My PW's cylinder is shot. It still runs, but it looks like a mirror on the inside, lots of blow-by. My machinist has one of my spares with an O/S piston and some detailed instructions that I hope will save me work in my porting experiments, however, he's backed up till eternity and since I'm a on-again/off-again customer, I get bumped when ever one of his regular customers who has a several thousand or ten-thousand dollar order comes in.
He did get some of the work I've asked for done, but not enough to use that cylinder and I've got an event this weekend I want to use the PW for.

So I picked up one of the Chinese cylinders on ebay for $84 and change, shipped, reportedly from New York.
I was a bit disappointed when the tracking said the package was in CANADA! Because I have a pretty good idea what shipping international costs, even for a business that ships a lot of stuff and that means instead of a $60 Chinese reproduction, I'm getting a $35 Chinese reproduction. Oh, nuts.
Shipping quoted at $26.36, 84.50-26.36=58.14, which I'd venture requires a profit of at least $10, $48, less paypal fees, ebay fees, import duties, yada yada.

It arrived yesterday.
Packaging is better than I expected.






Kind of a funky looking head, I'm not sure what I think of this cooling fin layout and I'm not sure if I'm even going to use it. Not because there's any major problems with it, but with the set-up I intend to run, this head would be detrimental. Note the casting flaw near the bolt-hole in the lower left  of this photo. This won't hurt anything where it is, but it doesn't inspire confidence.


Cylinder is also low, but usable after some work, quality. Note the casting flaws in the lower right hand, of this photo, part where the base is not close to square as well as the black mark on the "sleeve".

The black mark is a casting flaw filled with paint, again, doesn't affect anything.
See also the absence of any chamfer on the "boost"/3rd transfer port.

More casting flaws on the top of the cylinder. There's a chunk missing near the top, you can also see a chip out of the third fin from the bottom and some glob of something on the second fin (discussed further below).


Piston, wrist pin bearing and circlips.


Wrist pin, base and head gaskets. Base gasket is kinda cheesy and it's extremely tight. The die must have been made on a Monday.


Close up of the cylinder base flaws.


A flaw in the exhaust port roof. Also , no chamfer. The discoloration on the cylinder is oil, not rust.

Edited by Smacaroni, 23 May 2012 - 05:55 AM.

Transfers, there's no way to show this, but they're not even close to even. I don't have a stock PW cylinder to compare this to, but it's very unlikely the side transfers would open at drastically different times from each other. One can stagger them to broaden the power band, but I doubt this is intentional.


I have no idea what this is. It's a glob of crap that seems to have no purpose. Maybe they broke one of the fins off and decided to epoxy it back together, but it doesn't look like it. Clearly this was done after they painted the cylinder.


The hone and cross-hatch looks ok to me.


The exhaust gasket is completely absent, we checked the box over and can not find it. Also, the exhaust port "flange" is off drastically off center.


I forgot to bring the measurements with me, but the one thing that stands out most of all was the ring end gap on the black, I presume bottom, ring was almost invisible. I measured it at 0.015", it should be closer to 0.090" (Wiseco:  .0040”,   .0050” per inch bore diameter top, bottom respectively). The top ring was right.
The rings have minimal clearance to the ring lands, but I forgot to measure it.

There are no instructions.

For us, the casting flaw on the exhaust port didn't matter, we're grinding the port to open sooner.
We also changed the timing on the side transfers.
And we chamfered the ports top and bottom.
We used an LT80 exhaust port gasket.
Then we found out it uses 8mm bolts, instead of six or seven mm bolts for the exhaust flange. No big deal if you have bolts laying around, but if memory serves me right, I tapped one of the cylinders we've used to fit an 8mm after the threads got hosed up. Yamaha's part number is 97017-08020-00.

It sounds fine once it's running. We haven't had a chance to do a complete break in yet, I just hope everything else goes smoothly. Not that I want this to happen, but as long as it doesn't grenade before Sunday, I'll be OK with it.

Edited by Smacaroni, 23 May 2012 - 04:21 AM.

