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Ty250 Engine Mods


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#1 terry

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Posted 21 March 2006 - 08:29 PM

I just wondered what some of the engine mods people do to the TY250 engine. I rode another TY a while back and it had unreal power from idle and pulled like a train. That engine pulled like a modern engine and I just woudered what type of modifications had been made to the motor. I have had mine a while now and sold the modern bike so I am only going to ride the TY. It suits me and I love riding it but I think I am ready to see what can be done with one. Anybody taken thier TY past stock? I just picked up another frame last weekend and am going to put some Hebo pegs on it while moving them down and back. Then I might have the frame powder coated. Next will be to find another motor and build it up. I am just looking for what is possible, what works and what to stay away from. At this point, money and time are not an issue. What have you done to yours??


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#2 thomas_trial

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Posted 21 March 2006 - 08:43 PM

I have had two different TY250 in the late 80'th and early 90'th.

Here is what I did to power up the TY

- I changed the airfilter cap, so it had a much bigger hole -> less pressure drop -> more power

- I installed a power exhaust (back part of exhaust). That really made a big difference, it had the same power at very low rpm but from the middle and up into the high rpm’s it was like having a new engine.

- If the front part of the exhaust is full of old residues it has no power, so clean it out. I used to burn the residues out one time a year.

- The last thing would be to change the piston rings and check the tolerance between cylinder and cylinder.

I hope you can use my advice. Good luck with powering up your TY250.
Do it today, tomorrow doesn't exist.

#3 terry

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Posted 21 March 2006 - 08:57 PM

I appreciate it. I just rebored it and put a new piston and rings. I also have an extra mid muffler that I have cut in half with a dremel tool (lots of little wheels required but sure made a nice cut) to repack. I saw somewhere some mods you could do inside to put a little more bottom end in the bike but right now it is just cut in half. If you know what to do let me know. I also put a Mikuni on mine when the TK was worn out and that made a difference. Has anyone tried the Boysen reeds? Might try a set.

#4 andy m

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Posted 21 March 2006 - 10:38 PM

:) Hi, I dont know whether you have a twinshock or mono. I have just purchased a pinky that has been bored to 270 and the inlet manifold has been shortened, means you have the barrel machined to do this. J.K Hirst do 270 pistons. I know the bike pulls well and is still soft but as I only bought it on Sunday I cant really tell you any more. Good luck with it.
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#5 feetupfun

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Posted 22 March 2006 - 07:37 AM

I just wondered what some of the engine mods people do to the TY250 engine. I rode another TY a while back and it had unreal power from idle and pulled like a train.

<{POST_SNAPBACK}>

Please tell us which TY250 you are talking about. There are three different TY250 twinshock engines (TY250, TY250B and the later series from 1976 onwards with prefix 493) and then there are the air-cooled monoshock series engines and the watercooled TY250Z models.
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#6 terry

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Posted 22 March 2006 - 03:35 PM

My TY is a '74 model. I don't know if it is a standard TY250 or a TY250B. The bike I rode has different engine side covers and I think it is a '76. My engine side covers have 250 on the side. Mine also hade a fiberglass skid pan when I first got it. It is a twin shock and replacing the shocks with Falcons was money well spent.

#7 feetupfun

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Posted 23 March 2006 - 08:27 AM

Thanks Terry. It sounds like yours is the first model TY250 which some call TY250A. The cylinder porting and a few other less important motor internals on these is different to the later TY250 twinshock motors. A standard TY250B and later TY250 twinshock motor will pull noticably harder at low to mid RPM than the first TY250 due to their improved porting. The other changes between the first TY250 and later models is that the later ones have a lighter conrod, lighter(mass)clutch and a heavier flywheel weight.
This means that one option for you for more grunt is to get the barrel and head from or fit a whole motor from a later model TY250.
Another option for more grunt is to big bore your motor to 320cc which requires a bigger cylinder sleeve and piston, the head welded and machined and the crankcases machined to suit the sleeve. You may also need to raise the cylinder with a barrel spacer if the piston you use has a lower gudgeon pin location.
Another option for better low RPM power is to fit boyesen reeds and a reed case spacer.
An option for more power in the midrange is to have a specially designed expansion chamber and muffler made up to replace the standard exhaust.
I suggest that you have a ride of an unmodified B or later model TY250 before you decide on a course of action.
There is nothing good or bad, but thinking makes it so

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#8 terry

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Posted 23 March 2006 - 04:25 PM

I have been looking around for another TY instead of getting another modern bike. Sounds like I would be better to get a newer model 250 than another '74 model. What year models would you look for? I have a '74 and see alot of '74 models but it sounds like a later model would be a better bike to start with. I just don't seem to see that many '75 to '76 250's for sale. It seems like I see more 175cc bikes that are '75 and '76 models but not too many 250's. I think I might try the Boysen reeds and spacer in my bike and leave that one alone and start looking for another one. That is the beauty of old bikes, you can afford to spend a little on it and still not have as much in it as a used modern bike. If I spent 2000.00 on a TY I would have one nice bike. Who knows, I just might do it!!!! Thanks for the help.

#9 dgshannon

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Posted 23 March 2006 - 07:23 PM

Being in Tennessee, it would be tough for you to be any closer to a major source of knowledge on creating a performance TY engine.

Contact Bob Ginder at B&J Racing http://www.bjracing.com/ and he will certianly be able to help you out.

- Darrell
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but they are no substitute for brains!

#10 terry

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Posted 23 March 2006 - 08:03 PM

Bob's personal TY is the bike I have ridden. What a sweet machine!! He has worked on mine and will again.


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