500 Two-Stroke Tech

Does anyone know where to get the RD500 base gasket material?
It`s a sheetmetal layer covered with rubber on both sides.
Edit: It`s a 0,2mm aluminum layer coated with 0,2mm fiber gasket matierial on both sides (0,6mm total), not rubber.

I want to make RD350 base gaskets out of this material.
The original 350 gasket is a simple paper gasket and it failed after maybe 5000km.

Yes, it was installed dry, no oil on the gasket.

I've never seen the alloy material available for base gaskets Michael. Copper is more common.

If you coat both sides of the RD (TZR etc) base gasket with sealant it will last forever. Yamabond, MotoSeal 1, etc. I've never had one fail.

Quote.

The original 350 gasket is a simple paper gasket and it failed after maybe 5000km.

Yes, it was installed dry, no oil on the gasket.


Trust me, your problem is not the gasket material. do you know for a fact the mating surfaces are flat and true ? are you using genuine stock thickness base gaskets ?

It`s a well known issue of the 350 or better it`s a common problem for 2-stroke base gaskets.
One of my colleagues has exactly the same problem on his 1WW and I know from another 350, also left cylinder outside.

Basically this happens if you oil the gasket "for the next time to avoid that it sticks to the flange".
In this area you have negative and positive pressure.
In addition to this pressure the firing pressure pushes the cylinder up and reduces the clamping load of the gasket.

I did not expect to see this issue when using expensive Yamaha parts but they are also just cheap paper gaskets.

I could measure the flanges but I expect that they are true (at least as good as they were from factory). Compared to a cylinder head they are stiff and the thermal load to this area is low
Bike is 100% standard.


As already mentioned, the 500 base gasket has a 0,2mm Aluminum middle layer.
I`m 99% sure Yamaha had similar issues while testing of the RD500 and this special gasket is the countermeasure.

I always use paper with a THIN layer of Dirko (grey).
That never failed in 225.000 km on my RD350.

The latest DIY stuff was done with Abil from Elring which is available in different thicknesses.
http://www.elring.de/produkte/dichtungswerkstoffe/" onclick="window.open(this.href);return false;

You can easily draw the desired shape using a stock gasket and a pencil. Cut it with a sharp knife and you're done.
The luxury version would be using these dxf files to have 'em laser cut.
http://www.rd350lc.de/index.php/downloa ... Spacer.zip" onclick="window.open(this.href);return false;

I have also never had a fail in all the 500s or 350s I have owned and abused or any smoker.........
But then, I always coat the base and the intake gaskets with 3 Bond 1211.

I recently had a genuine Yam head gasket fail on my 350LC after 25 miles, fitted and torqued no different to any previous rebuild but it failed .

From doing some research, it appears opinions and advice on types & materials of gaskets and sealants/(or no sealants )are like assholes....every one has one!

I read some people put grease on all gaskets and seem to get away with reusing them multiple times, so they say anyway..

I bought a new one, cleaned the surfaces, fitted it again and 450 miles later, its fine. Sometimes shit just happens!

podman wrote: I read some people put grease on all gaskets and seem to get away with reusing them multiple times, so they say anyway..

I agree podman, sometimes you do everything right and it still goes wrong. That's life.

I've read that as well and I've also read about the leaks that follow. The trouble with grease is that it doesn't compress well and doesn't form a seal. What it does do well is create leak paths. Seen it happen recently on an RGV. Sealant is for sealing.

Why try and save a few bucks by reusing gaskets, it's not saving anything if you cook the engine by reusing gasket with grease on them. Not to mention the fact if the engine locks up at speed you could find yourself in the ditch.

I'm cheap, but not that cheap.

MK wrote:I always use paper with a THIN layer of Dirko (grey).
That never failed in 225.000 km on my RD350.

The latest DIY stuff was done with Abil from Elring which is available in different thicknesses.
http://www.elring.de/produkte/dichtungswerkstoffe/" onclick="window.open(this.href);return false;

You can easily draw the desired shape using a stock gasket and a pencil. Cut it with a sharp knife and you're done.
The luxury version would be using these dxf files to have 'em laser cut.
http://www.rd350lc.de/index.php/downloa ... Spacer.zip" onclick="window.open(this.href);return false;

Seems to be a common method to "glue" it onto the flanges with silicone.
I`m using ThreeBond1215.

Thanks for the link, safes me some time and effort to get a scan of a new standard gasket.
Really good idea to make one big gasket for both cylinders.
Lowers the risk that the gasket fails between the 2 cylinders where it`s not possible to check it.

Abil N gasket papier is also in my garage in various thicknes versions.
No need for laser cutting to get the same luxury version

I have made a new single gasket.
Don`t use the .dxf out of the link, it`s not the 100% correct shape for the gasket.





I have done some work with paper samples.
At first I made a copy of the crankcase flange:


Compared it to the cylinder base flange shape (transfer ports are slightly bigger than in the crankcase):


Did some adjustments to avoid that the gasket will reach into the transfer port:


But it still covers the full flange area:


Some detail work later:





If someone needs such a gasket => PM