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SC500 build
- turbodan
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SC500 build was created by turbodan
The biggest problem was the top end. They're scarce and almost always clapped out. I picked up a core and sent it off to Rich Taylor for a resleeve. While that was in process I gathered up a NOS crank, a set of cases and a transmission. Today the cylinder came back, shiny and new.
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- turbodan
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Replied by turbodan on topic SC500 build
Cylinder base machining is an option but when I need to subtract ten degrees from the exhaust port it would be a hell of a lot, and I would have to raise the transfers back up and make a large spacer for the top of the cylinder. Instead, I requested the port roof be lowered by 3mm to get the timing down into what I consider to be a reasonable range. This reduces exhaust port timing to about 185 degrees. Not exactly conservative but much more sensible than the original timing.
One thing I discovered with the DT360A is the unsuitability of the stock six petal reed block. It's too small for the soft spoken DT. It's certainly too small for the MX360 and it's wildly inappropriate for the SC500. Despite this, Yamaha used the exact same part on all three motors. I will be running the 500 with a modern 250cc reed block, which is about as wide as I can go within the stock casting. This is a four petal block that my 360 responded very well to. Should help the 500 bottom to top.
The goal is to build a reliable SC motor that makes good bottom end and pulls like a train through the mid-top. The stock SC comes on like a solid fuel rocket at about 4500 RPM and peaks at 6500. It'll rev higher but considering the size and weight of this piston, that seems like abuse. Power falls off past peak but it does hold onto 35 horsepower until 8000 RPM if you don't have the sense to shift by that point. Reducing the exhaust timing shouldn't hurt peak power and I expect a significant boost at low revs, below the RPM which the pipe is providing a beneficial effect.
These things were not well received by the magazines and it doesn't seem like they sold a whole lot of a lot of them. The potential is there though. 496cc's is enough to have fun, even with an antiquated air cooled design.
I will be finishing the porting over the next few days in my spare time. I asked Rich to leave it as is, in it's somewhat unfinished state. Wouldn't be as much fun if I didn't do it myself. As resleeves go, the ports actually match up very well. It doesn't need much but a little blending here and there will help.
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- RT325
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Replied by RT325 on topic SC500 build
Just to add--keep it rich & oily-'i think'. Lucky to find a piston.
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- turbodan
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Replied by turbodan on topic SC500 build
I was considering using the DT 5 speed gearbox but when you have it in hand and you can see how lightly constructed those cogs are, I think most would have second thoughts. The 4 speed gear set is thick and chunky. Should have no problems with the 500 torque.
I have seen that old NZ moto footage. Looks fast but it's hard to tell. The dyno test in the '94 Dirt Bike magazine issue shows 39 hp at the rear wheel at 6500 RPM. Not bad at all. I don't know what to expect but it should be pretty stout. Modern reeds will help tremendously. The pipe is still up in the air too. The MX360 pipe won't fit and I have not found a decent SC pipe. I could weld up something but it's not going to fit like the original through the frame design, I'm just not that good. It may well end up being a 2003 KX250 pipe with a lengthened head pipe and midsection.
I will probably run the DT360 oil injection pump. Been working great on the hopped up DT, always plenty of oil in the crankcase. Seems excessive, would probably be just right for the 500. This bike is no hill climber or drag racer, just an occasional ride around town bike. Won't be run hard enough for long enough to be much of a challenge in terms of lubrication.
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- turbodan
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Replied by turbodan on topic SC500 build
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- turbodan
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Replied by turbodan on topic SC500 build
I have some extreme heat jb weld on the way to fill in behind the sleeve in the exhaust port. Hopefully that stuff holds up. It's not going to be directly in the exhaust gas stream, just right next to it.
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- RT325
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- mdscott
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Replied by mdscott on topic SC500 build
Roseville, Ca.
'06 GL1800
'97 KDX220
'75 Norton
'73 CB500K
'81 Honda CT110
'87 PW50
'64 McClane Edger
'02 Honda XR70R
‘69 Honda CL350
‘02 Honda XR70R
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- msavitt
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Replied by msavitt on topic SC500 build
might kick back like a mule, are you planning for a compression release?
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- turbodan
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Replied by turbodan on topic SC500 build
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