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Post by 90GTVert on Sept 4, 2021 15:07:46 GMT -5
I had a comment on a video that EGT is unnecessary and over-complicating things. Just jet it right. We didn't have all of those gauges years ago.
I said that I don't know anyone with a fast 2T that hasn't wrecked a piston and if you haven't melted one, then you aren't trying hard enough.
I think that's true, but I was curious to find out if my perception is skewed. I'll be a bit surprised if the people that have done a lot of work with 2Ts don't have a small (or large) pile. I've got a small collection with holes in the crown or rings stuck due to erosion/melting on the edges of the crown or damage from losing clearance and scraping. I used to just throw them away, so I should have more than I do. This isn't even counting losing circlips or bearings coming apart.
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Post by captincvmn on Sept 4, 2021 15:13:19 GMT -5
I’m not trying hard enough.
One set of rings, two small end bearing failures.
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Post by 90GTVert on Sept 4, 2021 15:26:27 GMT -5
TBH, I only melted one piston on a ~70cc sport. That was the only aluminum kit before I went to the TPR. My father was riding the scoot. Downhill plus tailwind at part throttle (Airsal T6, Arreche carb, forget which pipe). It was fine for many miles before that.
Most of my failures with the bigger sport-type stuff (90/100cc) were from when I had jets of various brands and eventually discovered that when I up-jetted for safety, I actually down-jetted due to variations in orifice size vs numbering.
For me at least, it seems to change when you get beyond sport. With a bit of a change in porting and a lively exhaust, failures become more likely. Aluminum bores make it that much more likely because they don't just want to soft seize with minimal damage like the iron bores may do as a warning.
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Post by geoffh on Sept 4, 2021 15:32:21 GMT -5
13 years of 2T daily use,just one piston cooked due to oil pump failure,but I,m still 49cc and use a very mild street tune.
Geoff
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Post by aeroxbud on Sept 4, 2021 15:41:55 GMT -5
Had quite a few on bikes years ago. Scooters not so much so. A couple that have run lean, one ring snagged a port. Bent crankshaft, oil pump failing. Here is the last one. 🤦  |
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Post by nikola11 on Sept 4, 2021 15:45:28 GMT -5
I have some experience with some midrace cylinder kits on scooters and geared mopeds...
I must say that I have never melted a hole in a piston.
Once I have melted a spark plug due to running a to hot spark plug.
Other than that neved have I melted a piston.
When I get to tuning a fresh setup I start really rich and I usually tune the mixture to be always on the rich side.
Even when you know you are pushing the limits on an air cooled engine you can usually tell that something is not ok before it soft siezes.
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Post by oldgeek on Sept 4, 2021 22:08:16 GMT -5
More soft seizes than we can remember Couple of four cornered cylinders Snagged a ring a few times. Busted crank Broken piston Caved in piston Don't think I ever holed a piston.... Ill try harder, I promise! Probably lots more I cannot remember. Oh, and a couple gear boxes ruined I forgot to put gear oil in. I am the King of that one.  |
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Post by 190mech on Sept 5, 2021 17:59:17 GMT -5
Back in the 70's I worked at a few motorcycle shops when 2strokes were king (they still are in my book),,We had all sorts of smoked pistons come through from a wide variety of reasons..Eric Gorr's Motocross & Off-Road book has several pages of fried piston pics starting at page 119..I went many years without smoking a piston on my personal bikes,but that changed when I started back with scoots after a long break from 2strokes,,Scoots with their CVT system keep the engine at peak revs,thats good till you need to slow down,we cant down shift so the CVT simulates that..It's not the same as tapping that shift lever down a few clicks..So we are in that dreaded zone that Jan Thiel talks of,but cant down shift to keep it in the rev zone..So I guess this doesnt give an answer except to deal with careful tuning or buy a 4poke with twice the CC to overcome its skip fire process and hope those million other parts dont break while revving it to the moon trying to make the power a 2stroke does...
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Post by repherence2 on Sept 5, 2021 19:56:04 GMT -5
i ran a NCY 47mm squish band head on a 50mm bore. that thing ran like an animal. i was so green at tuning, i was in denial of hearing it Ping during idle. i was hard headed and kept running it because it felt like a champ. one day it died, from a hole in the piston.
it's like a coworker once told me, "an engine always runs the strongest right before you blow it up." so true.
i was so green at tuning, never checked squish and never bothered with compression either. no temp gauge too. straight up tuning stupidity. but you live, break, and learn.
