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Tillerman6

New piston and rings - sources and opinions?

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After some searching on Ebay and my local Yamaha bike shop (no help there) I am wondering about my next top end overhaul.  I don't ride it much, but I noticed last time out that it was dinging a bit louder than I would like going down hill with the throttle closed.  From what I am seeing, the time between overhauls on these 2 strokes is on the order of 30-40 hours!   So I'm going to do a compression test as soon as I can fabricate a right angle adapter for my compression gauge hose.  The hose I have with the compression gauge is too stiff to allow it to thread into the spark plug hole without risking damage because the frame is centered right above the spark plug hole. 

When I do run the compresion test, I expect that I will find the compression to be something less than ideal at 99PSI.  So the next question is what parts to buy and from where?. 

The original piston part numbers here are the range of what Yamaha used to provide, but they are all long gone.

Yamaha itself was not much help either.

438- 116331-00-96 or 98 (original size) 69.96 mm to 69.98mm

438-11635-00 ist os  70.25mm

438-11636-00 2nd os  70.5mm

438-11637-00 3rd os  70.75mm

438-11638-00 4th os  71mm

alternate p/n' from the manual :

434-11630-10, -20, -30,-40

 

The Wiseco pistons also do not seem to be a direct replacement for the original 438 or 434 part numbers although the rings and ring groove spacing looks about right.  Anyway the pictures do not show the holes in the skirt for the exhaust side of the piston. I do have a means of machining the holes if that is something that would be required.

The Ebay items are substitutions  using the 311 part numbers?,  I think these are from the older DT250's or IT 250's??  So what has to be done to a 311 piston to make it work with the TY 250 A? and there are lots of STD (not oversize) pistons on there right now for cheap, but I don't think the standard size would do me any good unless the cylinder could be brought back to standard dimensions by some means?. Nikasil?

And since some of you guys have been there done that, I wanted to humbly ask your opinion as to what the best course of action would be?.  I know it will be costly, but a new bike is a lot more costly than that, so any ideas and or advice would be much appreciated!.  Looking for a smooth running engine that is easy to start and lasts a long time.

I have some precision tools that I can measure the bore and piston with, and now the shop manual to read (thanks Jazzyman!) so the next thing will be parts and a good shop to mail my cylinder to for the re-work if that is even possible.

I tried to contact B & J racing but it was after hours and I can't tell if they are still doing engine work?  Most of their comments about their activities are several years old, so it's hard to tell what is going on there right this minute.

 

 

 

 

 

 

 

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"Dinging" downhill could be a loose exhaust / air leak. 

 

Overhaul 30 - 40 hours !!  Every decade more like with standard maintenance and sympathetic use.

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5 hours ago, section swept said:

TY Trials list a piston kit upto 2.00mm oversize £129 have a look. Obviously post and packaging to US will need to be added. Hope you get it sorted.🙂

Thanks SS I will check them out!  Does this reply constitute a recommendation as to the quality of the product? 

5 hours ago, b40rt said:

"Dinging" downhill could be a loose exhaust / air leak.

 

5 hours ago, b40rt said:

Overhaul 30 - 40 hours !!  Every decade more like with standard maintenance and sympathetic use.

 

5 hours ago, b40rt said:

"Dinging" downhill could be a loose exhaust / air leak. 

Not sure. I cannot wiggle it at all right now.  Uness it gets looser when it is hot.    I changed the timing just a bit last time I was working on the points/condenser and maybe that could influence the sound it makes? The two bolt exhaust clamp ring is deforming from the torque on the studs. maybe I over did it or it's missing the gasket, but I can't see that there is any leaking going on. And if it was leaking, wouldn't it also leak when you were accelerating? 

Overhaul 30 - 40 hours !!  Every decade more like with standard maintenance and sympathetic use.  Thing is the previous owner could have run it for 10 years and I was not around then to wirte it down, so no idea how much wear it's got inside.   I will try to get a look inside next week when my other duties taper off a bit.  The factory service manual is pretty specific for figuring out exactly how much wear is allowable.

