Need help with engine options for 400ex?

[5.0calypso93lx]

So I recently picked up a 400ex on the cheap and it is making some rowdy noises inside the engine case :lol:

I'm not looking to spend a crazy amount here, but what have you guys had good experience with? Is it best to just have the stock motor rebuilt or? What local shops around here do good work?

I've briefly dug around on exrider but I need to spend some more time researching.

I do not intend any doing any major riding with this thing. Just a fun weekend toy or trail bike that's reliable and low maintenance.

I'd appreciate any insight you guys can give.

[SN95N/A]

Bill at boretech did my stroker motor and converted it over to methenol he does really good work hes over by newtonsville ohio.This is on a suzuki ltz400

[Racin Jason]

Split the case and rebuild it man. Plenty of info on you tube and u can buy a book or dvd for it.

[exrider416]

Yeah they are not bad to rebuild. Bored it out to a 440 and youll have a torque monster!! So its something down low you think? Too loud to be valves out of adjustment?? 400ex's are extremely reliable quads. I beat the piss out of mine and it never let me down :bigthumb

[blown86lx]

416 kit. You can get a wiesco piston on ebay cheap and have it puched out. Just keep the compression on the lower end or you will not have to run race gas. My buddy has a 416 kit and a stage one hotcam in his and jumping off mine which is all stock except exhaust and sprockets and getting on his it is night and day difference. 416cc with a small cam still very reliable

[exrider416]

I had both a 416 and the 440. Both were reliable for me and i ran them both on pump gas. 440 would run slighly warmer on tight trail riding

[1987coupe]

ill just sell you one lol

[blown86lx]

ill just sell you one lol

Me too LOL. I want a snowmobile now

[bangingears]

i rebuilt mine about 5 years ago, had a hot cam, xr400 HG, rings and hone, ported the head and removed and expoxied choke blade in carb, jetted, etc. Basic budget rebuild and it ripped pretty good after.

[Xowner]

Stock rebuild or find a good used motor.

[4cammer]

keep it stock or stock bore with high comp piston

[blown86lx]

keep it stock or stock bore with high comp piston

This is where I disagree. You could probably make good power with high compression but then you better have some 100 octane gas or better fuel avalible or you will just melt it down again. I say go with a bigger bore and moderate compression. Different strokes for different folks in the end its your choice.

[5.0calypso93lx]

I would think when we're talking these tiny single cylinder engines, a few cc's of displacement isn't going to give you that much added power. Most power would be gained by upping the compression.

[89notch]

I would think when we're talking these tiny single cylinder engines, a few cc's of displacement isn't going to give you that much added power. Most power would be gained by upping the compression.

Go out and race any 450 sport quad out there and you will think about it differently :lol: The 440 kits really do add lots of power. The price of the 440 kits has really come down as well.

[Xowner]

Rebuilt it to stock cc's and just ride it, No matter what the Hp you wont keep up with the new 450's when it comes to handling.


I have been out of the 400ex's a long time did they ever get the head studs worked out where they dont pull out on the 440 kits?

[5.0calypso93lx]

I may have found the previous owner and he says it has a 440 big bore in it now. We'll find out

[exrider416]

Rebuilt it to stock cc's and just ride it, No matter what the Hp you wont keep up with the new 450's when it comes to handling.


I have been out of the 400ex's a long time did they ever get the head studs worked out where they dont pull out on the 440 kits?

I think so. Im pretty sure the reliability now is great on the 440. The 440 is great. But i have a trx450r with the hrc kit and it pulls way harder than a 440ex.

[chris91]

Just find a wrecked CBR 600 and fab that bitch in there! hah