To Buy Or Not?

[LeGaCyGiAnT124]

Someone I went to high school with has a 2002 400EX with a clear title for sale. He said it was just rebuilt with a new piston and rings, but needs anew timing chain and head gasket. Comes with extra tires, a arms, seat, plastic. Is it worth the $600? I have not seen the bike to see if it's smoking
Or anything but if the timing chain needs replaced, I'm sure the valves really chatter and it might leak a little oil from the gasket being blown. Please give
Your input, thanks.

-Brandon

[chronicsmoke]

Not worth it at all.. now what his number and address :D

I'd jump on it tbh

[honda250xrider]

I would be curious as to his reasoning it needs a new timing chain. Just remember when you buy something that needs replaced in the motor; it generally is more than what the owner is stating.

For the price though its hard to beat.

[xtreme762]

I'd go for it. All the parts for these bikes are fairly cheap if you think about it. It's not until you start buying parts after parts that it gets real expensive.

Sounds like a winner to me.

[CJM]

Rebuild topend is like $350 bucks or so. So for a G you got a quad.

Dont want it, vbet so long as it isnt beat to hell you can sell it for a G. id buy it.

[AtvKid4Eva]

def. worth it! you could always resell it for a lot more once its running anyway.

[LeGaCyGiAnT124]

I figured. Its been almost 4 years since I have had my 400, so I couldn't remember what the parts cost for this. I know the 450 motors cost double what these do so that's good to hear. I will fill you guys in. Thanks!

[LeGaCyGiAnT124]

Alright, so he claims it has a 12:1 Wiseco domed piston in it right now. I have not looked at this bike yet, but he dropped the price to 500 since it's torn apart. What CC does the 12:1 make it? And what gas would I have to run with it. Thanks!

[duneslider]

12:1 is the compression ratio not the cylinder size. So, unless it is a bigger piston it is still a 400cc engine. 12:1 will require race gas. I am guessing if he ran it with that piston and compression he may have pulled/stretched a head bolt. You will want to get the heavy duty head bolts if you keep running that compression.

If the bottom end is good $500 is a great deal. In my area you could get it running and resell it close to 2K if it looks like it is in good shape.

Since its all apart I would probably just get it a fresh hone and a new piston, upgrade the studs, and for under a $1000 total you have a fresh quad ready for years of use.

[LeGaCyGiAnT124]

The heavy duty studs were already in the process. I have heard that they like to pull them with high compression pistons. Thanks for reply!

[LeGaCyGiAnT124]

If I was to change the piston and what not, what would I all have to do to make it be able to run pump gas again? Thanks.

[Stickman400]

Just don't go over 11:1 compression on the piston and you can run pump gas all day long, regardless of what other internal mods you do.

[LeGaCyGiAnT124]

So all I would have to buy is a top end gasket kit, a new 11:1 Piston with the wrist pins, circlips, and rings? How would I determine the bore of the piston I need? Sorry if this sounds stupid, but I am clueless in understanding how motors work and what parts I need.

[LeGaCyGiAnT124]

While I am at it, maybe someone can explain these concepts that I am clueless about.


What is the standard bore of a stock 400ex?

What compression is set at?

What does the compression ratios say to the average person?

What does compression do? I know if your leaking or have low compression, you lose power.

What does it mean to bore a cylinder and how is it done? Does boring just allow a larger diameter to fit inside the cylinder due to scoring on the cylinder head from use and abuse?

What does honing a cylinder mean?

What does resleeving mean?

Why can you only bore so high?

Why are there 400 CCs? 406, 416, 426, 440, ect.

Like what does it mean to have those numbers?

Why can you only bore from .20, .40. .60 over?

Thanks for helping!!

[duneslider]

Honestly, if you don't know the bore I would take it to a shop and have it honed and a piston fit to it. Then you know all will be good.

A hone shouldn't cost that much either, been a long while since I have had one done. And you can get them to do the HD head studs too.

I bet for an additional 3-400 you could be in great shape.

Since it is all apart you can easily throw in a stage 2 cam ($130) and have a really nice cheap build.

