Sun, 14 Aug 2022 10:36:14 +0000

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Sun, 14 Aug 2022 10:36:14 +0000 linkquote
I'm running one off these sobs the piston cracked on a rock solid engine. The edge of the crown chipped off right over the start of the ring by the gap. The edge of the top ring now being exposed. Any of you guys or gals had the same issue any off you taken step to avoid this? When it goes back in I will increase squish and retard timing. And thoughts?



Sun, 14 Aug 2022 10:38:27 +0000

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Sun, 14 Aug 2022 10:38:27 +0000 linkquote
Here's another



Sun, 14 Aug 2022 11:24:47 +0000

Ossessionato
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Ossessionato
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Sun, 14 Aug 2022 11:24:47 +0000 linkquote
Post a few pictures of bottom side and exhaust side? Is there oil burnt to bottom or underside?
Sun, 14 Aug 2022 12:11:12 +0000

Ossessionato
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Sun, 14 Aug 2022 12:11:12 +0000 linkquote
Do you still have the idle adjuster screw in carb?
Does the exhaust rattle with whatever went down there?
What caused the top of the piston to rip off & cause those cracks, or was it just heat?



Sun, 14 Aug 2022 12:16:41 +0000

Hooked
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Sun, 14 Aug 2022 12:16:41 +0000 linkquote
Is your locating pin still on the piston? To me that looks like the ring has snagged to the edge of boost port when piston was going down.
Sun, 14 Aug 2022 15:01:05 +0000

Lucky
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Sun, 14 Aug 2022 15:01:05 +0000 linkquote
The wash on that piston says it's way too lean if it's been running for any period of time at all. What's your spark plug look like?

Also, while it's hard to tell with that much shrapnel in the mix, but are you sure there's no detonation marks on the piston? How about the cylinder head?
Sun, 14 Aug 2022 19:10:17 +0000

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Sun, 14 Aug 2022 19:10:17 +0000 linkquote
Hello thanks for your response. The plug shows no sign of detonation nor head just damage from the broken peice . I recon the same that it's snagged and lifted off. That's why I want to know if any other poor bugger has had the same. The way it has gone at that point of the ring and that peice passes a window. Hhhhmmmm. It was running rich.
Sun, 14 Aug 2022 19:15:36 +0000

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Sun, 14 Aug 2022 19:15:36 +0000 linkquote
Oh yeah it took in a load of oil from clutch side that has tainted everything hence the strange colour. The pressure spat oil from selector box too. What a carry on.
Sun, 14 Aug 2022 19:21:30 +0000

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Sun, 14 Aug 2022 19:21:30 +0000 linkquote
Here you are



Sun, 14 Aug 2022 19:23:36 +0000

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Sun, 14 Aug 2022 19:23:36 +0000 linkquote
More



Sun, 14 Aug 2022 19:53:26 +0000

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Sun, 14 Aug 2022 19:53:26 +0000 linkquote
Was it heat or snag I think snag but I would wouldn't i
Sun, 14 Aug 2022 21:05:13 +0000

Lucky
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Sun, 14 Aug 2022 21:05:13 +0000 linkquote
Narrator Voice: It was heat...

So you had a clutch side air leak and what might have been an already borderline too lean carb setup. Maybe too much ignition advance, too, but hard to say for sure without more pictures of the cylinder and exhaust side of the piston.

Tell us a little more about the setup. What parts other than the Parmakit? What's your carb setup? Port Timings? Ignition timing? How many miles on it? How much porting work?

It's possible that you caught a ring or just had bad luck (I've certainly been there) or the part was defective, but even if it was, I suspect it was running in an unfavorable environment, too.

The goal nowis to see what should be done to avoid the next iteration of top end destruction.
Sun, 14 Aug 2022 22:09:05 +0000

Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
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Sun, 14 Aug 2022 22:09:05 +0000 linkquote
it looks like the was hot/detonating for a awhile and then just finally gave up the ghost. I'd think that a ring would snap rather than lift off the edge of a piston crown unless it was already weakened and on its way out the door.
Sun, 14 Aug 2022 23:25:47 +0000

Jet Eye Master
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Jet Eye Master
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Sun, 14 Aug 2022 23:25:47 +0000 linkquote
+1
Running extremely lean. Air leak or jetting....or both.
Did the cylinder survive?
Sun, 14 Aug 2022 23:43:51 +0000

Ossessionato
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Sun, 14 Aug 2022 23:43:51 +0000 linkquote
Double doves wrote:
More
That oil burnt to bottom side shouldn't be there, that's overheating and incoming oil burning to bottom side of piston. She's been running hot.
Mon, 15 Aug 2022 04:54:20 +0000

Hooked
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Mon, 15 Aug 2022 04:54:20 +0000 linkquote
Usually ring is snagged on the wider exhaust port and not so often on intake side.

