Farm boy’s Rattle-can Racer

farmer92

Coast to Coast
So this is hopefully going to be completed by easter, or not so long after.
Wanted to buy a few T500 parts, but the fellow made me a deal for everything so he could clear out some space.
The idea here is a quick finish, fun little track days bike. Not trying to make it race legal, just something to beat around the track a few times a year. Most of the work was already done so inspection and tune up should be all that’s required.

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Starting with a standard t500 frame, braced and been cut off about 12” past the rear shock mounts. Early fz600 forks, twin disk brakes with a nicely seized calliper somewhere. Fairing is a little rough, but it’ll do, maybe a new windscreen will be needed.
Needs a front fender and an inner rear fender at the least. Also needs a belly pan, to be made at some point.

To the engine, twingle crank out.
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Standard crank in and kickstart back in. (For now)
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I then proceeded to snap off one of the screws holding the seal over the output shaft...
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After a few man tears, a bottle of blonde des Cantons from the local micro brewery, it was time to bust out the welder.

Best use for header wrap, heat proofing anything but headers...
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45 minutes, and 7 attempts later i was rewarded with this.
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Time to get everything buttoned up to check squish clearance.
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Interestingly, the engine was put together with a single ring per piston
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Got 2 sets of fresh rings ordered, don’t think this motor will see any of the advantages of running single ringed. Any 2 stroke experts have any insight?

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10mm squish band on the heads, roughly 50% squish area. Going to set the squish clearance somewhere between 1mm and 1.4mm.

Cylinders seem to be ported to the old tr500 specs, going to make pipes to match.
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I do “have” these pipes,
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Unfortunately the dumbass i am left them in my uncles back yard 700km away when i picked up the stuff...
Might try them out when he brings them at easter.

Going with what seem to be 38mm mikunis.
I was told one set was 36mm and another 38, but both sets i got measured the same. Not sure what they came off of, they’ll do nicely i thinks.

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Electronic Ignition is off a yamaha tr2 i believe, we’ll see how this goes.
Any suggestions on timing?
Going to go with the stock timing, unless suggested otherwise.
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That’s all for now, thanks for checkin in.
 
Interesting project. The heads looks like they were machined by RKTek. Only people I know that create that rippled squish band look. They should work well.

Ignition is Hitachi CDI from a TD or TR or early TZ but pickups look to be in off positions. They should be 180 degrees apart. Do you have the CDI box that goes with that and the right single lead coils? Rex's speed shop in the UK makes replacement CDI boxes and can sell you a pair of matched coils to go with it.

Single thin rings are great on race motors that above above 8,000. Below that, a 2 ring makes marginally more power and that's where your motor will run best.

Is that a straight cut primary gear set there? That should make a difference to crank bearing life as well as to power.

Nice starting point. No idea why he wanted to try a 360 degree crank though. That's a little odd.
 
Hey teazer, I’m not sure what was going on with this whole thing. Been trying to get in touch with the fellow who built it, see what he can tell me. He ran a machine shop in brampton Ontario, so i just figured he might have done the work.

Pickups can be moved around i believe, probably one was out a bit because it wasn’t being used with the 360 crank.
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I got a few spares, only 2 rotors though.
Thanks for the tip on the coils, will probably have to pick some up.

The primaries are indeed straight cut, ratio is a touch different i think, two teeth less than stock on the crank side. 26 vs 28

So any drawbacks to the single ring in terms of engine wear?
Thought the advantages were kinda negligent under 9k.
 
Yes, advantages at the revs that motor will reach are all losses..... Fit both rings on both pistons for sure.

The aluminum CDI marked TIA- 02 is the correct twin cylinder unit. Not sure what the plastic box is from, but probably a later model singles - as are the other stators.

Yamaha taper/diameter is smaller than Suzuki, so it may need to be machined out. I have a Motoplat that I believe is bored for a T500. Fortunately I have a few of them with different rotors and coils. Do not be tempted to try to machine down the crank to fit the rotor. The rotor can be bored to fit the crank though if necessary.

BTW, check the resistances of the low speed and high speed coils and the pickups to see if the stator is usable. I have had to have a couple of them rewound in the past. I have a test jig that I check ignitions on to see where they start to spark. If they don't fire until 800 or more revs, the low speed coil is dead. And if they fire at low revs and flame out higher up or the timing retards, the high speed coil is dead.

What are the 3 digit serial numbers on the CDI box and stator mount? They are supposed to be somewhat close to each other.
 
The numbers of the three cdi boxes i have are as follows.
Tia-02-01-2f
Tia02-01-109
Tia02-16a-108

Here are the three smaller stator units
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There was a fourth, significantly beefier unit, which looked to be the double of one of these.

These would run with a wasted spark correct? So it just fires both plugs every 180 degrees?

Edit: i just realized there are two different rotors i have. One is thicker, and has a bar magnet in it as well as a small U shaped magnet on another layer, to be used with the beefier unit. The other rotor simply has a bar magnet going from one side to the other, to go with one of the three stators above.

Or i am completely off base and in deep shit...
 
Also, upon closer inspection it would seem that their solution to making the rotors fit the gt crank was to turn up a reducer that fits halfway on each.
Not sure i like that idea... it sticks the rotor 3/4 of an inch further out.
 
