1975 Yamaha RD350(LC) Preservation-mod Hellride

irk miller

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This project has moved to this location, as it was handed off from brother @Hurco550. See it’s previous build here.

I’m slowly taking inventory, doing the research, asking a million questions and prepping parts for the engine. The build officially begins with a paint strip and vapor hone of the LC top end:
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I also cleaned the frame and polished the tank and seat. The tank is fiberglass with a corner repair. Since I want to preserve the original paint, it’s still to be determined how, or if, I clean up the repair. More on that later.
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teazer

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Looks good already. So are we talking full race tune or something slightly less extreme? LC top end is a good upgrade and simple to execute. Love that seat. Looks like an MT125 or similar.
 

irk miller

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Looks good already. So are we talking full race tune or something slightly less extreme? LC top end is a good upgrade and simple to execute. Love that seat. Looks like an MT125 or similar.
I need to figure out how the tune works on these, particularly at the bottom end. I plan to make it street legal, but I would love to work it out on some road courses. At the same time, I frequent Carolina Dragway 30 min up the road. Even though it will carry the bodywork of a road racer, I'd still love to throw it in the bed of my C10 and work'em both out on some 1/8 mile runs. I imagine I'm looking at completely opposite bikes at the same time.
 

teazer

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For mild street rides, stock or light porting works fine... But there's always more to be wrung out of that combo. 400 trans is better than 350 six speed, but not a job stopper if you don't have one.

For road race, you need more top end, but you also need a wide enough powerband to get you from corner to corner. For drag race you can go mad with huge ports and reeds and pipes, so to get one tune for all three is not so easy.

Start with reeds. RZ/Banshee fit and they are the same size as TZ750, but that's not the best set up. My preference is ported YZ85 reeds but you have to very carefully open up the reed box. They flow more than RZ reeds but are slightly slimmer and need less material taken out.

Obviously, you will raise and widen the exhaust port and match that to larger transfer ports which are rather tiny to begin with. Carbs and compression are a personal choice but I like lots of compression and smallish carbs. 34s are teh carbs of choice and larger Lectrons are always a nice option if you can get a pair.

For ignition, there's a few self energizing systems including PVL, Hiatchi (TZ), Motoplat or Femsa or several new systems from HPI/VAPE and you could always upgrade to Ignitech or Zeeltronic if the budget will stand it.
 

irk miller

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Thank you so much, Teazer. I do have Banshee reeds, but I'll look at the YZ. Powerdynamo VAPE igniton and the carbs that came with the bike are VM28. I have VM34 carbs from a snowmobile with a priming bulb on my XS that I'm thinking of moving to the RD.

Pulled the cylinder studs, which was quite an adventure. I have to swap for RD400 cylinder studs to fit the LC top end. Fortunately, RD400 cylinder studs carry Yamaha part number 90116-08232-00, which means they are studs found in XS650's and about 12 other Yamahas, including the liquid cool RD350.
 

Hurco550

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Glad to see this thing in good hands. Check out the boxes. I'm pretty sure the Reed cages I bought were banshee but the reeds themselves were the yz reeds, and possibly needed trimmed? Also @teazer and I corresponded heavily on the porting of those lc cylinders. They are pretty closely matching to tz specs iirc and will likely run well at high revs with a short and wild power band. "Oh what a lovely day."
 

teazer

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Crankcase/cylinder studs are a PIA on Yamahas and come in a couple of lengths in which some combos of stud and sleeve nut work and some don't. How tall ar the LC cylinders compared to aircooled or is it the thicker heads that create the need for longer studs? I have gone through this a few times, especially with race top ends on street cases. 400 barrels are taller than RD250/350 so that makes sense, but I never measured a set of LC barrels or head.

And just for fun, TZ studs are shorter than air cooled RD250 studs and TZ350 are longer.

Interesting that RD350 cylinder studs are the same as the 6 short crankcase studs and RD400 barrel studs are the same as the 2 long crankcase studs.

With YZ85 reeds on a ported RD350 with JL pipes, we saw 52 rear wheel HP on the dyno with stock 28mm carbs. That bike was a bit of a hooligan but perfectly streetable - just not well suited to commuting :cool: Your LC hybrid could easily manage that or a little more.
 

teazer

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he missing part is no biggie. Ugly perhaps and not unusual. How are you planning to mount the water pump and route the hoses? LC and RZ go through the crankcases, TZ go around the outside.

This is an RD bottom end and TZ750 top end with Blaster reeds and modified side cover with a TZ water pump. You could try an LC side cover and pump and modify the cases. As you can see, the top part of that side cover is removed

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We used LC radiators on our TZs because they were cheaper and more plentiful but the lower outlet had to be cut and welded. Using an LC side cover with oil and water pumps would be a clean solution.