Possibly a combination of many things gone wrong here.
Mon, 15 Aug 2022 05:25:35 +0000

Molto Verboso
71' Sprint Veloce , 05' Vespa PX150, 1978 P200E
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Mon, 15 Aug 2022 05:25:35 +0000 linkquote
I never had a Parmakit but that piston failure reminds me of the Pinasco 210 that i had. The piston broke like crackers, I could remove chunks of the piston with my nails.

At this moment I don't have any experience with Parmakit but I can tell you that if you ever need another kit please highly consider Malossi and Polini.
Tue, 16 Aug 2022 19:42:53 +0000

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Tue, 16 Aug 2022 19:42:53 +0000 linkquote
Hello here's the full story two days prior me and the scooter did about 80 miles . However this journey was so frigging important I needed to get there so I up jetted from 135 main (brown plug) to a 140 (black plug) just to be safe!!!!! about 20 miles into my journey I checked the plug and it was black, 10-15 miles later it went pop. My set up 190air. Be2 and 140 mj. That's why I think it may be a fault with piston. But I do think maybe it may have developed a leak. The marks on piston look like they are from the jettisoned piston section. And the plug shows no sign of detonation (intact, brownish and none of them bits that cover the electrode when it goes) and no little aluminum bits anywhere on head . Not sure about a new kit I'd love another parmakit but this has put me off them a bit. I'll probably cobble something up from the scraps in my garage. Gutted.just gutted.
Tue, 16 Aug 2022 21:07:28 +0000

Jet Eye Master
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Jet Eye Master
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Tue, 16 Aug 2022 21:07:28 +0000 linkquote
It is very unfortunate for sure. If it was prior advertised that you were planning to install the grenade jetting combo (190/BE2). We would all have said, no don't it, it will detonate until it seizes. I would buy another piston. Parmakits are great.
Tue, 16 Aug 2022 21:32:09 +0000

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Tue, 16 Aug 2022 21:32:09 +0000 linkquote
good lord. 190 AC? I didn't even know such a thing existed.

that with a BE2 you could've probably run no main at all and it still would've went kablooey.

I'm with jack though, assess the barrel and knock in a new piston.
Tue, 16 Aug 2022 21:54:52 +0000

Ossessionato
2007 Stella 225
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Tue, 16 Aug 2022 21:54:52 +0000 linkquote
Double doves wrote:
Hello here's the full story two days prior me and the scooter did about 80 miles . However this journey was so frigging important I needed to get there so I up jetted from 135 main (brown plug) to a 140 (black plug) just to be safe!!!!! about 20 miles into my journey I checked the plug and it was black, 10-15 miles later it went pop. My set up 190air. Be2 and 140 mj. That's why I think it may be a fault with piston. But I do think maybe it may have developed a leak. The marks on piston look like they are from the jettisoned piston section. And the plug shows no sign of detonation (intact, brownish and none of them bits that cover the electrode when it goes) and no little aluminum bits anywhere on head . Not sure about a new kit I'd love another parmakit but this has put me off them a bit. I'll probably cobble something up from the scraps in my garage. Gutted.just gutted.
It was running hot at some point, you have oil burnt to bottom side of piston.
Thu, 18 Aug 2022 17:43:51 +0000

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Thu, 18 Aug 2022 17:43:51 +0000 linkquote
Ohhh what's up with the 190 dudes ? I know it's a big mouthful of air. But with that comes more fuel doesn't it ? And allows for a much thicker mixture with large mj? A 160 ac gave much much leaner results . And according to what I figured out on other scoots me be2 gives richer mid range and top than a be3. Again I worked out that the larger and more numerous holes pulls through more petrol. Am I wrong? I am prepared to be . Bit it runs against all my previous results. Oh my . I've always used a be5 for lean? Does this mean be5 is richer than both be2 and be3? Oh dear. If so how comes a 125 uses a 120ac and a richer running 200 uses 160ac but then a 190ac is lean? Oh no my brain cell hurts and he's back in the 90's of his nut on E and LSD.Oh deary me.

