2003 Yamaha Pw50 Top Speed
Forum Main Tech Help/Race Shop eBay complete top end kits for PW50?
eBay complete top end kits for PW50?
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
FGR01
Posts: 3539
Joined: 10/1/2006
Location: AZ, USA
2/27/2017 6:18 AM
Do you even China Bro ???
Powerband in every gear !
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
2/27/2017 6:30 AM
FGR01 wrote:
Do you even China Bro ???
FGR01 wrote:
Do you even China Bro ???
I know they're china Bro.
FGR01
Posts: 3539
Joined: 10/1/2006
Location: AZ, USA
2/27/2017 6:40 AM
There's your answer, LOL. Seriously though, there's a member on here, forgot his name, who is the PW master. He'll be on soon to give you some useful info instead of bustin yer balls.
Powerband in every gear !
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
2/27/2017 6:45 AM
FGR01 wrote:
There's your answer, LOL. Seriously though, there's a member on here, forgot his name, who is the PW master. He'll be on soon ...more
FGR01 wrote:
There's your answer, LOL. Seriously though, there's a member on here, forgot his name, who is the PW master. He'll be on soon to give you some useful info instead of bustin yer balls.
Mike your ball busting is appreciated Bro!
Now for anyone else with PW knowledge for a brother on a budget. Let me know. A great friend set me up with a nice PW, that just needs a little TLC. It runs, but the carb is in need of a refresh. Needs an airbox, or an after market air filter. Perhaps new cables on brakes, and throttle. Finally some new plastics, and graphics. Trying to get this done for my son's birthday on April 1st.
Any experienced members feel free to send some info my way.
Thanks!
slipdog
Posts: 9982
Joined: 7/25/2009
Location: Nor Cal, CA USA
2/27/2017 6:57 AM
Got 2 for my twins this fall, one already had a 60cc China kit installed and ran fine. The other was a roached stocker like the one you got so I figured I match the other with an Ebay special. Kit showed up and the piston was inside the cylinder in the box and I had to almost force it out. I got out the bore gauge and micrometers and found the piston and cylinder bore had the exact same measurements.
After some back and forth with the seller explaining I know what I'm doing they exchanged it with a new kit with a .05mm P to B clearance and she runs like a champ. You just have to be careful when dealing with Gina!
FGR01
Posts: 3539
Joined: 10/1/2006
Location: AZ, USA
2/27/2017 7:02 AM
Powerband in every gear !
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
2/27/2017 7:25 AM
slipdog wrote:
Got 2 for my twins this fall, one already had a 60cc China kit installed and ran fine. The other was a roached stocker like ...more
slipdog wrote:
Got 2 for my twins this fall, one already had a 60cc China kit installed and ran fine. The other was a roached stocker like the one you got so I figured I match the other with an Ebay special. Kit showed up and the piston was inside the cylinder in the box and I had to almost force it out. I got out the bore gauge and micrometers and found the piston and cylinder bore had the exact same measurements.
After some back and forth with the seller explaining I know what I'm doing they exchanged it with a new kit with a .05mm P to B clearance and she runs like a champ. You just have to be careful when dealing with Gina!
Cool, thanks Slip!
speed_racer
Posts: 339
Joined: 7/29/2016
Location: Aiea, HI USA
2/27/2017 9:14 AM
These kits are fine the problem is the final hone to size is always to tight.
I check them for clearance, I never send them back that is a waste of time.
I have my local machine shop hone to size for $20.
After it's sized correct the rings go in the bottom of cylinder easy and they will run fine, but they always come tight and dirty. I can quick check them with a ring and see the ring gap is to small, but the overall new cylinder for pennies is nice and cheaper than a bore job. I buy the cheap cylinder and fix them so the PW won't seize in 2 minutes.
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
2/27/2017 12:12 PM
speed_racer wrote:
These kits are fine the problem is the final hone to size is always to tight.
I check them for clearance, I never send them ...more
speed_racer wrote:
These kits are fine the problem is the final hone to size is always to tight.
I check them for clearance, I never send them back that is a waste of time.
I have my local machine shop hone to size for $20.
