Getting very close now. I'm about halfway through adapting a modern 250 pipe to this thing and an SC exhaust finally comes up on ebay. More on that later.

The motor is assembled and sitting on the bench. I did have a little trouble with the clutch side cover. Turns out the SC cases were not drilled as deeply as the DT where the tach drive post mounts. The side cover refused to fully seat until I drilled the hole in the side cover about 8mm deeper. All good now.

The clutch got some oil holes drilled. That's another thing you see on modern stuff that I believe helps alleviate the clutch drag with the lever pulled in..

 

 

Went with the blue painted DT360 springs in the clutch. Of all the ones I have these had the longest free length and were the stiffest under compression. We'll see how it holds under power, hopefully soon. 

This mysterious object was listed as an SC500 pipe:

 

 

Apparently it's being sold by the guy that's always taking pictures of the Loch Ness Monster and Bigfoot.  Can't see shit.  I can tell from the few pics that are decent that it's got holes in it and will need some general repair.  Still far easier to fix one than to make one.  It does look like the proper 500 pipe though.  The joint between the stamped body and the head pipe is in the right spot.  When it gets here I'll have a better idea of what needs to be done.  Thank God somebody finally put one up though.  I've been scouring the Earth for several months.  Missed a pristine one back in May by filtering my eBay search to "used" condition only.  Who could have known that somebody was going to find a BRAND NEW NOS pipe in an old bike shop.  Whatever.  Someday I'll find a way to get over that,

 

I now have the final piece. The pipe arrived and it is indeed an SC500 pipe. Beat up, rusted out and in need of serious repairs. It is fixable though. You can really see the difference compared to the MX360 pipe:



I am also having some difficulty determining which dents are damage and which were intentional for clearance. This one, for example, appears to have been done intentionally. I will take it out though because it seriously disrupts the first half of the baffle cone.

 

I also splurged on some proper clutch springs. Barnett had them in stock. Good quality parts and much stiffer than the best used springs I have. I have little concern for clutch slippage at this point.

It runs.

 

 

I was almost expecting to be disappointed considering how well the 360 is running. Didn't really want to pull that motor out but the time had come to wrap this up.

The power is there, this thing hauls serious ass. Geared 17/44 like I had on the 360 and you cannot keep the front wheel on the ground in first gear. The low end torque is a little soft, comparable to the 360. The midrange hit is very strong and it signs off abruptly around 6500. The four speed box isn't bad but I would prefer the five speed if not for the question of durability.

I will get some video as soon as the jetting is sorted out, provided it doesn't grenade before then. So far so good though, I've put about 20 miles on it and a few 80+ mph pulls with no distress.

 

What Reed Intake did you end up using?  I  am trying to make one good SC500 motor out of the 2 I have.  The first motor suffered from bad chain whack and had a derailer and other transmission issues.  The second one smelled like pond water when I opened it up.  It had been seized but transmission may be good.  I am not 100% that I have a good piston or not from the first motor ( I need to go get out of storage).  I am glad I found this post but still have a ton of questions.

I had stuffed a late KX250 reed block in there. You can use anything that fits, though substantial grinding is required for the KX block. A late KX125 block fits too with less grinding.

My 500 motor is back on the bench. It was not street appropriate in it's existing state, imagine that. I did make some improvements in porting that should improve it's character but I have not put the motor back in to test it again. The 360 with the custom pipe is running extremely well with gobs of power. It is also perfectly happy cruising at part throttle. The SC is more of an "on or off" type of delivery. It should be better with improved porting, my first time around didn't make many changes. Wanted to see what the stock baseline was and go from there, and the stock baseline is pretty rough.

DT250A reed cage is exactly as my old SC
Funny it is identical

cliff

Just a story Joe Lunati (Lunati cams) has a SC500 that he would drag race some of his buddies on the weekends in the dirt his buddies had a 501 Maico ,YZ 465 etc. last time I saw him he told me I could have is 500 he’s to old to ride anymore it was definitely not stock did all the go fast stuff money was no object I guess I need to go see if he still has it also probably has a lot of parts

I going by to see Lunati to see what he has I’m pretty sure he has a custom made chamber we had a local guy who made custom chambers hopefully he still has all his parts my guess he has pistons,cylinders and heads he didn’t like to lose drag racing. He was the smartest man I know on building engines 2 or 4 stroke his son Joey was the world champion go kart several times in the 2 and 4 stroke man I could tell some stories on the 5 hp Briggs motor he built he used the exhaust port for the intake and intake for the exhaust and made a killer cam and piston ( he also had a piston plant) it had so much compression it would blow the head off so he bolted it to the frame it sounded killer 

A proper pipe would add a bunch of power. The difference it made on my 360 going from the MX360 pipe to the long header custom pipe was huge once I got the porting and tuning right. The SC needs the same fix, long header with a fat midsection and a long baffle cone. Yamaha did what they could with the stock routing but to fit as much head pipe as a big bore needs it's just going to have to stick out a bit as it snakes out to the left then back across to the right before it goes up and over.

The pipe on my 360 starts to come on at 2800 RPM and pulls to 6500. If I could have gotten the 500 to make power that low I would have been stoked. Might have helped me overlook the generally poor part throttle manners.