Help Planning My 1988 Ty250r Engine Rebuild

[kuelmuel]

Hello everyone,

I am planning to rebuild my engine later on in the year, and was wondering about a few things.

I am going to give it a new big end and little end, along with main bearing etc, the plan is to do it all at once then I won't need to strip it again for a while.

If it needs a rebore, I want to take it out to 270, but I also will want to get the inlet shortened and get the head and the top of the barrel machined down a bit to raise the compression. I have heard that Birketts are the best place to get this done, but do they have a website I could look at? If not does anyone have a phone number to hand for them?

I also have a very large amount of modifications to do to the rest of it, found here http://myweb.cableone.net/bcanderson/Mods.htm, these are for the TY350, but I think that they can be adapted for my bike, right? I don't plan to do them all at once. I will leave the carb until after my newly rebuilt engine has run in properly. I am going to modify the footpegs, rear shock (extended and preloaded), I don't think that there is anything else, but I am bound to think of things as I go along.

Thanks for any help in advance.

EDIT: I was wondering how much you think this is going to cost me, I can get any engineering fabrication work done for free, the only mod I can't get done is shortening the inlet manifold, as I can't get aluminium welding done.

Edited April 15, 2007 by KuelMuel

[scottt]

For Birketts site click here it doesnt get updated much (if at all) but the contact numbers are there and they are very helpfull.

Scott.

[arun1664]

I would second Scott T's comments abouts Birkett's, They did a rebore on my Beta earlier in the year, very helpful & good work fom their workshop.

[hughesy]

To be honest KuelMuel the 270 isn't really worth doing, it involves boring out so the liner is at it's thinnest limit, using a DT/IT piston and then machining the bottom of the barrel to get the port timing and squish back. I've had "270"'s before and don't get me wrong it was a lovely bike but not worth the extra hassle in my opinion, the extra capacity worked out at about 12cc

Instead, get the barrel ported (mainly raising and opening out the exhaust port). tidy up the transfer ports, shorten the inlet, lighten the flywheel and advance the ignition. I've recently done my Pinkie and am well happy with the motor.

[kuelmuel]

Thanks for that hughesy, do you know where I can get it ported and the inlet shortened?

I'm not sure if I'll go that far yet, I might just restore it, as it is a completely original UK bike.

EDIT: The reason I am thinking about taking it out to 270 is because it is already .50 oversize, but now I have read you comments I think I will go for .75 or 1.00 oversize.

Edited April 15, 2007 by KuelMuel

[scott_king]

Hey

I have done the lower foot peg mod and it does improve the bike handling. Takes abit of getting used to but I would say it is definetly worth it.

Cheers

Scott

[pitley]

Kuel mule, you need to PM paioli. He will give you an honest opinion of the 270.

He has gone back to the 250..

[scotty]

Whats wrong with the 250? ive got two pinkys (both 250's) does the 270 make the bike more responsive? if so ill leave mine as is!

ive got the mick andrews alloy silencer fitted to one , the others got a WES on it! the one with the M/A silencer runs beautifully weather this silencer makes the difference who knows? if think there both std barrels etc! as for moving the footrests back more im not to sure on this as i think the ty250r/pinky are already wheelie prone as they are , ive got loads of broken rear mudguards to prove it!

[scottt]

do you know where I can get it ported?

Birketts will do that for you.

Scott.

[andy m]

I bought a 270 Pinky off ebay, (big mistake) it was too sharp, almost like an old scrambler. Pinking and not running well at all. Sold it, but I will have another, unmolested one this time. Someone messed up a proven bike. Dont waste your money on a 270 conversion. Maybe Birketts can do something with the 250 porting, but I dont know about that. Yamaha knew what they were doing when they produced that one. I beleive the inlet mod improves response as long as its done properly ..

Edited April 15, 2007 by bo drinker

[scotty]

Thats what i thought the whole point of having the softest power you could get from an engine ( were talking older bikes here!) the better! the sharper more responsive an engine is the harder it is to control (IMHO) THOUGH if your an expert or at the top of the ladder then perhaps your better for it? your right bo drinker when yamaha designed this bike they made it as near perfect you could get a trials bike (at the time!)

likewise the twinshock ty250 got the engine spot on! only the chassis was lagging well behind until shirty and mick andrews sorted it out!