1975 Yamaha RD350(LC) Preservation-mod Hellride

Hurco550

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I'd love for this to be a track bike. You obviously know how close I am to mid Ohio. That was the plan for it. Maybe one day it'll still make it there
 

irk miller

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I'd love for this to be a track bike. You obviously know how close I am to mid Ohio. That was the plan for it. Maybe one day it'll still make it there
Shame on me for not saying Mid Ohio when I listed my tracks. That will happen, I promise, and you will make rounds on it.
 

teazer

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For either the drag strip or the race track, you might want to fit lighter forks and wheels and maybe a slightly longer stiffer swingarm.
 

ex119x

Been Around the Block
If you want to roadrace this, there are a couple of issues to be addressed. First, there are no suitable race tires available in 16". 17" has the most available, but there is a decent selection of 18" from Continental, Heidenau and Bridgestone. Most of the classes with WERA and AHRMA that this bike would fit in do not allow USD forks or brake calipers with more than 2 pistons. With AHRMA, the bike would fit in Formula 500 and open 2 stroke and Sound of thunder 1. With WERA, it would probably be in V4 or V5.
 

irk miller

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Man, building something to track can be tight. I have the parts to build 17” spoked GL wheels front and back. Also two to mount now. Maybe that’s a better wheel decision. These Ninja wheels just look cool.
 

ex119x

Been Around the Block
If you go with laced up 17" you will need to have at least a 2.5" wide front and 3.5 or 4.0" rear rim to fit a 110 -17 front and a 150 - 17 rear tire. For easy wheels I tend to go with CBR600F hurricane wheels. You could probably get away with running a 120 front and 160 rear but it is really a bit too much tire for that bike, but, that is what I would do and I would use SV650 or Katana 600 wheels, forks and brakes. That is what I have on my FZ600 and I doubt it will have any more HP than your bike.
 

teazer

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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.
When you bolt the head down, start off without the washers to check that the sleeve nuts don't bottom out. Some sleeve nuts may need to be threaded deeper if the stud is too long and some may need to be shortened if they are longer than the recess in the head and barrel.

For drag strip fun, fit the long swingarm and stock length shocks and then lower the forks o get it level.

http://www.2strokeworld.net/forum/index.php?topic=732.0 for more info on RD/LC/RZ parts swaps. Ed E did a great job of pulling together that list. There are a couple of LC top end projects over there too.
 

Rider52

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One of my friend's had a LC with Sportster hubs laced to 18" aluminum rims. The rear hub was drilled and a spacer made for sprocket. It is a nice tidy and clean application.
 

irk miller

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I like to use the CB550/750 hubs and GL rims, or the Akront style high shoulder rims for 40 spoke or smaller CB hubs for 36 spoke. I like to use the XS or GL hubs in particular, because I have a setup that matches common spacers, hubs, rotors, and calipers. The GL1000 and XS650 (and RD) front hub has the same rotor pcd. A CB550 and GL rear wheel also uses the same spokes.
One of my friend's had a LC with Sportster hubs laced to 18" aluminum rims. The rear hub was drilled and a spacer made for sprocket. It is a nice tidy and clean application.
 

irk miller

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Getting ready to order a head gasket and base gasket from Lani. Anyone have any idea a good baseline to order the first head gasket at? Do I go thick as stock, like in the .08" range or do what my first inclination is to do and go as thin as .035", maybe? Do I do a squish measurement with no gasket at all and go from there? This part of building a 2 stroke is where I am totally ignorant and it seems to vary wildly from the 4 strokes.
 

teazer

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Go with stock gaskets and then measure squish and adjust as required. Lyn Garland on 2strokeworld sells a neat one piece base gasket in different thicknesses. It's like a TZ gasket but has enough meat between the bores to work with AC or LC barrels. I have some in stock if you want one. But OEM are fine if you trim them to match the transfers.

For the head, Maybe check squish without a head gasket to determine what thickness you need to order.

I find copper head gaskets hard to seal on a watercooled motor. YMMV
 

irk miller

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The school year started Tuesday, so I reported to work. I’m doing my best keeping this project moving. Here is a mock-up of the Radian swing arm and a 13.5” rear shock. I’ll do better on the shocks, but this will do for a proof of concept.

F4B48C70-851C-4FBE-BC4B-2F4544F4D2B3.jpeg
 

ex119x

Been Around the Block
Shock length, angle and swingarm angle look about right to me. Those wheels do look good and if you don't plan on racing it, you can get good enough tires in those sizes. Even for a track day, Bridgestone BT45s would work and I think you can get those in the sizes for those wheels. I would go 100-16 front and 130-16 rear.
 

irk miller

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These are the pipes. Trying to figure out clearance for the kickstand and head pipe flanges to fit the LC exhaust side.
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ex119x

Been Around the Block
I think I'd cut off the sidestand mount, install the pipes and then put a sidestand back on where it fits. I know that you can lever an RD400 off its wheels by dragging the pipes and then you crash in turn 4 at Brainerd. After that the bike will catch on fire, but it is OK since it is your brother's bike not yours. So, get the pipes tucked in as well as you can since the 16" wheels probably won't help the ground clearance any.
 

Hurco550

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That pit stand you got from me was made for an elsinore with under slung expansion chambers iirc. Also, a simple tube welded somewhere to accept an mx style side stand could be an option? If your going after real bare bones race stuff that is.

20210808_212126.jpg
 

irk miller

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As thin as I bought for head and base gasket gets me to .062 on squish. 032 is the head gasket thickness, so 030 on the lip around the chambers. Do I stick with this number or mill it to something closer to 040?

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47158181-3BFC-45C0-A7F1-3D046E906DFD.jpeg
E354CCB7-353A-4C0C-8BFC-FF908526656E.jpeg
 

teazer

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If that were mine, I would want to see if it's possible to machine the barrels to take two O rings and then machine the head to get the squish right on the money.

The alternative is to deck the head to zero clearance without a head gasket and then use that gasket.

How thick are the base gaskets? You might get away with thinner base gaskets and no machining.
 

irk miller

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Base gasket is the thinnest Lyn makes, I think .014". I'll send the head off to Mototech USA and get Chris to cut this head down .020", which should put the squish to .042". If I get him to cut the head all the way to the base of that lip, it should put me at .030" - 032". I admittedly don't know the threshold for pump gas on these.
 

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