I just want to make sure it does not swallow a piston or ring before I get a chance to really take a hard look at the upper end.  Probably should have done it sooner, but I was having so muc fun riding it ya know?

 

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TY Trials sell Wossner piston kits, not specifically made for the TY but if they're selling them you will be safe to use them. The price is good as well, think my 70.25mm genuine Yamaha kit cost me more than that from a seller in France on eBay

 https://www.tytrials.co.uk/trailandtrialsuk/prod_2768676-812-Full-Piston-Kit-TY250-Twinshock.html

The 311 pistons are missing the taper on the skirt where the transfer ports are, the piston hits the crank without the taper & prevents the crank getting a full rotation. Piston is also heavier due to thicker skirt, all other dimensions are the same

089_zps62e3fdc1.jpg

This is a photo I took back when I bought a 311 piston kit showing the differences from the underside, 311 piston on the left, 438 piston from my TY on the right. I have a couple more photos but this shows the differences best

Edited by tony27
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Wossner and Wiseco TY250 pistons are both a good thing. The piston/bore clearance for a Wiseco will be different to what is in the Yamaha manual.

The reason there are lots of standard size genuine Yamaha pistons still available is that it is much more expensive to have a new sleeve fitted compared with a rebore.

Now that Wossner make pistons up to 2mm oversize there is even less demand for having TY250 cylinders resleeved.

TY250 cylinders last a long time between rebores if they are used for trials and have been looked after. There are still plenty around with the original piston and rings in them.

I had a TY250D motor rebored about 11 years ago and used a Wiseco piston and it still going great.

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Wow that 311 is built much heavier than the original 438.  I would imagine that it would not run very smooth because of that.  If I do actually need a piston after the inspection, I will go with the Wiseco first try because of the wait time and extra shipping costs.  If that does not work then the Wossner.  The last option is the Ebay 311's because most of them are the original size and that will not be big enough I don't think.

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Ok I decided to go ahead and tear down the top end of my TY 250 A and get a better idea of what sort of condition it is in,

I never did get a compression reading before the teardown, but looks like the wear on the piston , rings and cylinder would have dictated something less than a  perfect 99 psig.

As you can see, the piston pin did not want to come out of the piston without some encouragement.  The threaded rod and two sockets provided the persuasion, but there was a surprise involved.

The surprise is that one of the needles in the upper end con rod bearing was missing out of the cage.  I don't know how long it has been missing or if it just flew off when the cage was released from the piston pin during dis assembly today.  I noticed it was missing when the cage came half way out the end of the con rod, but I have no idea where it went or how long it has been AWOL.

As far as the piston itself goes - looks like it is a stock diameter 69.96 mm.  It has the reduced diameter above the top ring and there is a ring expander ring under the bottom ring.Does that make it a 311 part number?

There was some scuffing on the piston just to the left side of the intake port, and this by itself does not seem to be a big deal, but the rings are grooved in this same position on the piston for a short span of about .25" or 6mm wide.

I took the measurements below without honing the cylinder, so the cylinder measurements after honing to break the glaze will add another .001" at least to the already marginal service limits that exist for this standard piston.

So here are the measurements before the hone ( in inches)

Piston diameter 2.7535  to 2.754" ( Taken 1/2" from bottom edge of skirt and at right angles to the piston pin)

Bore diameter   2.7566  Taken just above the exhaust port.

Delta of  0.0026 to 0.0031  The max tolerance is .004"

Rings - I was surprised to see the "L shaped " top ring on my 74, because the previous owner did not say anything about having changed pistons and furthermore, the L shaped top ring came along later on the 75 model. Right?

So I am wondering if this piston is really off of a 75 or later machine? Maybe someone can tell me for sure. 
And inside the piston skirt it says YAMAHA, so it could be a 311 part off of a DT 250 or IT 250?  The top end of the piston is definitely a smaller diameter than the rest of the side walls. There are some numerical markings on the crown of the piston, but I am not sure what they mean.  You can see these in the pictures.

Rings- this piston has two rings and a ring expander inside the bottom ring.  There was 1/4 inch of damage of both rings near one end of the top and bottom rings.  looked to be vertical scratches about .005" deep

The free gap measurement on the top ring was 6.68 mm, free gap on the bottom ring was 7.22,, These are roughly in the ballpark.

