Different approach to rebuilding....

[MtnEX]

Well, I finally got to talk to a local builder, who really did tell me what I wanted to hear from a builder.... but at the same time, I've realized this is a bit different approach to a rebuild than I originally had in mind.

Basically, I wanted someone to take it appart and check all the service limits on everything so that I don't build on top of something else that will so break.

This is what this builder explained that he does, and then determines what it needs as far as a rebuild is concerned.

The good is, you know everything is checked.
The bad is, you have no idea what the finished build will be or what it will cost.
You really can't quote that.... and I understand that.


I have to call him back on 2/10 to see about getting it in.
So I have some time to think about it.

My idea is to take it by and offer him an hour's pay for diagnostics and his opinion from what he may be able to see and hear externally.


Before this, I was only considering like a 416 kit, stage 1 hotcam, head work, CRF cam chain and goodies, and possibly anything it needs in the bottom.

I'm not quite sure what to think about how it might come out if it only needs a cam chain and a re-ring or bore.


Has anyone just done the jug basically and not a lot else?

I'd hate to get out for hundreds less only to have something still mild in output.

[RaceinCircles]

I've only done the jug motor wise, but I've got it jetted and piped. I had a ring go out and didn't have much money, so all I did was have a stockcar buddy bore the cylinder for free and I put an 85.5mm wiseco 11:1 in it. It cost like $80 bucks from an ebay dealer. I can find the name if you'd like.

The only racing I do is when we make little tracks in the woods/fields/ice...and I am happy. Definitely put the cam chain in no matter what you do, I am having a ticking problem on mine and I believe that's the problem. I would on the other hand love to take up your deal if I had money! What kind of riding do you do/plan to do? Is there a problem with the motor now?

[MtnEX]

OK... here is the deal...

After riding a modded YFZ450 (too much for woods) I picked up a nice Polaris Sport 400.... 2 stroke and auto... it's pretty mean. Then I bought this 400EX used... just a stock bike as far as I know, other than a 14t front sprocket.

To me it was on the mild side, but I had in mind to set it up XC for mountain trails. So I did the tires, wheels, skids, etc... and I had exhaust, jetting and filter done.

The guy did a full Yoshi Exhaust, K&N and upped the main jet with an offbrand jet.

I still think it is mild. It runs well but the off jet does not allow it to run perfect if you know what I mean. It's not lean or rich, but not spot on... which makes it more sensitive to temp and elevation.


ANYWAYS... I started to pick up a noise on cold starts. I couldn't figure out what it was so I went to the valve adjustments and jetting. In time I learned it just does it on cold starts and as it gets hot it stops.

At one point while I had the carb off, I went ahead and pulled the cam chain tension plunger just to see what I could figure out. I put it back in fully extended and it didn't lack a lot of going all the way back in without retracting it. Maybe 1/4" or something.

So I guess that it turns out.... the noise is the cam chain slack. I guess it's nearing it's service limit and when cold it's tapping the chain guides.... and maybe when it gets hot and expands everything it tightens up?


SO.... I have no REAL idea, but I am guessing that if the cam chain is near it's service limit in a stock engine... other things are probably near their service limit too?

It doesn't smoke like a train or anything, but I figure if it has this much use it IS likely passing a little oil, loosing compression, etc.

I guess I could have the guy pop a compression gage on it, etc, to see more about where that really stands.



I really like the quad... how it handles, how it runs, how it lugs, and how it feels to me chassis-wise (old 250R guy). But at the same time, I myself have a problem with throwing another grand or two at the bike to freshen and liven it up.

Who knows what the build will cost.
Around $1,400 is the price for a used EX engine with reverse.
ETC....

For that kind of money I would rather trade it for something new, although I don't really just 'want to'.

Although I love the bike, depending on how you look at it.... I think I'd be better off trading, even if it was for a new Z400... because in the end, I think I might just end up with an EX in that performance range for around the same money.... where if I traded I'd gain reverse, liquid cooling and a brand new bike.


Dunno what I'll do.

