Top end time, piston and ring or just ring?

slipdog
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slipdog 12/14/2014 2:51pm
12/14/2014 2:51pm
Single ring small bore with some signs of wear on the ex. side, I replace the whole thing just to be safe. A little shiny at the top of the bridge, but the cylinder does look good.
Hondas4Life3
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Hondas4Life3 12/15/2014 10:55am
12/15/2014 10:55am Edited Date/Time 12/15/2014 1:41pm
Measure piston/cylinder clearance. If its good re-ring it

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JH911
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JH911 12/15/2014 12:12pm
12/15/2014 12:12pm
The piston looks good with virtually no wear. The wear on the exhaust bridge is caused by one of two things. Either once or twice the engine wasn't up to temp before you started railing on it or your exhaust bridge wasn't properly relieved when the sleeve was installed. Judging by the shape of the piston I'd lean towards the exhaust bridge as the culprit. You have no blow by or combustion below the ring so I'd say your ring is actually fine, but since your there might as well throw a new one on. Did you do a compression check prior to tear down?? The horizontal machining or oil retention grooves on the piston skirt look perfect like a new piston. If your piston were worn these grooves would be faint thin or the skirt polished smooth indicating wear from the piston rocking in the bore. Piston wear usually starts towards the bottom where the piston has the most movement (rocking) None of this is present in the pictures. Bore looks good from what I can see. Jetting like you said is a touch fat, but I like the coloring of the plug. Better than being on the lean side. Throw a ring on it since your there, but I say run it! As far as the head is concerned I'd say your fine.
Jakes Dad
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Jakes Dad 12/15/2014 12:30pm
12/15/2014 12:30pm
I always chamfer the holes over the exhaust bridge.
JH911
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JH911 12/15/2014 12:42pm
12/15/2014 12:42pm
Hondas4Life3 wrote:
Measure piston/cylinder clearance. If its good re-ring it
Interesting theory and makes sense, but I've rebuilt so many engines both stock and mod, very few that I can recall having a perfectly or evenly colored/carboned dome or piston crown. I question there being that much time on this piston unless your have an hour meter to back it up. It looks to me like maybe 7.5-10 at the most. Not really adequate time for things to color. Everyone has their theories and some make more sense whoever in real world/tuning applications don't always pan out even though the theory itself is sound. Speaking from the professional industry side of things, Forums have become both a blessing and curse. That being said the link to DIY porting is one of those bad ideas. Do you have a dyno and a flowbench at your disposal?? If not I wouldn't attempt it. There's a lot of good info out there, but there is 100X more bad info. When you start adjusting port angles with epoxy you may change many other things from scavenging to effective port timing. Having read through that thread the gentleman that posted seemed knowledgeable enough, however his setup clearly indicates a tight woods setup. This same thread you have people suggesting switching from a BR8ES to a BPR8ES or similar plug?? Is your goal to punch a hole in the piston or collapse a spark plug?? Follow that advice and see what happens. The "P" in BPR8ES stands for Projector type plug IE protrudes further down into the combustion chamber if your head is net properly setup for this; that thread of expert advise just cost you a lot of money. Unless you see a thread on porting posted by Eric Gorr, Mitch Payton, Terry Varner, Tom Morgan, Todd (TLR), BPM, PR2, KB5, etc I would highly suggest you not attempt certain things posted on forums or you tube.
Dragoo168
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Dragoo168 12/15/2014 12:48pm
12/15/2014 12:48pm
Maybe I'm seeing it differnet on my screen, but while i do see the machining marks, I also see slight "4-point" wear marks, which, as noted regarding the bridge, is also indication of not letting the engine warm up enough before riding. If it is a Gorr 144 kit, then it should have extra plating, and the bridge should not be an issue, as most machine work, and often porting is included with the kit. I would get the jetting closer, as you use a heavier oil, and while it provides a great "film strength", it also can decrease piston to wall clearance in slow to moderate riding situations, such as trail riding,etc. The plug shows a decent color, but is also evident of build up and rich conditions,...If you're cleaning it with the main jet being good, then you can't properly read it for running condition. As also mentioned, you should have a baseline compression reading, to verify where you're at fresh versus near the 20hr mark.
Dragoo168
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Dragoo168 12/15/2014 12:50pm
12/15/2014 12:50pm
Hondas4Life3 wrote:
Measure piston/cylinder clearance. If its good re-ring it
JH911 wrote:
Interesting theory and makes sense, but I've rebuilt so many engines both stock and mod, very few that I can recall having a perfectly or evenly...
