cam break in?

[Martin Blair]

Im going to be gettign a xr400 cam soon, how do you guys break them in, let it run in the driveway and get hot, cool down, and then get hot again? then re adjust the valve clearence and go riding?

Also with a stock bore hi comp piston do you need to hone the cyclender at all? I no in a car you have to remove the wear lip from the old rings, do you on a bike as well? The piston will be a JE 10.5:1 if i use xr 400 gaskets what compresion will it really be, and will the xr400 gasket be reliable?

[toby400ex]

Originally posted by HN400exracer
Im going to be gettign a xr400 cam soon, how do you guys break them in, let it run in the driveway and get hot, cool down, and then get hot again? then re adjust the valve clearence and go riding?

Also with a stock bore hi comp piston do you need to hone the cyclender at all? I no in a car you have to remove the wear lip from the old rings, do you on a bike as well? The piston will be a JE 10.5:1 if i use xr 400 gaskets what compresion will it really be, and will the xr400 gasket be reliable? Im pretty sure on breaking in a cam you arent supposed to let the engine idle very long at all. And you will need to get your cylinder honed to breakin in the new rings in the piston.

[F-16Guy]

Before you start your bike the first time, do a couple things first:
1. Install a 40 or 42 pilot jet; this will help keep your engine cooler during idle and also make it much easier to start. (see the "tech articles" forum)
2. Bump the main jet up to about a 158 with a stock bore 10.8:1 or 11:1 piston. Same as the pilot; a richer mixture keeps the engine cooler during break-in. You can fine tune later.

When you start it for the first time, make sure you:
1. Put oil in it. (sounds stupid, but...)
2. Do the above steps first. Keeping the engine cool is critical during break-in; it will only cost about $10 tops.
3. Keep the engine above 2000 rpm for the first 20-30 minutes. The best thing to do (in my opinion) is to start the bike and bring it up above 2000 rpm immediatly, and then check the bike for oil leaks. Once you determine that there are no leaks, ride it easy for 20 minutes. Make sure not to rev or lug the engine too much. A nice, easy ride shifting fairly frequently is good.

This will not only break in the cam properly, but will also help seat the rings. After the first ride, run a couple tanks of gas progressively a little harder, and then adjust the valves.

This is how I break my bikes in, and I've had really good luck. Hope you have the same.

--Evan

[Martin Blair]

ok thats jetting wont work, first off i dont have a stock carb and that would be way lean with my mods, anyway thanks for the info any other sugestions? when we go out for the first day i will ride easy for the first half hour or so, then go harder and harder.

[F-16Guy]

Originally posted by HN400exracer
ok thats jetting wont work, first off i dont have a stock carb and that would be way lean with my mods, anyway thanks for the info any other sugestions? when we go out for the first day i will ride easy for the first half hour or so, then go harder and harder.
Oops! I didn't see the carb in your sig. When you get your piston, even if it's for the stock bore, you need to take it and your cylinder to a machinist so he can mic the bore and check the clearances. He will probably have to hone the bore to size. While you're there, give him the rings and have him set the end gap. This is very important and often overlooked. When you break it in, just go easy for the first tank, and then ride progressively harder each ride. Just don't forget three things: Don't let it idle for the first 20 minutes for cam break-in, keep it above 2000 rpm and keep a light load on the engine (normal riding on flat ground). Change the oil and filter after the first couple short rides to get rid of all of the debris from the cam and ring break-in. Check the valve lash about the same time as the first oil change, but make sure the engine is cold. As far as the gaskets go, you'll have no problem with the OEM XR400 gaskets. Without measuring your combustion chamber you can't really determine the exact CR, but with those gaskets and a JE piston, I'm guessing a little under 11:1.

[Hondaluva]

www.rosspistons.com has a nice CR calc. If you know all your measurements (mechanic can help you) and the CC's of your head and the CC's of the valve pockets and piston dome (if any) you can punch it all into the CR calc. Check it out.