What mods required with 416, 425, 440?

[CranMan]

I want to take the next step with my EX and I'm thinking about a 416, 425, or 440 kit. I don't want to get carried away, and I'd like to stick with the stock carb and use the Megamax pipe I've already got. I plan on doing the teardown and reassembly myself. I guess the kits come with the sleeve, piston, and rings. And I think a XR400 cam would be good also. So what's the best choice for me, without throwing a ton of money into it?

[hogglett]

I think that you would be ok with the 416 JE piston 10.8 to 1
XR camshaft and modify your megamax


take your silencer and measure it , it should be 14 inches i think now come from the disk end and measure back 4 inches and cut the body into (you have to dissaemble it first ) then cut the inner tube down 4 inches as well and reassemble


I done this with just my stock engine and it helped the power of it all through the rpm range

[wyndzer]

Dan, Get with me and I'll show you what I've done and am currently doing. I should have my new 416 in if we ride this weekend.

[PsychoDave]

i am reading about everybody putting these bigger pistons in their ex's (416,440 etc). do you have any idea of what is involved????:eek:

to do it right you need a machine shop to install the sleeve.
next if you put a high comp piston with a big bore you NEED to change to a stronger rod. ( the stock rod is NOT strong enough to handle the power increase. the rod openings will stretch and get "egg" shaped and will eventually break) if you change the cam you need hardened rockers and new valve springs (the new cam has a longer duration to open the valve so the valves need to close quicker to build up the proper cylinder pressure, this increased valve spring pressure will destroy stock rockers) you need to regrind the valve surfaces to ensure a tight fit (any leakes means a burnt valve!!!) since you have the head off you should port and polish...it just makes sense!!! (more air and fuel means more power....which is why you want the big bore in the first place. you should get a ned header and muffler to lessen back pressure and allow the engine to "breath"....now you need to work on the carb and get the jetting right....it is more important now because you can burn a valve more easily because it is open longer.... To do it right will cost you $2000. if you think you can do it yourself and risk scratching the cylinder wall or installing the rings up-side-down or porting the head too much and weakening the walls.....or dont torque the head down right and have a leaky head gasket (which will have a loss of power) than go for it!!!!! i have had years of engine building in my resume and i have a knowledge of what to do!!! dont forget the more engine mods you do .....the less reliable it becomes....you dont have to take my word for it but i would rather ride than have to work on my ex day in and day out.....
just my opinions.............but take heed....i am a friend

[Smoker]

Hogglet, I did that to an E-Series but haven't tried it out yet, did you notice any specific spot where it made power, like low, mid or top? Just wondering.:p

[thorspapa]

Actually this is'nt quite correct. Though the intentions are good, the picture painted is bleaker than it need be.

A cam with more DURATION poses very little extra stress on the valve train, it's a cam with more LIFT that stresses things and demands hardened rockers/better springs for a long valve train life.

The higher lift cam imposes accelerated opening times due to the higher curve required to open the valve more in the same time period. This is somewhay alleviated if the cam is well designed and has a smooth opening and closing profile (also meaning more duration added), but too smooth a ramp means timing is also changed, and other things are compromised (let's not go there, it gets too complicated).

By comparison a longer duration cam will keep valves open longer, giving more time for fuel to come in (more fuel = bigger boom = more power) and more time for exhaust to go out, though not always necessary. This is where the XR400 cam is a good investment: more duration, only a tiny bit more lift, and it compromises none of the valve train.

The 400EX/XR400 motor DOES NOT require resleeving for the 416/426 kits. Those are merely oversized/higher compression pistons , and boring out the stock sleeve will do the trick.

Yes, the 440 pistons and larger require resleeving.

There's no reason to regrind valve seats just because a higher performance cam or larger piston id added, there's no connection here that I'm aware of. You may decide to have your valve seats reground IF there's leaks/damage/wear, or to go with the common 3-angle regrind offered by many shops. The shop you pick to do it can tell you the benefits of that.

Polishing and porting the 400EX/XR400 head is not necessary in many applications. The design of the head already flows more than the stock 400EX carburator is able to handle, so unless you're doing a lot of work to the motor, the small improvement (if any) on a stock carburated motor may not be felt. It's similar to adding more chrome parts: they look nice....

Yes, I agree that internal engine work should be performed by someone who has the experience, or by the guy that is very thorough, neat, can follow instructions very well, has the instructions to follow, and it's very mechanically inclined. If there's any doubt on your part, have someone else do it. There's variables that may not seem important, but are.

