Curiosity regarding 250cc / 6 speed conversions
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Thread: Curiosity regarding 250cc / 6 speed conversions

  1. #1
    Senior Member Spawner's Avatar
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    Curiosity regarding 250cc / 6 speed conversions

    I was reading a thread (below) started in 2014 that listed a number of parts required for the 250 conversion and had a few questions for those of you who have done it.
    1, Is the YA-5679 cylinder sleeve the same OD as the various 225 compatible heads he has listed, or will the head its self need to be opened to the correct tolerance?
    2, Does said sleeve need to be trimmed for height?
    3, Will Yamaha piston 3C5-11631-00-A0 fit perfectly, or does the sleeve need to be opened up some? Also, could the sleeve be bored for a sized up piston down the road?
    getting ready to start ordering parts, and am hoping to avoid costly mistakes. Thank you for any input.

    https://tw200forum.com/forum/performa...up-250-cc.html
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    Member BuddyMack's Avatar
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    Quote Originally Posted by Spawner View Post
    I was reading a thread (below) started in 2014 that listed a number of parts required for the 250 conversion and had a few questions for those of you who have done it.
    1, Is the YA-5679 cylinder sleeve the same OD as the various 225 compatible heads he has listed, or will the head its self need to be opened to the correct tolerance?
    2, Does said sleeve need to be trimmed for height?
    3, Will Yamaha piston 3C5-11631-00-A0 fit perfectly, or does the sleeve need to be opened up some? Also, could the sleeve be bored for a sized up piston down the road?
    getting ready to start ordering parts, and am hoping to avoid costly mistakes. Thank you for any input.

    https://tw200forum.com/forum/performa...up-250-cc.html
    Pretty good subject for Bench racing, but one that has rarely been attempted, and even much rarer, actually accomplished. Just buy a bigger bike and turn that into a larger TW style bike.

    Sent from my LG-TP260 using Tapatalk
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    Senior Member Spawner's Avatar
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    [QUOTE=BuddyMack;895586]Pretty good subject for Bench racing, but one that has rarely been attempted, and even much rarer, actually accomplished. Just buy a bigger bike and turn that into a larger TW style bike.

    Sent from my LG-TP260 using Tapatalk[/QUOTE

    There are a few people running (successfully) various larger displacement bikes, with 6 speeds on the forum. I enjoy tinkering on the tw (and I already own it), so the idea of just getting a bigger bike doesn't really appeal to me. still interested in the information from people who have done similar mods. thanks
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    Senior Member Tweaker's Avatar
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    Since there are a few guys that have made 6 speed and 250cc TWs and several new guys looking to do that it would be cool if there was a dedicated sticky thread for this topic, maybe a list of people who have done it and a consolidation of different threads. It would be an awesome resource.
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    Super Moderator Purple's Avatar
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    I think there's a thread or two on the 225 conversion that may "mention" the 250 - I'll try and dig it out later .....
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    Senior Member Spawner's Avatar
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    I've read about all I think there is on all the conversions, I just find it difficult to decide exactly what used parts are compatible. I like Tweakers idea to put all the info into 1 thread. If this conversion works out maybe ill have learned enough to do a write up. without one person building every combination I imagine it would be nearly impossible to have all the knowledge. maybe we could start a thread where people who were over bore could post exactly what is in their engine so we can see what is proven and what works.
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    Super Moderator Purple's Avatar
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    One person has - Macbig21k - any definitive parts thread has included comments and input from him - but that primarily covers 200 to 225 conversions

    I understated that he races a TW250, but there's considerably less detailed info on that one

    If someone want's to start a build thread with details, pictures and part sources for the 225 we can sticky it - same for anyone doing the 250

    Makes more sense to document a single build with input from others rather than try to combine build threads .....
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    Senior Member TW-Brian's Avatar
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    Here is the thread where I got the information that I needed and also where I posted my information on my TW226 6-speed.

    https://tw200forum.com/forum/performa...25-ttr230.html

  10. #9
    Senior Member Spawner's Avatar
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    just read all 34 pages. Lots of information. So far im looking at an 04 ttr225 bottom end, 87 moto4 225 head bored out to take a 74mm sleeve, modified tw output shaft, tw left engine cover, matching year and make head to the bottom end, left side output shaft bearing, and a gasket set. might add the kick starter depending on cost. would like to build the engine and swap it in just in case it fails...
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    Senior Member vanillagorilla1's Avatar
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    Im gonna take a whack at answering your questions bases on current and growing knowledge. Also you mention you're looking at a moto4 225 head and mention head in your first list and because of wording I think you mean cylinder. Also to state my marginal credibility I do have a current 225 6 speed with 15k or so on it now and a 250 on the bench in the works. I have a thread currently going as I make progress. So........ the la sleeve 5679 will not drop into any cylinder you choose. It has a larger OD than the 225 cylinder sleeves by a fair bit. The height is almost spot on so Im not thinking it will need to be trimmed. The one issue I see is that the lip at the top is also a fair bit larger and will be over the holes that the dowel pins go into. When I spoke with LA sleeve last week they said they prefer to let that happen and rebore the dowel holes. The piston will never be the perfect fit when you're doing this. Sleeves come undersized a bit and don't have an internal surface finish until they are done. This is because pistons vary slightly and once installed into a cylinder things can distort slightly. So the process goes remove old sleeve, machine bare aluminum cylinder to fit new sleeve, install new sleeve, FINISH BORE AND HONE SLEEVE TO PISTON SPECS. I don't see at this time a larger oversize piston for future bores and personally don't care to much about that. Now also understand that you're going to have to machine the case mouth as the new sleeve is also larger than any 225 sleeve. Ive had this done before multiple times and its no big deal. you already know about the output shaft, left cover ect. Fair warning my current ttr225 cases 01 model I believe didnt come bored for a kicker. I had it done and its possible but your 04 cases may not either. By this I mean the right cover AND the actual right side case. I am waiting for a piston and crank pin and things are all headed off for final work. I am having LA sleeve machine and install the ya5679, ken occonor is rebuilding my crank shaft, case machining done local by a friend for beer, some one in California (twbrians recommendation) machined the output shaft, and I will do all the wrenching. LA sleeve quoted me 250 for the sleeve itself and all of the machine work to install it and ill tell you that's more than fair. Do yourself a favor and send it to the place that makes the sleeves and does it all day every day. Now a closing statement then Ill include some pics past and present....... Your TW will never be fast and this isn't cheap. If you want significantly more power buy something else that has more power and better chassis/brakes/suspension. I spent over 1000 bucks last time on the 225 and that's what i'm doing again on the 250. If you're brave and like to play press forward as it is a fun process, but be prepared to shell out and don't cut corners. Unless you know the condition I would (and did) replace all bottom end bearings, valves, valve springs, all seals and gaskets, cam chain guides, cam chain, and have the crank rebuilt (crank pin, con rod, big end bearing). I will be keeping a good thread on the 250 as I go since theres not as much info on it. Good luck

    ttr225 cylinder with sleeve removed
    Untitled by dolphaxel, on Flickr
    heres where the kicker goes and you can see its not machined
    Untitled by dolphaxel, on Flickr
    after I did the machining
    Untitled by dolphaxel, on Flickr
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