I JUST finished bolting one of these together... landed on TT hoping to find a torque spec for the head.  Mine had corrosion in the bore, some discoloration on the head gasket surface.  Ports are rough.  I thought about using the stock Yamaha head, but decided to go with the PRC one instead:  look close at the compression chamber.  I found the wrist pin clips to be particularily cheesy.

Lots of 2 stroke oil and good intentions.  We'll see how it runs tomorrow, if I can find an exhaust gasket.

Edited by theraymondguy, 04 June 2012 - 08:03 PM.

I'm still trying to get ours to run right. It starts and will idle all day long. Now granted, I did raise the exhaust and transfers, however, I also chamfered the ports which out of the box needs to be done or you'll have big problems in short order.
First run, stalled three mail boxes away. I live in a development.
Pulled everything apart and re-checked the chamfers. One was a little bit sharp on one corner, so I chamfered it farther.
Next run, made it about two blocks, locked up the rear tire.
Because our PW is running very advanced timing and a high-compression head, which worked just fine on the factory cylinder, I decied to bring it back to where it was from the factory on timing.
Third run, made it about five blocks, locked up so hard the rear tire spun on the rim and ripped the tube. These are scooter tires, BTW, expensive scooter tires. And now one has a massive flat spot.
Needless to say, we didn't run it the weekend before last. I thought I was going to need the back-up bike for my KDX/KX hybrid, turns out it was the PW80 that was sidelined instead.
I haven't gotten back to it yet, but I think it's too tight. I'm going to open it up again and re-check everything. If it is too tight, it's almost as costly to bore/hone this one than it would be to bore/hone the factory one and install an O/S piston.
At this point, I think I'd have been better off buying five cases of Coors in cans, pouring it out and turning the cans in for recycling. Four cases of Yeungling would have been much more pleasant than either of the above.
I'm going to keep plugging away as I get time.

Edited by Smacaroni, 05 June 2012 - 04:43 AM.

None of that is terribly encouraging.  I can't hardly wait.

 theraymondguy, on 05 June 2012 - 04:12 PM, said:

Torque spec is 7.2 ft/lbs.  Not 8, not 6, not 10.  7.2 ft/lbs.

Fired on 2nd kick, runs well.  I replaced the exhaust gasket (including restriction) hoping to add some life to it.  Don't know anything about PW's.  It gets 'on the pipe' in all 3 gears, though I'd like it to have (alot) more power.  I'm sure removing the restriction plate will help.

Power can be found http://www.thumperta...w-80-questions/
These motors are closer to a weed whacker than a motorcycle. They're designed to run consistently with no maintenance for a long, long time. A now deceased friend of mine who was giving me pointers during the porting experiments thinks he could squeak 15 hp out of one. And I bet he could have. If I had known he was gonna kick the bucket in March, I would have sent him a complete motor and a blank check and told him to go nuts.
I'm still aiming for twelve, which is about three times the power output of a stock PW.
Granted, he's a go kart guy, and a very well respected go kart guy, so it probably wouldn't have made any power below 5K, which is near the max RPM of these motors in stock form. According to my calculations, this motor will self destruct around 11K.
More than likely, I'll call my PW80 experiments done when I throw a rod through the case, so I really do intend to find out how far you can push this 1970s era lawn equipment design.
Unfortunately, I have a limited amount of time to work on it right now.

From the referenced thread, and a few notes on other things.

 Smacaroni, on 17 January 2011 - 06:05 AM, said:

This was a reply to someone else's question, I recommend the KX60 shock as opposed to the X-tender. It's a little more work to get it to fit, the cost is roughly the same and it's world's better.

There's a # 4.5 as well, which is modifying the reed cage, basically you install the reeds, mark the cage where the reeds over lap and cut everything out leaving 0.5mm or 0.020" overlap for the reeds to seal on the finished piece, so 0.75-1mm or 0.050". You will remove the dividers so you can't go back to factory reeds unless you replace the reed cage. With what's left, grind and polish till a near-mirror finish and make sure it's a smooth curve shape.
Now once you get through this list, things become more dependent upon what you want the finished machine to do. Since I've moved into the road race circuit, my future mods will be of some interest to trail riders, but probably not ideal for a six year old plunking around the woods. More than likely the finished bike will be a high strung, low ground clearance (even with the KX60 suspension - you'll see when it's done), narrow harsh power band machine. That's how road race bikes are. Trail bikes are much better off with a wide consistent power delivery and a decent amount of torque. But the max HP numbers are going to be much smaller.
At the stage the bike was at before I decided to replace the top end, it would still be a decent trail bike and made roughly 50% more power than stock (a guess, I've never dyno'd a stock bike, but I'd like to).