After it's sized correct the rings go in the bottom of cylinder easy and they will run fine, but they always come tight and dirty. I can quick check them with a ring and see the ring gap is to small, but the overall new cylinder for pennies is nice and cheaper than a bore job. I buy the cheap cylinder and fix them so the PW won't seize in 2 minutes.
Ok, thanks for the info. Seems to be a common issue with the cylinder being too tight for the piston. What are the tolerance measurements for the cylinder bore to piston? Or what would be the proper way of measuring proper fit?
2/27/2017 8:02 PM
I've run more than one of those kits, measuring with nothing more than a .002 feeler gauge. Don't think I even did that with another one. They ran fine for me. used those carbs as well, with good results. Never have seized a PW, but it is common.
One thing I noticed is the port chamfer on the china kits is a bit sharp. Hard on the rings. If you have some small files, this is easily remedied.
Camp332
Posts: 7951
Joined: 8/16/2006
Location: Zoo Jersey, USA
2/28/2017 4:51 AM
project racer wrote:
I've run more than one of those kits, measuring with nothing more than a .002 feeler gauge. Don't think I even did that with ...more
project racer wrote:
I've run more than one of those kits, measuring with nothing more than a .002 feeler gauge. Don't think I even did that with another one. They ran fine for me. used those carbs as well, with good results. Never have seized a PW, but it is common.
One thing I noticed is the port chamfer on the china kits is a bit sharp. Hard on the rings. If you have some small files, this is easily remedied.
Cool! Im going to order that kit and go for it. Appreciate the info. At least I know what to check before i put the kit on the bike. Many thanks my Bros!
r.sal923
Posts: 554
Joined: 1/25/2014
Location: CAN
2/28/2017 6:20 AM
Better get one before Mr Trump implements the tariff on out of country goods.
3/1/2017 1:18 AM
There is a little bleed screw on the oil pump. If you are still using the oil injection, fill the oil tank at least half full, pull the bleed screw, and let it drain out for a few seconds to remove any possible air bubbles in the oiling system. It is messy, but you can use some aerosol brake cleaner to rinse the area when done. Make sure the pump arm where the cable attaches is clean and moves freely.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
4/30/2017 7:58 AM
I picked up one of these kits recently during an ebay promotion and I think it might be too tight of a fit like some of you have mentioned.
When I installed the rings on the piston the top ring didn't quite fit right and I think the bottom one was a bit loose. I swapped them around and they fit better but I'm still not sure if the (now) bottom ring is too big or something. I didn't measure them inside the cylinder before putting them on the piston, so I really need to do that I suppose... I could not see any markings or different colors to identify top/bottom ring.
I brought the cylinder down just past the rings and it felt way too tight, I had to put effort to push it further. I've read that it should slide on fairly easily, so something with mine must be a bit off.
The piston arrived inside the cylinder and I can't remember having to force it out so maybe it's not too bad? Unfortunately I don't have anything to accurately measure the piston and bore, is it somehow possible for me to judge if they fit together ok or do I need to get it properly checked?
I dropped the piston in the top of the cylinder (down to the rings) and it was a little tight but didn't need any effort to push it in. I think that's what it should be like, correct?
I will try to have another look at it tomorrow. If the piston with no rings (or just the current top one) is able to slide through with just a slight push, but doesn't want to go in with the other ring, does that sound like it just needs a different/new set of rings? Or is the bottom ring supposed to be a much tighter fit to the bore? Or perhaps the groove in the piston is a bit small/tight?
This kit did not come with the 3rd expansion ring, just two standard ones.
Will try to get some more information tomorrow.
Any help/advice greatly appreciated.
Thanks
4/30/2017 2:19 PM
With no rings on the piston, it should slide freely up and down the length of the bore. If it hits a spot where it starts to become stuck, it could be the bore is not straight, tapered from top to bottom.
For those little bikes, I use a long .002 feeler gauge. Lay the gauge in the bore, and try to slide the piston up and down the full length of the bore. If the piston won't travel the length of the bore with the.002 gauge in there, things may be a bit too tight.
Are the ring ends pressed up against the locating pins in the piston during install ?
At most, a few passes with a correct size ball hone should get the cylinder where it needs to be. Don't go too crazy. Check your progress with the gauge and piston after a few passes with the hone.