Last edited by Double doves on Thu, 18 Aug 2022 18:32:08 +0000; edited 1 time
Thu, 18 Aug 2022 17:48:13 +0000

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Thu, 18 Aug 2022 17:48:13 +0000 linkquote
Barrel has a hair line scratch right though th power section at top of barrel. I'm going to try it. But I'm not hopeful!
Thu, 18 Aug 2022 17:58:02 +0000

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Thu, 18 Aug 2022 17:58:02 +0000 linkquote
Going to do something even more stupid while I save up. Ive got a super barrel i'm cutting off the piece of skirt between the bottom ring and base off barrel around the 3rd top port as its snapped. cleaning it up and sticking on me scoot. What could possibly go wrong?
Sat, 20 Aug 2022 09:14:15 +0000

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Sat, 20 Aug 2022 09:14:15 +0000 linkquote
Guys? Hello? Trying to wrap my head around this granade combo theory. Don't leave me hanging! You've just turned me world upside down! Need closure need it bad I don't want to make another expensive mistake!! My wife will kill me and she's been looking for an excuse for the last 16 years of our marriage . I'm in a real pickle πŸ™ƒ. Any help massively appreciated! Was my stack really a time bomb? Free kudos for anyone who can explain everyone's reaction?
Sat, 20 Aug 2022 13:00:31 +0000

Hooked
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Sat, 20 Aug 2022 13:00:31 +0000 linkquote
Tuning vintage two stroke scoots is not an exact science so i don't think anyone can say what caused this for sure. That's why everyone have been tossing around ideas for you to make your own conclusion.

If the cylinder is ok, I'd just throw in a fresh piston, do a leak test and work on jetting.
Sat, 20 Aug 2022 13:54:35 +0000

Jet Eye Master
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Jet Eye Master
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Sat, 20 Aug 2022 13:54:35 +0000 linkquote
This is not a theory. The AC190 and BE2 can be used individually on very low tune builds but if used together on anything but a stock 50s motor, it's going to blow.
After 40 years of vespa tuning, the sum total of accumulated knowledge is, the more air in an atomiser the leaner it is.
Next time out, AC120 BE4 and work from there. First thing you'll notice is how fast it is. And that's not so bad.
Sat, 20 Aug 2022 14:51:07 +0000

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Sat, 20 Aug 2022 14:51:07 +0000 linkquote
Thanks guys. I really appreciate your help. I don't want to come across like I'm bustin your balls I'm just trying to pick your brains. Thing is I tried a 120ac and 140ac with be3 and with those it went into a mad heat cycle and reved its own bollcks uncontrollably. (Whist riding at speed)You know when that mad revving turns into something strange when the vibration goes panning through the scoot . A 160ac was better but not right. that's why I went higher. I will definitely try again from scratch with your recommendations. Maybe something affected my results πŸ€” πŸ˜” πŸ˜• 😒 again I've always thought on bigger more powerful engines you need a bigger ac or else you'll get a thin mix producing more heat. But again I'm hearing the exact opposite. I'm gonna give it ago. As I've an open mind. As for faster that's cool with me it would already hit GPS 66mph in 3rd.so I'm all for trying it your way. I might just be surprised!!
Sat, 20 Aug 2022 16:37:49 +0000

Molto Verboso
PX 200
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Sat, 20 Aug 2022 16:37:49 +0000 linkquote
Sounds like it's problems else where if ac 160, 140, 120 doesn't work for you.

It's a 177 kit right?

What gearbox are you using? You must be hammering it in 3rd!

What exhaust??
Sat, 20 Aug 2022 19:22:46 +0000

Jet Eye Master
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Sat, 20 Aug 2022 19:22:46 +0000 linkquote
Sounds very much like you have an oil seal or gasket leak. They only diesel at high rpm when the engine section is in poor condition and leaking air.
Work to do. Don't tell the missus until its fixed. And even then it's optional.
Sun, 21 Aug 2022 16:09:55 +0000

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Sun, 21 Aug 2022 16:09:55 +0000 linkquote
Yeah this is our little secret please don't tell her. I got bgm pro flowed crankshaft , sip xl exhaust. P2 gearing my inlet opens 130 before tdc and 70 after 24mm si . It did go like the clappers . Until the other day and it was a first kick starter. So that's why I'm gutted. Have not opened her up yet but hopefully my mallosi casings ain't funked. C'est le vie . But my little rocket will be back!!! Even better every time I fuck it up I make it faster so it don't get me down.
Sun, 21 Aug 2022 16:12:17 +0000

