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al pal
Level 1 Member
Victoria
2 Posts |
 Posted - 13 Feb 2006 : 09:15:17 AM
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Hi, I'm starting to build a T250 race bike and I'm hoping for some advice on where to get my crank balanced, and does anyone have any info on where to get electronic ignitions? Any other help/advice would be gladly welcome. Cheers.
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acotrel
Advanced Member
Victoria
2147 Posts |
Posted - 13 Feb 2006 : 8:31:12 PM
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I built a T250 in the 70s which was pretty successful. When I had it I blew off a good TZ350G in a straight line on Ballarat Airstrip. I sold it to Ian Whitedead in the Hartwell Club, and he won 23 races and 5 championships on it.
The T250 had 32mm carbies off a 315 (T350).
I used T20 Rods and pistons which meant the inlet ports could be about 8mm wider. I bought 2 new T20 rods and found that the weights when measured end to end were dramatically different. I ground a fair bit off the little end of one of them. Then I polished both rods which is probably a mistake, as they are shot peened and copper plated as standard to relieve stress and stop them breaking.
There are a couple of problems in using a T250. It's difficult to get a CR gearbox, where if you develop an R5 Yamaha, you can get racing boxes which fit. First gear on the T250 is just too low, and if you pick it up while racing, it's pretty horrible.
I didn't rebalance the crank, as the motor is 180 degrees crank throws, so they balance themselves out. The rods were balanced end to end.
A big problem is the ignition system, I wouldn't use points under any circumstances. A Krober is good news. A lot of problems in tuning 2 strokes come from the ignition system.
If you are running alcohol, I'd use standard advance, and I wouldn't reshape the head or change the volume.
The height of the transfers is critical, and I wouldn't lift them beyond 29.5mm from the top of the barrel. I only removed about 3 mm of metal from the top of the exhaust, and lowered the bottom of the inlet about 5mm.
The T20 pistons are wider at the skirt than T250, I only ran the top ring.
If you try to make a TZ out of a T250, it will be a disaster. You can only rev the T250 to about 8,500 revs before blowing up, and a TZ power band starts at 8,000 revs and goes to 12,000 or more if you're brave.
I used to set the oil pump at about quarter open, and used Castrol M with the Alky. Add some to the fuel.
The porting concept of a T250 is pretty different to that of a TZ, and the motor characteristics are radically different.
The TR250 works racer was a bit faster than a TD2 Yamaha.
I gave all the Peter Jones data sheets I had to Don Brisbane in Shepparton, who's got my old T250, and still races it. The frame is different, but looks the same as when I built it, and I believe all owners have copied, and carried on the porting.
If you ring Winton, theyll give you Don's number.
The chambers on my old T250 were off TZ250 with remade header pipes. You might be able to buy the bike.
If you want to use alky, put another post on this forum. It's the way to really get a two stroke going. |
Is your machine authentic or merely eligible? |
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acotrel
Advanced Member
Victoria
2147 Posts |
Posted - 13 Feb 2006 : 8:34:43 PM
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| If you need a crank rebuild, and you live in Melbourne, have a look for Eddie Catton. He's still around somewehere, Guys like Graham Lang in Sandringham Club should know where to find him. |
Is your machine authentic or merely eligible? |
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slimphil
Level 1 Member
Victoria
5 Posts |
Posted - 14 Jul 2010 : 10:06:43 PM
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Hi Al pal
Im new to the forum and have a
gt250 that I want to biuld up. You could start looking for electronic ignitions by calling city autolecs they do bike electricals and there very helpful. Will digg up the number if you want. |
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Alan Cotterell
In a time out state
Victoria
421 Posts |
Posted - 14 Jul 2010 : 10:52:44 PM
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| the ignition system is the most critical part of a two stroke. Have a look at the Electrix ad in Classic Racer, they're a really good thing, and easy to import. You shouldn't have to rebalance the crank, but it must be straightened, and the bearings and seals replaced. I think you'll find that TM125 pistons will fit, and they're lighter and have thinner rings than T250. I used T20 rods in my motor the little end is smaller, lighter, and stronger. |
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slimphil
Level 1 Member
Victoria
5 Posts |
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Alan Cotterell
In a time out state
Victoria
421 Posts |
Posted - 04 Aug 2010 : 08:09:44 AM
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| If you use T20 rods, you will be using T20 pistons, the skirts are wider than the T250 ones, and you can use a wider inlet port. |
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Alan Cotterell
In a time out state
Victoria
421 Posts |
Posted - 05 Aug 2010 : 09:01:03 AM
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| To use methanol in a T250 with 32mm mikunis the needle jet size is 0.113in. using a 5DP needle, and the main is about 500 (amal size)- just thought you might like to know this. |
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