if it aint broke, dont fix it...?

[400man]

I know alot of people have heard that term and probably go along with it....and thats the case I have with my 400. my motor is the only thing left that I havent really modded much except for a stage 1 hotcam, lightened flywheel and fcr carb, the rest is stock. the bike is 11 yrs old and still on the origional piston and bore. it runs just fine, doesnt smoke much or leak any oil. I know what all I want to do to it when I do rebuild it, but like the title says.....if it aint broke dont fix it. but I guess my question is, what would probably break first in the motor if I just kept riding it? I did forget to add that it does have a 1 year old new timing chain tensioner and crf450 timing chain and rings/valve seals. would the bottomend be more likely to fail before the topend, or vice versa?

[250rforlife]

if the motor has mostly everthing original from 11 years ago youll probley need a crank, bore it slightly over for fresh cylinder, pistion, valve seals, valves will probly need grinded for a better margin, maby new valve springs, maby new rocker arms, ect. but u never no. i wouldent let it blow up ino that. if i was you i would overhaul that motor before its spring. i would get pretty much everything new. bottomend,topend, valves, springs, ect. just because its all original. + ull have a fresh motor, and ull have more power. when you rebuild when you decide. id go with a 1.2k budget. thats alot of hp over stock. probly mid to high 30s. id get new valves, web cam, kibble white spring kit, hardface rockers, 11:1 pistion, 406 bore(keeping it small for reliability and low temps), and id get a new crank kit with brearings and seals. id get a full exhaust, uni filter and your good to go. and maby a port and polish if ou want 40hp. but this is all my own opinion. but i would never let the motor get so bad that it blew up or the crank seized. if you got the money, do a topend rebuild. and if the crank has play put a new crank in.

[slightlybent47]

You don’t go by age; you go by how many hours are on it. An old bike can have very few hours on it if it doesn’t get ridden much. If it has a lot of hours on it, then it may be time to freshen it up. Do a compression test and see what the compression is, that will tell you a lot. If it’s just a fun put around bike, then you may just leave it alone, if you are going to ride the piss out of it then I’d do the whole motor.

[liex21]

like stated above a overhaul wouldn't be a bad idea. Ya in a sense if its not broke don't fix it, but don't wait for failure either. Preventive maintenance is key for any machine you would like to last. Also why not make it faster while your at it :devil:

[AtvKid4Eva]

you WONT need a new crank or anything from the bottom end if it all runs fine. The most it would need is the top end freshened up with slight bore and new piston and rings. Ive never even seen the bottom end of a 400ex blow up or break. Top ends are more common, but your doing good for its age!

[jcs003]

Originally posted by AtvKid4Eva
you WONT need a new crank or anything from the bottom end if it all runs fine. The most it would need is the top end freshened up with slight bore and new piston and rings. Ive never even seen the bottom end of a 400ex blow up or break. Top ends are more common, but your doing good for its age!

x2...

if it was well maintained it might still be fine. do a compression test and a leak down test to ensure all is well. reglary check your spark plug to see how she is running. also, if it diesnt smoke much then your valve seals and seats are ok.

another thing. i personally never heard of a 400ex having a catastrophic failure. although im sure it has happened, just not in my experience.

[chronicsmoke]

Yah I'd check the crank when you have the top end off, before you just go ahead and buy one. but I would buy everything for the top end ahead of time and then if it needs a crank, just order what you need.

My 01 426 has been used and abused; Shattered the stock piston and went to a 426, its been through hell and back with the 426 piston in it and still runs like a champ, no bottom end mods

These engines are bullet proof! :p

[400man]

well if I can help it I dont want to have to split the motor enless I have a good reason to.......and when that time comes im puting in a stroker crank. but as for the topend, I was just planning on a 11:1 416 build. nothing to extreme I guess for now.