But I can't do anything till I get the Chinese top end working consistently or I get my Yamaha cylinder back from the machine shop.

The good thing with the PW80 no matter what your goals are is it's cheap. You can buy a used one for $300-500 (well in the US, Maple Leafs fans are charged a premium for some reason). Used factory parts are plentiful. As long as you don't do stupid things they run forever.

In the mean time, I have the KDX/KX mini-moto bike keeping me busy: http://www.thumperta...mebody-stop-me/

Edited by Smacaroni, 15 June 2012 - 03:31 AM.

It's been a while since I updated this, I simply have too many irons in the fire, and I can't seem to stop myself from putting even more in.
I took the thing apart again, measured everything again, took a little more out of the ring-end gap, noted the piston had the tell-tale four-corner seizure marks, a sign that the piston to bore clearance is too small.







(I could have done a cleaner job on the port alterations too, I cleaned it up before reassembly)
My mentor, now deceased, had told me that I should look for any shiny spots on a broken in piston and file them down as these are likely places for the motor to seize in the future. So on a whim, I decided to shave these spots down to see if it would resolve the problem.
I noted that the exhaust port is not centered in the flange as well.

Then I reassembled everything and handed it off to my daughter to test ride. Well, this time it warmed up and made it all the way around the neighborhood, so I thought the problem was resolved!

Yesterday, I took it to the track. It felt really funny being on the PW80, the suspension is so much softer than the KDX/KX/DR/DR-Z frankenbike. It makes about 1/4th the power. The auto clutch vs. a manual clutch, the pegs dragging... but it seemed like it was going well enough that I could put my daughter on it at the next event. And then the third lap rrrrrrenedSCREEEEEEEEEE, the engine cut out, the rear wheel locked up tight as a drum and we skid to a hal... rrrrRRRRRR wait! The motor's turning again, I'm going to try to nurse it back to the pits... RRRrrRRRSCREEEch. I hop off, drag it into the grass and throw it in neutral, then push it the rest of the way back. It's only a 3/5ths mile track, but it sure seems a lot longer than that when you're pushing.

I loaded it up on the trailer and gave up. Glad it only costs $5 to run an extra class.

This morning, I pulled it apart again.
First, the cylinder was stuck to the case. This isn't any big deal usually and I can simply give it a tap with a fist and it'll come loose. I had to whack it with a mallet. One of the fins broke off.


Starting to sound like a broken record, multi-point seizure. Look at the damage to the rings too.


The really reflective part is where I filed last time, all it did was seize in a different place:






The verdict, the piston to bore is too tight.


Now here's what's really weird. I had to hammer out the piston pin. I don't know if it's possible for an alloy to expand and not contract, but it seems like this is what's happened. The piston was not this tight the first, nor second time I assembled it. The piston pin slides in place the first time, now it needs serious help to get the pin into the piston. I can't explain why this would occur unless the piston material expanded in every direction (that too is weird, metal inside dimensions and outside dimensions expand and contract uniformly. The ID doesn't get smaller while the OD gets bigger to my knowledge).

My verdict: if I can't make it work, you can't make it work. Save your money, buy a decent O/S piston, overbore slightly, adjust your porting back to what it was (measure before and after, use files and Dremel bits to return to the same distance from the deck) and ride happy. Don't piss away a bunch of money and time on this crap. I can't even recommend buying a cylinder when you plan to put an O/S piston in with a local machine shop.
If anyone followed my path thinking it was a good idea cause I did it and failed in this case, I'm sorry. I really did expect it to be an OK deal. Not great, I didn't expect plug and play, but something that would work with ordinary prep work. I was wrong. Even the greats miss a shot now and then. I'm not that great to begin with.

Edited by Smacaroni, 28 October 2012 - 10:09 AM.

