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I have corresponded with him on facebook.  He had an interesting GT750 tracker there a couple of months ago.  Hi crank videos look promising but I have a local two stroke guy near me with his own machine shop.  He's a two stroke expert that worked at Johnson and then at Aaen in Racine, WI so he knows his stuff and builds and races hydroplanes.  Before that I sent all my GT750 cranks to Bill Bune Enterprises and my Yamaha TZ and RD cranks to Rick Merhar in Ohio.

It's nice to have choices though.

That was an interesting video, but the one on the BMW sidecar they too racing was more impressive in many ways.  Some amazing shots of Ari Henning hanging out the side of the chair at Shannonville.  I know it's not a two stroke, but a great video none the less.

I read an article years ago that IIRC concluded that 2 ring pistons made more power below something like 9,000 rpms and single ring made more power above that point. 

The idea of running a single ring in a two ring piston has been tried many times but no one that tried it, that I know of, has ever published the results.  I would imagine that if the piston has relatively thick rings, like one from that era, then ring flutter would be an issue and so would sealing if a ring is removed.  If the piston in question had thin rings - say 0.8mm to 1.0mm, then a single ring on a 2 ring piston would probably be OK as long as the ring land diameters were suitable.  I suspect that on a single ring piston they may be different.

Key thing in this instance, is that we are talking about a DS2 which won't rev very high before the clutch comes off and didn't make a huge amount of power, so why add to its stress and unreliability. If the OP is making a stronger crank, they could probably also find suitable 56mm pistons. 

Anyone remember how many rings in a TD1 piston? I suppose I could check the parts book if I could remember where I filed it.

Derek Pickard raced a DS2 Asama racer ie race kit back in the day in Australia but I have no idea if he's still around or what pistons he used.

I would hypothesize or guess that the frame tube is much lighter gauge that the average street bike frame. That bike isn't very heavy, fortunately, so you might get away with adding  a half tube to that bottom rail and weld the stand to that "outer tube" to spread the load.

What year/model?  I might (long shot) have a set in my stash.

Would also need to pre-heat the block and probably cut away a lot of metal just to get in there. I would be more tempted to machine in and press in an insert and ignore the rest of the pits.

What year/model?  I might (long shot) have a set in my stash.

It is fixable,  but will probably cost much more than finding a replacement cylinder.

Thanks for that info on sheet thickness.  I think it tells me to use 20 gauge for street chambers and 22 for lighter applications.

You might check teh length of those two sections to see if they are the same where they join. It is possible that one file is incorrect. BTW, I once had a good look at a really nice set of pipes that worked well and I realized that one cone was reversed on both pipes. Minor discrepancies don't seem to make a whole lot of difference at street levels of performance for some reason.

I have Bassani and jemco pipes and both have a step at at least one of joins. I suspect they would make slightly more power without those steps but not enough to make it cost effective for them to be perfect.  When I worked on a kart header pipe some years ago, the design that worked best was one which was closest to a smooth transition like a curve rather that sharp changes in direction or section.  I don't have software or the time to see if a continuous curve would work much better and if so by how much compared to different cones.  That's where hydro formed chambers might have a slight advantage.

Beautiful welding for sure.  Why do the last sections look like they are a size too large?  It almost looks like they are a step larger than the next smaller ones.  Probably an optical illusion.

And welding 22 gauge is super hard not to blow through.  Are pipes usually 20 gauge or 22?  I measured a few different pipes recently and metal thickness almost seemed to be 21 gauge which wouldn't make sense.

I remember that picture but couldn't find it when I was looking the other day. 

That exhaust is a mess for sure.  The small pits are not an issue but it would be best to have that floor welded or machined to take a spacer to replace the damaged metal.

I doubt that damage is from a crash.  It looks to be eaten away by caustic soda or someone put an oxy torch in the port to burn off carbon.  Either way it should be repaired or replaced. if anyone can repair it it's probably Josh at Bill Bune Enetrprises.

Thanks SoCal.  That's useful info.

When the fall on that side, the cover usually falls apart.  It's wide and thin.  Nice casting work but zero strength when a big fat bike lies down on it.

What happens next can be more serious.  I have one in the shop that was crashed on that side and it not only destroyed the rotor, but managed to bend the crankshaft.  In this case, the end was out of round by about .065" and had to be replaced.  The rest of the crank was fine though and the outer crank wheel was still round and it was only the part outside the bearing that was tweaked.  If anything is wrong with yours, Josh and his team should be able to make it right.   

Welded barrels sounds more serious though and most unusual.  Damaged exhaust threads are common enough and usually can be repaired by opening them out and welding in fresh metal and then drill and tap back to size. But I guess if a crash was bad enough and ripped off the pipes, that could cause substantial damage around the exhaust port.

Did you have any pictures of that damage or welding repair?

heres the thing. the ring is supposed to basically stop the leakage past the rod, which i get. but that leakage is a constant, albeit tiny, amount that can be compensated for by adjusting the valve. ergo, the ring isn't needed. ;)  .02

actually, thinking about it, you could lathe up a spacer with grooves around it , would basically do the same thing as the ring.

You may be right, but most later damper rod forks use a diagonally split phenolic resin piston ring to reduce that leakage an an aluminum spacer that restricts leakage would probably add too much stiction. Measure the ID of those fork legs and if it's around 28mm, I think that a spacer with a GL1000 or GT750 piston ring would work fine with less friction than racetech plastic rings.  In forks that already have a piston ring, the spaces is just a straight aluminum tube.  They don't need both seals/rings.

Misplaced cylinder sleeves are common on GTs and some are a long way out. Some match the heads but on many there is some offset between bores and chambers.

https://pinkpossum.com/GT750/GT750head.htm

That's why Suzuki and aftermarket suppliers supply head gaskets with 76-77mm bores so they don't overhang the bores. My preference is to use COmetic head gaskets with say a 72mm finished bore and then gently open up the stud holes as needed to let the gasket move to the correct position.   

On a stock motor, oversized (stock) gaskets are rarely a problem but if compression is raised they tend to detonate in that area and blow out the fire ring.

Tell us more about the crash damage.  I don't remember that being mentioned before.

when you get it its obvious what you need to do. looking at the rod from the top, the roll pin is pressed all the way across the opening. take the middle section out, to clear the bottom of the bolt/nut that protrudes into the rod. a dremel with a carbide bit to cut it i think is what i used.

as a side note, i did add preload adjusters from economy on my bikes since the original post. mine is on the lightweight rd, its about 115? lbs lighter than a stock bike, so i had to tune mine lighter, i used 5wt fork oil and actually reduced the preload a hair.  however, i've done this the other way as well. I know, for a fact, these make a huge difference (the emulators) when set up right.  heres the instructions for the XS forks, which the top is different than the earlier 34mm forks.

https://www.2strokeworld.net/wp-content/uploads/lightweight-rd/forks/fork-valve-emulators-1.pdf

That damper rod in the instructions is the same as late model RD250 or 400.  but on a 350 they really need a racetech adapter with piston ring IMHO.