I... blew it up. Rebuild?

Earbiter

New Member
Oct 22, 2013
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Denver, Colorado
Towards the end of last summer while riding home from work, bike was running great, then when i was coming to a stop the engine just died.
After i started going again, i tried to start it back up, it struggled but finally started. But now the exhuast was very loud and had a serious lack of power.
I finally got a chance to dig into it, found one of the piston retainer clips had broken and made it's way into the cylinder, where it dug two large gashes into the cyl wall and the piston skirt.
Found no evidence of bottom end damage, or the clip.

I know there are top end rebuild kits, but will this be ok? Or should i just replace the whole damn thing?
 

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Kioshk

Active Member
Oct 21, 2012
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Are you sure it was caused by a retainer-clip? I'm sure you verified that one was missing when you removed the piston. I ask that since the indentation-damage to your cylinder looks a lot like the indentation of a needle from the upper needle-bearing. Check that bearing too to make sure it's still in one piece.

That said, it's easy to rebuild the top-end; you'll just need to make sure you clean out the bottom-end properly. I usually remove the entire engine, fill the bottom-end with gasoline, and slosh it around by cranking the flywheel. Dump out the waste and repeat a few times. This should clean out any offending particles there. You'll need a new cylinder, piston, rings, and gaskets: lower and head. You may need a new needle-bearing.
 

Earbiter

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Oct 22, 2013
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Denver, Colorado
Sorry if i misspoke regarding the clip being gone, i have them both but one is clearly broken. What i meant was it wasn't in the bottom end. I'm guessing it got thrown out the exhaust. I'll prolly have to clean the pipe to make sure it's not floating around in there.
 

MotorBicycleRacing

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Jul 28, 2010
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I know there are top end rebuild kits, but will this be ok? Or should i just replace the whole damn thing?
There are 2 kinds of 47 mm / 66cc pistons.

Your piston is a high wrist pin hole for a Skyhawk type motor.

The ebay piston "photo" is a low type for a PK 80 type motor.
Whether that is the correct pic is anyones guess?

If that piece of the clip is in your bottom end you will destroy
your new top end.

I don't like those double clips, the single arm ones don't fail like that.
 
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crassius

Well-Known Member
Sep 30, 2012
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motors are cheap, when parts become chunks, why take a chance on trashing a new top end if an old chunk appears after the rebuild

if it were a cleanly seized piston or suchlike, that would be different
 

cannonball2

Well-Known Member
Oct 28, 2010
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Colonial Coast USA.
You can buy the complete basic engine in the $75 range shipped if you search around on eBay. Problem I have had with parts was not always getting exactly what was listed.

Just be sure if you go for a replacement that the intake\exhaust spacings are the same
 

sbest

Member
Nov 3, 2015
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Nova Scotia
Actually your piston and cylinder will work with a new set of rings.
There is no damage above the transfers.
Not exactly a rebuild, but it will run again with rings only if you wanted to try it.

I had the exact same fail. wristpin clip broke one of its legs.
Had about 1000 miles on the engine at very high speeds.

Steve
 

Earbiter

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Oct 22, 2013
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Denver, Colorado
So i got some funds and decided that it's not much more to buy a whole kit, rather than just an engine. Extra parts is never a bad thing, right?

So the new kit is coming later this week. With that said, I plan to port and polish it before it goes into my bike. I've done this a few times before on several different kinds of engines, with a very cheap dremal, so I bought a very nice pin die grinder from the cornwell to make it easier.

But I'm still left wondering, I've read about the "transfer port correction mod" does anyone have pictures of what this should look like? I know they need to be pointed at the spark plug, but I'm not really sure how this can be done without raising they're roof/messing with timing, and I'm not really looking to mess with that too much. Prolly just an extra base gasket or 2. Please help me understand.
 

Tyler6357

Well-Known Member
Mar 15, 2012
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Santa Barbara, CA
Ya im sure, i was planning on getting this kit http://www.ebay.com/itm/191550568760,
i know it's cheap but it's all i can afford right now.
Just wanted to know if it would be ok. Ty.
Your engine looks like a GT type and the link connects to a PK80 type. That won't work, the GTs have a longer connecting rod. Here you can see the differences in the wrist pin location on the piston. The GT is on the left and the PK80 on the right.
 

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