Don't use one of those three fingered type hones.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/1/2017 10:03 AM
Edited Date/Time: 5/1/2017 10:05 AM
I wasn't able to borrow a feeler gauge today so I didn't want to take the rings off and risk snapping them. I went around the piston and checked that both rings could fit completely into their grove, which they could. Then I put the bottom of the piston (up to the bottom ring) in both ends of the cylinder and there was minimal contact, felt good enough to me. So I put the piston completely in the cylinder and it feels much better than last time. I suppose I didn't quite have it 100% correct before.
Now I can just lightly push it up/down with one finger, not forcing, and it will slide through pretty easily. It feels nice and smooth, can't notice anything catching/scratching.
Should I check anything else or just install the piston/cylinder on the bike and turn it over by hand a few times to see if it's still smooth? If it's good, maybe a few proper kicks and then it should be fine?
Cheers
5/1/2017 6:29 PM
Run it. Burp the oil injection system. There is a little hex head screw with a Phillips head slot in it next to the oil line where it meets the pump. Pull the cover, fill the oil tank, remove the bleed screw, and let it flow for about 4-5 seconds.
You can use aerosol brake cleaner to clean up the pump area afterwards. Make sure the pump actuator arm is free and operating smoothly when the throttle is opened.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/2/2017 8:09 AM
Previous owner had removed the oil bottle so it's running 50:1 premix.
Part of the bottom ring had also snapped off (unless it was installed broken) and disappeared.
Hopefully the new parts are a nice improvement 
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/2/2017 8:54 AM
Do you put some oil on everything when you have done this in the past? I've read that some people recommend it (which is what the manual says to do) and others are against it. Does it make much difference with the pw50?
Can you confirm which way the head gasket faces, I'm guessing shiny side up?
Those photos turned out really bad, sorry about that. Left side is after it sits still. Right side (kinda) shows how much oil it is picking up from below when it turns over. Should I wipe out some of the excess or is it OK?
I'm still paranoid about the clearance, it felt a little tighter today haha. I'll see how it feels when it's all back together.
Cheers
5/2/2017 3:50 PM
You are correct on the head gasket. I usually oil the piston pin and bearing only. Once the engines fires, the lube is there for the bore in your premix. 32-40:1 is safe for a 50. They get hot, and air flow at their low speeds is not a lot.
The oil on the crankshaft has a color more of motor oil / gear oil than premix lube which should be the only residue in the lower crank cavity. Is the main seal on the clutch side in good shape ?
It would be best to have an idea of clearance if things still seem iffy. If the piston can not be installed in the bore with a .002 feeler gauge , it may be too tight. This is the least expensive, least technical way to give an idea of where clearances are at.
If nothing else, should you assemble it and go as is, get a large fan, direct it toward the cylinder / head area, and let the bike idle for a couple of minutes, then let it cool.
Repeat a few times. Eventually , let it run for about two -three cycles of 10 minute periods, with a cool down in between. Keep the fan on it. No heavy loads or revs for the first few cycles.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/3/2017 10:10 AM
OK I'll swap to 40:1. Is it alright to leave the 50:1 in there for now and then swap to 40:1 when (if) it starts getting ridden, or should I change that before?
I was getting help on here some months ago about this bike because it was blowing heaps of smoke, I replaced both crank seals back then. The left side had pushed itself outwards when I first looked at that side. The bike used to leak oil through this seal, I assume, and it would drip out the little cutout in the left side cover. The right side (clutch) was harder for me to remove, so probably not as bad as the other one.
The bike had only been started a few times since I did that and I believe there was some improvement but still wasn't as it should be. I was hoping replacing the top end would get it back to running good. Would the old top end contribute to the smoke? I'm hoping so, otherwise that means something else will still need to be replaced after this.
So that probably is gearbox oil that had come through the old seal, which I should clean out?
I have a fan to use and it's quite cool here at the moment, so that will help too.
I'll try and get a feeler gauge today/tomorrow. Depending how that goes I may take it to a shop just to be safe. There is one nearby that is highly regarded. What is a reasonable price to measure and fix the clearance, if it's required?
