2003 Honda 400ex Top End Rebuild - Honda ATV Forum
Performance Modifications Have Modifications? Want to ask about a mod? Having problems with a certain mod? Ask and post here! Carbs, Exhausts, Engines, Etc...

 
LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old 04-21-2019, 10:45 AM Thread Starter
Junior Member
 
Joe03400ex's Avatar
 
Join Date: Apr 2019
Posts: 5
2003 Honda 400ex Top End Rebuild

Hello all, My name is Joe i am From Central New Jersey.

I am currently Awaiting parts, but I am a little confused on what I should do with my upcoming project.


Currently the machine is bone stock with just a KN air filter with an outerwears sleeve over it... Quad started to burn some oil so here is my plan of action...

Wiseco top end rebuild kit .040 bore and 10:1 compression, all new gaskets and head studs, new cam gear and cam chain (keeping factory cam), rebuilding the head entirely hardware and seals. Kibble white stiffer valve springs, wiseco valves and all new hardware inside, going to add an ebc dirt racer clutch kit and completely rebuild the carb with factory jets.

The question I have is will I need to jet the carb and will I need to run a slip on exhaust? I like the stock sound on the bike it’s perfect for where we ride... I don’t want to change it if it is not necessary...

Any positive input would be greatly appreciated. Thanks in advance
Joe03400ex is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old 04-21-2019, 10:59 AM
Senior Member
 
Austin92's Avatar
 
Join Date: Mar 2019
Posts: 153
Liked: 35 times
Building my own engine right now too. Here’s what I’ve learned since I’ve been on here that might help you. JE makes the lightest piston. The crf450r timing chain is an upgrade for our 400EX motors. Gt thunder head studs are the only ones that address them pulling the threads out of the jug.

I still haven’t decided what I want to do with my valves and springs though.


Sent from my iPhone using Tapatalk
Austin92 is online now  
post #3 of 9 (permalink) Old 04-21-2019, 11:32 AM Thread Starter
Junior Member
 
Joe03400ex's Avatar
 
Join Date: Apr 2019
Posts: 5
I had listed the parts I have already ordered. Will I have an issue with new oem head studs. I’m not trying to go with a complete performance build looking to keep reliability and make it just a tad better than stock.
Joe03400ex is offline  
Sponsored Links
Advertisement
 
post #4 of 9 (permalink) Old 04-21-2019, 12:49 PM
Senior Member
 
Austin92's Avatar
 
Join Date: Mar 2019
Posts: 153
Liked: 35 times
I guess these 400’s are bad about blowing head gaskets and the gt thunder studs allow you to torque them a little tighter helping with the head gasket problem.

I would say you probably should’ve jetted with just the air filter, a larger bore will definitely need more fuel. These come from the factory lean.

I don’t think you’d NEED a slip on but it will make a difference in power. Dirt wheels magazine did an article on mufflers. Ct racing made the most power but you can change the disks out for different db levels. Stock is like 89db and the quietest the ct got was like 93db all the way up to like 101db. Louder settings made more power. Hmf has quiet core inserts for their mufflers too but wasn’t reviewed in that article. Something to think about


Sent from my iPhone using Tapatalk
Austin92 is online now  
post #5 of 9 (permalink) Old 04-21-2019, 01:54 PM Thread Starter
Junior Member
 
Joe03400ex's Avatar
 
Join Date: Apr 2019
Posts: 5
Quote:
Originally Posted by Austin92 View Post
I guess these 400’s are bad about blowing head gaskets and the gt thunder studs allow you to torque them a little tighter helping with the head gasket problem.

I would say you probably should’ve jetted with just the air filter, a larger bore will definitely need more fuel. These come from the factory lean.

I don’t think you’d NEED a slip on but it will make a difference in power. Dirt wheels magazine did an article on mufflers. Ct racing made the most power but you can change the disks out for different db levels. Stock is like 89db and the quietest the ct got was like 93db all the way up to like 101db. Louder settings made more power. Hmf has quiet core inserts for their mufflers too but wasn’t reviewed in that article. Something to think about


Sent from my iPhone using Tapatalk

What jet sizes would you recommend for the upcoming build? And when I drop everything off at the machine shop- should I just redo the head or should I have it ported and polished for the additional compression?
Joe03400ex is offline  
post #6 of 9 (permalink) Old 04-22-2019, 09:14 AM
Senior Member
 
XplicitRacing6's Avatar
 
Join Date: Feb 2017
Location: Missouri
Posts: 1,190
Liked: 533 times
Garage
Everyone has there own opinions, here’s mine.

GT head studs are a waste of money. Buy ARP Studs

Second, it’s hard too tell exactly what jetting you are going too need, it all depends on elevation, air temp, and all that good stuff


Sent from my iPhone using Tapatalk

  • 2001 Honda TRX 416ex
  • 2003 Honda TRX 416ex
  • 1999 Honda 300ex
  • 2014 Polaris 1000 xp Turbo
  • 1998 Yamaha PW 80
XplicitRacing6 is offline  
post #7 of 9 (permalink) Old 04-22-2019, 07:05 PM
Senior Member
 
Austin92's Avatar
 
Join Date: Mar 2019
Posts: 153
Liked: 35 times
2003 Honda 400ex Top End Rebuild

Depends on how you ride. Port and polish might kill your bottom end. Just a polish will help across the board though. When I was planning my build I was going to go with arp also but they use the same threads as stock. The gt thunders need drilled and retapped because they’re bigger so they’re less likely to pull out when you over torque them. More clamping force is less likely to blow the head gasket. But xplicit isn’t wrong. Arp makes quality stuff too


Sent from my iPhone using Tapatalk
Austin92 is online now  
post #8 of 9 (permalink) Old 04-23-2019, 06:53 AM Thread Starter
Junior Member
 
Joe03400ex's Avatar
 
Join Date: Apr 2019
Posts: 5
I’d use ARP over anything... that’s what holds down my turbo diesel....
Joe03400ex is offline  
post #9 of 9 (permalink) Old 04-23-2019, 06:54 AM Thread Starter
Junior Member
 
Joe03400ex's Avatar
 
Join Date: Apr 2019
Posts: 5
I’m in nj there’s no real elevation here... riding in say 50 to 80° weather sometimes colder...
Joe03400ex is offline  
Reply

  Lower Navigation
Go Back   Honda ATV Forum > Honda ATV Technical Discussions > Performance Modifications

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Honda ATV Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
2000 TRX450FM Build/Mods fishfiles Builds, Projects & DIY 1097 07-24-2019 05:48 AM
Revert back to thumb throttle OxfordMZ Repair & Maintenance 7 05-25-2018 09:56 AM
Honda 400ex Rebuild XplicitRacing6 Builds, Projects & DIY 54 04-25-2018 06:41 PM
2003 Honda 400ex Front Right Tire copenhagenjonah Honda TRX 2 02-24-2016 04:29 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome