Question for guys running the big bore kit options, 70mm -vs- up to 74mm w/case bore
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Thread: Question for guys running the big bore kit options, 70mm -vs- up to 74mm w/case bore

  1. #1
    Senior Member DougDotyTW200's Avatar
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    Question for guys running the big bore kit options, 70mm -vs- up to 74mm w/case bore

    Do you know if there is more cooling fin area to be found on the cylinders like the 225/230 or the yfm250 options referenced in Sebastians list of combinations, than what is found on the stock TW200 cylinder. logic would have me think they would have been designed with more ?? If there is, then that would justify the case boring to allow their use in lieu max boring the stock TW cylinder.

    EDIT: Also if you have a favorite or good experience with a machine shop for case boring and or bore and sleeving services, please throw out a name and location for them.

    Thanks.......
    Last edited by DougDotyTW200; 02-07-2018 at 05:20 PM.
    Smitty Blackstone likes this.
    2016, stock'ish and a 2003 Starting on a 225 or bigger 6 speed build as a spare for now and install later when done and ready on this bike.

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    Senior Member lbxr's Avatar
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    I have 2 motors that i used the YFM250 jugs....Externally the cooling fins are the same. I used ttr 225 cases so I did not have to bore out the cases. These are 71mm bores and work out 229cc. I built a spare motor for fun using a stock tw crank and a ttr 225 jug at 70mm and that works out to 214cc. I had to open the case on this one...not fun. All these jugs appear the same externally except for the displacement cc castings. The YFM 250 jugs are dirt cheap on ebay. I managed to find ones with almost no wear. I used Wiseco forged pistons in these jugs and since a forged piston requires more clearance than a cast piston I was able to hone to the proper clearance...Cheap, easy, and so far bullet proof....

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    Senior Member elime's Avatar
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    I honed a TW cylinder to 70mm using a cylinder hone, not a glaze breaking hone. It was a fairly slow process and I had to take a lot of measurements but it can be done with very good results. When I was done the bottom part of the cylinder was about as thick as a penny which seemed very thin to me but it has so far worked out OK. If you want to use a piston larger than 70mm you will need a cylinder from a 225 and the case will have to be enlarged to accept it.

    The 70mm piston with the TW200 crank gives a compression ration of 9.9 : 1. The same piston with a 225 crank yields a comp. ratio of 10.25 : 1.

    Some pictures that may answer some questions.

    New Wiseco Piston.
    70mm piston.JPG

    Cylinder wall thickness.
    P7300011 (2).JPG

    Thickness of a penny.
    P7300013 (2).JPG

    Ready for new piston and rings.
    P9080011 (2).JPG

    Stock size piston in 70mm bore.
    Std piston 70mm bore (1).JPG
    Last edited by elime; 02-07-2018 at 11:19 PM.
    admiral and Cornelis like this.
    Long live the internal combustion engine!

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    Senior Member DougDotyTW200's Avatar
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    I have read everything here that I could find that is relevant and now have several components coming in or already landed for my build, basically everything I know of short of head/cylinder bolts. Sourced everything from ebay as used parts and bought the best used parts for the best possible prices in every case. Spent a lot of time selecting particular components since I am retired.

    Will be opening cases mouths on stock 09 TW200 4000 mile short block that looks as clean as new and was obviously a street bike by all appearances.

    Complete 6 speed transmission components from 2005 ttr225, appear in perfect condition after inspection. Got these today from a neighboring state recycler. Came in today and looks great. Still not sure i want a 6 speed but too cheap to pass up.

    Cylinder and piston set is from 06 ttr230, with claimed low time and cylinder measurements, pictures match, description outer cosmetic finish still looks good, time will tell, if the #'s work, I may give a hone and re-ring to this jug and use as is.

    Cylinder Head from the same 09 Tw200 above.

    Upper cam sprocket used and appears clean ?? from a ttr230.

    Crank and Balancer Shaft from a 99 ttr225, claimed rod is tight, probably should read that as it is seized This was a too good deal crank and since it is vital, I will give it a reman if needed but supposed to be pristine.

    Tensioner used, looks new

    unrealized misc $$$$ still

    Spent a bunch on parts but I will get a 225 6 speed If I don't decide to keep my 5, that looks like the stock appearing clean 03 TW engine that is in my 330 mile bike now. Still a good bit less than any complete used 225's And I will still have my complete stock 330 mile 03 take out engine -carb on the stand for possible sale or oops Will have a 4000 mile tw200 crank set to sell.

    Question, I want to keep my stock clutch for now but am still a little confused about the 5 disc clutch on a 6 speed gear setup ?? I want to try to initially use the clutch and tw200 black right side cover that come with my short block. I read somewhere there might be an exact fit issue requiring some machining ??? This part of the plan is obviously subject to change for the 6 disc and 225 case cover as it may be cheaper than custom work if I cannot do it myself but I cannot remember where I found it. Really don't want to start over looking, can anyone chime in on this detail ???
    Ken, TW-Brian, littletommy and 1 others like this.
    2016, stock'ish and a 2003 Starting on a 225 or bigger 6 speed build as a spare for now and install later when done and ready on this bike.

  6. #5
    Senior Member TW-Brian's Avatar
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    Quote Originally Posted by DougDotyTW200 View Post

    Question, I want to keep my stock clutch for now but am still a little confused about the 5 disc clutch on a 6 speed gear setup ?? I want to try to initially use the clutch and tw200 black right side cover that come with my short block. I read somewhere there might be an exact fit issue requiring some machining ??? This part of the plan is obviously subject to change for the 6 disc and 225 case cover as it may be cheaper than custom work if I cannot do it myself but I cannot remember where I found it. Really don't want to start over looking, can anyone chime in on this detail ???
    Hi Doug,

    You have certainly been busy and seem to have things very well thought out!

    Here's what I can offer to answer your questions. If you want a 6-speed tranny, you will have to go with the 6-plate clutch. The reason why is that the transmission shaft that the clutch mounts to have a differing number of splines for the 5 and 6-speed shafts, so you will not be able to mix the shafts and clutches.

    I was able to fit a 6-plate clutch inside a stock TW right side engine cover so I know that it can be done. It is tedious and time consuming work that involves removing material from the end of the four posts on the inner clutch basket, removing material from the heads of the four screws that secure the clutch springs, and removing material from the inner ribs of the TW right side engine cover. This involves removing a small amount of material, then test fitting, then removing more material, then test fitting again, and so on, until the spinning parts clear the side cover. I described this with pics in post #126 in the following thread.

    https://tw200forum.com/forum/performa...-ttr230-6.html

    My recommendation would be to go with the 6-speed tranny and the 6-plate clutch. I am sure glad that I did!

    Hope this helps,

    Brian

  7. #6
    Senior Member DougDotyTW200's Avatar
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    Brian, Thanks a million !!

    Clear on that now. i will go back and read that section of the linked post. I am overly stubborn/hard headed but What will cause me to go 6 speed is now knowing I have to split the cases again rather than just do it incrementally through the right side cover which is what I had wanted to experience. I was one of the few that liked 4 and 5 speed cars and trucks better than 6's and i never learned to like the Harleys with the 6 speed either. With the TW in top gear all the time even on two lane local roads the bigger overdrive is very well utilized compared to the Harleys on these same roads. so I will install it. Gonna need a clutch setup and I will do the work to utilize my cherry matching TW right side cover. No biggie. I can't imagine ever selling my 5 speed gears for a dime so I might just as well toss those gears and use that shaft out on my builder engine.

    Some parts are here now and the rest ordered today and will sprinkle in over the next week. Had been building and sorting parts in and out of an ebay cart for days.

    Thanks again, you have been very helpful.
    Last edited by DougDotyTW200; 02-14-2018 at 10:51 PM.
    2016, stock'ish and a 2003 Starting on a 225 or bigger 6 speed build as a spare for now and install later when done and ready on this bike.

  8. #7
    Senior Member DougDotyTW200's Avatar
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    09 TW bottom end and cylinder head arrived. Got it unpacked this afternoon and it all looks absolutely like new parts. Gonna be hard to dismantle it for a few parts
    2016, stock'ish and a 2003 Starting on a 225 or bigger 6 speed build as a spare for now and install later when done and ready on this bike.

  9. #8
    Senior Member vanillagorilla1's Avatar
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    brian hit it on the nose for the clutch. You will have to use the 6 disk with the 6 speed, but its well worth it. I used an ebc plate and spring kit as well. to me the tranny is proabably a bigger deal that the displacement off road. I would also recommend the ytm/yfm piston. the higher compression really helps the bottom end torque and its drop in. The only thing I see missing from your equation is the counter shaft. I dont think that balance shaft is gonna work in the tw cases. Mine certainly didnt. reason being the tw vents through the top of the case and the ttr sends the vent through a hollow balance shaft and out a different way. I have a 200 balance shaft in my hybrid motor for better or worse. 10000 and counting on the build. I also dont see you mention machining of the counter shaft, but thats gonna have to be done if you havent already for the 6 speed. good luck.
    93 tw. running like clockwork
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  10. #9
    Senior Member DougDotyTW200's Avatar
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    Thanks for all of that, I am aware of the shaft machining but had no clue on the balance shaft incompatibility, kind of surprised in fact. Can you be elaborate on the ytm yfm piston ?? I was looking at 70 to 71mm at this point cause I cannot find someone to resleeve with out getting shipping involved to the plan is downgraded to 226 or 229 from original ideal of going all the way to 250. Is that ytm yfm piston the 74mm one mentioned in Sebastians write up ??

    Do you feel like you have any added vibration that the matching set in a ttr case would not have ???

    Thanks again...
    2016, stock'ish and a 2003 Starting on a 225 or bigger 6 speed build as a spare for now and install later when done and ready on this bike.

  11. #10
    Senior Member vanillagorilla1's Avatar
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    the piston im talking about will yield a 225. Its the one shown in tony's picture above. Fits right in without modification. as for the vibration I cant tell you the answer to that. my stock 200 buzzed like hell at high rpm and so does this. I dont think its excessive. Also the ttr didnt always have the same gearing. the 225 and 230s had different gear sets. 225s were wider that a tw and 230s were narrower. The wider one is the one you want and that I think you have. I run 15-47 and its great for me. Ive done high way and tight trail with it. I really dont know what the guys with the crazy low gears are doing to be honest. Ive never seen one go where I can't ,but thats a matter of opinion I guess.
    93 tw. running like clockwork
    225 6 speed complete!
    82 honda gl500 silver wing. sold to a new home 11-24-17
    03 ducati monster 800sie. full rebuild and a danger to the public Hidden Content for sale

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