You could also look at a Banshee side case but the kickstarter shaft is different and the water pump drive needs a boss on the crankcase. Kickstarter is easy to machine up a bush to fit a banshee shaft into RD cases. On the drag bike I may leave the water pump off, but for street or track it's crucial - you could use an electric pump though.
 

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irk miller

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The LC head gives you 23mm to make up over the stock studs. We get another 28mm with the XS stud.

I think we'll go with an electric water pump. I have a TZ style radiator.
 

teazer

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LC but cut and weld that lower outlet and it's almost the same as a TZ. TZ has filler cap at a different angle but the differences are small. Those are good radiators. I have one to put on my next/last TZ.
 

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irk miller

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Thanks for solving that debate, Teazer. Now I owe Hurco another dollar.

I assume you run everything on premix?

I finally got the engine apart and cleaned up. I have a spare bottom end that I’m scavenging a few parts from. This engine had a bent shift shaft that needed replaced, for example. If it's RD250, should I run that trans or go with the 350?

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I have what I understand to be a hybrid TZ/RD crank, but I haven’t learned what that means yet.

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teazer

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Race motor, so yes. Pre-mix. For a 2 stroke that's not doing a lot of miles, that works, and even for track days. Get an Accu-mix jug to mix the right ratio every time.

If you could find a way to use an LC (4LO) or RZ/Banshee side cover and oil pump that would be great but it's a challenge to get both pumps on the one crank gear. Banshees have a longer crank and an extra gear to solve that problem.

RD250 and 350 share the same trans but different primary ratios, so use 350 clutch and any combo of the best gears on the best shafts out of your pile of parts. Shift forks are the same as well. RD400 has slightly better ratios, but if you don't have one, the older trans should be fine. You could spend a fortune and go dry clutch TZ trans but that would be a nightmare on the street. There are some high dollar RD's with dry clutch and RD400 trans with special shaft but that's above my pay grade.

If the crank needs to be rebuilt, a Vito's crank is cheaper and all new parts. Not sure what the hybrid crank means but it may have TZ roller outer bearings which are not good for helical cut primaries because they can't take side loads. Inners bearings are the same on RD and TZ but TZ cases are grooved to take C rings to locate the center bearing. The crankwheels are actually different but the same size. Banshee are almost the same but a couple of MM wider, so the cases would have to be machined to get one in. These are left to right, Banshee (dead), RD400 and TZ350.

RD250/350 and TZ's share the same 110mm rod length but RD400 are 115mm - the so called Long Rod.
 

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irk miller

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I’ll confirm with Hurco what the deal is with this crank. It’s a good crank.
I honed the jugs. The left jug had a bit of aluminum transfer below the exhaust port. I did a little bit of work and got it all cleaned up. I’m running these jugs with stock bore, at least at first. We’ll see how that all plays out. Other than the aluminum transfer, these are actually in decent nick.
My steering bearings came in, so I’m at least able to do a bit of a mock-up. I’ll run the red 87 Ninja 750 rims (16”) and a GSXR 750 front end. The tire combo will obviously get swapped out for better sized tires front and back. On the floor in the pick is a Radian swingarm I plan to swap in, but likely shortened.
Heading to Utah tomorrow, so this ends my initial push. I had hoped to be a roller. It got close.
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irk miller

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Digging through AHRMA and USCRA rules to see if this thing has a place with the modifications I am doing. AHRMA is pretty much all together out. There is room within a few USCRA classes, but the RD Spec class is out. I'll have to seriously consider whether or not I plan to run USCRA races at all, or if I just do track days at Barber and Road Atlanta.
 

pidjones

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Digging through AHRMA and USCRA rules to see if this thing has a place with the modifications I am doing. AHRMA is pretty much all together out. There is room within a few USCRA classes, but the RD Spec class is out. I'll have to seriously consider whether or not I plan to run USCRA races at all, or if I just do track days at Barber and Road Atlanta.
I've heard reports that the Tennessee track near Crossville may be opened as soon as 2022. Doubting it, but those are the reports.
 

irk miller

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I've heard reports that the Tennessee track near Crossville may be opened as soon as 2022. Doubting it, but those are the reports.
That'll be great when it does. Crossville is 5 hours, which is basically the same as Barber. Road Atlanta is my local, but even that is 2 hours away. I have a dirt course, Aonia Pass, 45 minutes away I hope to run the Bighorn on when I get it running. That's a big reason I keep leaning towards a drag tune on this RD. I can street a drag capable ride, and get plenty of race out of it on a local strip. Not a lot of road course options, and the two orgs are pretty limiting in their classifications.
 

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