Should I be concerned about that missing piece of ring being down the bottom somewhere or would it be obvious if it was floating/stuck down there?
Thanks once again for all your help!
5/3/2017 7:34 PM
If only the ignition side seal was leaking, the oil was premix / fuel from the lower end getting past the seal.
If both seals were leaking, it could be a mix of transmission oil / premix that was getting past the ignition side seal, showing as a leak.
If there is an accumulation of oil in the lower end (crank cavity), it will smoke until the excess oil is burned off as the engine runs.
The main concern would be any stray metal in the lower end, such as a piece of broken ring. If there is any , it will surely come up and eat the new top end.
A lot of times, a broken ring will exit out the exhaust port. Shake the exhaust pipe and listen for a slight rattle, The ring piece may still be lodged in the pipe.
You can probe the lower end a bit with a small, telescoping magnet placed in between the crank wheel halves / rod area. Or try a flush by filling the crank cavity with a solvent, rotating the crank by grabbing the rod , spinning the engine over, and dumping the flush solvent out.
Be careful if you use gasoline. Any stray spark as you rotate the engine could be enough to ignite fuel. Mineral spirits or diesel would be safer.
Repeat a few times, and blow out the cavity with compressed air, with the engine upside down, cavity facing downward towards the floor. If the engine is still in the frame, just flip the bike upside down to dump the solvent and blow out the cavity.
Not a guarantee , but the best you can do without splitting the cases. I've done a few this way. Just try to be as thorough as you can in flushing things.
As a plus, you will rinse all of the excess oil from the case cavity. Start with a fresh load of fuel /oil. 40:1 is what I have had good luck with, using Yamalube R. Not the injector oil, but R.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/4/2017 11:17 AM
Edited Date/Time: 5/4/2017 11:19 AM
I borrowed a feeler gauge today but unfortunately it didn't have small enough blades to check the clearance. I checked my spark plugs gaps while I had it though and both NGK plugs were fine but the one that came with the kit was too big, .8 or .9 something millimetres. Do you ever use those no-name ones or stick to proper brand ones?
I put the piston and cylinder on the bike just to see how it went. I turned the flywheel (?) by hand and then the kickstarter, also by hand, maybe 15-20 (didn't count) times and they felt smooth and easy enough. Now there are marks on the cylinder and piston, nothing I can actually feel though. Is this normal or warning signs?
The bottom edge on both sides of the piston looks like it was rubbing but I can only see individual lines on the cylinder. The lines stop just below the top of the cylinder but seem to start from the very bottom.
Video:
Sorry about the barking dog...
Do you think I need to take it to get fixed up?
Cheers
5/4/2017 5:43 PM
Edited Date/Time: 5/4/2017 6:04 PM
The marks are from the rings. There is clearance , or it would be more difficult to roll the engine over. If you want to be safe, have it measured for clearance.
If not, run it for several heat cycles before putting a load on it. Things are not that expensive even if it sticks. I never got too awful concerned with the measurements on those things.
Heck, I've seized pistons before, pinned the ring into the groove. Carefully dug the ring out, sanded the piston and cylinder, and used the same head gasket, having only a new base gasket on hand at the time . Richened the pilot jet one number.
I was 200 miles from home, and wanted to race my vintage 360 Yamaha. It seized the first heat of the first night of a four race series.
After the above mentioned field repair, I raced it the rest of the series. It was a bit low on compression, rattled a bit, but it never missed a beat the rest of the events. Don't let this worry the fun out of things for you. If it breaks, oh well, it can be fixed.
And for what it's worth ,the top end on the 360 pictured here was set up to factory clearances by a highly reputable race shop . Many factors can cause a seizure, on top of poor clearances. My mistake was one needle clip position change on a cool night. After six laps of hard running, a full chop of the throttle let the needle close off the main jet a bit too much, combined with a border line lean pilot jet. Once the bike got some heat in it , this was enough to squeak it.
It nearly crashed me hard when the rear wheel locked up at about 70 mph at the end of a long straight. This was a flat track bike. Just lucky I got the clutch in before it kicked too far sideways as it stuck.
