More swingarm swap - LC/RZ on AC RD350

[IR8D8R]

 Stresa posted a photo in this thread of a swingarm captioned as a RD350 YPVS a while back.
https://www.2strokeworld.net/forum/index.php?topic=4031.

 It looks like a RD350LC arm. Doing some rabbit-hole research, I see that the watercooled to aircooled swingarm swap is not uncommon. Requires some cutting and welding to convert to twin shocks and clean up/patch some unnecessary things.

 I didn't realize that the LC and RZ swingarms were so different having never compared them side by side. Which is a better swap candidate? Main goal is additional tire clearance. Anyone have experience with the subject?

Thanks!
IR8D8R

[m in sc]

ive put an lc arm in an aircooled frame, or started to. . the geometry differences make it tricky to fit a shock and not have it go over center under an otherwise relatively stock aircooled frame. from what i remember, the working circle needs to be about 7.5" radius to get a contemporary ie: cbr600 etc shock to lay correctly so its perpendicular at full compression. ive seen a lot of these conversions done and it usually results in the rear end being too far in the air and the arm angle being off. but it can be made to work. its attractive in that otherwise, its a bolt in. the 1st time i did it i had an lc arm on hand, and still wound up modding a stock aircooled arm to get the pivot height correct. im sure there will have been somebody that figured it out but on an aircooled frame imho not worth it, nor is it really any lighter much to my surprise.  as far as an rz arm, same work as putting in an fz600 or fzr400 arm.

[rodneya]

How wide do you want to go? Wider rear tires on Rd's or RZ's really seem to upset a lot of people. Especially on facebook groups. You can get a 130 rear in a AC swingarm if you grind down the welds on the gusset plate.
I think the Canadian model RZ's came with the box section swingarm, but regardless RZ arms need 6mm removed from the pivot to fit an aircooled frame. And then you can only go 130 or 140 wide before the tire hits the gusset plate on the top of the arm.
Wicked Motors is selling an aluminum RZ arm that will take up to 160 rear tire, but not cheap.

I also got tired of the look of the skinny rear tire, and I am finishing off fitting a 180 rear tire on a Ducati spoked wheel with a GSXR swingarm on my 73 RD along with redoing the tail / seat that was cracking

[m in sc]

180 .ffs lol love it. i have a 130 on mine, it can take a 140 but IMHO thats plenty.

[bitzz]

That's not a RD-LC swinger
They look like a dirt bike swingarm, like this:

... sorta copied from a TZ-F or a YZ

From a handling standpoint you want to add some wheelbase to your RD350, RD400 and XS650 swingers add about 1 1/2" and are bolt on, laying the shocks down a bit helps too, no more than 45 degrees though.

I have a CMR swinger, 4130, takes a 150 easily (this is for a TZ-G, but he does one for aircooled dual shock RDs that is mostly the same

Yeah it's steel. After much argument on my part, I have been convinced you want a (properly designed) steel swing arm. We all want a stiff swing arm, but they flex, no matter what you bolt on there. To make a swinger that doesn't flex would be weight prohibitive. A steel swing arm will return to it's original shape faster than a comparably stiff aluminum one. (This doesn't apply to a big modern cast super sport swingarm, they're so big they just do not flex... but would look really stupid on a RD350)
... all that being said: if you're after actual real "performance" you don't want a big tire; the frame can't take it, the motor doesn't need it and they'll slow you down. 
And the DG swing arms are a bad joke.

[m in sc]

thats a sexy arm right there. i def dig it. and, makes sense

[IR8D8R]

Yeah, I wondered about the mono shock mount part. The RZ has dogbones.

I have a 120/80 rear tire on now and I don't care to go any wider. I'd just like to have less than a RCH clearance between the tire and swingarm. I ground the gussets and used an extra link in the chain but the adjusters are all the way out. About 3.5-4mm clearance on either side. 2.75" rim.

The pic Uwe posted does not look like an RZ. Unless the axle tabs were cut off. Hard to tell since it's so nicely finished. The one I posted as an LC looks more like it...  I think I found the answer (photo).

I guess you always have to take what AI says with a grain of salt. Same with internet searches and things sellers post. My discussion with AI had a number of flaws that I recognized. Having never spent much time with either RZ or LC I didn't know the difference. I wasn't really aware they were such different motorcycles. Beyond the YPVS system, rear drum and styling. Why did they go back to a drum brake anyway?
 I can get an RZ swingarm for $130. Cheapest aftermarket is ~$850. Steel is fine. I can save the most weight by losing 40 lbs. Seems there are a lot of improperly done arms out there bases on Mark's comment about shock placement.
 There doesn't seem to be a definitive answer as to what the best swap candidate is. We've had various threads without a conclusion.
 I really don't want an RD400+1", which seems to be the most common choice available as far as Motolanna and SR aftermarket pieces. I don't want to change to a rear disc so I'd have to modify a 400 arm anyway for the 350 brake stay. Which I've also strongly considered. That is more of a "sideways" move. Like everyone else, I'd love to find a DG swingarm for a 350 for a reasonable price.
 Thanks for the input guys. The more ideas the better.

IR8D8R

[m in sc]

to mod a 400 arm just open the slot on the lh side and use a sleeve on the right.  the brake stays will swap 350 to 400. just fyi.

[SmokeAddicted]

Just curious, what is your goal with a swing arm swap? If you want to keep drum brakes and are happy running a 120 tire, my opinion would be an SR500 swap which seems as straightforward as it gets.

I'm wrapping up with an SRX600 swap, but the only aspect I wanted to keep original was dual shock. I'm ready to stuff a 150-160 on this bad boy.

[m in sc]

tbh, not that anyone asked,  my reason was 2 fold. 1: wanted a longer arm as wheelies were, legitimately,  an issue. 2nd was i wanted wide gold spokes wheels.  did i go a bit too wide in the  back but honestly its really nimble  the frame is gusseted as well. i kept 2 shocks as well as thats what i liked and what the frame was made for. the goal was to go a bit lighter, but joke on me was the same weight.. lol,  but thats just me. 0.02

[pdxjim]

I still think an 'arm off an early-ish XJR400 is worth a try.

Extruded aluminum, twin shock, dirt cheap on Yahoo Japan.

https://auctions.yahoo.co.jp/jp/auction/c1186462431

https://auctions.yahoo.co.jp/jp/auction/s1215249153

[rodneya]

I bought an arm from a newer model SV 650 that I was planning on using with a 150 or 160 tire. But the GSXR 600 arm I had was too much temptation. I already have a RZ motor in the 73 frame whick moved the sprocket over 1/2". With the aircooled motor you would need an offset front of over an inch