Engine change


Which problems the change of 500ccm to 600ccm brings

translated by Jens HŲgemann Dez.2003

This mail reached me on the 21.12.99 from Heinz Langbauer:

Hello Volker!

I hope that I can contribute with this small story to help others on your site.

Since I havenít got a internet service provider, this is the only way I can get in tough with other drivers. I would like to ask you to publish my story on you page.

Last year I bought myself a XL500R, Bj. 86 (PD05). Unfortunately the cylinder was a little leaky. When I began to screw around, I had a glorious idea to exchange the cylinder with one with a diameter of a 100 mm. (XL500 becomes XL600). I only got a cylinder tube with a diameter of 101 mm from a windy parts dealer by cash on delivery. For this cylinder tube there were no more pistons (original 100.25 and 100.50) available, for then I purchased for a lot of money (approx. 260 euro) a "racing piston", which, as after the installation turned out, had a compression of 1:11. Since I didnít want to work the cylinder head over again, the compression itself rose to a relatively high level (no official measured values available). In order to use the increase of capacity and compression I decided adapt the fuel supply.

I asked a lot of people which nozzle they would try out. But I received more answers than I asked people and I decided to try it with a nozzle of 130 in both carburettors.

And here is the point where my story takes a fatal turn. The initial problems after assembly were not surprising, but some how I had a strange feeling about it.

I started by changing the standard spark plugs by using a platinum spark plug (15Ä) (I posses about 25 spark plugs from nearly every company that manufactures them), and there was some sort of better result.

After that I checked all electrical connections, but the values from the repair manual were reached. After excessive tries to start the engine with all aids (starter spray, plug change etc..) no improvement of the situation resulted. Even then when the engine ran it was not really satisfying. Till 3000 RPM nearly no performance could be achieved, with sudden acceleration the engine dies or runs fatty. Only starting from 3000 RPM it becomes interesting, then the performance is achieved and the power is present and leads to surprising results. ( what, that is a 500-er/Bj. 86 and takes off in such a way? Do you drive with methanol? Do you have a short translation?)

But these moments were rare and luckily I live in a hilly area so I could get by kicking and rolled down the hills to get the engine working. But to the end of the year I had the strongest kick in the area.

On my question: Why doesn't the engine start?

I got two fundamental answers from various experts:

1. The head of the 500 isnít identical to that of the 600, and has to small valve cross sections and creates for this reason at small revolutions, as for example when starting, no sufficient filling.

2. The compression is too high.

Before I fall into the cold season and start to rebuild everything I would like to here from some other suffering comrade to find out what I could do to regain the pleasure of driving my bike. Who can help me in this problem with advice? I am for assistance of which kind

( addresses, information etc..) gratefully thankful . In this sense I wish all XL infected a merry Christmas and many kilometres for the next millennium!

Greetings from the Steiermark