Those stators won't work with the TD CDI as far as I know. The stator should have two field coils and two pick ups. The thick one in that cardboard box in your earlier picture. I'll have to check my Hitachi race rotors but it should have two small steel cores that act on the pick ups (triggers) and a larger core that generates the pulse. CDI is probably TIA02 -01- 402 Rotor is probably something like M200-08-3xx or M200-03 and the stator should be stamped something like 403 or 123 or something similar.

I have one here that the CDI is TIA02-01-304 and the stator is also #304 - matching. I had one that was TIA02-01-210 and had stator #403 - not matching but tested OK on the jig.
 
After a bit of searching around on tz pages i found this

http://web.archive.org/web/20030810221829/http://tzrewinds.co.uk:80/database.htm#1

The tia02-16 cdi goes with the three single coil stators. They are early 80’s TZ250, 5f7-11 is on both the cdi and stators.
The tz engines as you know where parallel twins, but had 2 sparks per revolution so these can be run.

The tia02-01 cdi boxes go with the larger tz350 stator.
Rotor does have the 2 cores, and is stamped m200-08

Have not verified if any at all match up. Will check resistance of windings next.


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Nice build. As for squish-clearance, definitely don't go over 1mm or all the headwork would be more or less negated by the huge clearance. I personally keep squish as tight as possible on sporty two-strokes. So I'd aim for 0.7 to 0.8mm as the piston crowns will be cooled a lot better by the faster flow. I mostly do RDs though, so you may want to check with someone who knows T500 cranks a bit better, especially as I have no personal experience with them. What kind of bore & stroke are we talking here?

Cheers
Greg
 
Hi Greg,

The bore is 71mm and the stroke is 64mm. The squish band is about 10mm wide.
The 1mm - 1.4mm range i got from A.G.Bell Two Stroke Performance book, it was suggested 1-1.4mm min clearance for 250cc cylinders, and the next range down was 0.7-0.9mm and was for 100-125cc cylinders. Just noticed there is no range for 125-175... probably somewhere between .8 and 1.2mm i would guess.
I was going to aim for around 1mm if i can (fingers crossed).
I don’t know how far the pistons can stretch upwards at 9k rpm but i’m hoping to not find out the hard way.

Thanks
Jordan


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I did wonder if the single pickup units were form a J/K/L. They have a much bigger retard function built in to suit the higher revs of those motors. I'd start with the twin pick up unit with flat timing. A Gt500 doesn't seem to respond well to much advance or retard, so keep it simple and set timing to 19 degrees to start with.

Do not set squish too tight. Those rods stretch a bit at top revs. I would start by measuring what you have and set it for 1.0 -1.2mm Even with a narrow squish band, that should work fine. You can tighten it up later if you want more low to mid range and don't mind losing a little at the top end. Ask Jeff (Zunspec) on sundial what timing he runs on his race motors.
 
Teazer, do you by any chance have any of the ignition maps for either of these cdi boxes?
I can’t seem to find anything concrete but what i have found does seem to be a sharp increase in advance early on and then gradually being retarded after about 5k rpm.


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That's the only chart I have seen for them. The older twins are exactly like the chart on TZ Rewinds. That Later TZ chart looks like a typical late model ignition curve.
 
That is indeed quite a step up from the pesky lil' RDs I play around with, when it comes to bore and stroke. The thing is, once you're over 1mm the squishband won't have a large effect anymore. But I agree with Teazer, better play it safe, than be sorry. Still in this respect I'd aim for 1mm of clearance or slightly below.

Either way, keep us posted this is truly one of the more interesting builds on here.
Greg
 
Thanks for the interest guys, glad to have you all on board.

Haven’t set the squish yet, but did manage to dry fit tz350 ignition the way the PO had planned.
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I don’t like it.
The magneto/rotor sits an inch out from the crank bearing, and the taper has been trimmed down to yamaha size.
I don’t want a repeat of this.
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I also don’t like how the stator mounts into place.
Basically the crank cases have a recess machined into them so the backing plate of the stator is fixed in the XY plane, but is allowed to rotate. There is one bolt that holds the plate in place at the top, it also prevents it from rotating. You can kinda see the lip here.
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There isn’t a lot of clearance between the rotor and the stator, i would hate to find some destruction down there one day.

Side note, i think he was trying to mimic the tz250 crank with the twingle crank.
He also seems to have made up a new one piece extended crank pin with a yamaha taper on it.
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The joke now is that i have no choice but to run the TZ ignitions, because all the cranks have been modified to do so except the twingle.

Hurray
 
Also, i measured the interior diameter of the carbs outlets, all 4 measure 37mm at the edge and they narrow as i measure closer to the slide.

Would it be safe to assume these are in fact 36mm carbs?


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Mmmmm, blonde des Cantons - that'll take the edge off anything, even a sheared bolt ;)

Don't know much about these bikes (i.e. anything) but do know it's in good hands and do know I love that fairing. Here's to an Easter win!
 
That ignition looks right. On a TZ or RD that's how it mounts. That looks just like a TZ set up.

Yamaha cases have two standoffs for the mounting bolts 180 degrees apart. They also have a 3 hole set up just like yours that works well with a Motoplat.

You will probably have to add a small amount of weld for the bottom bolt.

BTW, have you cc'd the heads yet? They look very shallow and if so compression may be a touch high
 
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