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Sun, 21 Aug 2022 16:12:17 +0000 linkquote
Oh yeah and yes I ride it hard. Real hard. But actually when it went I was doing about 65 mph in 4th. Only cruising, Which ain't like me at all.
I'm still thinking air leak or faulty piston but I've heard no other complaints about parmakit pistons so Im starting to think its not the piston.
Sun, 21 Aug 2022 16:24:11 +0000

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Sun, 21 Aug 2022 16:24:11 +0000 linkquote
Still and I'm not saying I'm right but
125cc 120ac
200cc 160ac
50cc 190ac?
As I say I ain't saying anything about any one being wrong but I'm scratching my head like a flea ridden tramp.
Confusing little bastards ain't they!
Sun, 21 Aug 2022 19:36:35 +0000

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Sun, 21 Aug 2022 19:36:35 +0000 linkquote
What carb are you running?
Is the float bowl drilled.

I'm going to assume the answer is either a 20/20 or 24/24?

This may help:
- don't think of the AC higher number = power. It's a tiny hole. It's balancing against the main to get mixture right - not volume of total air into motor. There is no gulping.
- if your carb isn't drilled, then anything larger than a 120 mj (like a 140 mj) is acting only like… a 120 mj. The carb float hole will restrict flow.
- the benefit of smaller AC is to allow smaller main while getting same supply and mix rate of air fuel. Read that one again.
- so a 120ac will match with a 120 mj (estimate) but a 160ac would need a 135mj (estimate)
- a 190 ac, well, u r gonna need a honking big main jet and the carb channels simply weren't designed to allow that much flow. They will likely be your limiting factor.

So there is no Beni for to a larger ac, but there is plenty of downside.

It's also critical for these motors to be air tight.
Not almost airtight.
Not nearly air tight.
Airtight.
Simple to create a kit to test.
Lots of examples on this forum.

Make sure u have it tested air tight before u bother to try and jet.
Hope this helps.
-CM
Sun, 21 Aug 2022 21:28:00 +0000

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Sun, 21 Aug 2022 21:28:00 +0000 linkquote
Ahhh now that would make sense. Constriction of petrol but not of air so one overwhelms the other. Now that is making sense. so drill out the 'tap end' ( probably not correct term!) Down into the bowl . Your making alot of sense now. That's something I've not even looked at or considered may happen. Now that's some excellent πŸ‘Œ info . I like it. I like it alot. Yay!!!!! Give yourself 300 mega points. At least 300 fuck it have 310. Good on ya.
Oh yeah once it's put together I always test the pressure. I've learnt that the hard way before. Rock Solid advice . Thanks CM. Have a kiss. X
Tue, 23 Aug 2022 20:07:23 +0000

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Tue, 23 Aug 2022 20:07:23 +0000 linkquote
Yes yes CM just googled it frigging loads popped up ! Good on ya 4 the heads up on the drilling. And everyone else who helped me out . Definitely gonna do it.
Tue, 30 Aug 2022 09:06:07 +0000

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Tue, 30 Aug 2022 09:06:07 +0000 linkquote
OK done the carb. Started engine overhaul. Found that the flywheel side bearing had failed. Completely shot. Oh my. A real doozie. Not definite that caused any harm but it may have been a contributing factor. I Don't know. Them new honda scooters look nice Don't they.
Tue, 30 Aug 2022 19:46:03 +0000

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Tue, 30 Aug 2022 19:46:03 +0000 linkquote
Nice catch. Spotting the bad bearing might have saved your rotary pad
Wed, 31 Aug 2022 08:54:10 +0000

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Location: Cov
Wed, 31 Aug 2022 08:54:10 +0000 linkquote
I know phew! Managed to locate all the needle rollers except 1. Wasn't sure if it could make its way into casings there's not much of a gap once closed up. But I'm considering myself quite a lucky boy . So yeah small victory but yeah pleased I found it.
⬆️    About 27d elapsed between posts    ⬇️
Tue, 27 Sep 2022 19:05:44 +0000

Member
Px
Joined: Fri, 25 Sep 2020 20:17:41 +0000
Posts: 39
Location: Cov
 
Member
Px
Joined: Fri, 25 Sep 2020 20:17:41 +0000
Posts: 39
Location: Cov
Tue, 27 Sep 2022 19:05:44 +0000 linkquote
Yay! All sorted a massive thank you. All going again . Only needed to replace the piston that I had already, bearing and seals. New set up
Ac. 160
Be5
Main 122
Spaco 26mm carb
So thanks everyone.
   

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