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Post by hopwheels on Aug 17, 2006 12:55:21 GMT -5
I'm picking up a super-cheap TT500 this weekend (mainly for the aluminum swingarm, which based on current eBay prices, is what I'm paying for the whole bike!) Anyway, my question is... is the TT500 engine a better platform to build a race engine from, as opposed to the SR? What are the pros and cons? Thanks guys!
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Post by buddyj on Aug 19, 2006 8:45:30 GMT -5
IIRC, the TT and the XT share the same motor. The SR motor is modified with larger valves and stuff. To me, it seems that for a race application, you'd want the big valve, high flow head. Wish i could find a cheap SR/TT/XT  |
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Post by StewRoss on Aug 19, 2006 18:53:24 GMT -5
Hi Gary, Here's a collection of thoughts...(...and yes, a cheap TT would be nice...). The SR has a larger inlet valve...1mm I think..and larger head finning etc. Always better for racing...however an SR head would go straight on to a TT in any case. I recall seeing a pic of a late model XT from the US that appeared (...well from magazine pics anyway...) to have what looked almost like SR engines painted black...SR head, no points etc....you'd guys would know better than I on this...1981??? Otherwise depending on what ignition system you wanted, it probably wouldn't make a huge difference. If the TT has points ignition etc. then at least it would be easy to maintain and fix. This is what I have in the DCM... The flywheel magneto's never need any batteries which is a plus. Kick or push and go. The TT only has two bottom coils. No need for charging up batteries before the race as I have to do on my Honda. Of course the SR's can get away with no battery as well. People use the XT.TT as much for the lighter frame as anything else as I understand it... Sjef...Wizz954??? SR  |
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Post by frankyb on Aug 20, 2006 2:27:41 GMT -5
hi hopwheels, re tt sr differences, apart from already mentioned head and valves the tt crank is lighter so it spins the motor up quicker. this also means less engine braking and less torque.the tt frame is a little different from the sr, and supposedly has thicker wall tubes.sr stator will bolt straight in, much better than points. hope this helps, cheers franky b.
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Post by hopwheels on Aug 22, 2006 23:35:20 GMT -5
Thank guys. I did end up traveling on Sunday up the coast (about 530 mi. roundtrip) for the TT. Man, I've really got this thumper-itis baaaad. That swingarm's coming off pretty straight away, not sure about the rest. I found a guy locally that does polishing and porting, and since I have a choice which engine type to send him, thought I'd ask. Sounds like (since I'm feeling like these SR stators are a bit of a ticking time bomb) that a TT case (for the ignition) and SR head would be the ticket?
Gary
Hopwheels
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Post by StewRoss on Aug 23, 2006 3:53:43 GMT -5
Hi Gary, At least the TT system is easily fixed and simple to play around with. From my experience, all that ever goes wrong is the condensor...so get a spare just in case...and the points wearing...easily fixed. It's also usefull to get a white business card or similar and run it between the points contacts now and then to clean them up...I used to do this at the beginning of the day, before a ride. The best ignition of course would be a dedicated racing CDI or similar...not a cheap option however...  SR |
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Post by frankyb on Aug 23, 2006 6:57:25 GMT -5
Hi hopwheels, my sr dirttrack motor has had all charging and lighting coils unwound and left bare. From memory that only leaves two windings and the little trigger coil. I think there is only four wires that run to the cdi box, and a 10 amp wire to the coil. Splice a single wire kill switch that earths on the bars when you push the button into the 10 amp wire, and you have afairly cheap reliable ignition. I havent touched mine in about four years, just checked timing after top end rebuild. cheers franky b.
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Post by wizz954 on Aug 24, 2006 23:17:57 GMT -5
I have only started playing around with SRs since February this year, so I don't have as much background as some of the other guys but I have learnt a lot in a short space of time!
The biggest difference between dirt and road racing is the amount of time the engine spends at full throttle so keeping the engine cool is the priority. If the SR head has bigger fins then that's the way to go, but add an oil cooler to be safe. I melted my top end first time out and it only took one lap on a hot day so it's important to keep things cool!
The SR ignition I have seems to be OK so far... the stator has been rewound at some time in its past and looks like a good job. The motor can run without the battery which is a good thing, but I've been told to run a big capacitor (battery eliminator) if not running the battery.
I've heard the TT frame is stronger than the SR frame so maybe better for racing, but I've not found any real issues with the SR frame so far. The suspension is the area you need to get fixed for better lap times.
Crank and flywheel weight is something of a personal choice depending on whether you want good grunt or good top end power as Franky B has alluded to.
Let us know how you go, I'm really interested to hear how your development progresses.
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Post by hopwheels on Aug 25, 2006 0:22:06 GMT -5
Will do! I think I'm sticking with the SR motor in total. The frame I have is an XT500, which according to some other online info is more rigid than the SR as well. I think it's identical to the TT. Oil cooler is definitely on the list. I think I'm going to keep the TT intact, except for the swingarm. Probably swap out the alloy one for a steel XT one and sell it... (or perhaps an Aberg replica... yeah right!)
Here's what's in store for the SR race motor rebuild (depending on funds as always...)
90mm JE piston
Head ported and polished
Megacycle #25162 cam
RD valve springs and titanium retainers
Carillo rod
new valves and rockers
Barnett clutch
Going to try and sort out the electrical issue on my '79 SR cafe bike this weekend though and try to get it started. I'll keep you guys posted.
Gary
Hopwheels
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Post by kentrex on Aug 25, 2006 2:01:44 GMT -5
Hi
Thought I'd add my thoughts to the frame debate. The view's been expressed that the XT/TT frame offers more rigidity, I doubt that is the case for a couple of reasons. I read that at the time of it's launch, Yamaha actually made the point that the SR frame was made of thicker walled tubing. And if you check out the area of the swing arm mounting point (a prime source of flex on any bike used in earnest) you can see that on the XT it is a single plate, whereas on the SR it's a much more heavily gussetted affair. The SR weighs a fair bit more than an XT and I'g guess most of that weight is down to the frame
Cheers, Ken
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Post by StewRoss on Aug 25, 2006 4:07:22 GMT -5
Hi, Yes, I think that the reason that some racers use the dirt bike frame is purely down to weight...oh and maybe that they have made their bikes from XT/TT's in the first place... SR |
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Post by frankyb on Aug 25, 2006 18:49:53 GMT -5
Hi all, I think the main deal re sr versus xt frames, here in aus, and certainly in my case, was availability. There were a lot more xt/tt units sold here than sr units,so used parts always favored the dirt bikes. What kentrex says about the swingarm pivot is true, i think a road oriented frame is always going to be a better option on the tarmac. cheers franky b.
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