Interesting theory and makes sense, but I've rebuilt so many engines both stock and mod, very few that I can recall having a perfectly or evenly colored/carboned dome or piston crown. I question there being that much time on this piston unless your have an hour meter to back it up. It looks to me like maybe 7.5-10 at the most. Not really adequate time for things to color. Everyone has their theories and some make more sense whoever in real world/tuning applications don't always pan out even though the theory itself is sound. Speaking from the professional industry side of things, Forums have become both a blessing and curse. That being said the link to DIY porting is one of those bad ideas. Do you have a dyno and a flowbench at your disposal?? If not I wouldn't attempt it. There's a lot of good info out there, but there is 100X more bad info. When you start adjusting port angles with epoxy you may change many other things from scavenging to effective port timing. Having read through that thread the gentleman that posted seemed knowledgeable enough, however his setup clearly indicates a tight woods setup. This same thread you have people suggesting switching from a BR8ES to a BPR8ES or similar plug?? Is your goal to punch a hole in the piston or collapse a spark plug?? Follow that advice and see what happens. The "P" in BPR8ES stands for Projector type plug IE protrudes further down into the combustion chamber if your head is net properly setup for this; that thread of expert advise just cost you a lot of money. Unless you see a thread on porting posted by Eric Gorr, Mitch Payton, Terry Varner, Tom Morgan, Todd (TLR), BPM, PR2, KB5, etc I would highly suggest you not attempt certain things posted on forums or you tube.
And I definitely agree with the above statement, LOL! ^^^^^
nytsmaC
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nytsmaC 12/15/2014 2:40pm
12/15/2014 2:40pm
I did not take a compression test, nor did I check squish/head volume like I should have. I had the bike up on the lift stand loosening the head bolts before it had occurred to me, so I figured to hell with it, just do it when I get it back together and monitor compression next time. It's a stock TM 144, no sleeve, first rebuild.
BobPA
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BobPA 12/15/2014 4:05pm
12/15/2014 4:05pm
Looks fat on the jetting. For the couple extra bucks I would put a piston in it....like someone else said it looks like it was not warmed up before you gave her a whooping. A warmed up engine is a happy engine
Skerby
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Skerby 12/15/2014 5:41pm
12/15/2014 5:41pm
I've had good luck just throwing new pistons in stock cylinders.
moto314
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moto314 12/16/2014 12:57pm
12/16/2014 12:57pm
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if a piston is good by just looking at it. You really need to measure it, skirts, ring lands, pin bore, and do a hardness check to tell. You cannot see fatigue until a crack develops. Why not just replace it and be safe is my suggestion.
floridaflash
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floridaflash 12/16/2014 6:22pm
12/16/2014 6:22pm
I never waste my time pulling it apart and only replace the ring, I always do the complete top end. Just my 2 cents
JH911
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JH911 12/17/2014 10:46am
12/17/2014 10:46am
moto314 wrote:
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if...
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if a piston is good by just looking at it. You really need to measure it, skirts, ring lands, pin bore, and do a hardness check to tell. You cannot see fatigue until a crack develops. Why not just replace it and be safe is my suggestion.
Really?? And that's why people put new pistons in all the time and re-use rings?? I've heard of Re-Ringing a piston, but never Re-Pistoning a Ring?? And no it's not hard to tell if a piston is good by looking at it. It's actually quite simple as I explained above. If there is significant wear present then measuring the skirt wouldn't be a bad idea, but there is not. If there were significant wear you "would" see it, in which case he probably wouldn't be wondering if he should be replacing it. Sorry, to inform you, but piston rings maybe made of steel, but they are made of a softer steel than the Nikasil or Cast Iron Sleeve while being constant contact with the cylinder wall, a piston ring will wear out before a piston. Piston rings serve to seal the combustion chamber and a secondary function is to help limit the piston rock in the bore, which keeps the piston from wearing out. Funny, you didn't mention the importance of ring end gap? Please explain which tool you would use to measure the ring lands?? Are you measuring height or depth?? How many times have you heard of or experienced a pin bore being wore out without the piston being toast? In closing I say again there is some good advice in forums, but you have to sift through hundreds of posts with bad advice or plain BS from people wanting to sound like they know what they're talking about before you can find the good info. My .02 is run it, aside from the minimal scuff on the exhaust bridge it looks great as does the ring, but if he's got money to burn go ahead and throw a new piston in. Your already there, but don't be surprised when that new piston shows if it looks exactly like the one he just took out sans exhaust port scuffing. Grab a micrometer of caliper and your owners manual, I bet it's in spec. Do whatever you feel is best, but if your on a budget like most I wouldn't scrap a perfectly good piston. Sorry to anyone I may have offended, but it's frustrating to see all the misleading or bad info being passed around here. Also I apologize for my tone and attitude.
seth505
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seth505 12/17/2014 2:11pm
12/17/2014 2:11pm
moto314 wrote:
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if...
