400ex overheating?

[Holeshot36]

I have a '99 400ex and just put in 416 je 10:8 1, hotcam stg.2,mild port job, air scoops, and i'm running 110 octane. With about 20 mins of hard riding i run about 300F oil temp. Well when i was installing the 416kit i took the cylinder to a local machanic to get it bored and when i got it back i noticed that a rubber o-ring goes on the bottom of the cylinder and i did not have a o- ring in my gasket kit so i asked the mechanic about it and he said it won't hurt anything to run with out it just blow you gasket out earlier like in 2 years, could this be why its overheating? My jetting is right cause the plug looks good. Sorry for the long post.

dont know what your problem is but it sounds kinda fishy. If there isnt the proper stuff in the engine that could be a factor but that seems pretty hot.

[AtvMxRider]

Originally posted by Holeshot36
i asked the mechanic about it and he said it won't hurt anything to run with out it just blow you gasket out earlier like in 2 years,

I think it's time to find another mechanic:huh .

[xc400ex]

The o ring wont affect engine temperature. Go buy a 400ex plug with the 9 digit in it I know stock is 8...thats a colder plug..what kind of oil are you running?

[Aceman]

Why are you running 110 octane? Your motor only needs about 93-94 octane. I think I've read higher octanes create more heat than lower octanes and your engine doesn't need 110. I think a colder spark plug will only affect oil temp by about 5 degrees or so. Have you ever thought about an aftermarket oil cooler?

[xc400ex]

How would a sparkplug affect oil temperature? It will effect the temperature in the combustion chamber...but anyways if what you said was true Id pay $3 for 5* drop....but actually it will lower combustion chamber temps by much more than 5*

[BSTURDIVANT]

Check to see if your oil cooler is good and clean, but oil temps. on 400s run way up there, especially when hot out. Synthetic oil will lower temps considerably! Never put around- you have to run fast as well as hard to keep cool! avoid hard pulls at low speed!

Your temp. may come down after the rings break in.
Also check to make sure that you are properly jetted. Lean conditions create high combustion temps. that transfer to the oil
thru the head.

[Pro400EXC]

Aceman,he is runnin 11:1 comp cause he has the XR head gasket,plus w/ 93 octane it was pinging,which isn't good....

I'll try to let him know about the sythetic oil,and the colder plug (we live by ea other)

Thanks for the help fro my friend guys...

[flyin#5]

Originally posted by xc400ex
How would a sparkplug affect oil temperature? It will effect the temperature in the combustion chamber...but anyways if what you said was true Id pay $3 for 5* drop....but actually it will lower combustion chamber temps by much more than 5*

it doesnt really matter if its just on the top end.. where do you think most of the heat comes from? the top end... it gets distributed and the oil helps cool that also...

[Glamis400ex]

I have the same set-up minus the air scoops. I might suggest and second oil cooler like FST. I built mine and noticed it ran alot hotter so I did the second oil cooler.

I run 50/50 race gas with premium...comes out to like 100 octane or so. That should be way more than enough. Run a DPR9Z plug and sythetic oil.

I have done everything physically possible except scoops to lower the oil temp...race gas mix, oil cooler, cooler plug and synthetic oil.

Glamis

[ATVer14]

I thought that the higher the octane, the lower the temperatures, because I have an 11.5 to 1 piston and I run straight 110 in the engine, and it stays relatively cool, although i have never taken its temp after a race.

[xc400ex]

it doesnt really matter if its just on the top end.. where do you think most of the heat comes from? the top end... it gets distributed and the oil helps cool that also...

Yeah most of the heat comes from the combustion chamber which in turn a colder plug lowers the temp...and that lowers the overal motor temp and oil temp...but I said what I said because aceman said a colder plug would ONLY make the OIL 5* cooler...

[Holeshot36]

Alright thanks i try some of the things listed above. Does anyone else have a oil temp gauge and motor work or even if you don't have any motor work done what temp are you running?

[400exdad]

Somebody educate me please. How can a colder/hotter plug change engine temps? I thought the temp range of the plug was more suited to the engine (tempature if you will) than the other way around. I thought I did my home work on this back when I was building small blocks... :confused:

I'm running pretty decent compression in my 400 and I can tell a huge difference in motor temps when I putt around.. which is something that you do with a 6 year old.. :) and when the motor is under severe load for a long period of time. Such as duning.

I think I would switch to synthetic oil and check my jetting. Try putting your air box cover back on, if its not already. That should be an easy way to richen it up and see what happens. Also, you shouldn't need to run 110 octane gas unless you have a advance key in it.

[komatsu kid]

stick with the race gas it runs cooler than lower octane fuel

[RED121572]

Mine was doing that last year. There was a little loss of power, but the bike wasnt noisy and the plug was fine. It was just running extremely warm.

Turned out to be that a circlip fell out. It chewed up the walls of the piston and the piston was digging at the cylinder walls.

[400exdad]

Circlip falling out = bad. How long did it take you to find it?

Originally posted by Holeshot36
I have a '99 400ex and just put in 416 je 10:8 1, hotcam stg.2,mild port job, air scoops, and i'm running 110 octane. With about 20 mins of hard riding i run about 300F oil temp. Well when i was installing the 416kit i took the cylinder to a local machanic to get it bored and when i got it back i noticed that a rubber o-ring goes on the bottom of the cylinder and i did not have a o- ring in my gasket kit so i asked the mechanic about it and he said it won't hurt anything to run with out it just blow you gasket out earlier like in 2 years, could this be why its overheating? My jetting is right cause the plug looks good. Sorry for the long post.

There could be a few things that happened here, you could have got a bad bore job, you could have not set your piston's ring end gap right, or something else could have happened, such as the circlip falling. Plain and simple you are going to have to take it back apart and look at it. You will most likely end up getting a new cylinder and possibly a new piston.

[RED121572]

Originally posted by 400exdad
Circlip falling out = bad. How long did it take you to find it?

From the time I noticed there was a problem to the time I tore it down, Im guessing I put about 6 hours on the machine.

Ive got a pic posted in my profile of the piston at www.predatorowners.com

[Holeshot36]

Now you guys are scaring me. I'll try a few things today and if i can't get it running cooler i'll tear it down. I had a mechanic bore and gap the rings. Just curious, could a blown head gasket make it run hot?

[RED121572]

Yes. Careful, a blown headgasket can be dangerous to your health. It can cause a fire.