The installed end gaps - top ring .019" with .020 being max.  (ring is pushed down into the empty bore and end gap measured)

                                     bottom ring  .015 with .016" being max

The last test is with the rings re-installed on the piston. The gap from the inside of the groove in the piston to the adjacent surface of the ring in the same groove.

Top ring .003"  Max .0031" 

 

Bottom ring:.002  Max .0031"

There does not seem to be any wear ring or lip around the upper circumference  of the cylinder.

It looks like I could almost use another stock piston and rings and a new needle bearing and piston pin and call it good, but the scratches in the bore may not come out with just a hone.

 

As far as the missing needle bearing out of the cage - what do you guys think?  I think there was some cyclic vibration with this bike as it warmed up.  The vibration seemed to go away after it was warm - So the bearing could have been missing for years I don;t know.  I've only had this bike for one year. 5b70cd161463e_TY250topendteardown013.JPG.65f1e4dec322d15719a779ec38352f85.JPG The other needles look good with no flat spots and the cage is not cracked that I can tell.

 

 

 

 

 

TY 250 top end teardown 010.JPG

TY 250 top end teardown 011.JPG

TY 250 top end teardown 012.JPG

TY 250 top end teardown 014.JPG

TY 250 top end teardown 015.JPG

TY 250 top end teardown 018.JPG

TY 250 top end teardown 020.JPG

TY 250 top end teardown 025.JPG

TY 250 top end teardown 026.JPG

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Are the marks on the bore able to be felt with a fingernail? If they can be then you will probably need to go to the next size piston. Any of the quality aftermarket piston kits will be .5mm larger for each oversize where Yamaha had steps of .25mm 

From memory & looking at listings on eBay the 311 pistons are made by Izumi, the 438 were made by ART which are cast into the inside of the skirt.

If you can stay with standard bore then here is the piston you want, the same seller has rings as well but it looks like it will end up costing more than either a Wiseco or Wossner kit cost - the kits from both are actually for early YZs so you should be able to get both makes fairly easily

https://www.ebay.com/itm/YAMAHA-RT2-DT2-RT3-DT3-TY250-STANDARD-PISTON-96MM-OEM-NOS-438-11631-01-96/263601323881?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D52885%26meid%3Da91bf7daaf9446aaa81b98d5252b7047%26pid%3D100005%26rk%3D1%26rkt%3D2%26sd%3D201687499348%26itm%3D263601323881&_trksid=p2047675.c100005.m1851

Here is a listing for the Wossner kit, you should be able to read the part number off the box & ask your local dealer to see if they can source you 1

https://www.ebay.com/itm/NEW-WOSSNER-PISTON-KIT-1974-1979-YAMAHA-YZ250-IT250-TY250-MC250-DT250-69-64-mm/192451397914?hash=item2cceff491a%3Ag%3AX4UAAOSw9vlaexpX&_sacat=0&_nkw=ty250+piston&LH_ItemCondition=3&_from=R40&rt=nc

 

Edited by tony27
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I would be looking nearby or in the crankcase for the missing needle roller and next time if you warm the piston up, the pin will push out by hand

Edited by feetupfun
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17 hours ago, feetupfun said:

I would be looking nearby or in the crankcase for the missing needle roller and next time if you warm the piston up, the pin will push out by hand

you can be sure I tried that. I even turned the bike upside down on the handlebars, but nothing fell out.  (wish it did)

 

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18 hours ago, tony27 said:

Are the marks on the bore able to be felt with a fingernail?  yes barely.

 

If they can be then you will probably need to go to the next size piston. Yes unless they can plate the bore back to stock size.

 

Any of the quality aftermarket piston kits will be .5mm larger for each oversize where Yamaha had steps of .25mm  good to know.

From memory & looking at listings on eBay the 311 pistons are made by Izumi, the 438 were made by ART which are cast into the inside of the skirt. You are the piston GURU!