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if a piston is good by just looking at it. You really need to measure it, skirts, ring lands, pin bore, and do a hardness check to tell. You cannot see fatigue until a crack develops. Why not just replace it and be safe is my suggestion.
JH911 wrote:
Really?? And that's why people put new pistons in all the time and re-use rings?? I've heard of Re-Ringing a piston, but never Re-Pistoning a Ring...
Really?? And that's why people put new pistons in all the time and re-use rings?? I've heard of Re-Ringing a piston, but never Re-Pistoning a Ring?? And no it's not hard to tell if a piston is good by looking at it. It's actually quite simple as I explained above. If there is significant wear present then measuring the skirt wouldn't be a bad idea, but there is not. If there were significant wear you "would" see it, in which case he probably wouldn't be wondering if he should be replacing it. Sorry, to inform you, but piston rings maybe made of steel, but they are made of a softer steel than the Nikasil or Cast Iron Sleeve while being constant contact with the cylinder wall, a piston ring will wear out before a piston. Piston rings serve to seal the combustion chamber and a secondary function is to help limit the piston rock in the bore, which keeps the piston from wearing out. Funny, you didn't mention the importance of ring end gap? Please explain which tool you would use to measure the ring lands?? Are you measuring height or depth?? How many times have you heard of or experienced a pin bore being wore out without the piston being toast? In closing I say again there is some good advice in forums, but you have to sift through hundreds of posts with bad advice or plain BS from people wanting to sound like they know what they're talking about before you can find the good info. My .02 is run it, aside from the minimal scuff on the exhaust bridge it looks great as does the ring, but if he's got money to burn go ahead and throw a new piston in. Your already there, but don't be surprised when that new piston shows if it looks exactly like the one he just took out sans exhaust port scuffing. Grab a micrometer of caliper and your owners manual, I bet it's in spec. Do whatever you feel is best, but if your on a budget like most I wouldn't scrap a perfectly good piston. Sorry to anyone I may have offended, but it's frustrating to see all the misleading or bad info being passed around here. Also I apologize for my tone and attitude.
I'd agree with this dude. Ideally, I like to do a new ring in my 125 and full top-end every other.
slipdog
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slipdog 12/17/2014 5:10pm
12/17/2014 5:10pm
Hahaha!

He says to the engineer that designs pistons for a living... Fucking classic!!!
JH911
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JH911 12/17/2014 8:28pm
12/17/2014 8:28pm
moto314 wrote:
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if...
In normal conditions the piston will almost always wear out before the ring. Rings are made of steel, piston aluminum. It's pretty hard to tell if a piston is good by just looking at it. You really need to measure it, skirts, ring lands, pin bore, and do a hardness check to tell. You cannot see fatigue until a crack develops. Why not just replace it and be safe is my suggestion.
