Did I carve myself a doorstop?

Captain Janeway /
IMG_20190420_153031666.jpg

Put a Dr kit on an Urban. After 590 miles it died and I found a destroyed piston. Cylinder doesn't look bad, but did I take too much out of exhaust port? No point replacing piston if I trashed the cylinder.

Ideas?

https://photos.app.goo.gl/nTZiogkriFA4SQju7

Re: Did I carve myself a doorstop?

Looks like it got really hot. Maybe it's lean or high timing?

Re: Did I carve myself a doorstop?

Jack Rutherford /

on the bright side, you get to look forward to your new kit. going DR again or trying something else? Parma, Malossi, Athena, Metrakit?

Damn, now I'm looking at kits. See what you did Mary!(edited)

Re: Did I carve myself a doorstop?

kevin Smellaflange /

iv'e seen a piston out of an OSSA 250 pioneer have a D shape hunk missing in the front 1/5th of the top, leaving the rings alone, it kick started up on the 6th try. i found this out by de-carbonizing the head.

i never knew, it was like that with the old owner.

Re: Did I carve myself a doorstop?

Jack Rutherford /
janeway2.jpg

I've got my theory but I'll hold off to see what others have to say. It's related to this picture in her link.

Re: Did I carve myself a doorstop?

kevin Smellaflange /

champhered?

Re: Did I carve myself a doorstop?

Captain Janeway /
IMG_20170706_200927369.jpg

> Jack Rutherford Wrote:

> -------------------------------------------------------

> on the bright side, you get to look forward to your new kit. going DR

> again or trying something else? Parma, Malossi, Athena, Metrakit?

>

> Damn, now I'm looking at kits. See what you did Mary!

I'd need to buy new heads for the others you listed (I think). I've only bought a malossi before and didn't realize the piston height would be so different.

You learn expensive lessons doing this...

Re: Did I carve myself a doorstop?

looks like the exhaust literally torched the piston crown. head temps?

Re: Did I carve myself a doorstop?

Captain Janeway /

> pat splat Wrote:

> -------------------------------------------------------

> looks like the exhaust literally torched the piston crown. head temps?

Unfortunately I had loaned it to someone on a long rally ride. I'm thinking she didn't check temps while riding. I had to back off the one I was riding to lower temp, but I was still tuning it.

The bike that blew had been running fine prior to that. Those long slow grades are deadly

Re: Did I carve myself a doorstop?

Air leak at decompression hole?

Re: Did I carve myself a doorstop?

So when someone borrows a.bike and melts your Piston, do they offer to replace things?? Or is that simply the joys of lending?

Re: Did I carve myself a doorstop?

Captain Janeway /

> Jared Rut Wrote:

> -------------------------------------------------------

> Air leak at decompression hole?

Unknown and too late to find out now. I flip head gasket to cover decomp hole

The cylinder is amazingly clean, but if the rings are basically falling in the port I'll have the same problem with just a new piston.

I don't quite understand how the piston looks so trashed and the cylinder looks so clean.

Re: Did I carve myself a doorstop?

Captain Janeway /

> Marc Friedman Wrote:

> -------------------------------------------------------

> So when someone borrows a.bike and melts your Piston, do they offer to

> replace things?? Or is that simply the joys of lending?

Well, if it melted down because I cut the port wrong, that's not her fault. She did offer though.

Re: Did I carve myself a doorstop?

I probably would do the same but u are a better man than me because u lent it out.

Re: Did I carve myself a doorstop?

Captain Janeway /

> Marc Friedman Wrote:

> -------------------------------------------------------

> I probably would do the same but u are a better man than me because u

> lent it out.

Better it blew when there was a chase truck rather when I was riding alone. Cell can be spotty (at least on my POS phone), and I didn't have to wait hours for roadside pickup. $8 for the year and worth it.

Re: Did I carve myself a doorstop?

thats not a snagged ring, its a melted piston on the exhaust side.

aluminum is much softer than steel, piston gets damaged while cylinder is fine.

Re: Did I carve myself a doorstop?

Captain Janeway /

> pat splat Wrote:

> -------------------------------------------------------

> thats not a snagged ring, its a melted piston on the exhaust side.

>

> aluminum is much softer than steel, piston gets damaged while cylinder

> is fine.

Figure I can hone that out but trying to figure out what snapped the ring and shredded that poor piston.

Re: Did I carve myself a doorstop?

I'm not sure anything snagged the ring .

Seems there would have been more damage had that happened . So ???

Have identified what that bit might be ?

Re: Did I carve myself a doorstop?

Jack Rutherford /

I've seized a few but only ever had scoring on the exhaust side of the piston and was not missing chunks on the piston dome.

This piston only shows scoring to about halfway down. Usually they are scored all the way from top to bottom. I think the soft seize was secondary to the main problem. I doubt it even soft seized as the scoring is so light.(edited)

Re: Did I carve myself a doorstop?

Captain Janeway /

I made the mistake of taking that whole internal bump, bridge or whatever you call it in the exhaust port all the way down. It pretty well stopped the bike dead, but yeah I don't quite know why the piston is so trashed and the cylinder's basically fine.

I have Crazy Wayne telling me just slap this piston in and ride until it dies again (or the next sale whichever comes first). It was probably the overheating that drove the ring into the port. Well, maybe... It will probably sit until I can get next kit. I get tired of blown pistons, and over the past 3 years I've managed to blow out 4 (3 bikes).

https://www.ebay.com/itm/PISTON-KIT-FITS-ECHO-PB620-PB610-PB620H-PB620ST-REPLACES-PART-P021007450/182178265367

Re: Did I carve myself a doorstop?

Jack Rutherford /

the chainsaw guru strikes again. What do they want for a DR kit piston on treats? $100? That chainsaw piston looks pretty much the same.

ok here's my theory. Could be completely wrong. I think the piston did get hot, swelled up slightly but not enough for a soft seize. One of the rings bulged into the exhaust port and caught momentarily. Probably did this more than once until it broke - most likely as the piston was going down. Broke part of ring got caught ahead of the piston and the damage to the piston was caused by the piston driving into the broken ring on the upstroke.

anyhow, if it were me, I'd hone the cylinder and throw in that chainsaw piston and give it a whirl.(edited)

Re: Did I carve myself a doorstop?

Captain Janeway /

> Jack Rutherford Wrote:

> -------------------------------------------------------

> the chainsaw guru strikes again. What do they want for a DR kit piston

> on treats? $100? That chainsaw piston looks pretty much the same.

>

> ok here's my theory. Could be completely wrong. I think the piston did

> get hot, swelled up slightly but not enough for a soft seize. One of

> the rings bulged into the exhaust port and caught momentarily. Probably

> did this more than once until it broke - most likely as the piston was

> going down. Broke part of ring got caught ahead of the piston and the

> damage to the piston was caused by the piston driving into the broken

> ring on the upstroke.

>

> anyhow, if it were me, I'd hone the cylinder and throw in that chainsaw

> piston and give it a whirl

That was my guess on the piston marks. It was a smallish piece that broke off and flipped up.

I'll scuff up the cylinder and give it a go.

Re: Did I carve myself a doorstop?

Hone the cylinder. circular in both directions. If u widened the exhaust port then yes it's more likely to catch. That's why these kits come conservative. Just grab another Piston and rings if not too expensive.if it's inevitable to catch again toss the jug. Bells book gives guidelines for bigger engines on how wide a port can get to avoid this. The moped experts on here such a jbot can give you very specific numbers.

Re: Did I carve myself a doorstop?

Where’s waldo?

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