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Discussion Starter · #1 ·
What's up guys? I'm in need of a little bit of advice. I have been looking for a trx400ex on my local craigslist for a little while and stumbled upon a pretty nice one.

The quad is a 2000 trx400EX and has been bored out to 440 which is what I'm wondering about. He just bought it three months ago and had it rebuilt. The reason he is selling it is because he claims he's not much of a quad person and would rather put his time and money into his dirtbike and jeep.

Here is the list of what was recently replaced. All the parts on the list have less than 10 mins of ride time on it.

440 big bore kit piston & rings
Timing chain
Swing arm bearings
Carrier bearings
Clutch basket
Barnett Clutch springs
Stage two hot cams

It does need a couple of things.

Rear master cylinder (rebuilt or replaced)

New front hub bearings

Valves adjusted
- he says "When you put a big bore on it the valves tap. This one taps also, I'm not sure what is good and what is bad. I've never owned a four stroke before everything I've had has been 2 stroke. The shop that did the work for me never said that they needed adjusted but I don't know.. all I know is that has it tap. From what I have read that is fairly normal when you put a big bore."

He did agree to let me take it to the motorcycle shop down the street from me to let them check it out. They said they would run a compression test and that sorta stuff.

Here are my concerns.

I have read issues about the 440 kits so does
this setup sound like an issue?

What are my biggest concerns with a setup like this and how expensive can they get?

What's up with the "tap"

Really any advice you'd have for me id love to hear.

Also, in your opinion What would you guys say the quad is worth?

Thanks in advance for your help! :)

Super Moderator
4,643 Posts
Here's the deal - when the 440 "kit" is installed, it is imperative that the cylinder be sleeved. The valves do not tap when adjusted correctly and putting in a big bore kit does not change the adjustment. Most often, the inexperienced buider does not have the cylinder sleeved. The factory sleeve is too thin after boring and distorts causing the "tap". If the cylinder was sleeved for the 440 kit, then the tap is caused by incorrect piston to cylinder clearance, cam timing being off a tooth or pre-ignition caused by too low of an octane fuel. There may be other causes, but it would be wise to get it checked out by a qualified technician.

All the work done is impressive, but all the work still needing to be done is a red flag. This machine has been ridden hard and put away wet. It's much less burdensome to fix each deficiency as it occurs than to just ignore each until it becomes an unservicable hulk.

If you are capable of doing all the work youself, buy the POS and expect work on it after each ride to get it ready for the next ride.

It's kinda like the pitch that "it's tuned so only a professional can ride it". Translation: "it doesn't run right and I don't want to pay to have it fixed". If it was tuned so a professional could ride it, it would run perfect - no unusual noise, no hesitation, no lag in power, steers properly, tires don't go flat when setting, nothing bent and no bad bearings.

What is it worth? It is worth about the cost of the new parts that was put into it.

2 Posts
Discussion Starter · #3 ·
Thanks for the detailed reply!

Now that you mention the octane... I did notice most people run at least 100 and he says it only needs 93. Could that be the issue and if so did him putting the 93 possibly mess it up?

Also, is there any way to tell if they changed the sleeve?

I'm not sure if I would do the work my self or not... Id like to bit I'm not sure to what extent I'll be able to... Out of curiosity what is main reason you think it's going to be a problem? Is it the tap which could lead to problems?

Is there anyway I could maybe re bore it to like 416 or 426 and would that help the reliability? I definitely don't want an issue every single time I take it out...

Here's the main reason I'm stuck on it is because I'm not exactly buying it... I'm trading something for it and I have two offers I'm down to. It's either this one or a 1999 trx426ex. The reason I would like to get this on is because it has a all the new parts and the other one seems to have a decent (not a ton) of hours on it and I'm sure it's going to need the bearings and stuff done soon. Would that be safe to assume?

I mean I'm not too sure the trx426ex is definitely cleaner but I have a feeling it's going to start costing me some cash but from the sounds of it the trx440 might be worse. What's your opinion on the two?

Thanks again I greatly appreciate it!
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