Believe it or not, you can seize a top end with excessive clearance as well. When the clearance becomes excessive, heat transfer from the piston to the bore is lost. The piston can not dissipate the heat through the bore to the cooling fins, and heat build up can cause it to stick.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/4/2017 8:32 PM
Edited Date/Time: 5/4/2017 8:35 PM
Great, that's reassuring. I may take it in next week and see what they would charge, as I will only be a couple minutes away. If it's free/cheap enough it might be good just out of curiousity.
This kit only cost $30.98. They are normally ~$55 and up to buy here but ebay had a $20 promotion off which worked out great. A set of rings from my local dealer costs more than that!
I'm not too concerned about damaging rings/piston or any of this (although I'd rather not haha) it was only if it would cause damage to the connecting rod/crank or anything like that.
This is all pretty overwhelming to do for the first time when you don't know what you're doing. That's why I've been hassling you the whole way along. I think I could do it next time myself without needing you to walk me through the whole thing 
If all goes well this new top end should not have that tinkling/rattle noise, at least at the beginning, correct?
Thanks
5/6/2017 3:13 PM
Well, it has ingested a piece of ring, and from the looks of the piston photos, has seized at least once. No damage to the crank yet, I assume.
It's usually when the piston breaks a skirt that the damage starts to occur. Most PW's will seize or lose compression and just not run, before they break a piston. Usually, it's more of the lower rod bearing becoming littered with metal fragments that is the concern at that point.
It may not rattle at first, but a little rattle is common from most air cooled two strokes. Nature of the beast.
temppp
Posts: 32
Joined: 10/16/2016
Location: AUS
5/11/2017 10:37 AM
I was able to get a quick clearance measurement with a feeler gauge and I think it's fine. Smallest size I had was .038mm (.0015in) which I tested in a few spots. Might have been a bit tighter on top.
The old piston/cylinder was roughly 0.1mm (0.004in)
The range according to the manual is .034-.047mm (.0013-.0019in)
I poked a magnet around but didn't find anything. I never noticed anything in the exhaust either when I was cleaning that out. Hopefully that piece of ring is long gone. I will remove the engine from the frame and try to tip anything out, it will probably be easier to put it back together while it's out too.
I don't have a torque wrench. Do you think I can get away without it for the head nuts, or do I need to find one to use?
I think I will be replacing almost all of the fasteners for the exhaust and the rear arm. Some of the parts from the dealer are quite expensive so I was going to look into getting them from a local place. Would stainless steel be suitable or should I be looking for something else/better? Mild/High tensile zinc plated? I don't know... Some of the stuff on there are random bits the previous owner installed.
Yamaha Australia is also sold out of the circlip that goes underneath the clutch, it's going to take 2-3 weeks for dealers to be able to get stock which is annoying.
5/11/2017 7:24 PM
Edited Date/Time: 5/11/2017 7:50 PM
Torque wrench is nice, but the good ones are not cheap. Much like a compression gauge, no two are going to give the exact same readings. I prefer the old style pointer wrenches over the click stop. A cheap clicker can be all over the place on final settings
Have installed many PW & JR50 Suzuki top ends with a 1/4 inch ratchet . Just run the nuts down evenly. They are only 6mm studs, so no need to strong arm them. Criss cross pattern, with a few rounds about the pattern to a final fair snugging.
Recheck them after a few minutes of run time.
Had a lady off this forum bring her PW by one day. Someone put a new top end on it, and only used three nuts out of four for the head / cylinder. Had a new head gasket I donated to the cause, along with the nut. Ratcheted it on there, ran fine.
As long as thread pitch and length are the same, just buy the common zinc fasteners from a hardware store.
Most good hardware stores also have snap rings in various sizes. Or a local bearing outlet, auto parts store. Probably a 14 or 16mm snap ring would do it. Not an uncommon part
This is not going to be a show bike, is it ? More enjoyment for me the less $$ spent.
I had quite a bit of PW spares at one time. Got rid of all of it ,save for one bike.
5/11/2017 7:58 PM
Edited Date/Time: 5/11/2017 8:01 PM
$125. Before
After . About $400 in this one, including purchase cost.
Forum Main Tech Help/Race Shop eBay complete top end kits for PW50?
Source: https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/eBay-complete-top-end-kits-for-PW50,1315306
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