ4 uses fancy fast burn ALUMINUM vortec heads, pushes 385 hp with a smaller cam than what you have, and its compression ratio is 9.62:1. Understand, when people like you or me make motors, we dont need to warranty them. GM does. These engines are warrantied and gm will be slightly little conservative to make sure their customers dont blow em up. But that gives you a great guideline from the horse's mouth about what a safe long term compression ratio is.

Back in the 70s Camaros had 8.0:1 compression ratios. Most of the cars from the 80s did also. The IROCs and later third gen z28s pushed it on up to mid 9's in compression and that's basically the pinnacle of advancement for the Gen I smallblock chevy. A 2002 LS1 used a 10.0:1 ratio and it also used aluminum heads.

All Im saying is... better safe than sorry. Blowing up your **** isnt fun or cheap. Buying a thicker head gasket or some dished pistons is way easier.

This is quoted from Chevy High Performance

http://www.chevyhiperformance.com/te...ide/index.html

They call 10.6 too high, and your chambers were even smaller than that.

84transamdude

ok guys so its been a couple weeks since my last post. the new engine builder got the motor apart. take a look at the pics and tell me what you think caused it. also they didnt grind the block for clearance the grinded the rods. and some bearing are a brownish gold color. (whats that from)

ATOMIC

iTrader: (1)

are the rods press fit onto the pins?
do the pins move freely in the pistons? they should.
that looks like the wrong pins were used and cracked the pistons.
the pins should never be tight-fit in the pistons.

as for the crack/chunk out of the top of the piston, the ring gap was too tight.
you should measure it to be sure it was wrong.

InfernalVortex

iTrader: (4)

Even a properly fit ring will close up and rip off a chunk of piston if you're detonating and it gets hot. Considering he's running 11+ compression on regular gas...

Also I gotta agree, it's strange that the pin isnt moving freely within the piston. The pin should be tight in the rod, but the piston should rock freely on it unless you used free-floating pins, but given that it's seized together Im guessing your pins are press fit. Just not sure if it's not moving freely because its damaged or whether it was like that from the start. I can imagine it would have been fairly down on power with the piston seized to the rod like that.

84transamdude

the piston that is broke on bottom, the rod moves tightly. the other one move's back and forth fine even the pin moves freely.

all pistons the top ring is tight.

InfernalVortex

iTrader: (4)

It is usually filed to some gap when installed in the bore. IE you push the ring into the bore without the piston on it, and measure the gap with a feeler gauge. Generally the piston manufacturer will specify ideal ring gap for different situations. A lot of times if the compression is too high and you get a lot of detonation, it beats the pistons pretty violently, and creates a LOT of excess heat. This heat can spread to the rings and as the rings heat and expand, they can expand to the point that there is no longer any ring gap, and then from there they will expand until the ring siezes into the cylinder wall while the engine is running - this rips off the crown of the pistons at the ring land.

This is how ring gap is set, note this isnt an SBC:


Theres no way to know whether it was tight in the bore or not unless you remove the ring from the piston and place it in the bore and measure.

I still think your compression was so high the rings overheated from detonation. Is the broken piston the same one that the crown is damaged on? How does the cylinder wall look in the cylinder that the broken piston was in? How about the chamber in the head? All that is going to be your biggest clue. Is that chunk of missing piston in the oil pan?

Also I would assume the brown discoloration on the bearing is rust and gunk from the watery oil. But I havent seen a picture. It could be bearing wearing down into the copper base. That's bad news, generally means you had a bearing about to spin. This is an example of that:



It happens when the outer surface of the bearing wears all the way down. This can be caused by the bearings being too tight or loose, there being metal in the oil (such as piston particles), or simply there being water in the oil while you were driving the engine. Water doesnt lubricate the way oil does, so wear is increased exponentially. If you drove it a lot while there was water in the oil that will happen. If you had kept driving it you would have spun a rod bearing and had a bottom end knock assuming thats the same discoloration youre seeing.

ATOMIC

iTrader: (1)

true.
but you'd hope the engine assembler would have taken the overall compression ratio into account and gaped the rings a little large to compensate. maybe not.

"Theres no way to know whether it was tight in the bore or not unless you remove the ring from the piston and place it in the bore and measure. "
exactly.
as a point of reference, my speed-pro hyperutectics, 10.7 at 64cc (same brand and style, similar comp ratio) specify a .022-.024 ring gap.
sounds large, but hypers are brittle.
also these pistons don't come with the rings pre-fit, you must file them.
out of the box, mine were between .010 and .014, with one that was around .020.