So, I ended up with one of these topends as well. I do not have the same casting flaws, but the ports seemed to a bit.
Mine of course did not appear to be chamfered either...
Because of this posing,  I decided to do some measuring before installing...
I found the cylinder to be 1.8504". Exactly what the book says.
The piston 1.8490" measured. The book says it is supposed to be 1.8490" actual (which means 1.8474" measured +.0016")
I find this to either be an incredible coincidence, or the guy who made these parts didn't read the book correctly,

I guess I am buying a good(more expensive)  piston instead...

 pittss1c, on 18 December 2012 - 07:07 PM, said:

Wow, I never would have thought ot measure the piston before install. That's so tight! 0.0014" clearance? For the same Wiseco pistion, it's 0.0020"! A friend of mine, now passed on was a very well respected go-kart builder, when I asked him for some pointers on my other PW80 stuff, he said he liked 0.003" - more than double what this Chinese piston is.

Thanks for the update. Did yours ship from Canada even though the auction said New York too?

Yep... came from Canada even thought it said New York.
Not to discredit myself too much, but I had an odd thought..
Plan A... buy a properly sized piston...
But what if....
My old cylinder is not horribly scared. What if I honed the crap out of it? I wonder if I could get it to a size that this piston would work in and save the cylinder for next time I need a topend. Sure the original cylinder would need to be bored before I could put a regular piston in it, but that is no different than where I am now. If it trashes the piston/cylinder... sill, in no worse shape.... go with plan A.

I've put a 51.50mm piston from an LT80/KFX80 in a PW80 cylinder after a bore. 52 should fit too, but I'd say that's the practical limit using off the shelf pistons.
You will need to grind the ports back to where they were as a 4mm overbore is going to severely impact the port timing. It will still run, it will still run pretty well in fact, but you should return the ports back to where they were at a bare minimum.

interesting read Smacaroni
I was getting simular 4 corner seizing on my snowmobile from running to much timing.

Overly advanced ignition timing failures usually look like this:

My understanding is the upper layer of the piston melts and traps carbon creating a lava-rock like texture. I'm no expert, but I'd invest time in re-jetting your snowmobile or searching for another reason it may be lean, retarding timing is probably a band aid. As I said, I'm no expert here, but from what I know timing shouldn't cause a four-corner seizure. I've read four-corner siezures are often due to lean jetting. However I suspected that it was a clearance problem and Pittss1c confirmed it.

My sled was EFI so no jetting as such although I do run a fuel controller,you are correct too much timing and low octane fuel will cause pitting on the top of the piston,but running advanced timing can also cause enough heat to make a piston swell and do a 4 corner seize just like your picture(I have a milk crate full of Wiesco's just like the one in your pic from my old race sled) Not saying ist your problem but have you tried alittle race fuel?

No. Can't say I ever thought to try that on a poorly spec'd top end. I plan to mess with it more next summer. But it won't be this piston.

rgw  guy wants to do anything he can to make it right... wanted to send me another kit. I told him if he had a piston that measures right, that I would  try that... he fed-ex sent one the next day. Super helpful. We will see what the new one measures...

Cool, unfortunately, I let mine go way too long to expect any assistance from the seller. Also, I modified mine, which usually voids any expectation of a warranty, even if the modification has nothing to do with the problem.
Even if he fixes you "kit", it's not a good buy for other people. There's three that have been mentioned in this thread, two were duds - that's a horrible rate of errors. And these are the ones they sent out into the market. Imagine what their rejects are like!

Also, I think the seller is a bit shady from the get go, New York may border Canada, but it ships from Canada, even if it's only one kilometre over the border, the shipping is going to be much higher because of it. Higher shipping, lower product value when the total cost is the same. I wouldn't have bought it if he said it shipped from Canada - I'm pretty sure the seller knows that.

None the less, I'm curious as to how your new piston works out. I'm keeping my fingers crossed for ya buddy.

Well, the new piston is the same as the one with the kit... the man says... run it... it will work.
So I put it together as is (after chamfering the ports)
It hasn't locked up yet, but it is really cold here and I  couldn't push it too hard, but  it has made it around the hose a few doze times so far.