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winner3ty
Scoot Enthusiast
2 Strokes for life
Posts: 317
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Post by winner3ty on Sept 6, 2021 6:52:50 GMT -5
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Post by Lucass2T on Sept 6, 2021 7:09:28 GMT -5
Ruined one once from a customer. He asked the scoot shop (where I worked at the time) to tune it. It was an Aprilia SR50 minarelli with gilardoni 70cc kit, chamber, 17.5mm dellorto and some other go fast bits. Swapped some rollers and jets around and it ran really strong, then it stopped, no compression. Pulled the head and there was a hole in the piston. After some head scratching I pulled the ignition and found a key with a step. It had advanced the ignition timing to the point of holing the piston.  I once melted a piston after some deliberate WOT downhill overrevving. Did it kinda on purpose. And once on the 70mph daily, turned the top of the piston into a bowl. Didn't hole it and it still ran. Never understood why the top caved in but the motor never seized or anything. |
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winner3ty
Scoot Enthusiast
2 Strokes for life
Posts: 317
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Post by winner3ty on Sept 6, 2021 7:15:59 GMT -5
Ruined one once from a customer. He asked the scoot shop (where I worked at the time) to tune it. It was an Aprilia SR50 minarelli with gilardoni 70cc kit, chamber, 17.5mm dellorto and some other go fast bits. Swapped some rollers and jets around and it ran really strong, then it stopped, no compression. Pulled the head and there was a hole in the piston. After some head scratching I pulled the ignition and found a key with a step. It had advanced the ignition timing to the point of holing the piston. I once melted a piston after some deliberate WOT downhill overrevving. Did it kinda on purpose. And once on the 70mph daily, turned the top of the piston into a bowl. Didn't hole it and it still ran. Never understood why the top caved in but the motor never seized or anything. Wow! that's really unfortunate. I want that sr50 though  |
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Post by snaker on Sept 6, 2021 13:40:12 GMT -5
Back in the 70's I worked at a few motorcycle shops when 2strokes were king (they still are in my book),,We had all sorts of smoked pistons come through from a wide variety of reasons..Eric Gorr's Motocross & Off-Road book has several pages of fried piston pics starting at page 119..I went many years without smoking a piston on my personal bikes,but that changed when I started back with scoots after a long break from 2strokes,,Scoots with their CVT system keep the engine at peak revs,thats good till you need to slow down,we cant down shift so the CVT simulates that..It's not the same as tapping that shift lever down a few clicks..So we are in that dreaded zone that Jan Thiel talks of,but cant down shift to keep it in the rev zone..So I guess this doesnt give an answer except to deal with careful tuning or buy a 4poke with twice the CC to overcome its skip fire process and hope those million other parts dont break while revving it to the moon trying to make the power a 2stroke does... Old saying: "Good 2 strokes don't make crazy power, bad 2 strokes make crazy power". Some are very bad. |
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Post by Zino on Sept 8, 2021 21:18:06 GMT -5
As a kid I grew up in my GrandFathers Arctic Car Snowmobile Dealership .
I learned how to make them go fast then really fast and then Boom.
Decked heads to raise compression ,Leaned out the Carbs until they Screamed like a Raped Ape .
I would either show real well on the radar runs or I would have to drag the sled home and rebuild it .
It was an expensive habit .
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Post by 90GTVert on Sept 8, 2021 23:02:30 GMT -5
Thanks to everyone that has participated so far. Keep the stories coming.
It sounds like I had the right impression. Most of us melting stuff are pushing it, chasing that elusive beast that we call... More. Some of us manage to tame it, but often More gets the best of us and escapes through a hole in a piston. There must be a whole bunch of More out there, because even if we figure out how to get our hands on it without getting bit; some of us go right back on the hunt for More.
I'm guilty of thinking that a little extra is worth a little risk too often. Even my Dell on the TPR has the needle a slot leaner than it should be at for safety. Why? More response, more wheelies, more of an edge. Same deal with timing. It should probably be backed off 1-2 degrees for safety as well... but... More. More is all I've ever wanted, and I'm never happy for long when I get it.
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