[RaceinCircles]

Dilemma!!! haha. My guess is that a freshen up wont cost you a thousand. Maybe you would take the head off and atleast look through it before you up and trade it. It's really not that difficult to clean up the ports on the head and look at the cylinder. Just an option, but it sounds like you have many options :)

I'm actually not a big believer in the YFZ, when I first bought my used 02 it had bald tires, bent bars, piped, and jetted and I rode all over my friend on his 06 yfz450. Not long after that, my rings went, so I probly wasnt even running strong.

IMO 400ex is a pretty solid bike and you can actually do quite a bit of mods for a decent price. You mostly trail ride like me, and I agree 100% on the reverse comment.

On the other hand I'd be willing to bet you could get a pretty good deal on a new bike with the economy issues...

[MtnEX]

Originally posted by RaceinCircles
Dilemma!!! haha. My guess is that a freshen up wont cost you a thousand. Maybe you would take the head off and atleast look through it before you up and trade it. It's really not that difficult to clean up the ports on the head and look at the cylinder. Just an option, but it sounds like you have many options :)

I'm actually not a big believer in the YFZ, when I first bought my used 02 it had bald tires, bent bars, piped, and jetted and I rode all over my friend on his 06 yfz450. Not long after that, my rings went, so I probly wasnt even running strong.

IMO 400ex is a pretty solid bike and you can actually do quite a bit of mods for a decent price. You mostly trail ride like me, and I agree 100% on the reverse comment.

On the other hand I'd be willing to bet you could get a pretty good deal on a new bike with the economy issues...

Yeah, the deals are out there... to the point it almost doesn't make sense to throw very much money in the EX.

Sale prices on leftover 400's are in the $3,000 range (EX & Z). For the money I'd put in a nice build I could get a new one and for a bit more over that I can have a 450, 500, 525, 700... (all this is considering a decent trade).

[400Trooper]

MtnEX - This is just my opinion, not gospel or an arguable point. If you have any mechanical skills at all you can do the majority of the work yourself and save a whole lot of money. Get a service manual first off, that way you know exactly what to do!

With the exception of machine work, everything you might want to do you should be able to DIY. Definately do a compression check first.

If you do decide to bore the cylinder for a bigger size have a reputable shop do the bore for you! Also if you are having the cylinder bored, go ahead and do HD head studs just to be safe.
Since you're there have them port and polish the head , it should be reasonably cheap unless you go larger valves.

At that point you already have the engine apart, you might as well replace the timing chain. Definately do the HD chain instead of the stock 400ex one.

Order the gaskest ahead of time that way you have them when you go to reassemble the engine. For the head gasket and base I used Cometic's! I also got some of the Permatex copper spray and sprayed the head gasket a couple times( allowing the coats to dry a bit before I resprayed it!) before I assembled it. No leaks at all!

Also a HUGE thing, be sure to use a torque wrench to torque the head bolts exactly!!

I would estimate you'll be around $850.00 when done, most of the cost is parts and machining, your labor price is free!

[MtnEX]

Yeah, I could do all of the work myself except the inspection and machine work.

But not covered in this particular thread... is the fact that I do not have the place for it right now to have an engine torn apart.

[brian76708]

Originally posted by MtnEX
Yeah, I could do all of the work myself except the inspection and machine work.

But not covered in this particular thread... is the fact that I do not have the place for it right now to have an engine torn apart.

yea motor work can be pretty expensive. i am doing my 416 with a stg 2 cam and its already added up to around $600 but i think i got everything now. the only thing i would check in the bottom end is rod side clearance. which if you have a manual it tells you the specs so all you need is a feeler gauge and its really easy to get to when you have the jug off. as for space to do it thats always hard i was lucky enough my sister is letting me build my motor in her basement.

personally i would be more worried about your head before your bottom end.

[MtnEX]

Hopefully I will hear from a builder tomorrow, and hopefully I'll get to take my EX by there for a little professional diagnosis... and maybe I'll know a little more about where I actually stand.

If so I'll be closer to making a decision on building or trading.

If I decide it makes more sense to trade, I'm still no closer in deciding what to trade for.