[CJM]

Answers in red

Originally posted by LeGaCyGiAnT124
While I am at it, maybe someone can explain these concepts that I am clueless about.


What is the standard bore of a stock 400ex?
397cc

What compression is set at?

9:1 if I recall

What does the compression ratios say to the average person?
In a 4 stroke compression is power, more air/fuel you can compress the more power you got. Kinda like throwing a supercharger on a car, different principle but same outcome-more power

What does compression do? I know if your leaking or have low compression, you lose power.

See above

What does it mean to bore a cylinder and how is it done? Does boring just allow a larger diameter to fit inside the cylinder due to scoring on the cylinder head from use and abuse?

Basically drilling out the cylinder to accept a larger piston. While boring it out will increase power-its only slight. You usually bore when the cylinder gets worn and oblonged from use

What does honing a cylinder mean?

They take a special rotary file or brush and it sands the cylinder slightly. Enough to put cross hatching marks in the cylinder to reseat rings and make a good seal

What does resleeving mean?

Some motors use a sleeve thats press or sweated (like a pipe is) into the cylinder. The sleeve comes out when you heat the cylinder up. Resleeving is putting a new one in.

Why can you only bore so high?

On a 400ex the sleeve can only be bored to 426cc, this is b/c you dont leave enough sleeve material if you bore more. Also a larger sleeve than 426cc must be specially fit into the cylinder by boring the cylinder itself-IE 440.

Why are there 400 CCs? 406, 416, 426, 440, ect.

They like making it sound like round numbers. In all actuality its less b/c a 400EX has a 397cc bore originally. Infact a 440 is only 435cc. Why IDK

Like what does it mean to have those numbers?

You increased the bore of the sleeve. IE from 397 to 407, etc. The sleeve itself has been enlarged. In all actuality its like 1mm, 2mm, 3mm over in diameter.

Why can you only bore from .20, .40. .60 over?

See other answers

Thanks for helping!!

[LeGaCyGiAnT124]

Great Reply CJM. I would be interested in learning how to do my own motor work over the years if possible. I can do anything on my bike besides that. Too scared to mess something up.

[pickle_steve64]

Most of that is right except the bore is the inside diameter of the cylinder. were get the numbers 400, 406 ect. is from the displacment of the engine in cubic centimeters. you get this by multiplying the bore X stroke. the stroke is the distance the cylinder moves up and down in the cylinder. so you can change the displacment of the engine by changing either the bore or the stroker. this is were you get the terms BIG BORE and STROKER. with a longer stroke you gain more on the top end of the power band of your enigine this were the lager cams come into play they change when and how long fuel enters the engine and exhuast exits the engine to make it more efficent and take advantage of the change in power band. with more compression you basically magnify the explosion that happens in the engine. imagine holding a fire cracker in your open hand it explodes maybe stings a little leaves a black spot no big deal but if you close your hand and light it it blows your hand off(dont try this at home) when you have higher compression you need higher octane fuel that will burn slower or you have predetenation where the fuel air mixture explodes before the pistion is at the top of its stroke

[CJM]

Um right ok.

The thing is, they base everything off the engine actually being 400cc-but it is only 397.

[pickle_steve64]

yes a stock 400ex is only 397cc all manufacturers do this the 400 is basically the class it is in like a 450. 450s arent actually 450cc

i wasnt sure about the big bore kits on these so i looked some up these are the kits i found:
406
415
426
435

and i used the formula to get the displacement wich is pi X (radius sq) X length of stroke

stock bore is 85mm or 8.5cm
stoke bore is 70mm or 7.0cm

so

pi X (4.25)sq X 7.0=397cc

the bore for the 406 is 86mm

pi X (4.3)sq X 7.0=406.6cc

the bore for the 415 is 87mm

pi X (4.35)sq X 7.0= 416.1cc

the bore for the 426 is 88mm

pi X (4.4)sq X 7.0=425.7cc

the bore for the 435 is 89

pi X (4.45)sq X 7.0= 435.5cc

so no the big bore kits are in no way related to the claimed 400cc

[Stickman400]

I kinda think CJM already explained that they weren't.