P200 Holed Piston Recovery

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toigo
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P200 Holed Piston Recovery

Postby toigo » Wed May 02, 2012 3:44 pm

For anyone following my cannoball blog (http://www.matt-toigo.com/cannonball), I'm sure you saw it, but I managed to put a hole through the top of the piston on the last day. Don't fret I still had an awesome time and didn't let it get me down. So the matter at hand is getting the bike running again and I've got plenty of questions.

1. I'm pretty sure that this had to be the bike getting too hot and the fuel mixture lighting as the piston was traveling towards the spark plug, but want to be sure.
The top of the piston has pale grey carbon on top and it was the most cooked spark plug I have ever seen. I was also riding the bike very hard in hot weather after dropping down in altitude a lot so it was probably lean. The only other cause I could think of would be the ignition timing set too early. The bike came with an aftermarket Leo Vince exhaust, and I'm not sure if the timing was ever adjusted for this or even should be. I was using high octane gas as well. I've ridden it for over a year with no engine issues before this.

2. Should I absolutely split the case on it and see if any of the piston ended up down near the crank?
I heard varying opinions on this, but I was leaning towards definitely since I don't want to damage the crank with pieces of piston down there or for anything to get caught in one of the crank shaft bearings. It could just be somewhere in the exhaust, but I'd rather play it safe.

3. The bike has 15k miles on it. I'll have it back in a week to inspect more closely, but would it be worth having the piston bored to the first oversize with this kind of milage?
I know it depends on the condition of the cylinder walls, but if I'm going to be dealing with all this it may be worth it just to have this done as well. Any recommendations on when in the life of a Vespa this is usually done, or is it purely a judgement based on the condition of the cylinder.

Thanks

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toigo
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Re: P200 Holed Piston Recovery

Postby toigo » Wed May 02, 2012 3:45 pm

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normratscoots
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Re: P200 Holed Piston Recovery

Postby normratscoots » Wed May 02, 2012 4:10 pm

1. Regarding timing, what were you hearing? Were you hearing pre-ignition? You had several risk factors going on, so its difficult to say.

2. Regardless of where the piston material ended up, splitting cases sounds like a good idea with 15k on the bike and a 2.5k race just behind it. Some people get 30k out of a P200 engine with gentle commuter riding, some people break them down every winter. Motocross racers rebuild often.
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toigo
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Re: P200 Holed Piston Recovery

Postby toigo » Wed May 02, 2012 4:37 pm

I didn't hear anything and as the bike died it felt just like running out of gas.

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Mikeh
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Re: P200 Holed Piston Recovery

Postby Mikeh » Wed May 02, 2012 5:49 pm

I would not worry too much about the blown out piston pieces, they most likely got blown in very tiny pieces through the exhaust as the piston was worn away.

I suspect a timing problem, perhaps your CDI or electronic trigger started failing. Did you have any hesitation, misfiring, or backfiring prior to the break down? If not then the timing may have just been too far off (i am not saying too far advanced or retarded because that would make me think too hard to figure out). But if you set it to stock or close to stock this should not happen.

As far as rebuilding the motor, I would not crack the cases unless you have time and really want to check the rest of the motor out, but it's probably overkill.

If you have compressed air then you can blow the crank area out and leave the cases together. I would not mess with boring out the cylinder and getting a new piston, just buy a whole new matched cylinder and piston. It may set you back an extra $100 bucks but it will be money well spent since you won't have to worry about getting to a machine shop and buying a piston. OR just send the cylinder to Hot Rod Al and have him do it up for you and he can get the piston to make sure it's all good, this may cost the same as a new top end, but he will port it and make it a little faster and perhaps run cooler. I would not trust it to anyone else.

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Zeets
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Re: P200 Holed Piston Recovery

Postby Zeets » Wed May 02, 2012 9:53 pm

+1 Mikeh.

I don't think you had a mixture issue. Altitude makes the mixture rich (thin air = less air + same amount of fuel). I'd guess timing. It's widely accepted that timing specs for older bikes tend to be too far btdc. The fuel they used 25+ years ago was of a way better quality, and you could afford to run more (btdc) timing than you can now. Advancing the time 1 to 2 degrees makes a huge difference. Also, you should make sure that your timing mark is accurate.

Good Job on your cross country ride! Shame you didn't make it all the way.

Time to sell the Ninjette and buy your Dual Sport to start prepping for the TAT in 2013.

I think Mikeh should join us for the http://www.transamtrail.com/as well.
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Re: P200 Holed Piston Recovery

Postby dirtyhandslopez » Thu May 03, 2012 10:22 am

I would have to go with absolutely with no.2. Dropping a new or rebored top end on there without going in and cleaning all the swarf out if tantamount to a death threat for that new top end. Blowing out with an air line may very well just push swarf up to where it can't be seen, but that won't stop the swarf from falling back out. Also replace your fly side bearing as the seal for this is on the outside, meaning the bearing has been running in that fine grining paste that was once you piston crown.
I'm thinking it leaned out, need to retorque heads and everything else on a trip like you have just taken, specially on a P with no head gasket. When you get it all back together,set timing with a strobe to see if it is bouncing around, if it is, that is a good sign the cdi or pick-up is/was on the way out, whcih then could lead to preigniton and also be the cuase of the hole. 19 degrees should do ya.
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toigo
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Re: P200 Holed Piston Recovery

Postby toigo » Thu May 03, 2012 10:44 am

Thanks for the advice. I didn't hear anything out of the ordinary as far as misfiring or anything else before this happened and had run the bike for over a year without ever hearing anything like that. The bike acted just like it ran out of gas with no noticeably strange noises. I had recently gone down a lot in altitude so it's pretty likely that the bike was getting more oxygen and running leaner and then running hot. The plug also looks like it had gotten insanely hot.

I'm going to bite the bullet and split the case on it. The little white bits all around there are probably the pieces of the piston and they are all over the place. I need to put Mike's fancy yellow engine stand I won at the NOS Xmas party to good use anyway :) I've got a motorcycle to ride in the meantime and I like this bike too much not to take really good care of it. I'm going to call hot rod al for an estimate on boring the cylinder out to a 1st over piston size and order one. So while I've got this thing open, here's what I would guess I should replace.

    Both crank seals
    Cruciform
    Cylinder base gasket
    I'll checkout the crank shaft bearings and order them if they look questionable

Anything else that I should definitely look to replace while I have the engine open? I'll have plenty more questions I'm sure as well.

Thanks

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Susan
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Re: P200 Holed Piston Recovery

Postby Susan » Thu May 03, 2012 10:49 am

Zeets wrote:It's widely accepted that timing specs for older bikes tend to be too far btdc. The fuel they used 25+ years ago was of a way better quality, and you could afford to run more (btdc) timing than you can now. Advancing the time 1 to 2 degrees makes a huge difference. Also, you should make sure that your timing mark is accurate.


So if I think my bike is improperly timed, where do I start? I don't have a timing light and don't really have a decent grasp of how it's done.

It was set 5+ years ago, but lots of things have been broken/fixed/tinkered with since then and it's just feeling....funny when I ride it.

Sorry, that was kind of a hijack - timing has been on my mind and while part of me figured to just not worry about it, this whole thing is making me think that's not a great course of action.
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toigo
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Re: P200 Holed Piston Recovery

Postby toigo » Thu May 03, 2012 11:17 am

Hijacking my thread Susan....

Just got off the phone with Al and he had a very reasonable price for boring the piston. He also has all kinds of crazy porting options too which I'll debate since they are a good deal more cash. He also felt pretty sure it was an issue with the ignition as well. He said denotation usually causes wear on the sides of the piston rather than a hole in the middle.

starreem
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Re: P200 Holed Piston Recovery

Postby starreem » Thu May 03, 2012 1:08 pm

Here's some tools you'll need:
http://www.scooterhelp.com/tips/timing/ ... tools.html

And here's how to do it:
http://www.scooterhelp.com/tips/timing/ ... iming.html

Susan wrote:...So if I think my bike is improperly timed, where do I start? I don't have a timing light and don't really have a decent grasp of how it's done....
Starr

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Susan
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Re: P200 Holed Piston Recovery

Postby Susan » Thu May 03, 2012 1:31 pm

Thanks Starr.
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imjuanpablo
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Re: P200 Holed Piston Recovery

Postby imjuanpablo » Thu May 03, 2012 1:39 pm

Susan wrote:
Zeets wrote:It's widely accepted that timing specs for older bikes tend to be too far btdc. The fuel they used 25+ years ago was of a way better quality, and you could afford to run more (btdc) timing than you can now. Advancing the time 1 to 2 degrees makes a huge difference. Also, you should make sure that your timing mark is accurate.


So if I think my bike is improperly timed, where do I start? I don't have a timing light and don't really have a decent grasp of how it's done.

It was set 5+ years ago, but lots of things have been broken/fixed/tinkered with since then and it's just feeling....funny when I ride it.

Sorry, that was kind of a hijack - timing has been on my mind and while part of me figured to just not worry about it, this whole thing is making me think that's not a great course of action.


That's what tech-day was for!!
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Susan
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Re: P200 Holed Piston Recovery

Postby Susan » Thu May 03, 2012 2:08 pm

I know! But I didn't really decide it was a timing issue until the ride home. Classic Susan, eh?
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Serendipity
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Re: P200 Holed Piston Recovery

Postby Serendipity » Thu May 03, 2012 10:23 pm

toigo wrote:For anyone following my cannoball blog (http://www.matt-toigo.com/cannonball), I'm sure you saw it, but I managed to put a hole through the top of the piston on the last day. Don't fret I still had an awesome time and didn't let it get me down.


Aww, that's too bad Matt! We were kind of following the race and I forgot to check back on Monday to see the end results. But congratulations on the race anyway...I'm sure it was a great experience.
~Jennifer


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