There's many on this forum that managed to do all the work themselves without problems. There's also many that payed to have it done, but in neither instance did it make the bike unreliable or cost $2000 to do, unless the work done was truly extensive. I'd say the 400 motor can be modified to run very well for much less than that, without adversely impacting longevity or reliability.

Anyone not sure what to do, give Terry at MARCUN's a call. He'll take the time to give advice, prices and do it without an attittude like some shops have. He also delivers when promised, and that's rare.

This isn't intended as a flame in any way, but some of the info was, as I stated earlier, bleaker than need be, and not necessary. I don't make a living as a motor builder, for me it's only a hobby (and and a necessity, I have to do my own work because of time constraints). Anyone that does this for a living and wants to correct me, feel free to do so. But don't give info out that you're not sure of unlees you say so: it creates false impressions for those less familiar with the subject.

Good luck to you all.

[CranMan]

Thanks everyone for the input so far.....I'm starting to lean towards the 416/426. I had heard the XR400 cam didnt require any further mods to the valve train. So I guess if I go with the 416/426 I'll need:

416/426 kit
XR400 cam
XR400 head gasket?
Rejetting of carb
Machine shop to bore sleeve

Anything I'm missing here? Do you guys think the Megamax will work, will I ned to mod it (never heard of that one) or get a new pipe. (I don't want to spend more than needed).

Also what about my clutch, it's a 99 EX and there's not much adjustment left on the cable. Will my new mods be too much, should I do some clutch work at the same time? How much, and what's the best bang for the buck in the clutch area?

Thanks in advance for your help guys, this is why I love this site!!!

And I'm looking forward to checking out your 416 Wyndzer....

[kj400]

I just purchased the je 416 piston and gasket set $136, xr 400 cam $130, 4 valve seals 2.25ea from terry at marcums yesterday. If your doing the tear down yourself you'll be under $400 pretty easily.

[Matt Fisher]

CranMan, you'll only need to sleeve the motor if you do the 440. In any case, it'll need to be bored out.

The XR cam is a good cam for play riding, for more performance and/or for the larger diplacement motors, I'd suggest a "bigger" cam. GT Thunder makes a drop-in cam of this sort.

Drop-in means no new valve springs, guides, rockers, etc. needed. The XR cam is a drop-in.

The pipe will work fine. Don't screw with the clutch unless it gives you trouble. If it does slip, there are lots of options, and the stock clutch certainly isn't a bad one.

If you can take the motor apart, you can certainly put it back together. When the machine shop bores your cylinder, have them check/set the ring gap, and install them on the piston. It'll just add a couple of bucks, you then assemble the motor.

[PsychoDave]

ok, ok ,......my last post was not to scare off any engine mods!!! I am not a "professional engine builder", although I have built many before including very fast 1/4 mile drag cars and I have EXTENSIVE knowledge of 4 strokes and 2 strokes, I just want people to think before they leap. Yuo CAN get away without changing parts and using the stock stuff, but if its apart now you might as well change and upgrade to better stuff...... the main thing to change is the CONNECTING ROD.....the stock one is weak and cant handle the power of a 440, a 416 is at the stock rods limit.... I have another guy I know who is a "professional engine builder" claim he wont even do piston mod without doing a new rod..... he is soo good that he guarantees his work!!!! (but not with a stock rod)
I guess what I am trying to get across is....knowledge is power.
Look into all aspects of the mods you are doing, and choose the best that will fit your budget. If you guys question my opinion....jusy ask Micky in the forum....i bet he will agree with me on some stuff.....though not all because he is a god and I am a mere mortal.....good luck everyone!!!! and thanks for keeping me "in check"

[Dave400ex]

For just a JE 416 Piston and XR400 Cam you don`t need a New Connecting Rod. A lot of guys on here have that 416 Piston Kit and XR Cam. I have yet to hear any Problems with that Setup. TC didn`t say anything to me about a New Connecting Rod. His Cam is also a Drop-In and you don`t have to get New Valve Springs or Harden the Rockers. On Curtis Sparks site it says a New Rod is a good thing to add to a 416 Kit. There are Mods out there that you don`t have to do a bunch of things to make the Motor Reliable.

[hogglett]

SMOKER

I have a megamax that is 10 inches and a E series that is like 7 inches and both helped all through the rpm range


my local track has a few up hills that i was in second gear and after the pipe change i could do it in third