If you can stay with standard bore then here is the piston you want, the same seller has rings as well but it looks like it will end up costing more than either a Wiseco or Wossner kit cost - the kits from both are actually for early YZs so you should be able to get both makes fairly easily  IF i COULD GET A GUARANTEE THAT IT WOULD FIT!? 

https://www.ebay.com/itm/YAMAHA-RT2-DT2-RT3-DT3-TY250-STANDARD-PISTON-96MM-OEM-NOS-438-11631-01-96/263601323881?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D52885%26meid%3Da91bf7daaf9446aaa81b98d5252b7047%26pid%3D100005%26rk%3D1%26rkt%3D2%26sd%3D201687499348%26itm%3D263601323881&_trksid=p2047675.c100005.m1851

 

18 hours ago, tony27 said:

Here is a listing for the Wossner kit, you should be able to read the part number off the box & ask your local dealer to see if they can source you 1

https://www.ebay.com/itm/NEW-WOSSNER-PISTON-KIT-1974-1979-YAMAHA-YZ250-IT250-TY250-MC250-DT250-69-64-mm/192451397914?hash=item2cceff491a%3Ag%3AX4UAAOSw9vlaexpX&_sacat=0&_nkw=ty250+piston&LH_ItemCondition=3&_from=R40&rt=nc

 

 

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1 minute ago, Tillerman6 said:

the Wossner kits are still an option. If the plating cannot bring back the original inside diameter of the bore, then Wossner is the only game in town.

 

1 minute ago, Tillerman6 said:

 

 

 

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On 8/11/2018 at 3:43 PM, Tillerman6 said:

After some searching on Ebay and my local Yamaha bike shop (no help there) I am wondering about my next top end overhaul.  I don't ride it much, but I noticed last time out that it was dinging a bit louder than I would like going down hill with the throttle closed.  From what I am seeing, the time between overhauls on these 2 strokes is on the order of 30-40 hours!   So I'm going to do a compression test as soon as I can fabricate a right angle adapter for my compression gauge hose.  The hose I have with the compression gauge is too stiff to allow it to thread into the spark plug hole without risking damage because the frame is centered right above the spark plug hole. 

When I do run the compresion test, I expect that I will find the compression to be something less than ideal at 99PSI.  So the next question is what parts to buy and from where?. 

The original piston part numbers here are the range of what Yamaha used to provide, but they are all long gone.

Yamaha itself was not much help either.

438- 116331-00-96 or 98 (original size) 69.96 mm to 69.98mm

438-11635-00 ist os  70.25mm

438-11636-00 2nd os  70.5mm

438-11637-00 3rd os  70.75mm

438-11638-00 4th os  71mm

alternate p/n' from the manual :

434-11630-10, -20, -30,-40

 

The Wiseco pistons also do not seem to be a direct replacement for the original 438 or 434 part numbers although the rings and ring groove spacing looks about right.  Anyway the pictures do not show the holes in the skirt for the exhaust side of the piston. I do have a means of machining the holes if that is something that would be required.

The Ebay items are substitutions  using the 311 part numbers?,  I think these are from the older DT250's or IT 250's??  So what has to be done to a 311 piston to make it work with the TY 250 A? and there are lots of STD (not oversize) pistons on there right now for cheap, but I don't think the standard size would do me any good unless the cylinder could be brought back to standard dimensions by some means?. Nikasil?

And since some of you guys have been there done that, I wanted to humbly ask your opinion as to what the best course of action would be?.  I know it will be costly, but a new bike is a lot more costly than that, so any ideas and or advice would be much appreciated!.  Looking for a smooth running engine that is easy to start and lasts a long time.

I have some precision tools that I can measure the bore and piston with, and now the shop manual to read (thanks Jazzyman!) so the next thing will be parts and a good shop to mail my cylinder to for the re-work if that is even possible.

I tried to contact B & J racing but it was after hours and I can't tell if they are still doing engine work?  Most of their comments about their activities are several years old, so it's hard to tell what is going on there right this minute.

B & j   racing is still very much alive and well as of August 13 2018, so Please disregard my questions about that idea.

 

 

 

 

 

 

 

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