You can see in the pics of the two pistons that it was just about to blow through in the center before it seized. You can see the start of a blow hole, right in the center.

Yep - I also checked the #1 piston and it also has the mark there. Very strange.

I pulled a few pics from the animation to show how the pressure waves in the pipe does its thing and show the intake/stuffing charge I was referring to.

I borrowed theses from the web and marked up a few.

more

now the ones I add comment to.
There is more to it than this just do not want to over do it so you get an idea of why those hanging chads got to go.

One other item here to note on this charge density. When this hit the face of the piston it also fills the ring groves with intake charge or cool gas to dissipate heat from rings for the next cycle. This also help cool the boss area. One reason for good quality of oil to keep this area clean and doing its job.

It may be the angle or pic
#1 arrow just does not look right
#2 may be detonation issue. The thing is was the detonation due to charge density or pre ignition.
I was thinking about your head since it is untouched. measure the inside of ID area where the lip is. This sharp edge may also play a part in it. Also since its untouched your squish band thickness may not be right for your combination.

This will require a little head work in conjugation with your exhaust port timing.

So I would like to have both exhaust port roof to deck and transfer roof to deck.

I,m pretty darn sure your exhaust duration is to great so lets compare it to your blow down degrees.

The port roofs lowers every time you over bore and this may be a factor.

From the illustrations I posted you can see how the export and transfer play a Hugh part.
An example may be the exhaust port is not opening soon enough for hot gas to exit and the transfers may not be opening soon enough to help get the hot gas out and evacuate the cylinder.

The combustion process may be happening sooner the cylinder can handle, then it compounds upon its self.

The next area of concern is the silencer. Your expansion chamber stinger OD and you silencer ID.
What work if any did you do here? The high out put pipe should have had a larger OD than the factory ID silencer. This will mess up the pipes ability to function properly. Remember the pictures and the pressure waves. it all about timing.
Hot gas moves faster than cool gas.

Wow. Adnoh, Thanks for the effort - this breaks down the two stroke process to the nth degree.

This is actually a good read for all. I am a back yard hacker but over the last 18 months or so, I have amassed an incredible understanding of the two stroke process I really didn't sign up for. That said, I do enjoy garage time and the damn thing is awesome when it's running.
Seems there is some sort of a timing/ ignition/pre ignition issue so let's recap: the cylinder and head have never been ported, the CDI (Capacitor Discharge Ignition) is stock that came with the unit, plug is stock recommendation

So this has really gotten under my skin how it keeps happening and there is no distinct cause to point a finger at. Brings me to a conclusion:

Occam's Razor.

Looked for the post but couldn't find it - someone here previously asked "when did the first piston go?". The answer was "right after the previous owner installed the aftermarket 39mm kiehin, a powerbloc clutch and the Doug Turner pipe"

The simplest solution is usually the right one. Pilots typically (from what I've seen here) run pretty reliably but this one developed an appetite for pistons after the stock breathing equipment was replaced. Seems Adnoh's illustrations help to point to a possibility that it's the pipe.

Any thoughts on just putting the stock pipe back on, lightly hone the cylinder and do an R&R on the piston and rings? any advice on a starting point for rejetting the carb as well?

I have no emotional attachment to the pipe or carb. I just want that dam thing to run when I take it out.

Will post requested measurements from cylinder later today/tomorrow too.

thanks again for the input from all

dave

Here is an example for the numbers.
The first is a stock set up using an "A" cylinder for general reference.
The second is a educated guess on ex port change due to over bore and head gasket choice.
The effected CR or CCR ( corrected compression ratio) is still whit in acceptable pump gas numbers.
Please keep in mind this is just CCR.

With the numbers I can use another spreed sheet to do more calculations
Here is an example.
this shows two things that will burn it up
#1 blow down timing is to short. so as your rpm increases the time area gets smaller and it will not live to much heat
#2 the intake timing is to slow with not enough duration
#3 the exhaust port not opening soon enough with not enough duration for time area.

Then we can move onto the head and it story
If you notices on the pics I use cosmetic data of 1.1 and 82.55 compared to stock this increases squish distance approximately to 1.26 mm. I feel this is way to much for the other numbers. It will lead to cooking off the squish gases trapped there due to pre ignition
The stock head should also have a lip of 1.9 mm until the first angle the head id compared to the gasket id will leave a sharp edge that can heat up.

here is a pic of your head with arrows.
Pretty sure you can see the area I am referring to.
The #1 area could be the detonation result is eaten away like I think the picture shows. This is what I was referring to.

