TY250 project

Discussion in 'Trials' started by Junglejeff1, Nov 1, 2018.

  1. PMK

    PMK Been here awhile

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    For reasons unknown, the S3 head image would not isert when editing. This is the image referenced in the above post.

    Note that the modern head has less squish band area, and a wider shaped bowl area of the combustion chamber. If needed, this style head could easily handle a squish clearance in the 1mm to 1.5 mm range with ease, possibly even as tight as .5mm. The critical key being keen to not increase compression excessively.

    upload_2019-4-2_4-34-45.jpg
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  2. UstaKood

    UstaKood Been here awhile

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    Wondering what’s to be gained ?

    My TY has mild port / matching , miikuni and after adding Boysens it is very tractable ( stock flywheel ) Very happy with the results.

    Yes the mono benefited from the head work but haven’t ever experienced issues with TS .

    Inquiring feeble mind at work here .
  3. Junglejeff1

    Junglejeff1 Long timer

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    More low end power is main benifit.I would like to simply optimize the motor for premium fuel.
  4. Junglejeff1

    Junglejeff1 Long timer

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    I am going to check the volume.Also might get another head and send it to rb performance to let him work his magic.Shocked he still does this work as he is in his 70,s..For break in will run stock head in hopes of keeping heat down.Running pretty tight on my piston to wall clearance and going to really have to baby it 1st hour.My gg has a S3 head with the hi compression insert.Really like that bike alot.Had to put TY aside this week as 1st meet is in 2 weeks and going through my GG.
  5. Junglejeff1

    Junglejeff1 Long timer

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  6. PMK

    PMK Been here awhile

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    If the piston is not moly coated, do it. Consider running the modified head, since you need the heat for proper break in.

    Use caution if you send the head out, very possible they may make changes better suited for a different rpm than you care for.

    FWIW, This morning I bought a used MAR head and plan to modify it to make the engine better on modern fuel.
  7. Junglejeff1

    Junglejeff1 Long timer

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    Appreciate the info,I sort of hope I like it stock.
  8. PMK

    PMK Been here awhile

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    Optimizing the combustion chamber shape, volume, and clearance each plays a part in truly optimizing or building the motor to make power as you want. Yes a correctly ported cylinder, proper port height shimmed with gaskets or no gaskets factor in also, plus changes to the lower end.

    In simple terms, excessive squish clearance makes proper jetting more difficult to obtain, but also will detune the power to be smooth also. Yes you ported the cylinder to make the engine better, if your head is stock, with squish clearance similar to what was posted, it is very possible, the performance could have been better with a head mod alone and no port work.

    However, if it is working for you, ride the wheels off it.

    For others reading these posts, this is not about making big horsepower or something less easy to ride, actually more easy to ride is the focus.
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  9. Junglejeff1

    Junglejeff1 Long timer

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    Exactly what I am trying to achieve, just a clean running motor. Lucky I checked flywheel weights bolts also.2 were loose.leaving weight on and may trim down some but want to try it 1st.I have read some people run without a head gasket and it helps alot.Going to try the simple stuff 1st.
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  10. UstaKood

    UstaKood Been here awhile

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    K ,

    :thumb

    :ear
  11. Junglejeff1

    Junglejeff1 Long timer

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    20190409_193410.jpg Have the modern bikes ready for this weekends meet so worked on TY some.Front spokes were seized up,bent ect.Picked up a stainless spoke kit from speed and sport and laced it up tonight.
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  12. Junglejeff1

    Junglejeff1 Long timer

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    Did you have any issues getting the boysen reeds to lay flat.have a tiny bit of space under them that flipping does not help with.
  13. Junglejeff1

    Junglejeff1 Long timer

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    A friend of mine that builds performance motors is telling me the same stuff you are now.He recommended not to go under .100" on sqish on this head.He said a wider band is usually used on lower rpm engines also.Going to order some .020" copper off amazon for head gasket to bring it just above .100"
  14. Brewtus

    Brewtus Buffoonery, Inc.

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    Or cut out a beer can gasket. .003".

    Ask me how I know..... :evil
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  15. Junglejeff1

    Junglejeff1 Long timer

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    Interesting, I might have to buy some beer.
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  16. PMK

    PMK Been here awhile

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    Try it. Myself, I would be more headed towards .063” or 1.5mm. Often squish greater than that runs fat.

    As for squish band width and percentages, catch a look at the S3 head I posted. I need to measure an S3 to verify that photo is correct. However with proper squish and related stuff, plus proper band dimensions, most bikes will run better and be smoother in power output.
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  17. Junglejeff1

    Junglejeff1 Long timer

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    It kills me to not pull the S3 on my GG and take a look. Bikes is running so perfect right now.I don't get the sqish thing.My 2000 yz250 was set at .050" and it made it jet out real nice with no knock. It was set at stock compression by RB.Then I hear anything under .100" can cause pre ignition which is just the opposite of what I have experienced.Is .050" to tite for a old air cooled bike?
  18. UstaKood

    UstaKood Been here awhile

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    I don't recall any issues , its been a couple 2-3 years but it did make a noticeable improvement right from the get go . Smoothed it out low speed and pulled strong off idle , seemed to have a stronger mid range hit .

    Although I understand the pursuit for excellence , I might start with a baseline and go from there . Truthfully a TY is ... well... a TY , but at the same time it's still competitive . I bought one of the first ones to come to Michigan in 1974 and for most part had one around since .

    The suspension / peg mods you've made should helpful . Curious to see how the emulators work out for you .

    Quit dinking around and get that sucker running ! It's Spring !:happay
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  19. Junglejeff1

    Junglejeff1 Long timer

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    It needs to be done and broke in by June 2.Should not be a issue at this point.
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  20. Junglejeff1

    Junglejeff1 Long timer

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    Took a slider off ebay fork and powdercoated it black.Really wierd the way the one on bike was not right. Put forks together and used atf type f.Going to use the extra internals I have to experiment with later.Laced up front rim and started putting bike together. Installed new wheel bearings and swingarm bushings as they all were a wee bit loose.Going to try to build a hidden fork brace before I drill out the front fender. 20190417_154555.jpg
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