Well, let me just say that if Dan Rice is in fact the person who posted this; then any statement I made pointing at him not knowing what he is talking about would be entirely inaccurate and I would apologize. I know of Dan and RECMX, what he has done and continues to do with in the motocross industry. Especially for his work with privateers. I've got a lot of respect for him. So I guess I would have to say my problem/argument would not be with his knowledge I will be the first to admit it's far and away above my understanding, but with his actual statement. "In normal conditions the piston will always wear out before the ring. Rings are made of steel, piston aluminum." That's a.........a weird statement.....can't really think of a better word or term to describe it. If you were to take that statement at face value and pose that same statement to most any general mechanic, race mechanic, moto dad, etc. You would likely receive the same or similar response I've given. Which is what we've all been taught through say MMI, misc tech training, or just rebuilding engines in general. I can't count the number of times I've pulled an engine down and the piston mic'd out within spec, however compression was weak and there was significant blow by telling me the rings were worn out, but the piston was still within service limits. Or the piston and rings both had been in there so long they're both completely shot. I can see that visually. So I would ask then "How does under normal operation a piston wear out before the rings?" Again that being in most any case contradictory to everything I've been taught. Or "Please explain how/why I would measure ring lands or pin bore to determine if a piston is worn?" It would seem that at this point engineering of pistons would be such that wear of ring lands or piston pin bore would be the last place one would look to determine wear of the actual piston. Given my experience for those two areas or components of the piston to fail before say the rings break or the actual piston crown breaks would be somewhat an extremely rare occurrence which would be far outside the realm of normal conditions. Unless the wrong rings were installed and flutter was extreme. Or too small wrist pin were installed. For a piston to reach that point under normal conditions one would think you would visually see that the piston is worn out at that time, you probably wouldn't be inspecting the ring lands or pin bore. So again I took his statement at face value before taking the time to research who was making the statement. Given the opportunity Dan is one person I would jump at the chance to work under or have a Q&A with!! There is a ton that I could and would want to learn from someone like him. Forums are tough. They give anonymity to everyone allowing them to claim to be whoever or professional whatever they want to be and blow a lot of smoke. I myself peruse Vital from time to time, but for the most part keep from posting due to everyone has their own theory/opinion on things and it's just not worth the argument. I don't know everything and god knows I've made many of my own mistakes. So to Dan (if he is in fact who posted the response) my apologies I guess I should have asked for you to explain your statement rather than quote and jump it. I still would like to hear your reasoning for sure, but that would be an entirely new Thread/Post in itself. Sorry for hijacking your thread NytsmaC.

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Dragoo168
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Dragoo168 12/17/2014 9:21pm
12/17/2014 9:21pm Edited Date/Time 12/18/2014 9:22am
First of all, I would like to say that i've seen both good and not so great advice on many different forums, but for the most part, the moto community is generally trying to help eachother out by contributing in the best way they can. There is always the "know it all", and the "wiseguy", but most can discern between the two, and find a probable solution. Instead of bashing someone, or calling out everyone that we do or don't know, why not communicate, or even research to verify our own knowledge, and submit it in earnest? I would hope that MMi, and technician update seminars aren't the basis for discrediting someone's advice. The manufacturers recommendations are the basis for the question on this thread. Without getting into the science of metallurgy, design, rider ability, etc, the standard is to replace the piston at the time he stated, which i believe was 17hrs. I personally do not know Dan, but have heard of him, and while i may agree with his advice, i will step on a limb and clarify something about what he said. The ring(s) takes the bulk of the abuse, working in coordination with the camming design of the piston, and Piston wear is determined BY the ring, any engine builder should be able to tell you that. As the ring wears, compression decreases and blowby begins to develop, the piston gets battered and the skirt takes a beating. This is by design to increase cylinder wear, utilizing modern technology. Because a technician cannot determine absolutely, a riders ability, or riding practices, it is standard protocol to replace the piston with the ring, at the general time frames given. For a Pro rider, you would never even get close to those times, and many, many "Like new" pistons are tossed in the trash, week in and week out. Regardless, replacement of the piston is to prevent breakage, not based necessarily on wear. If you are running a forged piston, or are the kind of guy that can change his rings regularly, say every 10 to 15 hrs, you can likely skip a piston cycle to every other teardown, but to recommend to a customer, or a stranger that is asking, would be poor advice.
moto314
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moto314 12/18/2014 2:23pm
12/18/2014 2:23pm
slipdog wrote:
Hahaha!

He says to the engineer that designs pistons for a living... Fucking classic!!!
I don't actually design pistons full time anymore, but I am designing a custom piston for a race team right now.
moto314
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moto314 12/18/2014 2:55pm
12/18/2014 2:55pm
I guess I was just trying to keep my advise (statement) too simple. Yes ring(s) wear out and cause loss of compression and power. Putting in a new ring will bring most of this loss back. And yes the piston will probably work just fine. But 2 stroke pistons are cheap and I don't like probably. My point was just by measuring the piston skirt and looking at the skirt wear doesn't tell the whole story. Aluminum has a fatigue life and will anneal (soften) with use. Pin bores can gall and become out of round, ring grooves wear as well as the ring lands causing a less flat sealing surface for the rings. On 4 stroke pistons the ring lands above the skirt axis can wear as much or more than the skirts. Dragoo168 kind of hit the nail on the head already. The piston will usually fail (crack) before a ring would ever break, unless something abnormal happened. JH911 no need to apologize, and thanks for the kind words. Even though I have designed pistons, rods, pins, and cylinders, I don't know everything and definitely not a 2 stroke expert anymore. And how has someone heard of me? Guess my cover is blown, how am I going to talk smack now? Ok I don't want to jack nytsmaC thread anymore, he has a bike to put back together before the weekend!
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