I would consider bolting up your old head gasket to the head and taking a de burring tool and angling that area into the head getting rid of the that lip. the old gasket can act as a guide so you do not go too deep try to maintain a angle that is consistent to the depth of the lip.

Adnoh, I have read and reread these and it seems to me that it all keeps coming back to the pipe. They are the only non-stock equipment and the issues have persisted with an 81mm, 81.5mm and an82mm piston. The lip you are talking about above would have been barely noticeable for the first piston, no?

You asked about the pipe and where it connects to the silencer –there were no modifications made there and the pipe slips right into the silencer and seems to seal up fine with the stock clamp. I confirmed the expansion chamber stinger OD is the same on both the stock and aftermarket pipes.

I keep coming back to the fact that it ran great before the carb and pipe - it just seems to me that the simplest explanation is most likely the best one but again, backyard hacker I am.

Take a picture of inside the pipe below picture taken from this page. viewtopic.php?f=89&t=13671

Your pipe:



Took a couple so i could show as much detail as possible - you see there is a LOT more weld build up inside the pipe, lines @ 12:00 and 6:00 and a ridge on the left right at the inlet from 6:00 up to about 10:00 from manufacturing in addition to the leftovers from the repair job = opportunity for hots spots





Then there's this - dent in the bottom from hitting something while riding

I've been following this thread closely. This is like a good thriller novel that I just can't wait to get to the end of! dipnadactyl is the author and members are all helping with the story line. Looking forward to the end. Lots to learn from this thread. Thanks for sharing.

I am not sure I am seeing any evidence of a Wet Line inside the pipe no real carbon build up does that pipe have any run time on it since the repairs? http://pilotodyssey.com/PO/viewtopic.php?t=1932

Yes sir, probably only 4-5 hours though. Are you thinking the pipe is not the problem?

Any update?

Not yet. Work. Piston and gaskets should be in when I get home though.

Update: Diesel fueled motor (( Internal Combustion Engine ? )) and lower bearings out multiple times with a meat injection needle, dumped into a clean container until no metal flakes (there was minimal to start with) and blew out with compressed air, again multiple times. Then sprayed lower bearings with 2stroke and gas mixture. Light hone on cylinder, then rebuilt with new piston and rings, pressure tested and installed. Stock exhaust is on and running 110 full lead at 32:1. Started right up and sounds good.
Got high hopes.

More to follow tmoro.

I wish you all the luck. You deserve to be able to blast for more than a lap or two for your efforts.
Looking forward to the ride report.

Thanks, GO. Like I said, high hopes.

Compression was at 133 cold and prior to initial start up. Two more 15 min heat cycles - up to temp and complete cool down - and a quick run up and down the street a few times (as much as the neighbors can stand) and compression is now at 135. A little lower than I had hoped for but still tolerable. Other than that, so far so good.

On a side note - I had noticed the rear brakes would fade after a few hard days of riding which always required bleeding brakes. Came across the dust seal and piston seal for the rear brake in a box of spare parts previous owner had given me so took that apart and replaced while motor (( Internal Combustion Engine ? )) was heat cycling. Piston looks aged & a little pitted but cleaned and polished as best as I could. We'll see how it does now.

Back to work but should be able to get a quick ride in by Thursday/Friday and will update again from there.

Got some break in time today and now may have a new issue. Starts up and idles well and throttle response seems good in neutral. motor (( Internal Combustion Engine ? )) warmed up to temp and running up and down a long street, take off seems OK and at 1/2 throttle it sounds good but seems to sputter and fall flat in between 1/2 and 3/4 throttle. After about thirty minutes, seemed to improve a bit but still sputtering on top end. Pics of plug from roughly 15 minutes in and at the end, 30 minutes here:





As it sits, I know there are no air leaks, carb is clean, tank and fuel filter have been flushed. Has a 165 jet in it which is the jet that it was dyno'd on from previous rebuild and running 110 octane at 32:1. Also running stock exhaust all the way back. Plug in the second pic looks like it's pretty close to where it should be. Any insight out there?

Usually sputtering is an indication of to rich, but in this case the plug seems to look good.
This is important: What does the carb manufacturer recommend for the main jet for your carb ??
Get on the net and check it.