Installing a drop in cam

[Blysster]

Can anyone give my any pointers on how to install a drop in cam into a 400EX? I will be installing one on Monday, is there anything I should know? I don't have a service manuel and I couldn't find any threads on this.


Any help would be apreciated!

[VegasEx'r]

Make sure you are at TDC before you start to disassemble the motor. Be careful removing & reinstalling the head cover bolts. The 6mm ones are probably exposed to a fair amount of heat, so they can get a little brittle. The 8mm bolt in the middle should come out w/ no problems. When you reinstall those bolts, torque the 8mm to 17 ft-lbs. & the other to 10 ft-lbs. If you don't already have some, I would go buy some assembly lube. It is a good thing to put on all of the bolts as you reinstall them (helps prevent galling & stripping), and you want to put a fair amount on the cam as well. Do not let the cam chain (or anything else for that matter) fall down into the case. There are 2 lines that are on the cam sprocket, they line up w/ the top of the head, and install the cam w/ all of the lobes facing down. Use blue loc-tite on the two bolts that hold the cam sprocket to the cam, and I think they torque to 10ft-lbs, but I don't remember for sure. when you fire it up for the first time, do not let it idle. Keep the throttle in the 1/4 to 2/3 range. Run it like that for 5-10 minutes, vary the RPM's (nothing too wild, just smoothly up
& down from 1/4 to 2/3 throttle). Give it 20-30 min to cool down, then run it again for 5-10 min. (remember to never let it idle). You can repeat thet process once more if you'd like, or you can call it good. Change the oil & filter when you are done (the assembly lube that was on the cam will now be mixed in the oil, & it will make the engine run hot, so get rid of it).

If that is too much info, I apologize. If you have more questions, let me know.

[spliffy]

Go Here , Its Actually For a 250x... But Basically The Same directions For a 400ex http://www.off-road.com/atv/xupgrade/camchoice.htm :D

[Blysster]

Thanks VegasEx'r and spliffy..

Hopefully everything will go smoothly. I'll let you know how it goes.

Regards,
Pierre

[Blysster]

Well we are finally going to install the cam tonight or tomorrow... and I have another question.

Can I reuse the same valve cover gasket or should I wait to get a new one??

[dhines]

You can use the same one as long as it isn't damaged. Also, make sure you get the cam lined up right when you put it in and use lock-tite on the cam bolts.

Dennis

[Blysster]

We finally installed the XR400 cam last night. Things didn't go too well but we got it after about 7 hours and plenty of beer.. I think that could have been the problem.

Advice: If you have never seen someone install a cam in a 400ex before don't attempt to do so on your own... unless you have a service manual maybe.

I remembered that the two bolts right over the head pipe were more brittle than the others because they have been exposed to more heat.. well they came out all right but after taking them out we put them with all the other bolts (big mistake). When it came time to put the valve cover back on one of these bolts broke in the head of the motor. It took about 2 hours just to take the broken bolt back out. Good thing my neighbor had a junked 300EX.. the valve cover bolts off of it fit perfectly on the 400ex so we had a few spare ones laying around.

OK, and that was only one of the problems. after taking the stock cam out we couldn't put the timing chain sprocket back on the XR400 cam (with the lobs facing down), the timing chain was too tight. We tried for about 1 hour and it just wouldn't fit. We had to loosen the automatic chain tentioner thing (whatever its called). That wasn't too much of a problem after we figured out there was one and where it was. To get to it we had to remove the snorkel and the carb.

After we got it all back together we started the bike up, it was dark by then. We gave it 1/4 to 2/3 throttle for about 1 or 2 minutes and head pipe turned as red as the fenders. We immediately turned it off, took everything back apart. The spark plug was OK (brownish color). We checked everything over again and re-adjusted the valves. The intake valves had changed to .006 (we put them back at .004) and the exhaust valves were still at .005 inches. We couldn't find anything else wrong. This time it seemed to be running fine, no more backfirering. looks like my 400EX fixed itself again.. I hate when that happens!

OK, now for the questions. When we started the bike up the second time it worked fine but the pipe began to turn reddish (barely noticeable) after revving it for about 10 minutes. This is normal right? This was before changing the oil so it still had assembly lube mixed in it. The spark plug was still brownish like it should be.

Also, with the XR400 cam, the valves should be set with the same clearance as the stock cam right? (The exhaust valves at .005 inches of clearance, and the intake valves at .004 inches from TDC)

One more question. How much of a difference did you guys notice with the XR400 cam? I haven't taken mine out to try it yet.

Sorry this was so long.

The red header pipes sound like a lean condition but I dont' see were that came into effect..maybe kick your pilot jet up to a 40 or 42,,since your up north that would be a good thing anyway. Only change I made on my motor after the cam and piston upgrade was a main jet change...which was 1 size up.

[Blysster]

Originally posted by Rico
The red header pipes sound like a lean condition but I dont' see were that came into effect..maybe kick your pilot jet up to a 40 or 42,,since your up north that would be a good thing anyway. Only change I made on my motor after the cam and piston upgrade was a main jet change...which was 1 size up.

I am already running a 42 pilot jet. The bike was running a little bit rich before I put the cam in.. hopefully it will be better now. I will be keeping a close eye on it and the spark plug.

I changed the oil in it last night so maybe that will help too?!

[optikid123]

there is others on this site that says their pipe glows red at night too so i dont think its a problem but change the oil

[NVR2L8]

Yea, the XR400 cam uses the same clearance measurements as the stock cam.

Having the head pipes heat up to the point were they were glowing red means your engine was running hot. During the break-in of the cam you were running the engine at 1/2 throttle or more and probably didn't have any airflow over the engine...huh? If so, while you probably didn't do any harm during the cam break-in the motor ran a little hot...glowing head pipes is the first indication of a hot running engine.

Anyway, I can't comment on the difference the cam will make for you, since I installed mine at the same time I punched my motor to a 416 and added an FCR carb. All I can say is that my motor revs a lot quicker than a stock motor, and still has plenty of bottom end.

One last thing... If you were jetted a little rich before the cam, then you should be really close. Since the XR400 cam isn't all that agressive, it shouldn't have much of an effect on jetting. Still though, like you said, keep an eye on how it runs and check the plug often, and make any necessary jewtting corrections.