What Engine Mods? xr600

Hey guys,

One of my riding buddies who has a '92 xr600 is ready to do a rebuild this winter. His bike is tired, blows smoke and has lost compression. It is obvious that we are going to need to go to a big bore kit but I wanted to get more info from you guys who have rebuilt an airhead first hand. We want to make it into a real screamer since it is probably going to go to Motard after one more season on the dirt. What is the compression on a stock 600 is it 10:1? So, we were thinking about putting a bigger piston, maybe higher compression, over sized stainless valves (what size) hotter cam, exhaust, header---what else? Balance the crank? I dunno. Please give us a little more direction and any specifics would be highly appreciated!


Geoff :cry:

I did the XR600 and the one thing I regretted was the high compression piston. Back then we didn't have a hot start button......Get one! That would have fixed the starting problem with the high compression piston. On hot days it would get to hot and then would not start till you took out the spark plug :cry: what a pain on a hot XR600 :cry: With the cam, over bore, high compression piston, (with the head milled it turned out to be 12:1 compression) it was a monster. If I had done it over again I would not have gone over 11:1 maybe not over 10:1 for the hot day's that we have out here in the desert. I had to run race gas. I would have also ran it a little richer. Hind sight. On the Dyno I got 48hp. They did a mod to the timing chain adjuster (made it more like a XR400 or something like that) also and dialed in the cam (advanced it). Had the rod peened and the crank balenced. New clutch and stiffer clutch springs. Had a XR's Only header and a Supper Trapp.


Is the hot start simply a lever to drain the bowl? Do you know what the stock compression is on the 600? Thanks a lot! :cry:

The XR600 is 9:1 for stock compression ratio

The hot start button is a gate/tube that goes to the intake side. When the engine is hot you can press it and flood the combustion chamber with fresh air before you try and start the bike. Because that wasn't around in the mid 90's I had to take the plug out, put it back in and first kick it would start. Even if you would just press the compression release and try to clear it with the throttle open you will still be pulling fuel. You need fresh air. There easy to buy now. Hadn't ever heard of one back then.

Like I said, I wish I would have never gone with that high of compression. If I would have gone 10:1 I could have gott'n away with high octian pump gas and maybe 70/30 pump/race gas on hot (100+) days.

Something you may have already thought of, but isn't mentioned in this thread is to add an oil cooler to the XR600. SRC offers a kit that makes use of the oil cooler found on pre '96 XR250R, but I imagine you could also adapt a XR400R oil cooler as well (it is bigger).

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