4L0 Performance Mods

[begbie27]

Hi All,

Firstly, please forgive my ignorance, but I am a newbie to the RD350 engine, and I have a lot to learn... so don't mind me if I ask some stupid questions, or make stupid statements.

I recently bought an ex race bike (1981 RD350LC 4L0 engine) with a RGV suspension conversion.  The plan is to rebuild it and use it as a track day bike.  It needs a lot of work!

The crankcase seals are shot so it is smoking like a wet bonfire.  I will therefore start with a motor rebuild first, and the cosmetics will following. Before I start with the motor rebuild, I wanted to find out what performance modifications could be made to a 4L0 engine.  I believe that it has already been ported, but I am not sure how well it was done.  Can anyone suggest what mods can be done this motor?  From minor to major upgrades.  Your advice would be appreciated.

I love the idea of the Athena 421cc cylinder kits, but understand that they do not fit the 4L0 engine casings.  Are there any big bore kits specifically designed for an 1981 Elsie?

Thanks

[begbie27]

Sorry... probably should have put this under the Technical section of the forum.

[Bazille]

Hi
You are right in that the athena kits will not fit the 4lo engine, I have just had my 350 converted to big bore 400cc
I got banshee liners and 68mm single ring pistons from Norbo and had the liners fitted/bored/honed etc, not ridden it yet as I have a few jobs to finish on bike.

cheers colin

[dusty350]

Hi matey,
Welcome to the forum. Ask as many questions as you like, always lots of help on hand. The sky is the limit regards engine mods, but a lot depends on your wallet and how reliable you want the bike to be. Don't forget how old the design is. You could tune it to the hilt and still get smoked by a more modern 250 ! Plus the frame and cycle parts aren't exactly cutting edge anymore. Even with Rgv running gear, it's still bolted to a 30+ year old frame. A Ypvs motor slots straight into the Lc frame, allowing you to go the big bore route you mention. Good pipes like TSA's make a huge difference over standard, but it will all depend on your tune and where it makes power etc. If it's an ex race bike then maybe it's had the necessary work done for what you want it for. I would strip it and rebuild the engine so you know you have a good starting point, and look at the state of tune on the head and barrels to give you an idea of what more you could do. Use genuine seals and gaskets would be my advice, and reputable firms for crank rebuilds and rebores. I've had tuned motors before, and they usually need their neck wringing to get the best from them. Down side is more regular rebuilds after they go bang. I stick with standard now, apart from pipes, as I don't want to be tearing them down all the time. Mine are road bikes though so a bit different to what you are using yours for. There are a few guys that race Lc's on here so they will give you more advice for what you are looking to do.

Regards

Dusty

[begbie27]

You are probably right Dusty. Once I open the engine I will have a better idea of what I am dealing with.

Thanks

Begbie27

[spooch63]

you could check out the tuning section on the rdlc crazy website, some useful hints and tips there, also lightened flywheels are often available on ebay

[dusty350]

Hi
Norbo does lightened flywheels for £30.00 exchange if you need one. Check out the Lc trick parts section in his shop.

Dusty

[JonW]

Just drop in a YPVS (250 or 350) or banshee bottom end, not too expensive if you get it sans cyls. Then you can go big for cheap

Yamaha RD and RZ 250 / 350 big bore primer

[Norbo]

First welcome to the forum . Ask as many questions as you like people are only to happy to help on hear.
There is only 1 big bore made for the LC that's the banshee liners and single ring pistons . the Athena kits will only fit a ypvs bottom end.

[higgsy]

I raced an YVPS/LC up until last year. For easy and relativly cheap power a YPVS motor makes sense. 60+ hp and it won't break the bank doing it, the limiting factor is the frame, so going for mahooosive hp is a waste of time for a track bike, you won't be able to use it to it's full potential unless you are somethning really special on th erider front :-)

[begbie27]

Thanks for all the replies guys.

I am really enjoying this forum... loads of knowledgeable people willing to offer advice.